Dehydration during reductive amination

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). 

Metallic sodium. This metal is employed for the drying of ethers and of saturated and aromatic hydrocarbons. The bulk of the water should first be removed from the liquid or solution by a preliminary drying with anhydrous calcium chloride or magnesium sulphate. Sodium is most effective in the form of fine wire, which is forced directly into the liquid by means of a sodium press (see under Ether, Section II,47,i) a large surface is thus presented to the liquid. It cannot be used for any compound with which it reacts or which is affected by alkalis or is easily subject to reduction (due to the hydrogen evolved during the dehydration), viz., alcohols, acids, esters, organic halides, ketones, aldehydes, and some amines. 

Hydrogenation of 25 was accomplished using Pearlman s catalyst to provide amino-ester 28 as a 10 1 mixture of diastereoisomers favoring the desired cis isomer.Excess acid (>1 equiv of p-toluensulfonic or sulfuric acid) was necessary to facilitate the hydrogenation by promoting relatively rapid nitrile reduction to protonated amine 26. This protocol prevents catalyst deactivation. Acid also catalyzes the subsequent benzylic alcohol dehydration and the final reduction to 28. The observed increase in diastereoselectivity during the hydrogenation is consistent with acid-catalyzed elimination of water to form intermediate indene 27 followed by reduction from the least hindered face of 27 to afford the cis isomer of 28 as the major product. We did not observe elimination of water prior to nitrile reduction. ... 

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