The Preparation of Optically Pure 7‐Oxabicyclo [2.2.1]hept‐2‐ene Derivatives. The CD Spectrum of (+)‐(1R)‐7‐Oxabicyclo [2.2.1]hept‐5‐en‐2‐one

Abstract

Abstract(−)‐1‐Camphanoyloxyacrylonitrile (=(−)‐1‐cyanovinyl camphanate; 1) obtained from the commercially available (−)‐camphanoyl chloride and 2‐oxo‐propiononitrile added to furan at 20° in the presence of Cu (BF4)2 · 6H2O or ZnI2 and gave a mixture of 2‐cyano‐7‐oxabicyclo [2.2.1]hept‐5‐en‐2‐yl camphanates (2–5) from which isomer 5 could be obtained pure by crystallization. The latter was transformed into (+)‐(1R)‐7‐oxabicyclo[2.2.1]hept‐5‐en‐2‐one (6) in high yield and optical purity. Adducts 2–4 were recycled into 1+furan by heating in toluene, and (−)‐camphanic acid was recovered after saponification of 5. The absolute configuration of 6 was deduced from its CD spectrum which showed two 1200‐cm−1 Franck‐Condon series for its n→π transition.