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Birch reduction (see reviews [1-5]) is the name given to the reaction of unsaturated organic compounds with alkali metals and alcohols in liquid am monia. This method was first used for aromatic compounds in 1937 by Wooster [6J, who showed that benzene and its derivatives are reduced by sodium in liq uid ammonia in the presence of an alcohol, while this reaction does not take place in the absence of an alcohol. However, the general recognition and broad application of this reaction was achieved only after a series of investigations by Birch published from 1944 onwards [7J. Since the presence of an alcohol in the reaction medium is not indispen sable for pOlycyclic aromatic systems, the present review includes only deriv atives of the simplest aromatic compounds - benzene and naphthalene. 1 Reaction Mechanism The most probable mechanism of Birch reduction, adopted by the major ity of workers in this field [4, 8 -12] can be represented by the following stages: 'v I NH -'" ,. - i T 1 3 +--"'( a) , , ,e (NHa) NH 3) + ROH ----+ () ll. . (NHa) A H H 4) H H 5) ')', ",,\+ + RO" ~ Q + 110M,,,,,, / (NHa) . (NH:,) Q H H Ii Ij H H H H H+ X/~H M,l
Sommario
Reaction Mechanism.- Field of Application.- Side Reactions.- Methods and Examples of the Performance of the Reaction.- 2,5-Dihydroanisole.- 6-Alkylcyclohex-2-en-1-ones.- Piperitone.- 3-Methoxyestra-2,5(10)-dien-17 ?-ol.- Review of Literature Information.- Index of Reagents.- Literature Cited.
