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Paper | Regular issue | Vol 27, No. 5, 1988, pp.1207-1216
Published online, 1st January, 1970
DOI: 10.3987/COM-87-4461
Pyrazolo[1,2-a]indazole and its Reaction with Dimethyl Acetylenedicarboxylate

Angelo Albini, Gianfranco Bettinetti,* and Giovanna Minoli

*Dipartamento di Chimica Organica, Università di Pavia, V. le Taramelli 10, 27100 Pavia, Italy


Pyrazolo[1,2-a]indazole (2) is prepared by dehydrohalogenation of 2-bromo-2,3-dihydro-1H-pyrazolo[1,2-a]indazolium bromide (7). This diazapentalene 2 reacts with dimethyl acetylenedicarboxylate (DMAD) at room temperature. The main products in aprotic solvents are 10cH-1,2-dimethoxycarbonyl-10c-(1’,2’-dimethoxycarbonylethenyl)-1,2-diazocino[1,2,3-ab]indazole (15) and 11H-2,3-dimethoxycarbonyl-11-(1’,2’-dimethoxycarbonylethenyl) pyrazolo[1,2,3-ab]1,2-benzodiazocine (16) arising from a stepwise process involving addition of two molecules of DMAD and rearrangement. A minor product is 1,2-dimethoxycarbonyl-5,9c-diazapentaleno[1,7,6-ab]indazole (9). In methanol 1 to 2 addition and proton shift leads to 2,3-dihydro-1,2,3,4-tetramethoxycarbonyl-7,11c-diazaaruleno[1,9,8-ab]indazole (19) as the main reactions product. These processes are discussed in the frame of the general mechanism for heteropentalene addition reactions.