Birch reduction of aromatic compounds

Akhrem, A. A. Reshetova, I. G. Titov, Yu. A. 1972, Birch Reduction of Aromatic Compound, Plenum New York... 

Reduction of a conjugated enone to a saturated ketone requires the addition of two electrons and two protons. As in the case of the Birch reduction of aromatic compounds, the exact order of these additions has been the subject of study and speculation. Barton proposed that two electrons add initially giving a dicarbanion of the structure (49) which then is protonated rapidly at the / -position by ammonia, forming the enolate salt (50) of the saturated ketone. Stork later suggested that the radical-anion (51), a one electron... 

Dihydroaromatics find diverse applications. The main way to prepare them is through Birch reduction of aromatic compounds (Birch 1944, Wooster and Godfrey 1937, Hueckel and Bretschneider 1939). Aromatic compounds are hydrogenated in diethyl ether or liquid ammonia, with alkali metals as reductants and alcohols as proton sources. 

A. A. Akhrem, I. G. Rshetova, and Y. A. Titov, Birch Reduction of Aromatic Compounds, IFGI/Plenum, New York, 1972. 

For a monograph, see Akhrem Reshotova Titov Birch Reduction of Aromatic Compounds Plenum New York, 1972. For reviews, see Rabideau Tetrahedron 1989, 5, 1579-1603 Birch Suhba Rao Adv. Org. Chem. 1972, 8,1-65 Kaiser Synthesis 1972,391-415 Harvey Synthesis 1970,161-172 House. Ref. 144, pp. 145-150,173-209 Huckcl Fortschr. Chem. Forsch 1966, 6, 197-250 Smith, in Augustine Reduction Techniques and Applications in Organic Synthesis Marcel Dekker New York, 1968, pp. 95-170. 

The deep blue solutions formed by dissolving alkali metals in ammonia do not rapidly generate the amide unless a catalyst is added.9 However, a hydrogen acceptor will also initiate the reaction and this forms the basis of the important Birch reduction of aromatic compounds (equation 2).10... 

A. J. Birch and G. Subba Rao (1972). Reduction by metal-ammonia solutions and related reagents , in Advances in Organic Chemistry. Ed. E. C. Taylor, New York Wiley-Interscience, Vol. 8, p. 1. See also A. A. Akhrem, I. G. Reshetova and Y. A. Titov (1972). Birch Reduction of Aromatic Compounds. New York IFI/Plenum. 

Cyclohexadienes are avaiable by the Birch reduction of aromatic compounds, and converted to 1,3-diene complexes by heating with Fe(CO)5. l-Methoxy-1,4-... 

An interesting example, and the one where these ideas were first applied,40 is the Birch reduction of aromatic compounds by sodium in liquid ammonia containing alcohol. These reactions seem to take place by two successive electron transfers, each followed by capture of a proton, i.e. 

J. M. Hook, L. N. Mander, Recent Developments in the Birch Reduction of Aromatic Compounds Applications to the Synthesis of Natural Products , Nat. Prod. Rep. 1986, 3, 35. 

P. W. Rabideau and Z. Marcinow, The Birch reduction of aromatic compounds, Org. React. 1992,... 

The Birch Reduction of Aromatic Compounds Petar W. Rabldeau, Zbigniew Marclnow... 

Birch reduction of aromatic compounds involves reaction with an electron-rich solution of alkali metal lithium or sodium in liquid ammonia (sometimes called metal ammonia reduction). Usually a proton donor such as tert-butanol or ethanol is used to avoid the formation of excess amount of LiNH2 or NaNH2. The major product is normally a 1,4-diene. This reaction is related to the reduction of alkynes to frans-alkenes ° (section 6.2.2). 

There is no simple way to disconnect the TM shown below (dissonant charge pattern). However, the presence of a 1,6-dioxygenated compound suggests opening of a six-member ring. A variety of cyclohexene precursors are readily available via condensation and Diels-Alder reactions or via Birch reductions of aromatic compounds. 

It is also interesting to note that the formation of the enolates 15 and 16 in the above reactions resembles well the Birch reduction of aromatic compounds bearing electron-withdrawing groups [30], in which metal enolate intermediates are believed to be formed via monoprotonation of dianionic species. However, such species have never been well characterized. Complexes 15 and 16 are... 

Electrides are synthetically useful and form the basis of so-called dissolving metal reactions, of which the Birch reduction of aromatic compounds is the paradigm, shown below for benzene and naphthalene ... 

FIGURE 13.66 Birch reduction of aromatic compounds leads to 1,4-cyclohexadienes. 

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