Reaction of compounds I and II. A 1: 1 mixture of compounds I and II was heated in a sealed ampule until the methine proton signal at d 6.5 ppm disappeared completely from the 1 H NMR spectrum of the reaction mixture. After that the reaction mixture was exposed to high vacuum to separate volatile reaction products which were collected in a liquid nitrogen trap. Distillation of the residue and the condensate from the trap gave compounds IV and III. a. ...
