An Enantioselective Ketene−Imine Cycloaddition Method for Synthesis of Substituted Ring-Fused 2-Pyridinones
journal contributionposted on 13.09.2001, 00:00 by Hans Emtenäs, Lisa Alderin, Fredrik Almqvist
Previously, a method for the stereoselective synthesis of β-lactams, starting from 2H-Δ2-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-Δ2-thiazolines and Meldrum's acid derivatives were treated with HCl(g) in benzene at 5 → 78 °C. Further refinement of the synthetic protocol revealed that use of 1,2-dichloroethane as solvent at 0 → 64 °C 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 Δ2-thiazolines and Meldrum's acid derivatives and may be a general route to 2-pyridinones.