Diastereoselective Generation of C 2 -Azlactonized 2 H -Chromenes via Brønsted Acid-Catalyzed Oxo-Cyclization of Propargyl Alcohols.

A new Brønsted acid-catalyzed oxo-cyclization of propargyl alcohols with azlactones to synthesize C 2 -azlactonized 2 H -chromenes has been established that uses 1,1'-binaphthyl-2,2'-diyl hydrogen phosphate (BiNPO 4 H) as the catalyst and gives excellent diastereoselectivities (≥19:1 dr) in most cases. This protocol has a high compatibility with various substituents of substrates, offering a catalytic and useful entry to the fabrication of the synthetically important C 2 -functionalized 2 H -chromene scaffold.