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(SiMe 3 ) 2 with PhCO(OPh) in the presence of KOH (10 mol%) affords the Becker-type phosphaalkene, MesP=C(OSiMe 3 )Ph rather than MesP=C(OPh)Ph. Using stoichiometric Li[MesPSiMe 3 ] rather than catalytic KOH permitted isolation of the presumptive phospha-enolate intermediate following ester cleavage, MesP=C(OLi)Ph. The analogous MesP=C(ONa)Ph was obtained by treating a mixture of MesPH 2 and NaOt-Bu with PhC(O)Cl. Both are dimers in the solid-state. Treatment of the rare alkali metal phospha-enolates with Me 3 SiCl afforded known MesP=C(OSiMe 3 )Ph.When using ε-thiocaprolactone, O=CS(CH 2 ) 5 , as the substrate in the Lewis acid-mediated phospha-Peterson reaction with ArP(SiMe 3 ) 2 , three new C-chalcogen-substituted phosphaalkenes, RP=CS(CH 2 ) 5 (R = Mes, m-Xyl, Tripp) were obtained.