Asymmetric Carbene C–O Insertion Reaction Using Optically Active Bipyridine-Copper Complex as a Catalyst. Ring Expansion of Oxetanes to Tetrahydrofurans

Copper complex of (7R,7R′)-7,7′-di(1-t-butyldimethylsiloxy-1-methylethyl)-6,6′,7,7′-tetrahydro-5H,5′H-2,2′-bi-1,1′-pyrindine (3) was found to be an effective catalyst for asymmetric carbene insertion reaction into the C-O bond of oxetanes. For example, the reaction of dl-2-phenyloxetane and t-butyl diazoacetate in the presence of Cu-3 complex provided trans- and cis-t-butyl 3-phenyltetrahydrofuran-2-carboxylate of 75% ee and 81% ee, respectively.