An enantioselective ketene-imine cycloaddition method for synthesis of substituted ring-fused 2-pyridinones

Previously, a method for the stereoselective synthesis of P-lactams, starting from 2H-Delta (2)-thiazolines and Meldrum's acid derivatives, has been reported from our laboratory. We now report a new method for the synthesis of optically active, highly substituted ring-fused 2-pyridinones. This was discovered when 2-alkyl-Delta (2)-thiazolines and Meldrum's acid derivatives were treated with HCl(g) in benzene at 5 --> 78 degreesC. Further refinement of the synthetic protocol revealed that use of 1,2-dichloroethane as solvent at 0 --> 64 degreesC led to the desired 2-pyridinones;in good yields and with excellent enantioselectivity. Use of these conditions allowed preparation of 2-pyridinones from several different Delta (2)-thiazolines and Meldrum's acid derivatives and may be a general route to 2-pyridinones.