Oxazolinium salts reduction

Electrochemical reduction of oxazolinium salts 36 gives the anions 37, which add efficiently to alkyl halides or, in the presence of McsSiCl, to methyl acrylate, methyl vinyl ketone, and acrylonitrile. Simple acid hydrolysis then gives the ketone products 38 and 39, and this method is quite general since the starting salts are readily prepared from carboxylic acids, R C02H (87TL4411). 

Reduction of IV-alkyl iminium salts also ought to afford radical-derived products. Indeed, reduction of oxazolinium salts (31) results in isolation of the corresponding dimers, which can in turn be converted to the corresponding benzils by acid hydrolysis33 (equation 14). In a similar vein, electrochemical reduction of IV-butenyl iminium salts (32) affords cyclopentane derivatives (equation 15)34. 

Reduction of oxazolinium salts in DMF yields the anion of the tetrahydro-oxazole, which may be used as an acyl anion equivalent [278]. 

The synthetic utility of this method is increased by intercepting the oxazolinium salts with various nucleophiles to prepare lactams that bear an (o-fiinctionalized carbon chain. It is also possible to form azacycles containing a 2-dicyanomethylene group. Direct reduction of the oxazolinium salts with NaBH gives amines. ... 

The use of 2,4,6-tri-isopropylbenzenesulphonylhydrazides (in place of the tosylhydrazide) allows milder conditions to be used for the preparation of aromatic aldehydes by the McFadyen-Stevens reaction. Addition of hydrazine hydrate and traces of cupric sulphate suppresses formation of aromatic ester and alcohol by-products. Reduction of oxazolinium salts by sodium borohydride, as part of the well known sequence for the conversion of carboxylic acids into aldehydes, can lead to ring cleavage to form amino-alcohols. It is now reported that over-reduction is much less marked if potassium tri-s-butylborohydride is used as reducing agent (Scheme 2) ... 

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