Asymmetric synthesis of highly substituted β-lactones by nucleophile-catalyzed [2+2] cycloadditions of disubstituted ketenes with aldehydes

α,α-Disubstituted β-lactones can be obtained by the cycloaddition of the corresponding ketenes with aldehydes (see scheme). For the first time, a chiral PPY derivative, 1, serves as an efficient catalyst for the asymmetric synthesis of β-lactones (PPY = 4-pyrrolidin-1-ylpyridine). To date, this is the only catalyst that is effective for enantioselective cycloadditions of disubstituted ketenes with aldehydes. (Chemical equation presented).