Reduction with sodium in ethanol

Reduction of diphenylacetylene with sodium in methanol or with zinc yielded stilbene, whilst reduction with sodium in ethanol gave 1,2-diphenyl-... 

As a consequence of the wide choice of hydride reagents the classical methods such as reduction with sodium in ethanol almost fell into oblivion [579, 520]. Nevertheless some old reductions were resuscitated. Sodium di-thionite was found to be an effective reducing agent [262], and the reduction by alcohols [309] was modified to cut down on the temperature [755] or the time required [527], or to furnish chiral alcohols ( in good yields and excellent optical purity ) by using optically active pentyl alcohol and its aluminum salt [522]. Formation of chiral alcohols by reduction of pro-chiral ketones is... 

Tetrahydro- (133) and trcm.s-decahydronaphthyridines (134) can be selectively prepared from the parent ring systems by reduction in the presence of either platinum oxide or palladium or by reduction with sodium in ethanol or amyl alcohol.79"8- Hydrogenation in acetic acid with platinum catalyst affords a cis- and traas-decahydro mixture (135 and 134).81... 

The naturally occurring copabomeol (474) was oxidized to ketone 475 and then labelled with tritium at the bridgehead by heating with strong base and tritiated alcohol at high temperatures (Scheme 61) (231a). Reduction with sodium in ethanol yielded labelled copabomeol (474 ), which was administered to C.japonica (231b). 

Reductions of 5//-dibenz[/j,/]azepines to their 10,11-dihydro derivatives have been accomplished in high yield with sodium in ethanol,29 133 with copper(II) chromite (2CuO Cr203) and barium carbonate,224 with 5 % palladium on charcoal29 or platinum(IV) oxide30 in ethanol, and with magnesium in methanol.225 4//-Thieno[3,2-/)][1]benzazepine is reduced similarly with hydrogen and palladium on charcoal in ethanol.137... 

Many reductions with sodium are carried out in boiling alcohols in methanol (b.p. 64°), ethanol (b.p. 78°), butanol (b.p. 117-118°), and isoamyl alcohol (b.p. 132°). More intensive reductions are achieved at higher temperatures. For example reduction of naphthalene with sodium in ethanol gives 1,4-dihydronaphthalene whereas in boiling isoamyl alcohol tetralin is formed. 

Similar results were achieved when benzene was reduced with alkali metals in anhydrous methylamine at temperatures of 26-100°. Best yields of cyclohexene (up to 77.4%) were obtained with lithium at 85° [396]. Ethylamine [397] and especially ethylenediamine are even better solvents [398]. Benzene was reduced to cyclohexene and a small amount of cyclohexane [397, 398] ethylbenzene treated with lithium in ethylamine at —78° gave 75% of 1-ethyl-cyclohexene whereas at 17° a mixture of 45% of 1-ethylcyclohexene and 55% of ethylcyclohexane was obtained [397], Xylenes m- and p-) yielded non-conjugated 2,5-dihydro derivatives, l,3-dimethyl-3,6-cyclohexadiene and 1,4-dimethyl-1,4-cyclohexadiene, respectively, on reduction with sodium in liquid ammonia in the presence of ethanol (in poor yields) [399]. Reduction of diphenyl with sodium or calcium in liquid ammonia at —70° afforded mainly 1-phenylcyclohexene [400] whereas with sodium in ammonia at 120-125° mainly phenylcyclohexane [393] was formed. 

IsoquinoUne was converted to 1,2,3,4-tetrahydroisoquinoline in 89% yield by reduction with sodium in liquid ammonia and ethanol [473], and to a mixture of 70-80% cis- and 10% trans-decahydroisoquinoline by catalytic hydrogenation over platinum oxide in acetic and sulfuric acid [474]. Without sulfuric acid the hydrogenation stopped at the tetrahydro stage. Catalytic hydrogenation of isoquinoline and its derivatives is the topic of a review in Advances in Catalysis [439]. 

Benzamidine, 7V-ethylbenzamidine and 7V-phenylbenzamidine afforded benzaldehyde on reduction with sodium in liquid ammonia with or without ethanol in yields of 54-100% [1109]. 

The parent perhydroquinazoline diastereomers were synthesized by Armarego in the late 1960s. Reduction of 5,6,7,8-tetrahydroquinazoline with sodium in ethanol resulted in the trans-fused perhydroquinazoline 237 exclusively [69JCS(C)1635]. Both cis and trans isomers were prepared in an alternative way reaction of the cis and trans diamines 236 with formalde-... 

The reduction of iV-alkylpiperidones with sodium in ethanol has also been reported [139a, b]. 

The apparently simple procedures of partial dehydrogenation of pyrrolidines and partial hydrogenation of pyrroles afford Zl1-pyr-rolines. However, the reaction is complex and is of little preparative value.97-98 A 1-Pyrrolines may be obtained by isomerization of A 3-pyrrolines.100 From the preparative point of view, partial hydrogenation of quaternary pyridine salts in strongly alkaline media to give 1-alkyl-id 2-piperideines is more important.101 Formation of heterocyclic enamines was observed in the reduction of i -methyl-pyrrolidone with lithium aluminum hydride,102 -alkylpiperidones with sodium in ethanol,103,104 and in the electrolytic reduction of N-methylglutarimide.106... 

The reaction of esters with sodium in ethanol is referred to as the Bouveault-Blanc reaction. Prior to the discovery of complex metal hydrides, this reaction was the only method for the reduction of esters to alcohols. The diesters shown in Figure 17.59 produce a diol in this way. 

Alkyl fluorides.1 a-Fluoro sulfides, available by reaction of mercury(II) fluoride with thioacetals, are convertible into alkyl fluorides by reductive desulfurization with sodium in ethanol. 

---