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.