Reductions with Alkali Metals

Conjugated dienes are also reduced, usually via 1,4-addition to give an alkene. When the diene unit in 463 was treated with sodium metal in ammonia, a 65% yield of 464 was obtained, as part of Meyer s synthesis of (-)-trichodiene. As expected, a mixture of 1,4-reduction (to give 464) and 1,2-reduction (to give 465) was observed (in a ratio of 85 15), which is common with this type of reduction. Note that the nonconjugated exomethylene group in 450 was not reduced under these conditions. 

Reduction with metal deuteride complexes (section Ill-A) is undoubtedly the most convenient way to convert carbonyl compounds into the corresponding deuterated alcohols. For stereochemical reasons, however, it is sometimes necessary to resort to reductions with alkali metals in O-deuterated alcohols, or in liquid deuterioammonia-O-deuterioalcohol mixtures. 

A good example is the reduction of 11-keto steroids (69) which gives only the llJ -hydroxy derivatives (70) with metal deuterides. Generally, the 1 la-alcohols are obtained in good yield by reduction with lithium in liquid ammonia-methanol mixtures. By analogy, llj -dj-lla-alcohols (71) are expected when a deuterioammonia-methanol-OD system is used. (For an alternate preparation of an 11/5-dj-l la-hydroxy steroid, see section III-C). 

There are ample precedents for reductions of double bonds in conjugated enones with lithium in deuterioammonia (see section V-C). Examples of the reduction of saturated ketones in deuterated media appear only as side reactions (over reductions) during the above mentioned conversions. For experimental details, therefore, one should consult the literature for the analogous reductions in protic medium (see also chapter 1). The use of deuterioammonia is essential for labeling purposes since by using liquid ammonia and methanol-OD the resulting alcohol contains no deuterium. For the preparation of deuterioammonia see section IX-D. 

---

The reduction of porphycenes, e.g. 1, can be achieved by catalytic hydrogenation22-25 or chemical reduction with alkali metals.22 With alkali metals one of the C —C double bond bridges in 1 is reduced to yield a 19,20-dihydroporphycene2. On catalytic hydrogenation of porphycene (1), 2,3-dihydro porphycene (3) is formed which can be compared to chlorin, the dihydrogenated form of porphyrin. 

The cyclic voltammograms of these soluble assemblies show a behavior similar to that previously observed by Prato et al.121, that is, a continuum of cathodic current with the reduction onset voltage of —0.15 V versus SCE. Recently, Paolucci et al. were able to obtain the electrochemistry of reduced unfunctionalized carbon nanotubes that were solubilized by reduction with alkali metals to their respective polyelectrolyte salts.122... 

Proper solution electrochemical experiments on pristine SWNTs were only possible after the recent discovery of an innovative way to form thermodynamically stable solutions of unmodified and uncut SWNTs.17,60 Upon reduction with alkali metals, SWNTs produce polyelectrolyte salts (Scheme 9.16) that are soluble in polar organic solvents without the use of sonication, surfactants, or functionalization. Polyelectrolyte SWNT salts were obtained by reacting arc-discharge samples (a-NT) or HiPco samples (h-NT) with different alkali metals (Na, K). 

U is also found in the Soviet Union where there are sources in Karelia, near Dnepropetrovsk, the Kirghiz Soviet Republic and in Transcaucasia Whereas once U ores were processed for their Ra content, Ra has now lost its commercial importance and it is considered a contaminant. Only two U ores have been processed extensively, pitchblende and carnotite. The general procedure is to solubilize the U with an acid, convert the ion to a complex carbonate (thereby removing the Fe, A1 and Mn), ppt the Pb and Cu as the sulfide, and finally, to recover the U as the ammonium uranate and hence, as the oxide U metal can be obtained from the oxide or the halide by reduction with alkali metals or alkaline earth metals. U, being highly electropositive, cannot be deposited electrolytically from aq solns. Thermal decompn of the tetra-iodide is possible (Ref 1)... 

An example that demonstrates the possibilities inherent in the Hg cathode —(C4H9)4N + electrolyte method, for the preparation of products which are inaccessible by other methods, is found in the reduction of diphenyl ether 12). The only products of 12 from reduction with alkali metals in liquid NH3, amine solvent or HMPA 43b-e) were phenol and benzene, presumably arising from cleavage at the radical anion stage. Similarly phenol and benzene were formed by cathodic reduction... 

The reaction of Rh6(CO)i6 with a primary amine gives the monoanionic derivative containing a carboamide group, whereas the analogous carbo-alkoxy derivatives have been obtained by reduction with alkali metal alkoxides in anhydrous alcohol (45) ... 

Reduction with alkali metals The solvents used for alkali metal reductions include hydrocarbons, ethers and, most commonly, liquid ammonia. Alcohols may also be used, but usually as co-solvents, since they react vigorously with these metals. Aldehydes are not usually reduced in this manner, because they react with ammonia to form unreactive imine condensation products. 

Synthesis of Dianions by Reduction with Alkali Metals... 

In the steroid field, a comparison of product ratios with those resulting from reductions with alkali metals reveals both similarities and differences, which led Dauben and co-workers [i] to postulate in 1956 that the observed stereochemical composition of products is a consequence of the interplay of two opposed factors. So successful was Dauben s treatment that it provided a virtually complete qualitative explanation of the relative proportions of axial and equatorial alcohols from reduction of each of the common steroid ketones. Dau-ben s approach developed from Barton s recognition in 1953 [46] that sterically unhindered ketones are reduced by complex hydrides as well as by metal/alcohol systems to give... 

Open-chain acetylenes yield pure trans alkenes on reduction with alkali metal in liquid ammonia. However, reduction of cyclodecyne (111) with sodium in liquid ammonia led to a mixture of cis- (112, > 90%) and /rn/w-cyclodecene (113, > 4%y -The formation of the cis isomer (112) was attributed to the reduction of 1,2-cyclo-decadiene (114) formed by a rapid isomerization of the starting cycloalkyne, while the formation of the trans isomer (113) was ascribed to the direct reduction of 111. 

Reductions of cyclic ketones by dissolving metals are frequently highly stereoselective and these reductions have been used to obtain secondary alcohols which are difficult or impossible to prepare by metal hydride reduction. In terms of yield, the best results are usually obtained either by reductions with alkali metals (commonly Li) in liquid NH3 in the presence of proton donors or with active metals in an alcohol. Although a number of explanations have been advanced for the stereoselectivity of these reductions, they are all rationalizations with dubious predictive value." There are, however, a number of empirical generalizations which are based on a considerable body of experimental data, specifically ... 

J.J3.2.J Reduction with Alkali Metals in Liquid Ammonia 308... 

The anion radical of 2-methyl-2-nitropropane being formed by reduction with alkali metal or electrolysis fragmentates to tert-butyl radicals and nitrite ions. Thus formation of di-tert-butylaminyloxide is initiated85. Treatment of 2-methyl-2-nitro-propane with sodium phenyl gives tert-butyl-phenylaminyloxide the reaction proceeding through an intermediate hydroxylamine oxide salt 65 which is even isolable86. ... 

The new P-alkoxyiminophosphine 78 was prepared from the P-chloro analogue and shown to exist in a trans configuration, contrary to other known P-alkoxyiminophosphines. Some very hindered diphosphenes (79) have been prepared and their behaviour upon reduction with alkali metals or at an electrode studied. ... 

An example of such a reaction is discussed. Reaction of bis(1,1-diphenyl ethylene) linked by a chain of aliphatic hydrocarbon yields on reduction with alkali metals or suitable electron donors, e,g, naphthalenide, a product of poly-dimerization. For example ... 

The Birch reduction with alkali metals in liquid ammonia has been described for Cso already in 1990, just shortly after its isolation. A mixture of highly hydrogenated fullerene compounds QqHj, (18 < x < 36) is generated especially with lithium in ammonia in the presence of tert-butanol. Again C >Hi8 and CgoHsg are the major products. Derivatives with even more hydrogen attached carmot be obtained by Birch reduction as they decompose at the conditions applied. 

In contrast to para-substituted naphthylic ketones, which show no significant diastereose-lectivity on reduction with alkali metals in ammonia, the corresponding acyl-substitutcd anthracenes 9 are reduced with a high degree of cis selectivity96,97. 

Organoaluminum halides, obtained as above, can also be converted into tri-alkylaluminums by reduction with alkali metals and, conversely, alkylaluminum chlorides can be obtained from trialkylaluminums and aluminum chloride.236... 

---