Birch reduction of aromatic

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... 

Benkeser, R. A. etal., Tetrahedron Lett., 1984, 25, 2089-2092 The use of calcium in 1,2-diaminoethane as a safer substitute for sodium or lithium in liquid ammonia for the improved Birch reduction of aromatic hydrocarbons is described in detail. 

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. 

III. The Birch Reduction of Aromatic Steroids /II Mechanism of the reduction of aromatic compounds / 12 Factors influencing the rate of reduction / 14 Protonation of reduction intermediates / 17... 

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). 

SMP amide enolates have been employed by several research groups. Alkylation of SMP amide enolates gives a-substituted acids (eq 3). Excellent yields and stereoselectivities are observed in the Birch reduction of aromatic SMP amides with subsequent alkylation (eq 4). ... 

The Birch reduction of aromatic hydrocarbons and ethers to the 2,5-dihydro derivatives proceeds most satisfactorily when the substitution pattern allows the addition of hydrogen to two unsubstituted positions in a para relationship. If this requirement is satisfied, better yields are obtained from more highly substituted aromatic rings than from (say) anisole itself, which affords a substantial amount (20%) of 1-methoxycyclohexene (c/. Scheme 1). Extra substitution presumably hinders protonation at the terminus of the dienyl anion (which would lead to a conjugated diene and overreduction). The utilization of anisole moieties as precursors to cyclohexenones has been of very limited value with many 1,2,3-substitution patterns and more densely substituted derivatives. Compounds (23) to (26), for example, have only been reduced by employing massive excesses (200-600 equiv.) of lithium metal,2 while the aromatic ring in (28) is completely resistant to reduction. ... 

The Birch reduction of aromatic hydrocarbons or of double bonds with alkali metals in liquid ammonia or amines [37] resembles in yield and selectivity the cathodic reduction with lithium halide as supporting electrolyte (for example, Ref. 38). 

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. 

Donohoe, T. J., Guyo, P. M., Raoof, A. Birch reduction of aromatic heterocycles. Targets in Heterocyclic Systems 1999, 3,117-145. 

Birch reduction of aromatic ethers is well known to afford alicyclic compounds such as cyclohexadienes and cyclohexenones, from which a number of natural products have been synthesized. Oxidation of phenols also affords alicyclic cyclohexadienones and masked quinones in addition to C—C and/or C—O coupled products. All of them are regarded as promising synthetic intermediates for a variety of bioactive compounds including natural products. However, in contrast to Birch reduction, systematic reviews on phenolic oxidation have not hitherto appeared from the viewpoint of synthetic organic chemistry, particularly natural products synthesis. In the case of phenolic oxidation, difficulties involving radical polymerization should be overcome. This chapter demonstrates that phenolic oxidation is satisfactorily used as a key step for the synthesis of bioactive compounds and their building blocks. 

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