Synthesis and steric structure of pyrrolidine- and piperidine-fused 1,3,4,2-oxadiazaphosphinanes

Pyrrolidine-and piperidine-fused 1,3,4,2-oxadiazaphosphinane 2-oxides were prepared by cyclization of the corresponding pyrrolidine-and piperidine-hydrazino alcohols by using phosphorus-containing reagents.Stereochemical and conformational analyses were carried out in order to determine the effect of the ring size on the conformational behavior of the nitrogenbridged bicyclic system.It was found that the chair conformation in the pyrrolidine-fused 1,3,4,2-oxadiazaphosphinane 2-oxides can be shifted toward twisted or distorted conformations.