Carboxylic reaction with ketones

Diazabicyclo[5.4.0]-undec-7-ene (DBU) has been successfully immobilized on methylhydrosiloxane support (HMS-DBU) for C02 capture with 100 % degree of functionalization (Scheme 6.2) [19]. Notably, HMS-DBU is found to be recyclable and shows retention of activity in five recycles. C02 is absorbed under ambient temperature and could be desorbed at 120 °C, which renders the material suitable for carrying out carboxylation reactions of ketones to jS-keto esters at 25 °C with excellent yields. 

Alkali amides, MNH2, in situ prepared in liquid ammonia, are efficient deprotonating agents in reactions with ketones, carboxylic t-butyl esters, N,N-dialkylcarboxamides, and the analogous sulfur compounds. Primary-alkyl carboxylic esters RR CHCOOR" and the sulfur analogues RR CHCOSR" and RR CHCSOR" (R" is prim.-alkyl), however, undergo serious competitive substitution of OR" or SR" by NH2 [6]. 

One route to o-nitrobenzyl ketones is by acylation of carbon nucleophiles by o-nitrophenylacetyl chloride. This reaction has been applied to such nucleophiles as diethyl malonatc[l], methyl acetoacetate[2], Meldrum s acid[3] and enamines[4]. The procedure given below for ethyl indole-2-acetate is a good example of this methodology. Acylation of u-nitrobenzyl anions, as illustrated by the reaction with diethyl oxalate in the classic Reissert procedure for preparing indolc-2-carboxylate esters[5], is another route to o-nitrobenzyl ketones. The o-nitrophenyl enamines generated in the first step of the Leimgruber-Batcho synthesis (see Section 2.1) are also potential substrates for C-acylation[6,7], Deformylation and reduction leads to 2-sub-stituted indoles. 

The zwitterion (6) can react with protic solvents to produce a variety of products. Reaction with water yields a transient hydroperoxy alcohol (10) that can dehydrate to a carboxyUc acid or spHt out H2O2 to form a carbonyl compound (aldehyde or ketone, R2CO). In alcohoHc media, the product is an isolable hydroperoxy ether (11) that can be hydrolyzed or reduced (with (CH O) or (CH2)2S) to a carbonyl compound. Reductive amination of (11) over Raney nickel produces amides and amines (64). Reaction of the zwitterion with a carboxyUc acid to form a hydroperoxy ester (12) is commercially important because it can be oxidized to other acids, RCOOH and R COOH. Reaction of zwitterion with HCN produces a-hydroxy nitriles that can be hydrolyzed to a-hydroxy carboxyUc acids. Carboxylates are obtained with H2O2/OH (65). The zwitterion can be reduced during the course of the reaction by tetracyanoethylene to produce its epoxide (66). 

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