Anthracene Birch reduction

Table 11 shows some representative results from the cathodic reduction of some aromatic hydrocarbons. These include cases with Ei j2 near the cathodic limit or in the discharge region of the SSE (benzene, toluene) and cases with Ex j2 at considerably more positive potential (naphthalene, anthracene again we must anticipate the discussion of reactivity and refer to Table 21). Reactions nos. 1, 2, 6, and 7 immediately demonstrate one difficulty with such studies in that the catholyte of a divided cell becomes strongly basic as electrolysis progresses. In sufficiently basic medium, the initial product, a 1,4-dihydro derivative (cf. the Birch reduction Birch and Subba Rao, 1972), will rearrange to a conjugated system which, in contrast to the 1,4-dihydro derivative, is further reducible to the tetrahydro product (nos. 1 and 6). In a non-divided cell the acid production at the anode balances the base production and thus only a little rearrangement occurs. It is therefore not a trivial problem to find out if the tetrahydro product is formed from the conjugated dihydro product, formed directly or by rearrangement [eqn (78)].

Photo-Birch reductions. Irradiation of aromatic hydrocarbons in aqueous acetonitrile in the presence of sodium borohydride and 1,2-, 1,3-, or 1,4-dicyanobenzene with a high-pressure mercury arc results in reduction to dihydro derivatives. Phenahthrene is reduced to 9,10-dihydrophenanthrene (71%), anthracene to 9,10-dihydroanthracene (70%), and naphthalene to 1,4-... 

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