The Preparation of Optically Pure 7‐Oxabicyclo [2.2.1]hept‐2‐ene Derivatives. The CD Spectrum of (+)‐(1<i>R</i>)‐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 (BF 4 ) 2 · 6H 2 O or ZnI 2 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 (+)‐(1 R )‐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.