Further optimization of the aluminate catalyzed reaction (Table ), by variation of aldehyde (2a/2c), diazoacetamide (1a/1b), additive, and ligand led to the identification of (S)-VAPOL ( ) derived aluminate complex as the most efficient catalyst system -the reaction of 1a and 2a catalyzed by 10 mol% of the aluminate complex of (S)-VAPOL prepared without any added DMSO delivered the desired cis-epoxide 11 in 80% yield and 96% ee (Table , entry 5). It is worth noting here that the borate complex of (S)-VAPOL did not give any useful reaction with aldehyde 2a (see Supporting Information).