Microwave-Assisted Synthesis of P-Heterocycles*

Abstract

The direct esterification, thioesterification and amidation of cyclic phosphinic acids, such as 1-hydroxy-3-phospholene 1-oxides, 1-hydroxy-phospholane 1-oxides and a 1-hydroxy-1,2,3,4,5,6-hexahydrophosphinine 1-oxide, which do not take place on conventional heating, were carried out under MW conditions in excess of the alcohol, thioalcohol and amine, respectively. The cyclic phosphinates were also prepared by MW-assisted alkylating esterification of the corresponding phosphinic acids in solid–liquid phase. Using alkyl halides of normal reactivity, the application of a phase transfer catalyst was also beneficial. In addition, MW-assisted Diels–Alder reactions, so-called inverse Wittig-type reactions furnishing β-oxophosphoranes, a few kinds of phospha-Michael additions leading to precursors of bidentate P-ligands, and a few Kabachnik–Fields condensations affording α-aminophosphonates and α-aminophosphine oxides are discussed.