METAL-AMMONIA REDUCTION .4. SINGLE-STAGE REDUCTION OF POLYCYCLIC AROMATIC HYDROCARBONS

Reduction by lithium dissolved in liquid ammonia of a series of representative polycyclic aromatic hydrocarbons (naphthacene, dibenz[a,h]anthracene, 9-alkyl- and 9,10-dialkylanthracene, 7-methyl- and 7,12-dimeth ylbenz[a]anthracene, 3-methylcholanthrene, phenanthrene, and pyrene) was selectively directed to the dihydro stage. Product structure accorded, in general, with predictions based upon molecular orbital calculations of the positions of highest electron density in the corresponding anionic intermediates. Reduction of 9,10-dialkylanthracene proceeded stereospecifically when the alkyl function was ethyl, benzyl, or n-butyl to furnish trans-9,10-dialkyl-9,10-dihydroanthracene; when the alkyl group was methyl, cis and trans diastereomers were formed in equal proportion. The cis-diethyl, dibenzyl, and di-n-butyl isomers were independently synthesized, and differences in the chemical reactivity of the cis and trans diastereomers were related to the conformational properties of the hydrocarbons and their anionic derivatives; preferential axial attack during alkylation or protonation is proposed. © 1969, American Chemical Society. All rights reserved.