The Birch Reduction Key Words

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A. J. BIRCH* (DYSON PERRINS LABORATORY, OXFORD UNIVERSITY, UK) Category Reduction by Dissolving Metals Metals in Synthesis J. Chem. Soc. 1944, 430–436. The Birch Reduction Key words reduction ammonia H lithium Na or Li NH3 (liquid) sodium R R EtOH H Selected examples: OMe OMe O OMe OMe O Na, NH3 acid Na, NH3 acid EtOH EtOH 20% yield 12% yield OMe OMe O OMe OMe O Na, NH3 acidNa, NH3 acid EtOH EtOH 42% yield 33% yield Reduction of benzoid hydrocarbons: Na, NH3 Na, NH3 EtOH EtOH 4-cymene γ-terpinene Significance: In 1944, Arthur Birch reported the Comment: The birch reduction is of great interest selective 1,4-reduction of aromatic rings to the cor- for organic synthesis, since other catalytic hydroge- responding unconjugated cyclohexadienes by alkali nations reduce the aromatic ring all the way to the metals dissolved in liquid ammonia in the presence cyclohexane. Heterocycles, such as pyridines, pyr- of an alcohol. The regioselectivity thereby depends roles and furans, are also reduced under these con- on the nature of the substituent. Subsequent treat- ditions. In contrast, ordinary alkenes are not affect- ment with mineral acid produced the correspond- ed by the birch reduction. If the substituent is ing ,-unsaturated ketones in moderate yields. electron-donating, the rate of reduction is lower This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited. The synthetic scope is limited due to the low solu- than unsubstituted compounds and the substituent bility of many compounds in liquid ammonia. is found on the non-reduced part of the product. If the substituent is electron-withdrawing, the result is opposite (see Reviews below). Reviews: A. J. Birch Pure Appl. Chem. 1996, 68, 553–556; G. S. R. Subba Rao Pure Appl. Chem. 2003, 75, 1443–1451. SYNFACTS Contributors: Paul Knochel, Juri Skotnitzki Synfacts 02072019, 15(07), 0775 Published online: 17.06.20191861-19581861-194X DOI: 10.1055/s-0039-1689953; Reg-No.: P07819SF ©Georg Thieme Verlag Stutgart · New York © 2019. Thieme. All rights reserved. 775 Georg Thieme Verlag KG, Rüdigerstraße 14, 70469 Stuttgart, Germany.

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