Light‐Induced and Thermal π‐Skeletal Rearrangement of Heptalenes with Retention of Configuration

Abstract

Abstract It is shown that dimethyl 5, 6, 8, 10‐tetramethyl‐ ( 3 ) and 8‐ ( tert ‐butyl)‐5,6,10‐trimethylheptalene‐1, 2‐dicarboxylate ( 5 ), and their derivatives rearrange reversibly on irradiation or on heating to yield the corresponding 1,6,8,10‐tetramethyl‐ ( 4 ) and 8‐( tert ‐butyl)‐1,6,10‐trimethylheptalene‐1,2‐dicarboxylate ( 6 ), and their derivatives by double‐bond shift (π‐skeletal rearrangement) via a transition state with D 2 symmetry as the highest possible one. This follows from the fact that (−)‐( P )‐ 3 is photochemically as well as thermally rearranged to give (−)‐( P )‐ 4 i.e. the π‐skeletal rearrangement occurs with retention of configuration of the heptalene skeleton and without loss of optical purity.