Recent developments in the Birch reduction of aromatic compounds: applications to the synthesis of natural products

Abstract

Reviewing the literature published to May 1985 L 2.1 2.2 I-Naphthoic Acids 7.6 Di hydrophenan threnones 8.1 Arylsilanes 8.2 Benzylsilanes 9.1 Hydrogenolysis of Nuclear Substituents 8 Reduction of Aryl-and Benzyl-silanes 9 Reductive Fission of Hetero-substituents 9.1.1 Simple Ethers 9.1.2 Deoxygenation of Phenols 9.1.3 Alkoxy-substituted Aromatic Acids and Ketones 9.2.1 Benzylic Alcohols 9.2.2 Benzylic Acetals 9.2.3 Benzylic Amines 9.2 Hydrogenolysis of Benzylic Substituents 10 Conclusion 1 1 References * This review was prepared to mark the occasion of the 70th birthday of Professor 2-Acetylnaphthalenes Birch on 3rd August 1985.

Some aspects of radical chemistry in the assembly of complex molecular architectures

“…Another powerful reaction that can be associated with the radical chemistry of xanthates is the Birch reduction [42]. The radical process is employed to create the substituted aromatic motif, which is then reduced by the dissolving metal.…”

Reduction of Acetals, Azaacetals and Thioacetals to Ethers

“…Steric crowding between R I and R3 in the transition state leading to (18) has a strong effect; thus 2,2,4,4-tetramethyl-l ,3-dioxolane cleaves to give (17), contrary to initial expectations on steric and electronic grounds. 44 Norcamphor ethylene ketal (19) gives almost exclusive exo reduction (equation 24) but camphor ketal (20) gives predominant endo reduction (equation 25),94 consistent with the behavior of the parent ketones with HAICI2. 93 Borane in THF gives comparable results (Table 9).…”

“…That this is due to a steric retardation is shown by the fact that 2,2,4,4,5,5-hexamethyl-I,3-dioxolane is untouched after 1 h and only 30% reduced after 48 h. 92 Consistent with this, cis-2,4-dimethyl-I,3-dioxolane (14; R2, R4 = Me) cleaves more selectively at 0-1 than does the trans isomer (14; R I, R4 = Me) or any of the other materials shown in Table 9; it reacts faster than, and during reaction isomerizes to some extent to, the trans isomer.9 2 It hy-drolyzes faster, too. O~H O~OH (20) 78% 22% 44 Norcamphor ethylene ketal (19) gives almost exclusive exo reduction (equation 24) but camphor ketal (20) gives predominant endo reduction (equation 25),94 consistent with the behavior of the parent ketones with HAICI2.…”

Partial Reduction of Aromatic Rings by Dissolving Metals and by Other Methods

“…6 (201) The 1,4-disilyl derivative (201) is reduced exclusively in the substituted ring to give (202), while 2-trimethylsilylnaphthalene (203) affords a 4: 1 mixture of (204) and (205), respectively.l02 As would be expected, the reduction of C-silylbenzoic acids and their esters is controlled by the carboxy function.…”