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 1,111‐trifluoropentane‐2,4‐dione ( 2b ) into the P‐H bonds of phosphane gave the primary a‐hydroxyphosphanes 3 and 4, precursors for the resulting secondary phosphanes, 6,9‐dioxa‐2‐phosphabicyclo[3.3.l]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)°, and a characteristic heteroadamantane geometry for 7 , with the corresponding angle being smaller by 4.9°.