Biphenyl/lithium radical anion

Scheme 1-51. Biphenyl formation by accidental oxidation of phenyllithium and of the biphenyl/lithium "radical anion" (74).

A powerful access to lithiiun carbanions is from phenylthio ethers and acetals using lithium radical anions such as lithium naphthalenide (42a, LN), S- N,N-dimethylamino)-naphthalenide (42b, LDMAN) or 4,4 -di(ferf-butyl)biphenyle-nide (42c, LDBB) [Eq. (15)] [30-32]. The reaction is not usually stereospecific since a configurationally labile radical 43 is involved [Eq. (15)] [33]. 

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). 

The study of the photochemistry of aryl carbanions has been restricted to aryllithiums with only a limited number of studies available. Hence, a general picture of their photochemistry is not available at this time. Photolysis of phenyllithium in the presence of aromatic hydrocarbons such as naphthalene, biphenyl, phenylene, etc. in diethyl ether results in electron transfer from the phenyllithium to the aromatic hydrocarbon, with production of the corresponding hydrocarbon radical anion, as observed by ESR spectroscopy [6-8] (Eq. 1). Photolysis of phenyllithium or 2-naphthyllithium alone gave the corresponding biaryl products and metallic lithium [9-10]. For this reaction, it is possible to write a mechanism which does not require electron transfer from the anion [9,10],... 

Winkler et al. (1966) have obtained the spectra of the lithium salts of the radical-anions of aromatic hydrocarbons such as naphthalene and biphenyl by irradiating the corresponding hydrocarbon in the presence of phenyl-lithium this method has several advantages over others for generating hydrocarbon radical-anions, one being that studies may be made in a wide range of solvents. 

This blue radical anion is formed by addition of slivers of lithium to the biphenyl in THF at low temperatures (argon). The reagent decomposes slowly at 20". 

Among the arene-metal reagents, lithium 4,4 -di(f-butyl)biphenyl (LiDBB) i has been used in a series of transformations as a catalyst for SET reactions. With carbonyl groups, according to the conditions, the reaction product is either the ketyl radical anion or the dianion. 

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