Diastereoselective synthesis and molecular structure of a bicyclic and a cage phosphane

A two-step formal insertion of 1,1,1,5,5,5-hexafluoro- (2a) and 1,1,1-trifluoropentane-2,4-dione (2b) into the P-H bonds of phosphane gave the primary alpha-hydroxyphosphanes 3 and 4, precursors for the resulting secondary phosphanes, 6,9-dioxa-2-phosphabicyclo[3.3.1]nonane (6a) and 2,4,8-trioxa-6-phosphaadamantane (7), both formed diastereospecifically. The molecular structures of 6a and 7 were established by single-crystal X-ray structure analysis which revealed two independent molecules for 6a in the unit cell possessing a chair-boat conformation with a C-P-C angle of 95.4(2)degrees, and a characteristic heteroadamantane geometry for 7, with the corresponding angle being smaller by 4.9 degrees.