Reaction of Diazoindenothiophenes with Acetylenic Esters and the Thermal Behavior of the Adducts

Article abstract of DOI:10.1021/jo00333a006

Reaction of three diazoindenothiophenes (5a-c) with dimethyl acetylenedicarboxylate (2a) and methyl propiolate (2b) was investigated.Reaction of 5a and 5b with 2a gave thermally labile pyrazoles 7a and 7b which rearranged at 25 deg C into the corresponding 3H-pyrazoles 13a and 13b via Van Alphen-Huettel rearrangement and migration of an ester group.On thermolysis, 7a afforded the cyclopropene 14a, along with 13a, while 7b gave the unstable 14b which afforded the lactone 15 during workup by hydrolysis and ring closure.The reaction of 5c with 2a gave a 2:1 adduct witha loss of nitrogen, 8, which, on photolysis or thermolysis, gave butadiene derivative 9.Reaction of 5a with 2b gave NH pyrazole 10a, while, in the reaction of 5b and 5c with 2b, the formation of the expected diazoalkenes 11a and 11b was detected spectroscopically; however, the isolation of 11 was unsuccesful.The steric effects of the thiophene ring on the above reactions are discussed.