A method for the synthesis of allyl substituted γ-butenolides via carbonyl ylide rearrangement of vinyl sulfoxonium ylide-derived carbenes has been developed. At rt, the mechanism involves a carbonyl ylide generation/allyloxy furan formation/[3,3]-sigmatropic rearrangement/isomerization sequence for the generation of 3-allyl butenolides. At 70 °C, instead of the final isomerization step, the resulting [3,3]-sigmatropic rearrangement product undergoes further [3,3]-sigmatropic rearrangement to produce 5-allyl butenolide. In the absence of the catalyst, the reaction affords a diene via [2,3]-sigmatropic rearrangement.

In this review, the coupling of two carbene precursors for the synthesis of alkenes is surveyed.The key to selective carbene coupling is the difference in the rate of carbene generation between the two carbene precursors. This strategy requires judicious selection between two carbene precursors as well as fine-tuning of reaction conditions to obtain the desired chemo-and stereoselectivity. These couplings were carried out in the presence and absence of a metal catalyst. The present review describes inter-and intramolecular coupling of diazo compounds and cross-coupling between diazo and non-diazo compounds. 1.Introduction 2.