Corey-Winter olefin synthesis mechanism

However, evidence opposing the intermediacy of a carbene species in the Corey-Winter olefin synthesis also exists.3 Thermal decomposition of hydrazone salt 14, which is proposed to proceed via carbene 12, leads to a mixture of products 13, 15, and 16.7 Thus, an alternative mechanism has been proposed for the Corey-Winter reaction that invokes a phosphorus ylide. In this mechanistic scenario, initial reaction of thionocarbonate 10 with trimethylphosphite affords zwitterion 11. Cyclization generates... 

---