The Adducts of Isobenzofuran and cis-3,4-Dichlorocyclobutene, and Their Conversion Into Formal Dewar Furan Adducts

Abstract

cis-3,4-Dichlorocyclobutene (19) reacts with isobenzofuran (4) to produce three of four possible [ π;4₅+π 2₈] cycloaddition products. The isomer (27) is the dominant cycloadduct , which indicates that significant stabilization by the chlorine atoms with isobenzofuran occurs in the transition state leading to this product. Both adducts (26) and (27) are dechlorinated to form the exo cyclobutene (31), and the other adduct, the isomer (28), yields the endo cyclobutene (33); these products correspond to the formal adducts of cyclobutadiene with isobenzofuran . Separate reactions of cyclobutenes (31) and (33) with 3-chloroperbenzoic acid produce a single anti epoxide in each case, (32) and (34), respectively; these products are identical with the pair of isobenzofuran adducts derived from Dewar furan itself, as reported elsewhere.