THERMAL-REACTION OF AZULENES WITH DIMETHYL ACETYLENEDICARBOXYLATE IN SUPERCRITICAL CARBON-DIOXIDE

1,3,4,6,8-Pentamethylazulene (9), when heated at 100 degrees in superc ritical CO2 at 150 bar in the presence of 4 equiv. of dimethyl acetyle nedicarboxylate (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-dicarboxcylate 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 degrees/170 bar) in the presenc e 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 A DM in supercritical CO2 (100 degrees/150 bar) gave the corresponding b enzo[d]heptalene-6,7-dicarboxylate 31 (22%) and dimethyl b,10-etheno-1 0H-benz[a]azulene-11,12-dicarboxylate (30; 25%; Scheme 5).