Control of stereochemistry in an intramolecular Diels–Alder reaction by the phenylsulfonyl group; an improved synthesis of pisiferol

Abstract

Thermolysis of 4a (X = H) gives 6a and 6b (X = H) in a ratio of 1∶4 whereas 4b (X = SO₂Ph) gives more of the trans-ring junction product 6a (X = SO₂Ph) suitable for the synthesis of pisiferol [ratio 6a∶6b (X = SO₂Ph) = 1.5∶1]. Base catalysed elimination of the phenylsulfonyl group from 6a (X = SO₂Ph) gives 18 which is hydrogenated to 6a (X = H), an intermediate in the synthesis of pisiferol. Both 6a and 6b (X = SO₂Ph) have ring B in a half-boat conformation.

References

1. T. Kametani, H. Kondoh, M. Tsubuki and T. Honda, J. Chem. Soc., Perkin Trans. 1, 1990, 5.
2. D. Craig, D. A. Fischer, O. Kemal, A. Marsh, T. Plessner, A. M. Z. Slawin and D. J. Williams, Tetrahedron, 1991, 47, 3095.
3. S. Niwayama and K. N. Houk, Tetrahedron Lett., 1993, 34, 1251; E. Piers and K. A. Ellis, ibid., 1993, 34, 1875 and references cited by these authors Unlike the CHO group, CO₂Et generally prefers outward conrotation in competition with hydrogen (but compare K. Shishido, E. Shitara, K. Fukumoto and T. Kametani, J. Am. Chem. Soc., 1985, 107, 5810; C. W. Jefford, G. Bernardinelli, Y. Wang, A. B. Spellmeyer and K. N. Houk, J. Am. Chem. Soc., 1992, 114, 1157).
4. T. Kametani, M. Tsubuki, Y. Shiratori, Y. Kato, H. Nemoto, M. Ihara, K. Fukumoto and F. Satoh, J. Org. Chem., 1977, 42, 2672.
5. C. W. G. Fishwick and D. W. Jones, ortho-Quinonoid Compounds in The Chemistry of Quinonoid Compounds, ed. S. Patai and Z. Rappoport, Wiley, 1988, vol. II, pp. 403–453 and cited references.
6. Preliminary communication of some of these results: E. J. Bush, D. W. Jones and M. Thornton-Pett, Tetrahedron Lett., 1994, 35, 9755.
7. E. J. Bush, D. W. Jones and F. M. Nongrum, J. Chem. Soc., Chem. Commun., 1994, 2145.
8. B. J. Hunt and W. Rigby, Chem. Ind. (London), 1967, 1868.
9. D. D. Perrin, W. C. F. Armagego and D. Perrin, The Purification of Laboratory Chemicals, Pergamon, Oxford, 2nd edn., 1980.