Chiral DMAP-N-oxides as Acyl Transfer Catalysts: Design, Synthesis, and Application in Asymmetric Steglich Rearrangement.

A DMAP-N-oxide, featuring an α-amino acid as the chiral source, was developed, synthesized and applied in asymmetric Steglich rearrangement. A series of O-acylated azlactones afforded C-acylated azlactones possessing a quaternary stereocenter in high yields (up to 97 % yield) and excellent enantioselectivities (up to 97 % ee). Compared to the widespread use of pyridine nitrogen, which serves as the nucleophilic site in the asymmetric acyl transfer reaction, we discovered that chiral DMAP-N-oxides, in which the oxygen now acts as the nucleophilic site, are efficient acyl transfer catalysts. Our finding might open a new door for the development of chiral DMAP-N-oxides for asymmetric acyl transfer reactions.