Benzotriazole adds to aliphatic open-chain and cyclic alkenes at 80 de
grees C under toluene-p-sulfonic acid catalysis. Terminal aliphatic ol
efins give solely 2-(benzotriazol-1- and -2yl)alkanes, which are stabl
e to acid. In the presence of an excess of acid, all possible non-term
inal benzotriazol-1- and -2-yl addition products are obtained, owing t
o a facile migration of the double bond in the starting olefin. Additi
on also occurs to phenylalkenes with the intervention of some bond mig
ration.