Hexacarbonylmolybdenum-induced Reaction of Isoxazoles. Cycloaddition of Isoxazoles with Acetylenic Esters and Related Reactions

Article abstract of DOI:10.1246/bcsj.58.152

In the presence of hexacarbonylmolybdenum, substituted isoxazoles undergo a cycloaddition reaction with dimethyl acetylenedicarboxylate across the C-4-C-5 bond to give 3,4-bis(methoxycarbonyl)pyridine derivatives.In a similar cycloadition of isoxazoles with methyl propiolate, 4-(methoxycarbonyl)pyridine derivatives were also obtained.The β-carbon atom of methyl propiolate could intervene in the bonding with the C-5 position of the isoxazoles regioselectively.A mechanism involving a complexed 2-oxa-3-azabicyclo<3.2.0>hepta-3,6-diene derivative and the subsequent N-Oand C-1-C-5 bond cleavage leading to a complexed (β-ketovinyl)nitrene intermediate is proposed for the formation of pyridine derivatives.In order to clarify the mechanistic aspect, the reaction of 4-phenyl-2-oxa-3-azabicyclo<3.2.0>hepta-3,6-diene and its related compounds were also studied to give pyridine derivatives.