Stereoselective syntheses of cryptocarya diacetate and all its stereoisomers in optically pure forms

Abstract

Cryptocarya diacetate and each of its stereoisomers were stereoselectively synthesized in 8–16 steps. One of the three chiral carbons was converted from the chiral center of a yeast-reduction product. The other two chiral carbons were constructed by employing stereoselective allylation and syn-and anti-1,3-reductions. The enantiomeric excesses of the synthesized cryptocarya diacetate and its stereoisomers were determined to be more than 99%ee using a chiral column.

Graphical Abstract

Cryptocarya diacetate and its all stereoisomers were stereoselectively synthesized through 8-16 steps. The enantiomeric excess of all stereoisomers were determined as more than 99%ee.

Key words:

• Cryptocarya diacetate
• Yeast-reduction product
• 6-substituted 5, 6-dihydropyran-2-one

The 6-substituted 5,6-dihydropyran-2-one structures have a variety of useful properties.¹⁾ Although each biological activity is interesting, the effect of stereochemistry on the activity is unknown. Cryptocarya diacetate (1a) has been isolated from the African medicinal plant Cryptocarya latifolia²⁾ and its absolute configuration is determined³⁾ (Fig. 1). The stereochemistry–bioactivity relationship is an interesting area of research: hence, in this project, we focused on the stereoselective syntheses of each of the stereoisomers of cryptocarya diacetate. Cryptocarya diacetate is an important synthetic target^4–9) and the synthesis of all the stereoisomers of cryptocarya diacetate has been reported;¹⁰⁾ however, the enantiomeric excess of each stereoisomer has not been determined. The development of new synthetic routes to get an optically pure natural compound and optically pure stereoisomers is necessary in order to pursue research on the structure–activity relationship.

Fig. 1. Cryptocarya diacetate (1a) and its stereoisomers 1b–1h.

The retrosynthetic analysis is shown in Scheme 1. In this research, the synthesis of each of the eight optically pure stereoisomers (1a–1h) was started from the yeast-reduction products, 8 and 9.¹¹⁾ The stereoselective allylation to aldehyde, obtained from the yeast-reduction product 8, gives alcohols 6 and 7. After the conversion of allyl alcohols 6 and 7 to β-hydroxy ketones by Wacker oxidation, syn- and anti-stereoselective reductions give the syn-diols 2 and 4 and the anti-diols 3 and 5, respectively. These compounds can be transformed to a 6-membered lactone by employing Baeyer–Villiger oxidation as the key reaction, giving cryptocarya diacetate (1a) and its stereoisomers 1c, 1e, and 1g. The remaining enantiomers 1b, 1d, 1f, and 1h can be obtained from the yeast-reduction product 9 using similar processes. This is the new stereoselective synthetic strategy for obtaining optically pure stereoisomers of cryptocarya diacetate.

Scheme 1. Retrosynthetic analysis of cryptocarya diacetate (1a) and its stereoisomers.

Results and discussion

Our synthesis started with stereoselective allylation to aldehyde 10a,¹²⁾ which was prepared from the yeast-reduction product 8, using (+)-Ipc₂BOMe and (-)-Ipc₂BOMe¹³⁾ with allylmagnesium chloride to give secondary alcohols 11a (47% yield, along with 8% of 11b) and 11b (53% yield, along with 8% of 11a), respectively. The stereochemistries of 11a and 11b were determined by the modified Mosher’s method¹⁴⁾ (Scheme 2). The secondary alcohols 11a and 11b were converted to (S)- and (R)-α-methoxy-α-(trifluoromethyl)phenylacetate (MTPA) 12a and 12b by employing MTPACl and pyridine, respectively. The Δδ_S−R values on the left side of the C2 position of 12a were negative, and those on the right side were positive, showing that the C2 position of 11a was 2S. On the other hand, the Δδ_S−R values on the left side of the C2 position of 12b were positive, and those on the right side were negative. With these results, the C2 position of 11b was assigned to be 2R. Stereoselectivity was not observed in the allylation to aldehyde 10a without (+)- and (−)-Ipc₂BOMe, which gave 11a (46%) and 11b (47%), respectively.

Scheme 2. Determination of stereochemistry of allyl alcohols 11a and 11b. Chemical shift differences (Δδ_S−R) of (S)- and (R)-MTPA 12a and 12b.

To construct the chiral carbons at the seventh and ninth positions, syn and anti- reductions of β-hydroxy ketone were planned (Scheme 3). To achieve this plan, allyl alcohol 11a was subjected to Wacker oxidation using PdCl₂ and Cu(OAc),^2,15) giving β-hydroxy ketone 13a (48% yield). Subjecting the β-hydroxy carbonyl compound 13a to 1,3-syn-reduction— employing the Et₂BOMe-NaBH₄ system—¹⁶⁾ provided syn-diol 14a (90% yield) as a single isomer. Diacetylation of the resulting diol using acetic anhydride in pyridine (95% yield), followed by the removal of the triisopropylsilyl group by treatment with tetra-n-butylammonium fluoride, gave the secondary alcohol 16a (67% yield), which was subjected to pyridinium chlorochromate oxidation to give ketone 17a (76% yield). By employing m-chloroperoxybenzoic acid, Baeyer–Villiger oxidation was performed to give lactone 18a (70% yield), which was converted to (+)-cryptocarya diacetate (1a) (84% yield) by treating it with benzeneseleninic acid anhydride.¹⁷⁾ The NMR spectroscopic data of the synthesized compound 1a were identical to those previously reported for this compound.⁹⁾ To obtain stereoisomer 1c, the application of 1,3-anti-reduction, using Me₄NHB(OAc)_3,¹⁸⁾ to β-hydroxy ketone 13a was attempted as the first step. The obtained anti-diol 14c (76% yield, along with 11% of syn-diol) was converted to diacetate 15c (92% yield). The cleavage of the silyl ether group from 15c, led to the formation of the secondary alcohol 16c (77% yield), which was then subjected to pyridinium chlorochromate oxidation (75% yield) followed by Baeyer–Villiger oxidation, to give lactone 18c (74% yield). Finally, conversion to α,β-unsaturated lactone gave the stereoisomer 1c (80% yield). Stereoisomers 1e and 1g were obtained from 11b, using the same synthetic method described for the syntheses of (+)-cryptocarya diacetate (1a) and stereoisomer 1c, respectively. The syn-reduction of 13b exclusively proceeded to give 14e as a single isomer with 88% yield. In the case of anti-reduction of 13b, the desired anti-diol 14g was stereoselectively obtained (79% yield) along with a syn-product (0.9% yield). The NMR data of all the stereoisomers agreed with those in the literature.^4,10) The syntheses of enantiomers 1b, 1d, 1f, 1h were accomplished from the yeast-reduction product 9 via aldehyde 10b by employing the same method described for the syntheses of 1a, 1c, 1e, and 1g (Scheme 4). The enantiomeric excesses of 1a–1h were determined to be more than 99%ee by HPLC analysis using a chiral column.

Scheme 3. Syntheses of cryptocarya diacetate (1a) and its stereoisomers 1c, 1e, and 1g. (a) PdCl₂, Cu(OAc)₂ · H₂O, O₂, DMF, r.t., 48 h (13a: 48%, 13b: 51%). (b) Et₂BOMe, NaBH₄, THF-MeOH, −70 °C, 3 h, warmed to 0 °C (14a: 90%, 14e: 88%). (c) Ac₂O, DMAP, pyridine, r.t., 12 h (15a: 95%, 15c: 92%, 15e: 98%, 15g: 94%). (d) n-Bu₄NF, THF, r.t., 12 h (16a: 67%, 16c: 77%, 16e: 73%, 16g: 78%). (e) PCC, MS 4A, CH₂Cl₂, r.t., 12 h (17a: 76%, 17c: 75%, 17e: 80%, 17g: 79%). (f) MCPBA, Na₂HPO₄–NaH₂PO₄ buffer (pH 8.0), CHCl₃, r.t, 12 h (18a: 70%, 18c: 74%, 18e: 69%, 18g: 69%). (g) (C₆H₅Se = O)₂O, ClC₆H₅, 130 °C, 72 h (1a: 84%, 1c: 80%, 1e: 81%, 1g: 85%). (h) Me₄NHB(OAc)₃, MeCN, AcOH, −40–0 °C, 1 h (14c: 76%, 14g: 79%).

Scheme 4. Syntheses of stereoisomers of cryptocarya diacetate 1b, 1d, 1f, and 1h. (a) (1) 2 M aq. NaOH, EtOH, 60 °C, 16 h; (2) TIPSOTf, 2,6-lutidine, CH₂Cl₂, r.t., 1 h (84%, 2 steps); (3) HCO₂H, ether, r.t., 1 h (86%); (4) PCC, MS 4A, CH₂Cl₂, r.t., 16 h (84%).

A stereoselective synthetic method for producing cryptocarya diacetate (1a) and all its stereoisomers was exploited by employing the yeast-reduction products 8 and 9 as starting materials. The enantiomeric excesses of all the stereoisomers 1a–1h were determined to be more than 99%ee. The three chiral carbons were constructed by yeast-reduction, asymmetric allylation, and 1,3-syn- and anti-reductions. This is the new report on the syntheses of all the optically pure stereoisomers of cryptocarya diacetate. The success of this work provides a significant contribution to biological research.

Experimental

Optical rotations were measured on a Jasco P-2100 polarimeter. IR data were obtained using a Horiba FT-720 instrument. NMR data were obtained using a JNM-EX400 spectrometer. EIMS data were recorded with a JMS-MS700 V spectrometer. The silica gel used was Wakogel C-300 (Wako, 200–300 mesh). The purity of each compound containing enantiomers was confirmed by ¹H NMR. HPLC analysis was performed with Shimadzu LC-6AD and SPD-6AV instruments. The chiral column used for HPLC analysis of enantiomeric excess was CHIRALCEL AD-H (DAICEL Chemical Industries Ltd, Tokyo, Japan).

[(1S,2R)-2-(Triisopropylsilyloxy)cyclopent-1-yl]acetaldehyde (10b)

A reaction solution of benzoate 19¹⁹⁾ (4.56 g, 9.57 mmol) in 2 M aq. NaOH solution (84 mL) and EtOH (240 mL) was stirred at 60 °C for 16 h before the addition of CHCl₃ and H₂O. The organic solution was separated and then dried (Na₂SO₄). Concentration of the solvent gave crude secondary alcohol. To an ice-cooled solution of the crude secondary alcohol and 2,6-lutidine (2.47 mL, 21.2 mmol) in CH₂Cl₂ (10 mL) was added TIPSOTf (3.44 mL, 12.8 mmol), and then the reaction solution was stirred at room temperature for 1 h before the addition of sat. aq. CuSO₄ solution. The organic solution was separated, washed with sat. aq. NaHCO₃ solution, and then dried (Na₂SO₄). Concentration of the solvent followed by silica gel column chromatography (2%EtOAc/hexane), gave silyl ether (4.67 g, 8.83 mmol, 92%) as a colorless oil. To a solution of silyl ether (4.67 g, 8.83 mmol) in ether (260 mL) was added formic acid (230 mL) at −10 °C. After stirring at room temperature for 1 h, CHCl₃ and H₂O were added. The organic solution was separated, washed with sat. aq. NaHCO₃ solution, and then dried (Na₂SO₄). Concentration of the solvent followed by silica gel column chromatography (5% EtOAc/hexane) gave primary alcohol (2.18 g, 7.61 mmol, 86%) as a colorless oil. A reaction mixture of the primary alcohol (2.18 g, 7.61 mmol), PCC (1.97 g, 9.14 mmol), and MS 4A (0.5 g) in CH₂Cl₂ (20 mL) was stirred at room temperature for 16 h before the addition of ether. After the mixture was filtered, the filtrate was concentrated. The residue was applied to silica gel column chromatography (5% EtOAc/hexane) to give aldehyde 10b (1.82 g, 6.40 mmol, 84%) as a colorless oil, [α]²⁰_D −45 (c 1.3, CHCl₃). NMR data agreed with those in the literature.¹²⁾

(2S)-1-[(1R,2S)-2-(Triisopropylsilyloxy)cyclopent-1-yl]-4-penten-2-ol (11a)

To a solution of (-)-Ipc₂BOMe (1.04 g, 3.19 mmol) in ether (30 mL) was added allylmagnesium chloride (1.64 mL, 2 M in THF, 3.28 mmol) at −75 °C, and then the mixture was stirred at −70 °C for 15 min before warming to room temperature. After stirring at room temperature for 1 h, the mixture was cooled to −70 °C, and then aldehyde 10a (0.47 g, 1.65 mmol) in ether (15 mL) was added. The resulting reaction solution was stirred at −70 °C for 1 h, and then warmed to room temperature. The reaction was quenched by the addition of 1 M aq. NaOH solution and 30% aq. H₂O₂ solution. After the resulting mixture was stirred at room temperature for 12 h, the organic solution was separated and then dried (Na₂SO₄). Concentration of the solvent, followed by silica gel column chromatography (5% EtOAc/hexane), gave (2S)-1-[(1R,2S)]-11a (0.25 g, 0.77 mmol, 47%) as a colorless oil, Rf = 0.40 (EtOAc/hexane = 1/9 × 2), [α]²⁰_D +47 (c 0.7, CHCl₃); ¹H NMR (400 MHz, CDCl₃) δ:1.06 (21H, s), 1.18 (1H, m), 1.36 (1H, m), 1.56–1.62 (3H, m), 1.72 (1H, m), 1.85–1.92 (3H, m), 2.18–2.29 (2H, m), 3.13 (1H, s), 3.70 (1H, m), 3.90 (1H, ddd, J = 5.4, 5.4, 5.4 Hz), 5.10 (1H, d, J = 9.8 Hz), 5.11 (1H, d, J = 17.3 Hz), 5.83 (1H, m); ¹³C NMR (100 MHz, CDCl₃) δ: 12.6, 18.10,18.14, 21.2, 29.3, 34.5, 41.0, 42.4, 45.5, 70.1, 80.3, 117.7, 135.0; IR ν_max (CHCl₃): 3410, 2947, 1643, and 1103 cm⁻¹. HRFABMS m/z (M + H)⁺: calcd for C₁₉H₃₉O₂Si: 327.2720, found: 327.2739. (2R)-1-[(1S,2R)]-(ent-11a). By employing (+)-Ipc₂BOMe and allylmagnesium chloride against aldehyde 10b, (2R)-1-[(1S,2R)]-(ent-11a) was obtained in 56% yield, [α]²⁰_D −50 (c 0.3, CHCl₃).

(2R)-1-[(1R,2S)-2-(Triisopropylsilyloxy)cyclopent-1-yl]-4-penten-2-ol (11b)

By employing (+)-Ipc₂BOMe and allylmagnesium chloride against aldehyde 10a, (2R)-1-[(1R,2S)]-11b was obtained in 53% yield as a colorless oil, Rf = 0.34 (EtOAc/hexane = 1/9 × 2), [α]²⁰_D +39 (c 0.8, CHCl₃); ¹H NMR (400 MHz, CDCl₃) δ: 1.07 (21H, s), 1.20 (1H, m), 1.42 (1H, m), 1.53–1.66 (3H, m), 1.70 (1H, m), 1.84–1.95 (3H, m), 2.00 (1H, br. s), 2.15 (1H, m), 2.30 (1H, m), 3.77 (1H, dddd, J = 7.3, 7.3, 7.3, 7.3 Hz), 3.90 (1H, ddd, J = 5.9, 5.9, 5.9 Hz), 5.12 (1H, d, J = 9.9 Hz), 5.13 (1H, d, J = 17.1 Hz), 5.84 (1H, m); ¹³C NMR (100 MHz, CDCl₃) δ: 12.6, 18.13, 18.17, 21.5, 29.6, 34.6, 41.0, 41.6, 45.1, 69.7, 80.0, 117.9, 135.0; IR ν_max (CHCl₃): 3409, 2946, 1643, and 1103 cm⁻¹. HRFABMS m/z (M + H)⁺: calcd for C₁₉H₃₉O₂Si: 327.2720, found: 327.2718. (2S)-1-[(1S,2R)]-(ent-11b). By employing (-)-Ipc₂BOMe and allylmagnesium chloride against aldehyde 10b, (2S)-1-[(1S,2R)]-(ent-11b) was obtained in 60% yield, [α]²⁰_D −39 (c 0.4, CHCl₃).

(4R)-4-Hydroxy-5-[(1R,2S)-2-(triisopropylsilyloxy)cyclopent-1-yl]-2-pentanone (13a)

A reaction mixture of allyl alcohol 11a (0.22 g, 0.67 mmol), PdCl₂ (12.0 mg, 67.7 μmol), and Cu (OAc)₂·H₂O (27.0 mg, 0.14 mmol) in DMF (7 ml) was stirred under O₂ gas at ambient temperature for 48 h before filtration with ethyl acetate. The filtrate was washed with H₂O and brine, and then dried (Na₂SO₄). After concentration of the solvent, the residue was applied to silica gel column chromatography (EtOAc/hexane = 1/5) to give β-hydroxy ketone 13a (0.11 g, 0.32 mmol, 48%) as a colorless oil, [α]²⁰_D +48 (c 1.3, CHCl₃); ¹H NMR (400 MHz, CDCl₃) δ: 1.06 (21H, s), 1.10–1.26 (2H, m), 1.51–1.61 (2H, m), 1.67 (1H, m), 1.73 (1H, m), 1.83 (1H, m), 1.90–1.98 (2H, m), 2.17 (3H, s), 2.58–2.60 (2H, m), 3.17 (1H, br. s), 3.90 (1H, ddd, J = 5.6, 5.6, 5.6 Hz), 4.10 (1H, m); ¹³C NMR (100 MHz, CDCl₃) δ: 12.4, 18.0, 18.1, 21.2, 29.1, 30.7, 34.5, 40.7, 44.9, 50.6, 66.6, 79.9, 209.5; IR ν_max (CHCl₃): 3745, 2945, 2362, and 1705 cm⁻¹. HRFABMS m/z (M + H)⁺: calcd for C₁₉H₃₉O₃Si: 343.2669, found: 343.2667. (4S)-5-[(1S,2R)]-(ent-13a). 59% yield, [α]²⁰_D −48 (c 0.8, CHCl₃).

(4S)-4-Hydroxy-5-[(1R,2S)-2-(triisopropylsilyloxy)cyclopent-1-yl]-2-pentanone (13b)

51% yield, [α]²⁰_D +54 (c 0.8, CHCl₃); ¹H NMR (400 MHz, CDCl₃) δ: 1.06 (21H, m), 1.19 (1H, m), 1.43 (1H, m), 1.51–1.64 (3H, m), 1.70 (1H, m), 1.73–1.94 (3H, m), 2.19 (3H, s), 2.52 (1H, dd, J = 17.4, 9.2 Hz), 2.65 (1H, dd, J = 17.4, 2.7 Hz), 3.13 (1H, d, J = 2.7 Hz), 3.90 (1H, ddd, J = 5.9, 5.9, 5.9 H), 4.13 (1H, m); ¹³C NMR (100 MHz, CDCl₃) δ: 12.5, 18.10, 18.14, 21.4, 29.4, 30.8, 34.5, 40.6, 45.0, 49.7, 66.8, 79.8, 209.7. IR ν_max (CHCl₃): 3745, 2945, 2362, and 1705 cm⁻¹. HRFABMS m/z (M + H)⁺: calcd for C₁₉H₃₉O₃Si: 343.2669, found: 343.2650. (4R)-5-[(1S,2R)]-(ent-13b). 51% yield, [α]²⁰_D −53 (c 0.8, CHCl₃).

(2R,4S)-1-[(1R,2S)-2-(Triisopropylsilyloxy)cyclopent-1-yl]pentane-2,4-diol (14a)

To a solution of β-hydroxy ketone 13a (0.60 g, 1.75 mmol) in THF-MeOH (4/1, 13 mL) was added Et₂BOMe (1.91 mL, 1 M in THF, 1.91 mmol) at −70 °C. After the mixture was stirred at −70 °C for 15 min, NaBH₄ (72.0 mg, 1.90 mmol) was added. The reaction mixture was stirred at −70 °C for 3 h before warming to 0 °C. The reaction was quenched by the addition of 3 M aq. NaOH (2.5 mL) and 30% aq. H₂O₂ solution (1 mL). The mixture was then extracted with ether. The organic solution was separated, washed with brine, and then dried (Na₂SO₄). Concentration of the solvent, followed by silica gel column chromatography (EtOAc/hexane = 1/3), gave 1,3-syn-diol 14a (0.54 g, 1.57 mmol, 90%) as a colorless oil, [α]²⁰_D +75 (c 0.7, CHCl₃); ¹H NMR (400 MHz, CDCl₃) δ: 1.05 (3H, s), 1.07 (18H, s), 1.18 (3H, d, J = 6.0 Hz), 1.21 (1H, m), 1.41 (1H, ddd, J = 11.0, 6.4, 3.2 Hz), 1.50–1.64 (5H, m), 1.71 (1H, m), 1.83–1.94 (3H, m), 3.80–3.87 (2H, m), 3.88–3.93 (2H, m), 4.05 (1H, dddd, J = 15.3, 5.7, 5.7, 3.2 Hz); ¹³C NMR (100 MHz, CDCl₃) δ: 12.7, 18.0, 18.1, 21.0, 23.8, 29.5, 34.4, 42.7, 45.2, 45.7, 68.8, 72.6, 80.5; IR ν_max (CHCl₃): 3500, 2945, 1458, 1092, and 1061 cm⁻¹. HRFABMS m/z (M + H)⁺: calcd for C₁₉H₄₁O₃Si: 345.2825, found: 345.2817. (2S,4R)-1-[(1S,2R)]-(ent-14a). 92% yield, [α]²⁰_D −77 (c 0.4, CHCl₃).

(2R,4R)-1-[(1R,2S)-2-(Triisopropylsilyloxy)cyclopent-1-yl]pentane-2,4-diol (14c)

To a solution of Me₄NHB(OAc)₃ (0.89 g, 3.38 mmol) in MeCN (2.5 mL) and AcOH (1.5 mL), a solution of β-hydroxy ketone 13a (0.26 g, 0.76 mmol) in MeCN (1.5 mL) was added at −40 °C. The reaction mixture was stirred at 0 °C for 1 h before the addition of sat. aq. NH₄Cl solution and EtOAc. The organic solution was separated, washed with sat. aq. NaHCO₃ solution, and brine and then dried (Na₂SO₄). Concentration of the solvent, followed by silica gel column chromatography (EtOAc/hexane = 1/2), gave 1,3-anti-diol 14c (0.20 g, 0.58 mmol, 76%) as a colorless oil, [α]²⁰_D +43 (c 0.8, CHCl₃); ¹H NMR (400 MHz, CDCl₃) δ: 1.05 (3H, s), 1.07 (18H, s), 1.14–1.24 (2H, m), 1.22 (3H, d, J = 6.0 Hz), 1.28 (1H, m), 1.39 (1H, ddd, J = 13.7, 7.6, 2.7 Hz), 1.54–1.64 (3H, m), 1.67–1.75 (2H, m), 1.86–1.93 (2H, m), 3.12 (1H, br. s), 3.44 (1H, br. s), 3.91 (1H, ddd, J = 6.4, 6.4, 6.4 Hz), 3.99 (1H, m), 4.15 (1H, m); ¹³C NMR (100 MHz, CDCl₃) δ: 12.6, 18.0, 18.1, 21.0, 23.4, 29.5, 34.4, 41.6, 44.3, 46.1, 65.4, 69.1, 80.5; IR ν_max (CHCl₃): 3500, 2945, 1457, 1093, and 1061 cm⁻¹. HRFABMS m/z (M + H)⁺: calcd for C₁₉H₄₁O₃Si: 345.2825, found: 345.2819. (2S,4S)-1-[(1S,2R)]-(ent-14c). 81% yield, [α]²⁰_D−40 (c 4.3, CHCl₃).

(2S,4R)-1-[(1R,2S)-2-(Triisopropylsilyloxy)cyclopent-1-yl]pentane-2,4-diol (14e)

88% yield, [α]²⁰_D +32 (c 0.8, CHCl₃); ¹H NMR (400 MHz, CDCl₃) δ: 1.08 (21H, s), 1.19 (3H, d, J = 6.0 Hz), 1.19–1.27 (1H, overlapped), 1.46–1.62 (6H, m), 1.72 (1H, m), 1.85–1.91 (3H, m), 3.39 (1H, br. s), 3.69 (1H, br. s), 3.92 (1H, ddd, J = 6.4, 6.4, 6.4 Hz), 3.99–4.08 (2H, m); ¹³C NMR (100 MHz, CDCl₃) δ: 12.7, 18.08, 18.13, 21.3, 23.9, 29.6, 34.6, 42.3, 44.28, 44.34, 69.0, 71.8, 80.1. IR ν_max (CHCl₃): 3500, 2946, 1458, 1092, and 1060 cm⁻¹. HRFABMS m/z (M + H)⁺: calcd for C₁₉H₄₁O₃Si: 345.2825, found: 345.2823. (2R,4S)-1-[(1S,2R)]-(ent-14e). 85% yield, [α]²⁰_D −33 (c 0.4, CHCl₃).

(2S,4S)-1-[(1R,2S)-2-(Triisopropylsilyloxy)cyclopent-1-yl]pentane-2,4-diol (14g)

79% yield, [α]²⁰_D +43 (c 0.6, CHCl₃); ¹H NMR (400 MHz, CDCl₃) δ: 1.05 (3H, s), 1.07 (18H, s), 1.21 (1H, m), 1.23 (3H, d, J = 6.0 Hz), 1.50–1.59 (2H, m), 1.59–1.64 (3H, m), 1.68–1.78 (2H, m), 1.81–1.93 (3H, m), 2.73 (1H, br. s), 2.88 (1H, br. s), 3.92 (1H, ddd, J = 6.5, 6.5, 6.5 Hz), 4.10 (1H, m), 4.16 (1H, m); ¹³C NMR (100 MHz, CDCl₃) δ: 12.6, 18.08, 18.12, 21.4, 23.4, 29.5, 34.6, 41.5, 43.4, 44.8, 65.4, 68.0, 80.0; IR ν_max (CHCl₃): 3500, 2945, 1458, 1091, and 1060 cm⁻¹. HRFABMS m/z (M + H)⁺: calcd for C₁₉H₄₁O₃Si: 345.2825, found: 345.2818. (2R,4R)-1-[(1S,2R)]-(ent-14g). 83% yield, [α]²⁰_D −40 (c 0.2, CHCl₃).

(1S,3R)-1-Methyl-3-[(1R,2S)-2-(triisopropylsilyloxy)cyclopent-1-yl]methylpropylene diacetate (15a)

A reaction mixture of syn-diol 14a (0.39 g, 1.13 mmol) and DMAP (10.0 mg, 81.9 μmol) in pyridine (3 mL) and Ac₂O (3 mL) was stirred at room temperature for 12 h before the addition of ice. After 6 h at room temperature, the mixture was extracted with EtOAc. The organic solution was washed with 1 M aq. HCl solution, sat. aq. NaHCO₃ solution, and brine and then dried (Na₂SO₄). Concentration of the solvent, followed by silica gel column chromatography (EtOAc/hexane = 1/9), gave diacetate 15a (0.46 g, 1.07 mmol, 95%) as a colorless oil, [α]²⁰_D +24 (c 0.8, CHCl₃); ¹H NMR (400 MHz, CDCl₃) δ: 1.05 (21H, s), 1.05–1.15 (1H, m), 1.24 (3H, d, J = 6.4 Hz), 1.28 (1H, m), 1.51–1.58 (2H, m), 1.65 (1H, ddd, J = 14.2, 6.0, 6.0 Hz), 1.68–1.84 (4H, m), 1.86–2.05 (2H, m), 2.03 (3H, s), 2.04 (3H, s), 3.83 (1H, ddd, J = 5.5, 5.5, 5.5 Hz), 4.94 (1H, m), 4.97 (1H, m); ¹³C NMR (100 MHz, CDCl₃) δ: 12.3, 18.1, 20.1, 21.2, 21.3, 21.4, 28.9, 34.6, 38.4, 41.0, 44.5, 68.0, 69.9, 79.6, 170.4, 170.6; IR ν_max (CHCl₃): 2945, 2360, 1734, and 1250 cm⁻¹. HRFABMS m/z (M-H)⁺: calcd for C₂₃H₄₃O₅Si: 427.2880, found: 427.2866. (1R,3S)-3-[(1S,2R)]-(ent-15a). 95% yield, [α]²⁰_D −22 (c 1.3, CHCl₃).

(1R,3R)-1-Methyl-3-[(1R,2S)-2-(triisopropylsilyloxy)cyclopent-1-yl]methylpropylene diacetate (15c)

92% yield, [α]²⁰_D +20 (c 0.9, CHCl₃); ¹H NMR (400 MHz, CDCl₃) δ: 1.05 (21H, s), 1.14 (1H, m), 1.21–1.28 (1H, overlapped), 1.22 (3H, d, J = 6.0 Hz), 1.50–1.59 (2H, m), 1.68–1.84 (6H, m), 1.96 (1H, m), 2.01 (3H, s), 2.02 (3H, s), 3.85 (1H, ddd, J = 5.5, 5.5, 5.5 Hz), 4.92 (1H, m), 5.05 (1H, dddd, J = 13.3, 4.6, 3.6, 3.6 Hz); ¹³C NMR (100 MHz, CDCl₃) δ: 12.2, 18.01, 18.03, 20.4, 20.9, 21.1, 21.3, 29.1, 34.5, 38.9, 41.1, 44.5, 66.9, 68.9, 79.5, 170.4, 170.5; IR ν_max (CHCl₃): 2944, 2360, 1732, and 1251 cm⁻¹. Found: C, 64.50; H, 10.41. Calcd for C₂₃H₄₄O₅Si: C, 64.44; H, 10.35. (1S,3S)-3-[(1S,2R)]-(ent-15c). 96% yield, [α]²⁰_D −20 (c 1.3, CHCl₃).

(1R,3S)-1-Methyl-3-[(1R,2S)-2-(triisopropylsilyloxy)cyclopent-1-yl]methylpropylene diacetate (15e)

98% yield, [α]²⁰_D +40 (c 0.3, CHCl₃); ¹H NMR (400 MHz, CDCl₃) δ: 1.05 (21H, s), 1.23 (3H, d, J = 6.0 Hz), 1.38 (1H, m), 1.50–1.60 (3H, m), 1.67–1.82 (5H, m), 1.83–1.94 (2H, m), 2.02 (3H, s), 2.03 (3H, s), 3.83 (1H, ddd, J = 5.5, 5.5, 5.5 Hz), 4.89–4.98 (2H, m); ¹³C NMR (100 MHz, CDCl₃) δ: 12.3, 18.08, 18.11, 19.8, 21.3, 21.4, 28.8, 34.2, 38.3, 39.8, 45.3, 68.2, 71.1, 79.5, 170.4, 170.5; IR ν_max (CHCl₃): 2945, 2360, 1733, and 1249 cm⁻¹. Found: C, 64.30; H, 10.62. Calcd for C₂₃H₄₄O₅Si: C, 64.44; H, 10.35. (1S,3R)-3-[(1S,2R)]-(ent-15e). 94% yield, [α]²⁰_D −42 (c 1.0, CHCl₃).

(1S,3S)-1-Methyl-3-[(1R,2S)-2-(triisopropylsilyloxy)cyclopent-1-yl]methylpropylene diacetate (15g)

94% yield, [α]²⁰_D +52 (c 0.7, CHCl₃); ¹H NMR (400 MHz, CDCl₃) δ: 1.05 (21H, m), 1.23 (3H, d, J = 6.4 Hz), 1.25 (1H, m), 1.39 (1H, ddd, J = 13.3, 10.3, 5.2 Hz), 1.48–1.61 (2H, m), 1.62–1.93 (7H, m), 2.01 (3H, s), 2.02 (3H, s), 3.82 (1H, ddd, J = 5.5, 5.5, 5.5 Hz), 4.89–4.98 (2H, m); ¹³C NMR (100 MHz, CDCl₃) δ: 12.3, 18.07, 18.10, 20.5, 21.19, 21.23, 21.3, 28.6, 34.3, 38.5, 40.0, 45.2, 67.0, 70.0, 79.7, 170.5, 170.6; IR ν_max (CHCl₃): 2945, 2360, 1733, and 1250 cm⁻¹. Found: C, 64.47; H, 10.65. Calcd for C₂₃H₄₄O₅Si: C, 64.44; H, 10.35. (1R,3R)-3-[(1S,2R)]-(ent-15g). 92% yield, [α]²⁰_D −50 (c 0.6, CHCl₃).

(1R,3S)-1-[(1R,2S)-2-Hydroxycyclopent-1-yl]methyl-3-methylpropylene diacetate (16a)

To a solution of silyl ether 15a (0.45 g, 1.05 mmol) in THF (10 mL) was added n-Bu₄NF (1.16 mL, 1.0 M in THF, 1.16 mmol). After the reaction solution was stirred at room temperature for 12 h, sat. aq. NH₄Cl solution and EtOAc were added. The organic solution was separated, washed with sat. aq. CuSO₄ solution, sat. aq. NaHCO₃ solution, and brine and then dried (Na₂SO₄). Concentration of the solvent, followed by silica gel column chromatography (EtOAc/hexane = 1/3), gave alcohol 16a (0.19 g, 0.70 mmol, 67%) as a colorless oil, [α]²⁰_D +27 (c 0.6, CHCl₃); ¹H NMR (400 MHz, CDCl₃) δ: 1.14 (1H, m), 1.23 (1H, m), 1.24 (3H, d, J = 6.4 Hz), 1.42 (1H, ddd, J = 13.7, 9.1, 4.6 Hz), 1.50–1.62 (2H, m), 1.65–1.73 (2H, m), 1.71 (1H, ddd, J = 14.2, 6.0, 6.0 Hz), 1.81 (1H, ddd, J = 13.7, 8.2, 5.5 Hz), 1.86–1.99 (2H, m), 2.03 (3H, s), 2.05 (3H, s), 2.17 (1H, s), 3.80 (1H, ddd, J = 6.4, 6.4, 6.4 Hz), 4.96 (1H, m), 5.02 (1H, m); ¹³C NMR (100 MHz, CDCl₃) δ: 20.0, 21.17, 21.21, 21.3, 29.8, 34.3, 38.2, 40.5, 44.1, 68.0, 70.1, 78.9, 170.5, 170.7; IR ν_max (CHCl₃): 3745, 2962, 2360, 1734, 1774, and 1252 cm⁻¹. HRFABMS m/z (M + H)⁺: calcd for C₁₄H₂₅O₅: 273.1702, found: 273.1709. (1S,3R)-1-[(1S,2R)]-(ent-16a). 65% yield, [α]²⁰_D −27 (c 2.9, CHCl₃).

(1R,3R)-1-[(1R,2S)-2-Hydroxycyclopent-1-yl]methyl-3-methylpropylene diacetate (16c)

77% yield, [α]²⁰_D +17 (c 0.8, CHCl₃); ¹H NMR (400 MHz, CDCl₃) δ: 1.16 (1H, m), 1.23 (3H, d, J = 6.4 Hz), 1.38 (1H, ddd, J = 13.7, 8.9, 5.0 Hz), 1.49–1.62 (2H, m), 1.63–2.00 (7H, m), 1.93 (1H, br. s), 2.02 (3H, s), 2.03 (3H, s), 3.80 (1H, ddd, J = 6.4, 6.4, 6.4 Hz), 4.93 (1H, m), 5.06 (1H, m); ¹³C NMR (100 MHz, CDCl₃) δ: 20.4, 21.1, 21.2, 21.4, 30.2, 34.3, 38.8, 40.9, 44.3, 67.1, 69.3, 79.1, 170.65, 170.74; IR ν_max (CHCl₃): 3745, 2962, 2360, 1734, 1774, 1694, and 1252 cm⁻¹. HRFABMS m/z (M + H)⁺: calcd for C₁₄H₂₅O₅: 273.1702, found: 273.1707. (1S,3S)-1-[(1S,2R)]-(ent-16c). 82% yield, [α]²⁰_D −19 (c 1.9, CHCl₃).

(1S,3R)-1-[(1R,2S)-2-Hydroxycyclopent-1-yl]methyl-3-methylpropylene diacetate (16e)

73% yield, [α]²⁰_D +13 (c 0.9, CHCl₃); ¹H NMR (400 MHz, CDCl₃) δ: 1.19 (1H, m), 1.24 (3H, d, J = 6.0 Hz), 1.52–1.64 (3H, m), 1.65–1.75 (4H, m), 1.83–2.00 (3H, m), 2.04 (3H, s), 2.07 (3H, s), 2.35 (1H, br. s), 3.81 (1H, ddd, J = 6.4, 6.4, 6.4 Hz), 4.96 (1H, m), 5.09 (1H, m); ¹³C NMR (100 MHz, CDCl₃) δ: 20.0, 21.26, 21.29, 22.2, 31.2, 34.5, 38.8, 40.4, 44.6, 67.9, 70.6, 78.6, 170.5, 171.2; IR ν_max (CHCl₃): 3745, 2962, 2360, 1734, 1694, and 1252 cm⁻¹. HRFABMS m/z (M + H)⁺: calcd for C₁₄H₂₅O₅: 273.1702, found: 273.1710. (1R,3S)-1-[(1S,2R)]-(ent-16e). 72% yield, [α]²⁰_D −12 (c 3.1, CHCl₃).

(1S,3S)-1-[(1R,2S)-2-Hydroxycyclopent-1-yl]methyl-3-methylpropylene diacetate (16g)

78% yield, [α]²⁰_D +18 (c 0.7, CHCl₃); ¹H NMR (400 MHz, CDCl₃) δ: 1.20 (1H, m), 1.23 (3H, d, J = 6.4 Hz), 1.53–1.63 (4H, m), 1.64–1.72 (2H, m), 1.72–1.82 (2H, m), 1.83–1.96 (2H, m), 2.02 (3H, s), 2.05 (3H, s), 2.48 (1H, br. s), 3.84 (1H, ddd, J = 6.5, 6.5, 6.5 Hz), 4.96 (1H, m), 5.10 (1H, m); ¹³C NMR (100 MHz, CDCl₃) δ: 20.4, 21.1, 21.2, 22.4, 31.3, 34.6, 39.4, 40.8, 44.7, 66.7, 69.6, 78.6, 170.6, 171.5; IR ν_max (CHCl₃): 3744, 2962, 2360, 1733, 1692, and 1252 cm⁻¹. HRFABMS m/z (M + H)⁺: calcd for C₁₄H₂₅O₅: 273.1702, found: 273.1703. (1R,3R)-1-[(1S,2R)]-(ent-16g). 80% yield, [α]²⁰_D −17 (c 1.3, CHCl₃).

(1S,3R)-1-Methyl-3-[(1R)-2-oxocyclopent-1-yl]methylpropylene diacetate (17a)

A reaction mixture of alcohol 16a (0.24 g, 0.88 mmol), PCC (0.23 g, 1.07 mmol), and MS 4A (0.50 g) in CH₂Cl₂ (10 mL) was stirred at room temperature for 12 h before the addition of ether. After the mixture was filtered, the filtrate was concentrated. The residue was applied to silica gel column chromatography (5% EtOAc/hexane) to give ketone 17a (0.18 g, 0.67 mmol, 76%) as a colorless oil, [α]²⁰_D +89 (c 0.4, CHCl₃); ¹H NMR (400 MHz, CDCl₃) δ: 1.24 (3H, d, J = 6.4 Hz), 1.41–1.51 (2H, m), 1.67 (1H, ddd, J = 14.2, 5.5, 5.5 Hz), 1.72–1.83 (2H, m), 1.97 (1H, ddd, J = 14.2, 7.3, 7.3 Hz), 1.98–2.16 (3H, m), 2.04 (3H, s), 2.05 (3H, s), 2.28–2.36 (2H, m), 4.95 (1H, m), 5.02 (1H, m); ¹³C NMR (100 MHz, CDCl₃) δ: 20.2, 20.7, 21.3, 21.4, 30.0, 34.5, 37.9, 40.9, 45.9, 67.9, 69.3, 170.6, 170.7, 220.6; IR ν_max (CHCl₃): 3026, 2972, 2359, 1732, 1375, 1250, and 1022 cm⁻¹. HRFABMS m/z (M + H)⁺: calcd for C₁₄H₂₃O₅: 271.1545, found: 271.1528. (1R,3S)-3-[(1S)]-(ent-17a). 81% yield, [α]²⁰_D −89 (c 2.3, CHCl₃).

(1R,3R)-1-Methyl-3-[(1R)-2-oxocyclopent-1-yl]methylpropylene diacetate (17c)

75% yield, [α]²⁰_D +90 (c 0.7, CHCl₃); ¹H NMR (400 MHz, CDCl₃) δ: 1.22 (3H, d, J = 6.4 Hz), 1.33–1.52 (2H, m), 1.71–1.82 (3H, m), 1.97–2.07 (2H, m), 2.025 (3H, s), 2.030 (3H, s), 2.07–2.15 (2H, m), 2.29–2.42 (2H, m), 4.92 (1H, dddd, J = 13.3, 6.4, 6.4, 6.4 Hz), 5.10 (1H, m); ¹³C NMR (100 MHz, CDCl₃) δ: 20.4, 20.6, 21.0, 21.2, 30.2, 35.0, 37.8, 41.0, 46.0, 66.9, 68.3, 170.6, 170.7, 220.5; IR ν_max (CHCl₃): 3025, 2971, 2358, 1731, 1374, 1251, and 1021 cm⁻¹. Found: C, 62.11; H, 8.14. Calcd for C₁₄H₂₂O₅: C, 62.20; H, 8.20. (1S,3S)-3-[(1S)]-(ent-17c). 78% yield, [α]²⁰_D −89 (c 1.6, CHCl₃).

(1R,3S)-1-Methyl-3-[(1R)-2-oxocyclopent-1-yl]methylpropylene diacetate (17e)

80% yield, [α]²⁰_D +70 (c 0.9, CHCl₃); ¹H NMR (400 MHz, CDCl₃) δ: 1.24 (3H, d, J = 6.0 Hz), 1.48–1.62 (2H, m), 1.66–1.81 (3H, m), 1.95 (1H, ddd, J = 14.2, 6.4, 6.4 Hz), 2.00–2.12 (3H, m), 2.038 (3H, s), 2.042 (3H, s), 2.21 (1H, m), 2.30 (1H, m), 4.95 (1H, dddd, J = 12.3, 6.4, 6.4, 6.4 Hz), 5.06 (1H, m); ¹³C NMR (100 MHz, CDCl₃) δ: 20.0, 20.7, 21.3, 30.1, 34.2, 37.4, 40.1, 46.5, 67.9, 70.4, 170.5, 170.6, 219.8; IR ν_max (CHCl₃): 3026, 2972, 2359, 1733, 1376, 1251, and 1021 cm⁻¹. Found: C, 62.09; H, 8.04. Calcd for C₁₄H₂₂O₅: C, 62.20; H, 8.20. (1S,3R)-3-[(1S)]-(ent-17e). 85% yield, [α]²⁰_D −68 (c 2.9, CHCl₃).

(1S,3S)-1-Methyl-3-[(1R)-2-oxocyclopent-1-yl]methylpropylene diacetate (17g)

79% yield, [α]²⁰_D +104 (c 0.8, CHCl₃); ¹H NMR (400 MHz, CDCl₃) δ: 1.23 (3H, d, J = 6.4 Hz), 1.48–1.63 (2H, m), 1.68–1.86 (3H, m), 2.00–2.12 (4H, m), 2.02 (6H, s), 2.22 (1H, m), 2.30 (1H, m), 4.93 (1H, dddd, J = 16.0, 9.3, 3.2, 3.2 Hz), 5.07 (1H, m); ¹³C NMR (100 MHz, CDCl₃) δ: 20.4, 20.7, 21.1, 30.1, 34.7, 37.3, 40.5, 46.7, 66.8, 69.6, 170.5, 219.8; IR ν_max (CHCl₃): 3024, 2971, 2360, 1732, 1375, 1250, and 1021 cm⁻¹. Found: C, 61.99; H, 8.45. Calcd for C₁₄H₂₂O₅: C, 62.20; H, 8.20. (1R,3R)-3-[(1S)]-(ent-17g). 83% yield, [α]²⁰_D −101 (c 1.1, CHCl₃).

(5R,7S,9S)-7,9-Diacetoxy-5-decanolide (18a)

A reaction mixture of ketone 17a (0.20 g, 0.74 mmol) and MCPBA (0.40 g, 70%, 1.62 mmol) in CHCl₃ (8 mL) and Na₂HPO₄-NaH₂PO₄ buffer (pH 8.0, 8 mL) was stirred at room temperature for 12 h before the addition of sat. aq. Na₂S₂O₃ solution. The organic solution was separated, washed with sat. aq. NaHCO₃ solution, and then dried (Na₂SO₄). Concentration of the solvent, followed by silica gel column chromatography (EtOAc/hexane = 1/1), gave lactone 18a (0.15 g, 0.52 mmol, 70%) as a colorless oil, [α]²⁰_D −35 (c 0.5, CHCl₃); ¹H NMR (400 MHz, CDCl₃) δ:1.25 (3H, d, J = 6.4 Hz), 1.51 (1H, m), 1.77 (1H, ddd, J = 14.2, 6.0, 6.0 Hz), 1.82–1.95 (3H, m), 1.95–2.02 (2H, m), 2.04 (3H, s), 2.04–2.09 (1H, overlapped), 2.07 (3H, s), 2.44 (1H, ddd, J = 17.6, 8.7, 7.1 Hz), 2.58 (1H, dddd, J = 17.6, 6.7, 6.7, 1.0 Hz), 4.37 (1H, m), 4.97 (1H, dddd, J = 13.3, 6.4, 6.4, 6.4 Hz), 5.11 (1H, m); ¹³C NMR (100 MHz, CDCl₃) δ: 18.3, 20.1, 21.1, 21.3, 27.7, 29.3, 40.1, 40.3, 67.7, 67.9, 77.3, 170.5, 170.6, 171.1; IR ν_max (CHCl₃): 3026, 2360, 1734, 1373, 1244, and 1049 cm⁻¹. HRFABMS m/z (M + H)⁺: calcd for C₁₄H₂₃O₆: 287.1495, found: 287.1484. (5S,7R,9R)-(ent-18a). 74% yield, [α]²⁰_D +35 (c 0.6, CHCl₃).

(5R,7S,9R)-7,9-Diacetoxy-5-decanolide (18c)

74% yield, [α]²⁰_D −40 (c 0.7, CHCl₃); ¹H NMR (400 MHz, CDCl₃) δ: 1.23 (3H, d, J = 6.4 Hz), 1.51 (1H, m), 1.76–1.86 (4H, m), 1.89 (1H, m), 2.01–2.10 (2H, m), 2.02 (3H, s), 2.05 (3H, s), 2.44 (1H, ddd, J = 17.4, 8.7, 7.3 Hz), 2.58 (1H, ddd, J = 17.4, 6.2, 6.2 Hz), 4.35 (1H, m), 4.94 (1H, m), 5.14 (1H, m); ¹³C NMR (100 MHz, CDCl₃) δ: 18.3, 20.4, 21.0, 21.1, 27.8, 29.2, 40.7, 40.8, 66.6, 66.9, 77.3, 170.5, 170.7, 171.2; IR ν_max (CHCl₃): 3025, 2359, 1734, 1373, 1244, and 1048 cm⁻¹. HRFABMS m/z (M + H)⁺: calcd for C₁₄H₂₃O₆: 287.1495, found: 287.1490. (5S,7R,9S)-(ent-18c). 75% yield, [α]²⁰_D +39 (c 1.3, CHCl₃).

(5R,7R,9R)-7,9-Diacetoxy-5-decanolide (18e)

69% yield, [α]²⁰_D −57 (c 0.9, CHCl₃); ¹H NMR (400 MHz, CDCl₃) δ: 1.25 (3H, d, J = 6.4 Hz), 1.58 (1H, m), 1.75 (1H, ddd, J = 14.2, 6.0, 6.0 Hz), 1.80–1.96 (5H, m), 2.01 (1H, ddd, J = 14.2, 7.3, 7.3 Hz), 2.04 (3H, s), 2.06 (3H, s), 2.44 (1H, ddd, J = 17.9, 7.8, 7.8 Hz), 2.58 (1H, ddd, J = 17.9, 6.9, 6.9 Hz), 4.34 (1H, m), 4.96 (1H, dddd, J = 12.9, 6.4, 6.4, 6.4 Hz), 5.18 (1H, m); ¹³C NMR (100 MHz, CDCl₃) δ: 18.4, 20.1, 21.1, 21.3, 28.0, 29.2, 40.5, 40.6, 67.7, 68.0, 76.8, 170.4, 170.5, 171.0; IR ν_max (CHCl₃): 3026, 2360, 1734, 1373, 1244, and 1049 cm⁻¹. HRFABMS m/z (M + H)⁺: calcd for C₁₄H₂₃O₆: 287.1495, found: 287.1489. (5S,7S,9S)-(ent-18e). 70% yield, [α]²⁰_D −55 (c 0.6, CHCl₃).

(5R,7R,9S)-7,9-Diacetoxy-5-decanolide (18g)

69% yield, [α]²⁰_D −46 (c 0.6, CHCl₃); ¹H NMR (400 MHz, CDCl₃) δ: 1.24 (3H, d, J = 6.4 Hz), 1.59 (1H, m), 1.76 (1H, ddd, J = 14.2, 9.4, 3.7 Hz), 1.83–1.95 (6H, m), 2.03 (3H, s), 2.04 (3H, s), 2.45 (1H, ddd, J = 17.4, 8.2, 8.2 Hz), 2.58 (1H, m), 4.34 (1H, m), 4.94 (1H, m), 5.19 (1H, m); ¹³C NMR (100 MHz, CDCl₃) δ: 18.3, 20.4, 21.0, 21.2, 28.1, 29.1, 40.9, 41.1, 66.7, 67.3, 77.0, 170.4, 170.6, 171.2; IR ν_max (CHCl₃): 3025, 2360, 1734, 1373, 1244, and 1049 cm⁻¹. HRFABMS m/z (M + H)⁺: calcd for C₁₄H₂₃O₆: 287.1495, found: 287.1499. (5S,7S,9R)-(ent-18g). 70% yield, [α]²⁰_D +45 (c 1.0, CHCl₃).

(+)-Cryptocarya diacetate (1a)

A reaction mixture of diacetate 18a (89.0 mg, 0.31 mmol) and benzeneseleninic acid anhydride (0.18 g, 70%, 0.35 mmol) in chlorobenzene (10 mL) was heated at 130 °C for 72 h. After concentration of the solvent, the residue was applied to silica gel column chromatography (EtOAc/hexane = 1/1), to give 1a (74 mg, 0.26 mmol, 84%) as a colorless oil, [α]²⁰_D +49 (c 0.5, CHCl₃), [α]²⁰_D +47.5 (c 0.6, CHCl₃) in literature.⁹⁾ NMR data agreed with those in the literature.⁹⁾ >99%ee (AD-H, 250 mm × 4.6 mm i.d., 5 μm, 5% iso-PrOH/hexane, 1 mL min⁻¹, 210 nm, t_R35 min).

(-)-Cryptocarya diacetate (1b)

[α]²⁰_D −49 (c 1.2, CHCl₃), [α]²⁰_D −44 (c 0.46, CHCl₃)¹⁰⁾ in literature. NMR data agreed with those in the literature.⁹⁾ >99%ee (AD-H, 250 mm × 4.6 mm i.d., 5 μm, 5% iso-PrOH/hexane, 1 mL min⁻¹, 210 nm, t_R30 min).

(5R,7S,9R)-7,9-Diacetoxy-2-decen-5-olide (1c)

80% yield, NMR data agreed with those in the literature.¹⁰⁾ [α]²⁰_D +57 (c 0.2, CHCl₃), [α]²⁰_D +30 (c 0.62, CHCl₃) in the literature.¹⁰⁾>99%ee (AD-H, 250 mm × 4.6 mm i.d., 5 μm, 10% EtOH/hexane, 1 mL min⁻¹, 210 nm, t_R24 min).

(5S,7R,9S)-7,9-Diacetoxy-2-decen-5-olide (1d)

83% yield, NMR data agreed with those in the literature.¹⁰⁾ [α]²⁰_D −57 (c 0.1, CHCl₃), [α]²⁰_D −41.5 (c 1.02, CHCl₃) in literature.¹⁰⁾>99%ee (AD-H, 250 mm × 4.6 mm i.d., 5 μm, 10%EtOH/hexane, 1 mL min⁻¹, 210 nm, t_R16 min).

(5R,7R,9R)-7,9-Diacetoxy-2-decen-5-olide (1e)

81% yield, NMR data agreed with those in the literature.¹⁰⁾ [α]²⁰_D +39 (c 0.7, CHCl₃), [α]²⁰_D +25.6 (c 0.6, CHCl₃) in literature.¹⁰⁾ >99%ee (AD-H, 250 mm × 4.6 mm i.d., 5 μm, 10% EtOH/hexane, 1 mL min⁻¹, 210 nm, t_R43 min).

(5S,7S,9S)-7,9-Diacetoxy-2-decen-5-olide (1f)

80% yield, NMR data agreed with those in the literature.⁴⁾ [α]²⁰_D −39 (c 0.6, CHCl₃), [α]²⁰_D −20.5 (c 0.6, CHCl₃)¹⁰⁾ and [α]²⁰_D −35.6 (c 0.75, CHCl₃)⁴⁾ in literatures. >99%ee (AD-H, 250 mm × 4.6 mm i.d., 5 μm, 10% EtOH/hexane, 1 mL min⁻¹, 210 nm, t_R30 min).

(5R,7R,9S)-7,9-Diacetoxy-2-decen-5-olide (1g)

85% yield, NMR data agreed with those in the literature.¹⁰⁾ [α]²⁰_D +40 (c 0.8, CHCl₃), [α]²⁰_D +43.5 (c 0.8, CHCl₃) in literature.¹⁰⁾ >99%ee (AD-H, 250 mm × 4.6 mm i.d., 5 μm, 10% EtOH/hexane, 1 mL min⁻¹, 210 nm, t_R 22 min).

(5S,7S,9R)-7,9-Diacetoxy-2-decen-5-olide (1h)

80% yield, NMR data agreed with those in the literature.¹⁰⁾ [α]²⁰_D −40 (c 0.5, CHCl₃), [α]²⁰_D −32 (c 0.17, CHCl₃) in literature.¹⁰⁾ >99%ee (AD-H, 250 mm × 4.6 mm i.d., 5 μm, 10% EtOH/hexane, 1 mL min⁻¹, 210 nm, t_R20 min).