... I Research fellow of the Alfred P. Sloan Foundation ... H 2b R = SiMe, 3b R = SiMe, dR 4aR-H 4b R ISiMe$ - RO- OR BaR=H 6aRmH Sb R = Bb R 9 S-8 OR ... 123 (1990) 1667 - 1671 0 VCH Verlagsgesellschaft mbH, D-6940 Weinheim, 1990 OO09-2940/90/0808- 1667 $ 3.50+.25/0 ...