Phospha-Peterson reactions with esters and thioesters: isolation of phosphaalkenes bearing C-heteroatom substituents

Abstract

Several phospha-Peterson routes to phosphaalkenes from silylphosphines and various ester or thioester reagents are investigated. Treatment of MesP(SiMe₃)₂ with PhCO(OPh) in the presence of KOH (10 mol%) affords the Becker-type phosphaalkene, MesPC(OSiMe₃)Ph rather than MesPC(OPh)Ph. Using stoichiometric Li[MesPSiMe₃] rather than catalytic KOH permitted isolation of the presumptive phospha-enolate intermediate following ester cleavage, MesPC(OLi)Ph. The analogous MesPC(ONa)Ph was obtained by treating a mixture of MesPH₂ and NaOt-Bu with PhC(O)Cl. Both are dimers in the solid-state. Treatment of the rare alkali metal phospha-enolates with Me₃SiCl afforded known MesPC(OSiMe₃)Ph. When using ε-thiocaprolactone, OCS(CH₂)₅, as the substrate in the Lewis acid-mediated phospha-Peterson reaction with ArP(SiMe₃)₂, three new C-chalcogen-substituted phosphaalkenes, RPCS(CH₂)₅ (R = Mes, m-Xyl, Tripp) were obtained.