Lithium biphenyl

Finally the chemical aromatization of Ring A which occurs in nature in the biosynthesis of estrogens must be mentioned. It can be done by thermal cleavage of the C-19 methyl group in 1,4-dien-3-ones (H.H. Inhoffen, 1940 C. Djerassi, 1950) and was later achieved at lower temperatures with lithium — biphenyl in THF (H.L. Dryden, Jr., 1964). 

The backbone of poly(phenylene oxide)s is cleaved under certain extreme reaction conditions. Lithium biphenyl reduces DMPPO to low molecular weight products in the dimer and trimer molecular weight range (20) and converts poly(2,6-diphenyl-l,4-phenylene oxide) to 3,5-diphenylphenol in 85% yield (21) (eq. 4). 

Interest in the synthesis of 19-norsteroids as orally active progestins prompted efforts to remove the C19 angular methyl substituent of readily available steroid precursors. Industrial applications include the direct conversion of androsta-l,4-diene-3,17-dione [897-06-3] (92) to estrone [53-16-7] (26) by thermolysis in mineral oil at about 500°C (136), and reductive elimination of the angular methyl group of the 17-ketal of the dione [2398-63-2] (93) with lithium biphenyl radical anion to form the 17-ketal of estrone [900-83-4] (94) (137). 

Tetrasilapentanes 4, R = Pr or neo-pentyl, were synthesized by reductive coupling of the linear 1,5-dichloro-l,2,4,5-tetrasilapentane with lithium biphenyl in 77-87% yields <2002EJI1772>. 

Lithium/amines, reduction with, 55. 115. 199 Lithium/biphenyl, 285 Long-range effects, i6et seq., 439,... 

PPO is readily cleaved by reaction with alkali metal aromatic hydrocarbon adducts such as lithium-biphenyl and sodium-naphthalene." In a model reaction with the trimer 39 only two products 40 and 41 were obtained. Exhaustive cleavage of the polymer gives about a 20% yield of 41. (Scheme 14)... 

In contrast P3O (5) is converted in >80 % yield to 3,5-diphenylphenol when exhaustively cleaved with lithium-biphenyl in THF... 

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