Imidyl radicals, 4([≠]). - Radical addition of N-bromophthalimide to linear and cyclic alkynes

Abstract

Addition of N-bromophthalimide (1) to alkynes 3 via phthalimidyl radicals 2 introduces a bromine atom and an imidyl moiety to vicinal C atoms, and highly functionalized alkenes 5 are generated. The regioselectivity of the radical attack is controlled by steric and electronic effects, whereas the stereochemistry at the newly formed C=C double bond can be explained by the Curtin-Hammett principle. When this free-radical addition is applied to the medium-sized cycloalkyne 8, the regular addition product 9 is obtained in addition to products resulting from a transannular cyclization. Furthermore, a parallel bromine radical chain is initiated to yield the highly brominated products 11 and 12.