Homolytic base-promoted aromatic alkylations by alkyl halides

Electron-transfer chain reactions leading to regioselective alkylations of benzenes bearing electron-withdrawing substituents can be observed with alk yl halides in the presence of the radical initiator (Bu3Sn)(2) and the prot on acceptor 1,4-diazabicyclo[2.2.2]octane (DABCO). Yields vary from low to high depending on the benzene derivatives. The role of DABCO is to abstract a proton from the substituted cyclohexadienyl adduct radical to form a rad ical anion which then transfers an electron to RX and is converted to the a lkylated product itself. The rate of this electron-transfer step is probabl y not fast enough to sustain a good radical chain reaction so that further generation of R-. from excess (Bu3Sn)(2) and RX is necessary.