Imidyl radicals, 4 - Radical addition of N-bromophthalimide to linear and cyclic alkynes

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 hig hly functionalized alkenes 5 are generated. The regioselectivity of the rad ical attack is controlled by steric and electronic effects, whereas the ste reochemistry at the newly formed C=C double bond can be explained by the Cu rtin-Hammett principle. When this free-radical addition is applied to the m edium-sized cycloalkyne 8, the regular addition product 9 is obtained in ad dition to products resulting from a transannular cyclization. Furthermore, a parallel bromine radical chain is initiated to yield the highly brominate d products 11 and 12.