Esters dissolving-metal reductions

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... 

In an amazing reaction, dissolving metal reduction of dichloro diester 859 generates dianion 860 which can be conventionally methylated (Scheme CIII) Irradiation of keto ester 861 introduces yet another framework bond. Dehydration of the newly... 

An alternate route to 90 commenced with the Robinson annelation of the aryl pyruvic acid 97 with methylvinyl ketone followed by dehydration and dissolving metal reduction of the resulting mixture of unsaturated acids to provide the cis-keto acid 98 (Scheme 7) (112b). Transformation of 98 to the rrans-ketal ester 99... 

This method is an inexpensive substitute for LAH reductions of esters in industrial production, and was the only alternative prior to the development of the metal hydride reducing agents. This dissolving metal reduction is also related to the Birch Reduction. 

Extension of the dissolving metal reduction of enones to a,[3-unsaturated carboxylic acid esters converts the ester moiety to an amide. However, a, 3-unsaturat-ed esters undergo double bond reduction on treatment with magnesium in methanol. ... 

One of die most popular reactions in organic chemistry is dissolving metal reductions [1-3], Two systems are frequently used - sodium dissolved in ammonia with alcohol and lithium dissolved in alkylamines [4]. Although calcium is seldom used, it has been successfully applied to the reduction of a variety of compounds and functional groups [5], including aromatic hydrocarbons, carbon-carbon double and triple bonds, benzyl ethers, allyl ethers, epoxides, esters, aliphatic nitriles, dithianes, als well as thiophenyl and sulfonyl groups. 

Then the carboxylic acid was converted (via the acid chloride) to the diazoketone (Chapter 9), and decomposition of the latter via the carbene and insertion produced the substituted cyclopropane. Next, the keto group was converted to a methylene unit via the Wittig, and thermolysis generated the third cyclopentyl ring. Dissolving metal reduction and epimerization in sodium ethoxide set the stage for conversion of the ester to an alkyl group. 

Protection.—Alkyl ester protection of alcohols is normally removed by methods such as base hydrolysis or reduction with LiAlH4. It has now been shown that dissolving-metal reduction of the Bouveault-Blanc type has value in this field [equation (7)] and allows recovery of primary and secondary alcohols from their... 

It has however long been known sodium in ethanol effects "dissolving metal reductions", such as the classical Bouveault-Blanc reduction of carboxylic esters to alcohols, in good yields ... 

In dissolving-metal ester reduction, the ester carbonyl is believed to accept an electron to form a radical oxyanion 37 (Scheme 12.12). Chelation with a lithium counterion then ensues to produce a tertiary radical 38 which then captures a second electron to become a carbanion. Protonation of 39 next yields 40, whose fate is to collapse to aldehyde 41. Another multiple electron transfer/protonation sequence subsequently yields the product alcohol 46. 

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