Reaction of stabilized sulfur ylides with alpha,beta unsaturated alkoxy-chromiumcarbene complexes in MeCN as solvent forms vinylenol ethers 3, cyclopropanes 4, and vinylcyclopropanes 5, depending on the reagent ratio, the temperature and the nature of the ylide. The results obtained in these reactions suggest that factors apart from steric hindrance may control the chemoselectivity of the addition. Less stable ylides would add preferentially to the carbene carbon, 1,4-addition increasing as the stability of the ylide does. For more stable ylides 1,4-addition is preferred and substitution at the p-carbon has little effect in the chemoselectivity. Methoxycarbonylmethylentriphenylphosphorane exclusively add to the carbene carbon while ethyl diazoacetate is unreactive towards alpha beta-unsaturated alkoxychromium-carbene complexes in the conditions studied. Copyright (C) 1996 Elsevier Science Ltd.
