1,3-Bis(diarylmethylidene)-2-methylidenecyclohexanes in cycloaddition and cyclodimerization reactions. The role of stereoelectronic factors

Abstract

Cycloaddition and cyclodimerization reactions of 1,3-dibenzylidene- and 1,3-bis(p-methoxybenzylidene)-2-methylidenecyclohexanes, i.e., the diaryltrienes with fixed S-cis-configurations of exocyclic double bonds are studied. These compounds undergo in situ cyclodimerization of the [4+2]-type upon dehydration of the precursor tertiary alcohols and form endo-adducts in the Diels–Alder reaction with N-phenylmaleimide. In the presence of CF₃COOH, acid-catalyzed cyclodimerization takes place leading to methylidene-substituted spirocyclodimers, which undergo intramolecular cyclization upon prolonged contact with CF₃COOH to form a fused carbocyclic system containing a central, ‘three-petal’ fragment of six-membered rings.