STEREOSELECTIVE PREPARATION OF THE ENDO-2-PHOSPHORUS SUBSTITUTED BICYCLO[2.2.1]HEPTANE SYSTEM

The secondary phosphonate ester endo-2-(diethoxyphosphoryl)bicyclo[2.2 .1]heprane 6 was prepared in stereoselective fashion for the first tim e by hydrogenation of 2-(diethoxyphosphoryl)bicyclo[2.2.1]hept-2-ene 1 . The precursor vinylphosphonate 1 was prepared by two different route s, Of these, the direct preparation of phosphonate 6 from norbornene i n 76 % overall yield proved to be the most convenient, Treatment of 6 with PCl5 at 105 degrees C gave exclusively endo dichloride 7. This sa me reaction at 120-140 degrees C gave a 3:1 ratio of endo- to exo-phos phonic dichlorides 7 and 8, respectively. When pure 7 or 8 were expose d to PCl5 at 120-140 degrees C isomerization of each occurred.