Merostabilization of Biradicaloid Intermediates as a Factor in Determining Rates and Regioselectivity in Cycloaddition Reactions of Reissert Hydrofluoroborate Salts with Alkenes and Alkynes.

Article abstract of DOI:10.1021/jo00137a014

Reactions of 2-benzoyl-1,2-dihydroisoquinaldonitrile hydrofluoroborate with ethylene, acetylene, 1-hexyne, 1-phenylpropene, and cis-stilbene have been carried out.Also, reactions of 2-benzoyl-1-cyano-1,2-dihydrophthalazine and 2-benzoyl-1,2,3,4-tetrahydroisoquinaldonitrile hydrofluoroborates, respectively, with dimethyl acetylenedicarboxylate and with ethyl phenylpropiolate have been effected.The structures of most of the products have been established by unambiguous, independent syntheses.The kinetics of these reactions and of several additional ones reported previously have been measured.Arguments are presented that the rate and orientation data of these particular <4 + 2> cycloaddition reactions are better rationalized by invoking the concept of the formation of merostabilized biradicaloid intermediates than by invoking the concept of orbital symmetry allowed concerted ring closures.