The cheletropic ene-reaction and its reversal; additions to 1,2,3,4-tetrachloro-5-methylenecyclohexa-1,3-diene

Abstract

The cheletropic ene-reaction is presented as an extension of the known pericyclic additions. No example of this process is known but some decarbonylations have been discussed as its reverse. The scope of these reactions is extended by the facile decarbonylation of the alicyclic trienal 11 to give o-xylene. The dramatic lowering of the activation energy when an arene is formed and the finding that in this system phenyl isocyanide can also act as a chelefuge underline the pericyclic character of this reaction. In quest of a cheletropic addition to an ene 1,2,3,4-tetrachloro-5-methylenecyclohexa-1,3-diene was reacted with CO under pressure but to no avail. The reactive ene however readily adds an electron deficient ketone and molecular oxygen.