BF3.OEt2-mediated C-C bond-forming reaction of α-hydroxyketene-(S,S)-acetals with active methylene compounds and its application in the synthesis of substituted 3,4-dihydro-2-pyridones

The C-C bond-forming reaction between alpha-hydroxy-ketene-(S,S)-acetals 2 and active methylene compounds is described. Mediated by boron trifluoride etherate (BF3 center dot OEt2), a series of C-C bond coupling products, 2-(2-acetyl-1-methyl-3-oxobutyl)-N-aryl-3,3-bis(ethylthio)acrylamides 3 was obtained in high to excellent yields by the reaction of 2a-e (R-1 = Ar) with acetylacetone. Various N-aryl-substituted 3,4-dihydropyridones 5 were prepared in high yields from 3 via a two-step procedure. Upon the reaction of 2f (R-1 = H) with active methylene compounds, 3,4-dihydropyridones 6 and/or 7, were obtained in a one-pot reaction with moderate to good yields.