The reduction of aromatic compounds by alkali metals in liquid ammonia represents an important method for the preparation of partially unsaturated six-membered rings. The reaction was discovered by Wooster and Godfrey, but the major development resulted from the efforts of A. J. Birch, and the reaction has since come to bear his name. Although a variety of metals can be used, the most common are sodium and lithium, and, to a lesser extent, potassium. Cosolvents such as ether or tetrahydrofuran (THF) are often used to improve solubility, and weak acids such as alcohols may be employed during the reaction as proton sources. The latter are necessary for the reduction of benzene and its unactivated derivatives. Improvement in experimental procedures by Wilds and Nelson, the application to polynuclear compounds by Huckel and later by Harvey, and the development of methods for the alkylation of the anions generated in this process (i.e., reductive alkylation) have made this reaction an important approach to the synthesis of a wide variety of organic compounds.


Keywords:

Birch reduction;
regiochemistry;
mechanisms;
stereochemistry;
intramolecular effects;
polynuclear aromatic compounds;
aryl ethers;
aromatic ketones;
aromatic carboxylic acids;
aromatic carboxylic esters;
aromatic amides;
phenols;
aromatic amines;
arylsilanes;
bond cleavage;
dimerization;
Benkeser reduction;
silylation;
electrochemical reductions;
catalytic hydrogenation;
method comparisons;
experimental procedures;
scope;
limitation

The Birch Reduction of Aromatic Compounds

Although the conjugated systems of polyenes and unsaturated carbonyl compounds are somewhat similar in terms of structure and bonding, their chemical reactivities are significantly different. The number of available methods for partial reduction of unsaturated carbonyls is overwhelmingly greater than the number of known methods for polyene reduction, and this review deals almost exclusively with unsaturated carbonyl compounds, concentrating upon the reduction of the CC double bond. We subdivide it according to synthetic methodology rather than substrate nature, an arrangement that provides a general view clarifying the scope and limitations of a given method and saving repetition. Dienes and styrenes are discussed at the end of the review.

Partial Reduction of Enones, Styrenes and Related Systems

A One-pot Synthesis of 6-Isopropyl-7-methoxy-1-tetralone and 6-Isopropyl-7-methoxy-2-tetralone

This article reviews the literature published dealing with the synthesis of some bioactive diterpenes. It describes the biological activity and synthesis of only four diterpenes: pisiferic acid, carnosic acid, triptolide and miltirone. This review excludes the discussions of Taxodione, a bioactive diterpene, because it has already been reviewed [85] . The utility of several reagents in the total synthesis of terpenoid compounds has been documented. It can be observed that several routes have been developed for the synthesis of a single diterpene.

Synthesis of Bioactive Diterpenes

The Birch reduction of 2,7-dimethoxy-3-isopropylnaphthalene (IIb), which itself was made from IIa in five steps, followed by acid hydrolysis yielded the tetralone IIIa and the latter was carboxymethylated to IIIb by reaction with dimethyl carbonate and sodium hydride. Michael condensation of IIIb with methyl vinyl ketone yielded the unsaturated ketone IV. The tricyclic ketone IV on methylation followed by thioketalisation gave the thioketal IXa and the latter on Raney nickel desulfurisation yielded Ic.

P. Kurian Oommen

Papers

A Potential Synthetic Intermediate of dl-Carnosic Acid

Birch reduction of 2-methoxy-1-naphthoic acids

A potential synthetic intermediate of dl-carnosic acid