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Pyridinones from Reaction of Vilsmeier-Haack Reagents with Ketene Dithioacetals
L. Chen, Y.-L. Zhao*, Q. Liu*, C. Cheng, C.-R. Piao
Northeast Normal University, Changchun, P. R. of China
23 January 2008 (online)
Reported is a synthesis of 4-halo-2(1H)-pyridinones by reaction of ketene dithioacetals with an excess of the Vilsmeier-Haack reagents. The halo substituent in the pyridinone product is dependent on the starting Vilsmeier-Haack component. A complex, yet plausible mechanism is proposed that is supported by experimental evidence. The authors explain the formation of significantly different products from the six- and five-membered dithiane-ring starting materials through different levels of overlap of the carbon-sulfur s orbitals with a proposed α-carbocation.