Thermal and Photochemical Transformations of Hetero-1,3,5-hexatrienes into Five-Membered Rings—Possible Pericyclic Reactions

Heterosubstituted 1,3,5-hexatrienes undergo thermal and photochemical cyclizations, most of which can be viewed as pericyclic reactions. Numerous cyclizations of this type have been reported in the literature. This article presents a systematic account of such reactions, classified according to the number and nature of the heteroatoms.