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 MnO 2 as an oxidant and catechol as a Brønsted acid additive.