Organometallic Catalysis: Formation of 1,3-Dioxolanes and Their Analogs Catalyzed by Methylrhenium Trioxide (MTO)

Methylrhenium trioxide (MTO) catalyzes several cycloaddition reactions. 1,3-Dioxolanes were obtained in good yields from the reactions of epoxides with aldehydes or ketones; the geometric configuration of the epoxide substituents remains unchanged in the product, which was shown to be the consequence of two configuration inversions in sequence. The independently known bis(alkoxy)rhenium complex formed from MTO and the epoxide is an intermediate that could be detected at a low level during the reaction; indeed, its formation limits the rate of the overall reaction. Related cycloaddition reactions are the formation of ketene acetals from diphenylketene and epoxides and of oxazolidines from aromatic imines and epoxides, both MTO-catalyzed.