The regiospecific cycloaddition of 8,8-dimethylisobenzofulvene with isobenzofuran, 1-methylisobenzofuran and 1,3-dimethylisobenzofuran

Abstract

The mixed 1 : 1 adduct formed upon reaction of isobenzofuran with 8,8-dimethylisobenzofulvene is shown to have structure (5) resulting from a [10 + 8] cycloaddition in which the isobenzofulvene serves as the 10 π reagent and the isobenzofuran as the 8 π reagent. The reaction occurs stereospecifically and forms exclusively the endo adduct. Lanthanide-induced shift spectroscopy, ¹³C n.m.r. and ¹H n.m.r. spectroscopy, and deuterium-labelling techniques have been used to establish this structure. The structure of the adducts (24) and (26) derived from 1-methylisobenzofuran and 1,3-dimethylisobenzofuran, respectively, have also been established. A PMO treatment of this reaction correctly predicts the structure of these products including the regiochemistry of the product (24) formed from 1-methylisobenzofuran.