Asymmetric Dihydroxylation of Esters and Amides of Methacrylic, Tiglic, and Angelic Acid: No Exception to the Sharpless Mnemonic

Literature findings on the facial selectivity of the Sharpless asymmetric dihydroxylation (SAD) of isobutyl angelate are contradictory and partly in conflict with the Sharpless mnemonic. We systematically screened the SAD of esters and amides of angelic, tiglic, and methacrylic acid. Enantiocontrol arose in 14 of the 15 reactions, culminating at 99 % ee for the Weinreb amide of tiglic acid. The absolute configurations of all the nonracemic products were established by (stereo)chemical correlations. Without exception, they conform to the Sharpless mnemonic. The Sharpless mnemonic is generally accepted as a predictive tool for the stereochemical outcome of Sharpless asymmetric dihydroxylation reactions. However, it was claimed that isobutyl tiglate is dihydroxylated with the opposite facial selectivity because of a preference for a “Chapleur transition state”. We have investigated this claim and proved it false.