REFERENCES AND NOTES
- ApSimon , J. 1992 . The Total Synthesis of Natural Products , Vol. 3 , 34 – 41 . New York : John Wiley & Sons Inc. .
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- Mori , K. and Waku , M. 1985 . Tetrahedron , 41 : 5653
- Chamy , M. C. , Piovano , M. , Garbarino , J. A. , Miranda , C. and Gambaro , V. 1990 . Phytochemistry , 29 : 2943
- Charlwood , B. V. and Banthorpe , D. V. 1991 . Methods in Plant Biochemistry , 263 – 287 . New York : Academic Press .
- Pelletier , S. W. , Chappell , R. L. and Prabhakar , S. 1968 . J. Am. Chem. Soc. , 90 : 2889
- Wakselman , C. and Molines , R. 1979 . Synthesis , : 622
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- Direct formylation with alkyl formate, carboxylation with CO2 or alkylation under various reaction conditions were not successful. Only carboalkoxylation with LDA and alkyl cyanoformate or alkyl chloroformate gave the desired product. However, carboallyloxylation with allyl cyanoformate provides higher yield.
- Each isomer was separated by flash column chromatography and their structures were determined by NOE (500 MHz) studies of H-8 and methyls at C-10 and C-13. Further structural confirmation of the desired diastereomer was carried out at the late stage of this synthesis.
- Morrison , J. D. 1984 . Asymmetric Synthesis , Vol. 3 , 50 – 73 . New York : Academic Press, Inc. .
- Gemal , A. L. and Luche , J. L. 1981 . J. Am. Chem. Soc. , 103 : 5454
- Hartwig , W. 1983 . Tetrahedron , 39 : 2609
- Friedrich-Bochnitschek , S. , Waldmann , H. and Kunz , H. 1989 . J. Org. Chem. , 54 : 751
- Carda , M. , Arno , M. and Marco , J. A. 1986 . Tetrahedron , 42 : 3655
- Careful spectral analysis (DEPT, COSY and NOESY of 500 MHz NMR) reveals cis-relationships of H-8 and methyls at C-10 and C-13 with all axial orientations.
- Spectral data for the synthetic isopimarol diterpene 1: IR (neat) 3380, 1645 cm−1; 1H NMR (CDCl3, 400 MHz) δ 5.75 (dd, 1H, J = 17.6, 10.7 Hz), 5.23 (d, 1H, J = 5.9 Hz), 4.86 (dd, 1H, J = 17.6, 1.5 Hz), 4.80 (dd, 1H, J = 10.7, 1.5 Hz), 3.74 (d, 1H, J = 10.7 Hz), 3.39 (d, 1H, J = 10.7 Hz), 2.17 (br s, 1H), 1.99 – 0.76 (m, 15H), 0.94 (s, 3H), 0.88 (s, 3H), 0.84 (s, 3H); 13C NMR (CDCl3, 400 MHz) δ 150.2, 149.4, 112.8, 109.2, 65.3, 54.3, 42.5, 39.2, 38.9, 37.6, 37.2, 36.4, 35.5, 34.7, 31.1, 29.7, 26.8, 21.9, 21.8, 18.7; MS 288 (M+), 273, 257, 255, 229, 220; HRMS Calcd. for C20H32O 288.2453, found 288.2462.