Dissolving metals esters

C1O3/ACOH, 25°, 50% yield, [- ROCOPh (- ROH + PhC02H)]. This method was used to remove benzyl ethers from carbohydrates that contain functional groups sensitive to catalytic hydiogenation or dissolving metals. Esters are stable, but glycosides or acetals are cleaved. 

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. 

Many other examples of chemoselective enone reduction in the presence of other reducible functionalities have been reported. For instance, the C—S bonds of many sulfides and thioketals are readily cleaved by dissolving metals. " Yet, there are examples of conjugate reduction of enones in the presence of a thioalkyl ether group." " Selective enone reduction in the presence of a reducible nitrile group was illustrated with another steroidal enone. While carboxylic acids, because of salt formation, are not reduced by dissolving metals, esters" and amides are easily reduced to saturated alcohols and aldehydes or alcohols, respectively. However, metal-ammonia reduction of enones is faster than that of either esters or amides. This allows selective enone reduction in the presence of esters"" and amides - -" using short reaction times and limited amounts of lithium in ammonia. 

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... 

It is also noted that the formation of methyl cyclohexanoate ester is less in the presence of ultrasound, suggesting enhanced adsorption of carboxylate with concomitant suppression of solvent discharge. This has precedent since ultrasound is thought to enhance adsorption phenomena in some dissolving-metal chemical reactions [58]. 

Dissolved metals and metal-containing surfaces play an important role in the transformation of organic contaminants in the subsurface environment. Metal ions can catalyze hydrolysis in a way similar to acid catalysis. Organic hydrolyzable compounds susceptible to metal ion catalysis include carboxylic acids, esters, amides, anilides, and phosphate-containing esters. Metal ions and protons... 

Smolen JM, Stone AT (1998) Organophosphorous ester hydrolysis catalyzed by dissolved metals and metal containing surfaces. In PM Huang et al. (eds) Soil chemistry and ecosystem health. Soil Sci Soc Am Spec Publ 52 Madison, Wisconsin, pp 157-171 Spencer WF, Shoup TD, Spear RC (1980) Conversion of parathion to paraoxon on soil dusts and clay-minerals as affected by ozone and UV-Ught. J Agric Food Chem 28 366-371 Stevenson FJ (1982) Humus chemistry. Wiley, New York Stevenson FJ (1986) Cycles of soil. Wiley Interscience, New York... 

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. 

Dissolving metals initially convert aldehydes, ketones, and esters into radical anions. Subsequently, proton donors may react with the latter, which leads to neutral radicals. This mode of reaction is used, for example, in the drying of THF or ether with potassium in the presence of the indicator benzophenone. Potassium and benzophenone react to give the deep-blue potassium ketyl radical anion A (Figure 14.45). Water then protonates ketyl A to the hydroxylated radical B as long as traces of water remain. Further potassium reduces B via another electron transfer to the hydroxysubstituted organopotassium compound C. C immediately tautomerizes to the potassium alkox-ide D. Once all the water has been consumed, no newly formed ketyl A can be pro-tonated so that its blue color indicates that drying is complete. 

Indole-2-carboxylic esters undergo reduction with magnesium in methanol to give the 2,3-dihydroindole (indoline). Dissolving metals reduce the heterocyclic ring of isoindoles. 

Although Smh is more chemoselective than traditional dissolving metal reagents, it does react with sulfoxides, epoxides, the conjugated double bonds of unsaturated ketones, aldehydes and esters, alkyl bromides, iodides and p-toluenesulfonates. It does not, however, reduce carboxylic acids, esters, phosphine oxides or alkyl chlorides. In common with most dissolving metal systems, ketones with an a-hetero substituent suffer loss of the substituent rather than reduction of the carbonyl group. ... 

In general, the dissolving metal or electrochemical reductions of acyl halides or acyclic anhydrides are not useful for the preparation of primary alcohols. Such reductions invariably provide acyloin esters, ene-diolate diesters or related species. Cyclic anhydrides may be reduced to give lactones. For example, the reduction of phthalic anhydride at a mercury cathode has been used in the synthesis of phthalide (90%). In general, however, such reduction are not widely employed in synthesis. 

Mesylates, which tend to undergo O—S scission with dissolving metals, were reduced electrochemi-cally in DMF. Yields of 70-85% were reported under conditions which left esters, nitriles and epoxides unchanged. The conversion of (30) to (31) again indicated a carbanionic intermediate. 

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