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

Abstract

The secondary phosphonate ester endo-2-(diethoxyphosphoryl)bicyclo[2.2.1]heptane 6 was prepared in stereoselective fashion for the first time by hydrogenation of 2-(diethoxyphosphoryl)bicyclo[2.2.1]hept-2-ene 1. The precursor vinylphosphonate 1 was prepared by two different routes. Of these, the direct preparation of phosphonate 6 from norbornene in 76% overall yield proved to be the most convenient. Treatment of 6 with PCI₅ at 105 °C gave exclusively endo dichloride 7. This same reaction at 120–140 °C gave a 3:1 ratio of endo- to exo-phosphonic dichlorides 7 and 8, respectively. When pure 7 or 8 were exposed to PC1₅ at 120–140 °C isomerization of each occurred.

Key Words:

• Bicyclo[2.2.l]heptane
• bicyclo[2.2.1]hept-2-ene
• norbornyl
• norbornenyl
• phosphonate
• stereoselective
• isomerization