Rationale for predominance of 1,3-dipolar cycloreversion in thermolysis of 3,4-dihydropyrazole from ethano-bridged diphenyldiazomethane and 2,5-dimethyl-1,4-benzoquinone. An X-ray study

Abstract

The X-ray crystal structure of the title dihydropyrazole indicates that the steric and π-conjugative effects associated with the conformational locking of the two phenyl rings are the crucial factors in the predominance of 1,3-dipolar cycloreversion rather than nitrogen extrusion to give the cyclopropane derivative.