Reduction dissolving-metal

The mesylate group, introduced with methanesulfonyl chloride, can be cleaved with lithium aluminum hydride and dissolving metal reduction (Na, /-BuOH, HMPT, NH3, 64% yield). ... 

Na or Li and ammonia, excellent yields. " A dissolving metal reduction can be effected without cleavage of a sulfur-carbon bond. Note also the unusual selectivity in the cleavage illustrated below. This was attributed to steric compression. ... 

This group was developed to prevent participation of the BnO bond during cationic reactions. It is formed from the bromide [C6H3F2CH2Br, Ba(0H)2 8H20, DMF, 25 h, 94% yield] and cleaved by dissolving metal reduction (Ca, NH3, 79% yield). ... 

The dissolving metal reduction is not suitable, because it effects a cleavage ol the benzylic C-N bond. b The cleavage of the N-N bond by hydrogenolysis is affected by some racemization. 

One study showed that the Cram s mle product predominates with metal hydride reducing agents, but the other product with Bouveault-Blanc and dissolving metal reductions Yamamoto, Y. Matsuoka, K. Nemoto, H. J. Am. Chem. Soc., 1988, 110, 4475. 

Reduction of Ketones and Enones. Although the method has been supplanted for synthetic purposes by hydride donors, the reduction of ketones to alcohols in ammonia or alcohols provides mechanistic insight into dissolving-metal reductions. The outcome of the reaction of ketones with metal reductants is determined by the fate of the initial ketyl radical formed by a single-electron transfer. The radical intermediate, depending on its structure and the reaction medium, may be protonated, disproportionate, or dimerize.209 In hydroxylic solvents such as liquid ammonia or in the presence of an alcohol, the protonation process dominates over dimerization. Net reduction can also occur by a disproportionation process. As is discussed in Section 5.6.3, dimerization can become the dominant process under conditions in which protonation does not occur rapidly. 

Dissolving-Metal Reduction of Aromatic Compounds and Alkynes. Dissolving-metal systems constitute the most general method for partial reduction of aromatic rings. The reaction is called the Birch reduction,214 and the usual reducing medium is lithium or sodium in liquid ammonia. An alcohol is usually added to serve as a proton source. The reaction occurs by two successive electron transfer/proto-nation steps. 

Phosphate groups can also be removed by dissolving-metal reduction. Reductive removal of vinyl phosphate groups is one method for conversion of a carbonyl compound to an alkene.224 (See Section 5.7.2 for other methods.) The required vinyl phosphate esters are obtained by phosphorylation of the enolate with diethyl phospho-rochloridate or /V A /V -tetramethyldiamidophosphorochloridate.225... 

This reaction, called a dissolving metal reduction, produces an (E)- or r[Pg.310]

Removal of the 9-phenylfluoren-9-yl group has been accomplished by three different procedures acidolysls with trifluoroacetlc acid,2 8 10 12 catalytic hydrogenolysis,3 7 9 14 15 and dissolving metal reduction.15... 

Reactions of 1,2,4-thiadiazoles with radicals and carbenes are virtually unknown. Catalytic hydrogenations and dissolving metal reductions usually cleave the N-S bond in a reversal of the oxidative cyclization procedures used in synthesis of 1,2,4-thiadiazoles (see Section 5.08.9.4). 

The stereochemistry of the photocycloadducts can be predicted from the result of a dissolving metal reduction of the same ,/)-unsaturated ketone. For example, sodium/ammonia reduction of 3,4-dimethylcydohexenone yielded trans- and cis-dimethylcyclohexanone 37 in a ratio of 84 16, which was similar to the ratio of the two photocycloadducts 38 (80 20) [33b, 42],... 

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