?-Acceptor-Induced Reactions: Unusual Selectivity in Bond-Cleavage Reactions through the Use of Photochemical Excitation

Article abstract of DOI:10.1021/jo00250a030

Bond-cleavage reactions of benzyl ether (BE) and 4,4'-dicyanobenzyl ether (DCBE) can be induced in the presence of various ?-acceptor compounds. ?-Acceptors used in this study are 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (TCNQF4), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), and 7,7,8,8-tetracyanoquinodimethane (TCNQ).The products of these reactions are the corresponding benzaldehydes and benzyl alcohols regardless of the ?-acceptors used in this study.Activation of these reactions can be achieved either thermally or photochemically.The relative reactivities of benzyl phenyl ether (BPE) and BE with these ?-acceptors have been determined for both thermal and photochemical activation.BE is more reactive under all conditions than BPE.The selectivity of the BE bond-cleavage reaction initiated by photochemical excitation of DDQ is increased by 2 orders of magnitude when compared to thermal activation. ΔΔH(excit.)s for the bond-cleavage reactions of BE and BPE as induced by DDQ and TCNQF4 have been determined.These results are interpreted with respect to the stability of the ionic intermediates and the tightness of ion pairing.