tereochemical Model For Electrophilic Attack on Allylsilanes Electrophilic Attack on Allylsilanes PhMe mCPBA The products on the left r Path a Path B 91 2g If A> Me, then Path a dominates due to a(1, 3)strain I IfA H, then Path B can compete a Larger R groups result in higher selectivity a The size of R is more important in locking the substrate into the ading to Path A than in shielding the E Afynsianes and the sicon g fect Dec 1l, 190 5 425.0 Fleming, JCS Perkin Trans L, 1992, 3303-3308 OA-07-Allylsilanes 1018/00 8: 13 PMScott J. Miller Evans Evening Seminar, "The Chemistry of Allylsilanes and the β Silicon Effect," Dec 11, 1990, p 45. Path A Path B Paddon-Row, Rondan, and Houk JACS 1982 104, 7162. + + El+ El+ ■ If A = H, then Path B can compete ■ If A ≥ Me, then Path A dominates due to A(1,3) strain tereochemical Model For Electrophilic Attack on Allylsilanes Model assumes: 1. Electrophilic attack anti to the silyl moiety 2. The silyl group is the "large" substituent Electrophilic Attack on Allylsilanes mCPBA Me iPr PH 61 : 39 >95 : 05 89 : 11 R Ratio R Ratio 58 : 42 >95 : 05 91 : 09 Me iPr PH AlMe3 OsO4 Me iPr PH 34 : 66 67 : 33 92 : 08 R Ratio CH2I2 ■ Epoxidation ■ Cyclopropanation ■ Osmylation The products on the left correspond to attack by Path A ■ Larger R groups result in higher selectivity ■ The size of R is more important in locking the substrate into the conformation leading to Path A than in shieldieng the El+ Fleming, JCS Perkin Trans I, 1992, 3303-3308. El C R SiR3 R' A H R PhMe2Si R Me SiR3 C H H C El C R' H R SiR3 H C A R' R El R R' Me R A Me PhMe2Si C H PhMe2Si O O PhMe PhMe2Si 2Si R R Me R Me R H R SiR3 H C Me PhMe2Si PhMe2Si R Me C A R Me R Me PhMe2Si R' PhMe2Si OH OH OH OH A El A A R R' SiR3 R' 0A-07-Allylsilanes 10/8/00 8:13 PM