Aldehydes, coupling carboxylic esters

The reductive coupling of aldehydes or ketones with 01, -unsaturated carboxylic esters by > 2 mol samarium(II) iodide (J.A. Soderquist, 1991) provides a convenient route to y-lactones (K. Otsubo, 1986). Intramolecular coupling of this type may produce trans-2-hy-droxycycloalkaneacetic esters with high stereoselectivity, if the educt is an ( )-isomer (E.J. Enholm, 1989 A, B). 

Air, the cheapest oxidant, is used only rarely without irradiation and without catalysts. Examples of oxidations by air alone are the conversion of aldehydes into carboxylic acids (autoxidation) and the oxidation of acyl-oins to a-diketones. Usually, exposure to light, irradiation with ultraviolet light, or catalysts are needed. Under such circumstances, dehydrogenative coupling in benzylic positions takes place at very mild conditions [7]. In the presence of catalysts, terminal acetylenes are coupled to give diacetylenes [2], and anthracene is oxidized to anthraquinone [3]. Alcohols are converted into aldehydes or ketones with limited amounts of air [4, 5, 6, 7], Air oxidizes esters to keto esters [3], thiols to disulfides [9], and sulfoxides to sulfones [10. In the presence of mercuric bromide and under irradiation, methylene groups in allylic and benzylic positions are oxidized to carbonyls [11]. 

Finally, a different type of coupling reaction is achieved by molybdenum 0x0 complexes as catalysts. Aldehydes react with diazoacetate in the presence of PPhs to give a,jS-unsaturated carboxylic esters and Ph3P=0. Molybdenum carbene intermediates have been suggested (Scheme... 

A variety of terminal functional groups and their chemical transformations on SAMs have been examined for example, (i) olefins—oxidation [23,24,131,132], hydroboration, and halogenation [23,24] (ii) amines—silyla-tion [145,146], coupling with carboxylic acids [22,146], and condensation with aldehydes [22,147] (iii) hydroxyl groups—reactions with anhydrides [148,149], isocyanates [150], epichlorohydrin [151], and chlorosilanes [152] (iv) carboxylic acids—formation of acyl chlorides [153], mixed anhydrides [154], and activated esters [148,155] (v) carboxylic esters—reduction and hydrolysis [156] (vi) thiols and sulfides—oxidation to generate disulfides [157-159] and sulfoxides [160] and (vii) aldehydes—condensation with active amines [161], Nucleophilic... 

Most resolution is done on carboxylic acids and often, when a molecule does not contain a carboxyl group, it is converted to a carboxylic acid before resolution is attempted. However, the principle of conversion to diastereomers is not confined to carboxylic acids, and other groupsmay serve as handles to be coupled to an optically active reagent. Racemic bases can be converted to diastereomeric salts with active acids. Alcohols can be converted to diastereomeric esters, aldehydes to diastereomeric hydrazones, and so on. Even hydrocarbons can be converted to diastereomeric inclusion... 

On the pages which follow, general methods are illustrated for the synthesis of a wide variety of classes of organic compounds including acyl isocyanates (from amides and oxalyl chloride p. 16), epoxides (from reductive coupling of aromatic aldehydes by hexamethylphosphorous triamide p. 31), a-fluoro acids (from 1-alkenes p. 37), 0-lactams (from olefins and chlorosulfonyl isocyanate p. 51), 1 y3,5-triketones (from dianions of 1,3-diketones and esters p. 57), sulfinate esters (from disulfides, alcohols, and lead tetraacetate p. 62), carboxylic acids (from carbonylation of alcohols or olefins via carbonium-ion intermediates p. 72), sulfoxides (from sulfides and sodium periodate p. 78), carbazoles... 

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