Photochemical Reactions of Aromatic Compounds. 35. Photo-Birch Reduction of Arenes with Sodium Borohydride in the Presence of Dicyanobenzene

Article abstract of DOI:10.1021/jo00317a028

Birch-type reduction of phenanthrene, anthracene, naphthalene, and several substitued naphthalenes efficiently occurs upon irradiation of 9:1 acetonitrile-water solutions in the presence of sodium borohydride and m- or p-dicyanobenzene.The reduction products of phenanthrene and anthracene are the respective 9,10-dihydroarenes, whereas naphtalene, 2,6-dimethylnaphthalene, acenaphthalene, and 2-methoxynaphthalene are exclusively photoreduced at C1 and C4.With the naphthalenes having alkyl groups on the one ring, the photoreduction gives both the 1,4- and 5,8-dihydronaphthalenes.The exception is the photoreduction of 1-methoxynaphthalene that gives both the 1,2- and 1,4-dihydronaphthalenes.The reaction mechanism has been discussed in terms of electron transfer from the excited singlet state of arenes to the dicyanobenzenes followed by the nucleophilic attack of borohydride anion on the cation radicals of the arenes.