Ru-Catalyzed Heptalene Formation from Azulenes and Dimethyl Acetylenedicarboxylate

Article abstract of DOI:10.1002/hlca.19920750707

It is shown that azulenes react with dimethyl acetylenedicarboxylate (ADM) in solvents such as toluene, dioxane, or MeCN in the presence of 2 mol-percent already at temperatures as low as 100 deg and lead to the formation of the corresponding heptalene-1,2-dicarboxylates in excellent yields (Tables 1 and 2).The Ru-catalyzed reaction of ADM with 1-(tert-butyl)-4,6,8-trimethylazulene (31) takes place even at room temperature, yielding the primary tricyclic addition product 32 and its thermal retro-Diels-Alder product dimethyl 4,6,8-trimethylazulene-1,2-dicarboxylate (23; Scheme 4).At 100 deg in MeCN, 32 yields 90percent of 23 and only 10percent of the corresponding heptalene.These observations demonstrate that catalyzes the first step of the thermal formation of heptalenes from azulenes and ADM which occurs in apolar solvents such as tetralin or decalin at temperatures >180 deg (cf.Scheme 1).