The reactions of tetrachloro- and tetrabromo-o-benzoquinone with acyclic dienes

Abstract

The formation of spirodihydropyrans by the cycloaddition of acyclic dienes to one of the carbonyl groups in tetrachloro- or tetrabromo-o-benzoquinone is reported. The products are Claisen rearrangement intermediates, and are thermally converted into benzodioxans. The spirodihydropyrans are shown to react further with dienes to give 2 : 1 adducts. In some cases these adducts undergo Cope rearrangements, the results of which establish their structures.