Inverse-Electron-Demand Diels-Alder Reactions of N-(Heteroarylsulfonyl)-1-aza-1,3-dienes Catalyzed by Chiral Lewis Acids

The feasibility of using chiral Lewis acids as catalysts to promotethe inverse-electron-demand Diels-Alder reactions of 1-azadieneswith vinyl ethers has been demonstrated. Two catalyst systems wereidentified for this reaction, both relying on the presence of acoordinating 2-pyridylsulfonyl or 8-quinolylsulfonyl group at theimine nitrogen of the 1-azadiene. The combination of a 8-quinolylsulfonylmoiety and nickel(II)/DBFOX-Ph proved to be highly efficient,allowing the synthesis of substituted piperidine derivatives ingood yields, excellent ENDO selectivity,and enantio-selectivities typically in the range of 77to 92% ee.