2. For example:- M. Isobe, M. Kitamura, and T. Goto, J. Amer. Chem. Soc., 1982, 104, 4997; Y. Takeda, T. Matsumoto, and F. Sato, J. Org. Chem., 1986, 51, 4728; H. Iio, T. Mizobachi, and T. Tokoroyama, Tetrahedron Letters, 1987, 28, 2379; G. Rosioni, R. Galarini, E. Marotta, and P. Righi,J. Org.Chem., 1990, 55, 781; J.-M. Escudier, M. Baltas, and L. Gorrichon, Tetrahedron, and references cited therein.

3. H. Iio, T. Mizobachi, and T. Tokoroyama, Tetrahedron Letters, 1987, 28, 2379; Y. Takeda, T. Matsumoto, and F. Sato, J. Org. Chem., 1986, 51, 4728.

4. W.R. Roush, J.A. Straub, and M.S. VanNieuwenhze, J. Org. Chem., 1991, 56, 1636, and references cited therein.

5. Y. Takeda, T. Matsumoto, and F. Sato, J. Org. Chem., 1986, 51, 4728.

6. Y. Takeda, T. Matsumoto, and F. Sato, J. Org. Chem., 1986, 51, 4728.

7. J.J. Eisch and J.E. Galle, J. Org. Chem., 1990, 55, 4835.

8. H. Urabe, T. Matsuka, and F. Sato, Tetrahedron Letters, 1992, 33, 3355.

9. P.J. Murphy, J.L. Spencer, and G. Procter, Tetrahedron Letters, 1990, 31, 1051.

10. H. Urabe, T. Matsuka, and F. Sato, Tetrahedron Letters, 1992, 33, 3355.

11. G.P. Howe, Ph.D. thesis, Salford, 1987.

12. K.J.M. Beresford, G.P. Howe, and G. Procter, Tetrahedron Letters, 1992, 33, 3355.

13. G.J. Karabatsos and D.J. Fenoglio, J. Amer. Chem. Soc., 1969, 91, 3577; B.A. Arbuzov, A.N. Vereshchagin, and A.I. Donskova, Izv. Akad. Nauk SSSR, Ser. Chim., 1979, 6, 1257, and references cited therein.

14. For examle, see P.A> Bartlett, Tetrahedron, 1980, 36, 2, and references cited therein.

15. J.R. Hanson, P.B. Hitchcock, and H.J. Wadsworth, J. Chem. Soc., Perkin Trans. 1, 1981, 3025; F. Baert, M. Foulon, G. Oudon, and S. Moreau, Actc Cryst, Sect. B, 1980, 36, 402.

16. We thank Dr. A.D. Redhouse and Mr. R. Thompson (Salford) for the determination of this structure.