Studies towards the synthesis of rapamycin: Regiocontrol in the addition of carbanions to enantiomerically pure epoxides and the formation of a highly substituted tetrahydrofuran

Reaction of trimethylaluminium, dimethyllithium cuprate and lithium tetramethylaluminate with the homochiral epoxide 8 has been studied. Intermolecular epoxide ring-opening was observed with dimethyllithium cuprate and lithium tetramethylaluminate, but acetal ring-opening followed by intramolecular epoxide ring-opening was observed with trimethylaluminium.