Set Photochemical Reactions between 1,4-Naphthalenedicarbonitrile and Benzylic Donors. Medium Effects

The electron transfer induced photochemical reactions of 1,4-naphthalenedicarbonitrile (NDN) with toluene,diphenylmethane,p-methoxytoluene and benzyltrimethylsilane in MeOH, MeCN and 0.1 M KOH-MeOH-MeCN were examined. The results were compared with those of reactions occurring in neat MeCN. Under the former conditions, the cation radical derived from la undergoes deprotonation after diffusion from (rather than within) the geminate ion pair (as in MeCN). The formed benzyl radical abstracts a hydrogen from MeOH leading to hydroxymethylation of NDN competitively with its benzylation. Under basic conditions MeO- adds to la+' yielding IC. Thereaction of lb in MeOH-MeCN and 0.1 M KOH-MeOH-MeCN is similar to that of la. However, in the reaction of IC under these conditions, the arene cation radical undergoes deprotonation out of cage. Finally, desilylation of the cation radical from Id is a fast process occurring from the geminate pair in all the media explored.