Proline-tetrazole-catalyzed enantioselective N-nitroso aldol reaction of aldehydes with in situ generated nitrosocarbonyl compounds.

A highly enantioselective method (up to 98% ee) for the preparation of β-amino alcohols was achieved by using the readily available proline-tetrazole as the catalyst for the N-nitroso aldol reaction of aldehydes with in situ generated nitrosocarbonyl compounds. The key to success of this reaction is the use of MnO2 as an oxidant and catechol as a Brønsted acid additive.