Simmons-Smith reaction with vinyl ethers

The Simmons-Smith reaction often starts very slowly and proceeds quite slowly at room temperature. The method of the preparation of active zinc-copper couple has been improved 93, 196, 298, 376, 443, 466). The use of zinc dust/cuprous chloride instead of zinc-copper couple gives higher yields in the Simmons-Smith reaction 407). The reaction with homoallylic alcohols of low reactivity was facilitated by use of excess Simmons-Smith reagent and distillation of ether to a halfvolume followed by heating in a stainless steel tube 182). The Simmons-Smith reaction was successfully applied to vinyl trimethylsilyl ethers to prepare, after methanolysis, cyclopropyl alcohols unobtainable by other methods 109). Here, the zinc-silver couple was used instead of the zinc-copper couple, and the quenching of the reaction mixture of the Simmons-Smith reaction was improved by using pyridine under nonaqueous conditions. 

Considering the selectivity of this reaction (terminal vs. 1,2-disubstituted alkenes) and the fact that an electron-rich alkene such as isobutyl vinyl ether does not undergo cyclopropanation, it seems that the reactive species formed from the lithiated sulfone and the nickel catalyst does not behave as an electrophilic carbenoid. In this respect, one should note that the Simmons-Smith reagent is electrophilic whereas the methylene transfer reagent arising from treatment of dibromomethane with nickel(O) can achieve cyclopropanation of electron-deficient alkenes only. ... 

---