Synthesis of dimeric 1,3,2λ5-benzoxazaphospholes from phosphinic acid derivatives by silylation/desiloxylation

The reaction of N,N,O-tris(trimethylsilyl)-o-aminophenol with two equivalents of phosphinic chloride yielded dimeric 2,2-disubstituted 1,3,2λ⁵-benzoxazaphospholes and trimethylsilyl phosphinate. The chlorides having the bulk substituents (o-chlorophenyl or tert-butyl) at phosphorus or containing P N and P O bonds (instead of a P C bond) either didn't react at all or reacted to retain the phosphoryl group. Being stable in solution at 20°C, the individual diastereoisomers of dimeric 1,3,2-benzoxazaphospholes were converted upon warming to an equilibrium mixture of isomers. When reacted with another dimer each gave a mixed dimeric compound having two different phosphorus atoms in the molecule.