o-Quinonoid compounds. Part IX. Photodecarboxylation of 2-benzopyran-3-one adducts and photoreactions of the derived o-quinodimethanes

Abstract

Photodecarboxylation of the 2-benzopyran-3-one–trimethylmaleimide adducts (10; R = H, Me, or Ph) gives the non-isolable o-quinodimethanes (2), (4), and (3), respectively; these are air-sensitive and undergo further photoreactions including conversion into cyclobuta[3,4]cyclobuta[1,2]benzenes of types (21) and (31) and cycloprop[a]indenes (23). The cyclobutacyclobutabenzenes revert to the o-quinodimethanes on heating or on heating or on irradiation.