Formation of dimethyl tricyclo[6.2.2.01,7]dodeca-2,4,6,9, 11-pentaene-9, 10-dicarboxylates from azulenes and dimethyl acetylenedicarboxylate under high pressure and thermal rearrangement of the tricyclic compounds into heptalene-1,2-dicarboxylates

Abstract

Abstract It is shown that alkylated azulenes (see 1, 12, and 13) react with dimethyl acetylenedicarboxylate (ADM) in hexane under a pressure of 6–7 kbar already at 30° to yield the corresponding dimethyl tricyclo[6.2.2.01,7]dodeca-2,4,6,9, 11-pentaene-9, 10-dicarboxylates (see 14, 15, and 16). These compounds decompose in apolar solvents such as decane at temperatures > 50° mainly (>95%) to the starting materials. However, in polar solvents such as MeCN or DMF the formation of the corresponding dimethyl heptalene-1,2-dicarboxylates (see 2, 18, and 20) competes effectively with the decomposition into the starting materials. In polar and protic solvents such as EtOH or O(CH2CH2OH)2 instead of the heptalenes the corresponding (E)-and (z)-configurated dimethyl 1-(l′-azulenyl)-ethylene-l,2-dicarbox-ylates (see 17, 19, and 21) are formed. All experimental findings clearly show that the tricyclic compounds (14 to 16) are the crucial intermediates in the thermal formation of heptalenes from azulenes and ADM and t...