A Comparison of Methods Using Lithium/Amine and Birch Reduction Systems

Treatment of unsaturated organic compounds with sodium and alcohols in ammonia (the Birch reduction) or with lithium in low molecular weight amines (the Benkeser reduction) generally affords partially or fully reduced products, respectively, though reductive cleavages sometimes also occur. This review discusses the similarities and differences between the Birch and Benkeser methods as illustrated by their application to aromatics, heteroaromatics, alkynes, alkenes, ethers, alcohols, amines, carboxylic acids, ketones, heterocycles, and other compounds. In general, the Benkeser reduction is more powerful but less selective than the Birch reduction; however, the selectivity of the former method is increased by a judicious choice of solvents. 1. Reduction of Aromatic Hydrocarbons 2. Reduction of Alkynes 3. Reduction of Alkenes 4. Reduction of Unsaturated Ethers 5. Reduction of Acetals, Ketals and Related Compounds 6. Reduction of Unsaturated Alcohols 7. Reduction of Unsaturated Amines 8. Reduction of Aromatic Nitro Compounds 9. Reduction of Carboxylic Acids and their Derivatives 10. Reduction of Ketones and their Derivatives 11. Reduction of Epoxides 12. Reduction of Five- and Six-Membered Heterocycles 13. Reduction of Miscellaneous Sulfur Compounds