ASYMMETRIC CATALYSIS - ASYMMETRIC CATALYTIC INTRAMOLECULAR HYDROSILATION AND HYDROACYLATION

Catalysts of the type [Rh(chiral diphosphine)](+) efficiently catalyse the intramolecular hydrosilation of silyl ethers derived from allylic alcohols. The products can be converted to chiral 1,3-diols. High ena ntiomeric excesses (ee's) are observed for substances bearing an aryl group at the olefin terminus. These same catalysts produce chiral cycl opentanones from 4-substituted 4-pentenals. Tertiary, acyl and ester s ubstituents give nearby quantitative ee's. The mechanism of hydrosilat ion is inferred to involve silyl olefin insertion, whereas the key ste p in hydroacylation probably involves reductive elimination of the met allacyclohexanone intermediate.