Copper(I)‐ and Copper(II)‐catalyzed Diels‐Alder Additions of α‐Substituted Acrylonitrile to Furan. The Synthesis of 7‐Oxa‐bicyclo[2.2.1]hept‐5‐en‐2‐one

The difficult Diels ‐ Alder additions of α‐acetoxy‐ and α‐chloroacrylonitrile to furan can be run at 20–35° and atmospheric pressure in the presence of CuCl. Cu(BF 4 ) · 6 H 2 O, Cu(OOCCH 3 ) 2 · H 2 O or cupric tartrate · 3H 2 O. Under kinetic control, the exo ‐carbonitrile adducts 2 and 8 , respectively, are favoured. Saponification of the 2endo ‐acetoxy‐7‐oxabicyclo[2.2.1]hept‐5‐ene‐2 exo ‐carbonitrile ( 2 ) furnished the 7‐oxabicyclo[2.2.1]hept‐5‐en‐2‐one ( 4 ). Basic hydrolysis of the adducts ( 8 + 9 ) of α‐chloroacrylonitrile to furan and its 5 exo , 6 exo ‐isopropylidenedioxy derivatives did not give the corresponding ketones, the carboxamides 14 + 15 and 16 + 17 , respectively, were isolated.