Strong Participation of Selenium Substituents in Decomposition of Pyrazolines Formed by 1,3-Dipolar Cycloaddition of Appropriate Vinyl Selenides with Diazoalkanes

Article abstract of DOI:10.1021/jo00277a039

Decomposition of 4-(arylseleno)pyrazolines (3) bearing two electron-withdrawing groups such as COOMe, COMe, and CN at C-3, which were prepared in situ by reaction of the corresponding aryl vinyl selenides (2) with diazoalkanes, are reported.The pyrazolines decompose below 0 deg C to give allyl aryl selenide derivatives (4) by migration of 4-arylseleno group to C-5 concerted with extrusion of nitrogen.Facile decomposition of the pyrazolines with migration of the selenium substituent is explained by strong contribution of intramolecular diazonium salt resonance structure, within which arylseleno groups strongly participate in the decomposition.Most reactions of 2 with 2 mol of diazoalkanes gave the pyrazolines 5, whereas reaction of 2c with 2 mol of 2-diazopropane gave a reverse orientation adduct, the pyrazoline 9.