Synthesis of β, γ-Unsaturated Valerolactones

References

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• The preparation of 3a-d was essentially based on the reported one,3,8) except the fact that these diacids 3a-d were all crystalline (3a: mp 98–99° from (i-Pr)2O-PhH, 3b monohydrate: mp 54–55° from aq. THF, 3c: mp 127–128° from Et2O-petroleum ether, 3d: mp 129–130° from Et2O-petroleum ether)
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• Et3N was suitable for the supporting electrolyte, since the use of stronger bases, such as NaOMe, afforded a considerable amount of the conjugated isomers. Furthermore, more than 1.0 mol equivalent of Et3N seems to be essential; otherwise the high acid strength of the malonic acids causes the formation of the half ester thereof in MeOH solution
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• The use of platinum electrode gave rather complex products
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• The structure of these acid- and moisture-sensitive orthoesters 4c and 4d was determined by 1H- and 13C-NMR analyses; 4c: 1H-NMR(CDCl3) δ 5.62 (m, 2H), 4.40(br m, 1H), 3.34(s, 3H), 3.27(s, 3H), 2.32(m, 2H), 1.27(d, J = 7 Hz, 3H); 13C-NMR(CDCl3) δ 129.58(d), 120.99(d), 112.01(s), 69.03(d), 49.31(q), 48.24(q), 30.81(t), 20.60(q). 4d: 1H-NMR(CDCl3) δ 6.45(m, 2H), 4.70(m, 1H), 3.33(s, 3H), 3.23(s, 3H), δ3–4(m, 1H), 1.15–2.25(m, 4H); 13C-NMR(CDCl3) δ 133.29(d), 131.19(d), 102.19(s), 69.33(d), 49.56(q), 48.58(q), 35.15(d), 24.65(t), 17.13(t)
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• The spectral data of the lactones 5a, 5b, and 5d were identical with those of reported ones, 3)
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• New compound 6 had satisfactory IR, 1H- and 13C-NMR properties and gave a correct elemental analysis
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• The reactions effected in more concentrated solutions or at higher current density (ca. 0.02 A/cm2) gave similar results
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