Thermal Reaction of Azulenes with Dimethyl Acetylenedicarboxylate in Supercritical Carbon Dioxide

Abstract 1,3,4,6,8‐Pentamethylazulene (9), when heated at 100° in supercritical CO2 at 150 bar in the presence of 4 equiv. of dimethyl acetylenedicarboxylate (ADM), led to the formation of 16% of a 1:1 mixture of dimethyl 3,5,6,8,10‐pentamethylheptalene‐1,2‐dicarboxylate 12a) and its double‐bond‐shifted isomer 12b as well as 4% of the corresponding azulene‐1,2‐dicarboxylate 13 (Scheme 4). The formation of the [1 + 2] adduct 11 (cf. Scheme 2) was not observed. Similarly, benz[a]azulene (25) yielded in supercritical CO2 (150°/170 bar) in the presence of 4 equiv. of ADM dimethyl benzo[d]heptalene‐6,7‐dicarboxylate (29; 30%) and dimethyl benzo[a]cyclopent[cd]azulene‐1,2‐dicarboxylate (28; 22%; Scheme 5). The reaction of 5,9‐diphenylbenz[a]azulene (26) and ADM in supercritical CO2 (100°/150 bar) gave the corresponding benzo[d]heptalene‐6,7‐dicarboxylate 31 (22%) and dimethyl 5,9‐diphenyl‐4b,10‐etheno‐10H‐benz[a]azulene‐11,12‐dicarboxylate(30; 25%; Scheme 5).