Synthesis of New Sulfonium Ylides Bearing the Chiral Diazaphospholidine Group as Reagents for Asymmetric Cyclopropanation

Sulfonium ylides derived from chiral N,N'-substituted (benzyl, isopropyl, neopentyl) phosphonamides were prepared by reacting appropriate chiral diamidophosphites with potassium hydride and chloromethyl methyl sulfide, and then with methyl iodide in the presence AgBF4 to give the corresponding sulfonium salts in high yields. One of them was analyzed by X-ray crystallography. The salts upon treatment with different bases (LithiumDiisopropylAmine, BuLi, K2CO3) were converted in situ into ylides, which were reacted with activated olefins to produce phosphonocyclopropanes as a mixture of two diastereoisomers with moderate-to-high diastereoselectivities.