1
932
preferred conformationl0,11 through appropriate substitution, as shown by the 4:1 p/o: ratio obtained in the
alkylation of compound 19, which is fixed in conformation III.10,11 It is worthwhile to mention that in this case
the alkilafion proceeds mainly upon the [3 face of the molecule. Such manipulations allowed us to control the
stereochemistry of the angular substituent. 12
In conclusion, herein we have described the optimum conditions for the direct introduction of an angular -CH2OR
moiety through a reductive alkylation in mono-, hi- and tricyclic benzylic ketones, in the later, for the 4a-MethyI
trans series, the reaction proceeds with high stereoselectivity producing an and disposition of the angular
substituents, as in the fusidanes. In addition, in the cis series the stereoselection can be manipulated toward the
desired isomer through appropriate substitution The dienes obtained through this procedure may be seen as
versatile intermediates in natural product synthesis, i.e., for the construction of polyfunctionalized decalins, tri-
and tertracyelic di- and triterpenoids with stereochemically defined angular substituents. Additional work in this
direction is in progress.
Acknowledgements: The authors wish to thank CONICET and the Universidad Nacional de Rosario for financial support. A.EV.
also thanks CONICET for a fellowship.
Refernees and Notes:
1
2
3
. R, B. Boar, Nat. Prod. Report, 53 (1984).
. L. Larsen and J. K. Sutherland, J, Chem. Soc., Chem. Comm.. 784 (1989).
. For excellent updated reviews, see: a) P. W. Rabideau, Tetrahedron, 1579 (1989) b) J.M. Hook and L.N.Mander, Nat. Prod.
Report, 3, 35 (1986).
4
. M. Narisada and F. Watanabe, J.Org.Chem., 38, 3887 (1973); J.M. Brown, T. M. Cresp and L.M. Mander, ]Org.Chem, 42,
3
984 (1977).
. R. McCague, C.J. Moody and C.W. Rees, J.Chem.Soc., Rerkin Trans 1, 2399 (I983); Z. Lidert, R. McCague, C.J, Moody and
C.W. Rees, ibid., 383 (1985); C.J. Moody and C.W. Rees, Ibid., 735 (1985); C.J. Moody and J. Toczek, Tetrahedron Left, 5253
1986).
. C. Reichardt. "Solvent effects in organic chemistry", 3rd Edition, Verlag-Chemie, N.Y., pp. 167-170.
. M.T. Bogert, D. Davinson and M. Aptelhaum, J.Am.Chem.Soc., 56, 959 (1934); R,B. Miller and C.G, Gatierrez,
5
(
6
7
J.Org.Chem., 43, 1569 (1978).
8
.A.L. Campbell, H.N. Leader, C.L. Spencer and J.D, McChesney, J.Org,Chem.., 44, 2746 (1979); M. Gonzalez-Sierra, H.M.
Leader and J.D. McCbesney, ZOrg.Chem., 50, 4450 (1985);M. Gonzalez-Sierra, T.N. Thompson and LD. McChesney,
J.Org.Chem., 50, 4447 (1985).
9
1
1
. All new compounds had satisfatory spectral and analytical data, including n.O.e, experiments and selective irradiations.
0. A.L. CampbelI, H.N. Leader, M. Gonzalez-Sierra, C.L. Spencer and J.D. McCbesney, J.Org.Chem., 44, 2755 (1979).
1. A.J. Vila, R.A. Spanevello, A.C. Olivieri, M. Gonzalez-Sierra and ED. McChesney, Tetrahedron, 4951 (1989).
1
2. The relative esterec~hemistry of C-8a epimeric compounds was clearly established by 13C NMR. The C-5 signal shows a
substancial shielding (5 to 6 ppm) when the C5 H bond is envolved in a compressing stem to-stem interaction with the C-8a
substituent, i.e., those with an anti relationship in the trans series or a syn stereocbomistry in the cis series. In this connection
see: LK. Saunders, H. Beierbeck, Can.J.Chem., 55, 2813 (1977); and compounds 16 and 17 in M. Nishizawa, H. Takenaka and
Y. Hayashi, J.Org.Chem.. 51,806 (1986).
(
Received in USA 4 January 1991)