COMPARATIVE-STUDIES ON THE SYNTHESIS OF AN ANTI,SYN STEREOTRIAD WITH CHIRAL ALLENYLSTANNANE AND ALLENYLINDIUM REAGENTS

Addition of the chloroallenylstannane derived from the Bu3Sn allene (S )-2 and SnCl4 to nonracemic alpha-methyl-beta-oxygenated aldehyde 1a a fforded mixtures of anti,syn and anti,anti adducts 3a and 3b. When InC l3 was employed in the transmetalation of allenylstannane (S)-2, a mix ture of adducts 3a and ent-3b was produced. Experiments with the beta- ODPS aldehydes 1b and 5 showed that InBr3 and InI3 yield a transient I nXn species from allenylstannane (S)-2 with mainly retention of config uration. In contrast, transmetalation of (S)-2 with SnCl4 or BuSnCl3 a ffords an intermediate allenyl species of inverted configuration. The (S)-2/BuSnCl3 reagent showed high enantio-and diastereoselectivity in addition to aldehydes 1a, 1b, and 5. The (S)-2/InBr3 or InI3 reagent, while somewhat less selective, afforded enantiomeric or diastereomeric adducts.