A New Method of Formation of Tributyl-β- keto- and Tributyl-β-alkoxycarbonylalkylidenephosphorane from Tributyl[(trimethylsilyl) methylene]phosphorane and Their Application in the Wittig Reaction

A new and efficient method of the synthesis of tributyl-β-keto- and tributyl-β-alkoxycarbonylalkylidenephosphorane via treatment of tributyl[(trimethylsilyl)- methylene]phosphorane with acid chlorides or chloroformate is described. These compounds have been studied less often than their triphenyl analogues (Maryanoff and Reitz, Chem Rev 1989, 89, 870; Taillefer and Cristau, Top Curr Chem, 2003, 229, 41; Appel, Loos, and Mayr, J Am Chem Soc 2009, 131, 704) because trialkyl-stabilized ylides are very reactive, highly perishable, and more difficult to synthesize. This paper also presents the reaction of in situ generated tributyl-β-keto- and tributyl-β-alkoxycarbonylalkylidenephosphoranes with p-nitrobenzaldehyde as a model aldehyde to obtain α,β-unsaturated ketones and esters. All reactions result in Wittig products in a completely E-stereoselective manner.