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Mechanism and Regioselectivity of the Cycloaddition of Thiones Derived from Meldrum’s Acid, Malonates, or Other Dicarbonyls

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posted on 03.10.2008, 00:00 by Stéphane Perreault, Maude Poirier, Pascal Léveillé, Olivier René, Pascal Joly, Yves Dory, Claude Spino
Several α,α-dioxothiones were generated in situ and reacted with 1,3-dienes of varying electronic and steric properties. It was found that thiones 10a and 11a reacted well with electron-rich or electron-poor dienes and are complementary in their regioselectivities when steric effects are at play. The calculated preferred mechanistic pathway implies a thiiranium zwitterion intermediate.