3- Aminopyridine-2-thiol, reaction with

Similarly, reaction of 3-aminopyridine-2-thiol (330) with 4-chloro-5-nitropy-rimidine derivatives provided usually high yields of the corresponding triazaphe-nothiazines (75JOC2753, 77EJM249). 

Product equilibration is not likely under room temperature reaction conditions, but there are some cases where it has been deliberately used to enhance the ( )-enoate selectivity of reactions that otherwise afford mixtures. Entries 47-49 in Table 19 demonstrate that catalytic amounts of p-dimethyl-aminopyridine (DMAP) will induce the Z E equilibration of a, -unsaturated thiol esters at room temperature (chloroform solution), resulting in enhanced ( )-enoate selectivity (101b). This procedure is not effective with the corresponding oxygen esters, however. 

This procedure offers a convenient method for the esterification of carboxylic acids with alcohols and thiols under mild conditions. Its success depends on the high efficiency of 4-d1alkyl aminopyridines as nucleophilic catalysts in group transfer reactions. The esterification proceeds without the need of a preformed, activated carboxylic acid derivative, at room temperature, under nonacldic, mildly basic conditions. In addition to dichloromethane other aprotic solvents of comparable polarity such as diethyl ether, tetrahydrofuran, and acetonitrile can be used. The reaction can be applied to a wide variety of acids and alcohols. Including polyols,a-hydroxycarboxyl 1c acid esters, and even very acid labile... 

Thioesters.—Mixed anhydrides prepared from 2,4,6-trichlorobenzyl chloride and a carboxylic acid react with various thiols in the presence of 4-dimethyl-aminopyridine to give thioesters in 78—86% isolated yield.Somewhat less impressive yields were obtained in a few of the cases studied when l-fluoro-2,4,6-trinitrobenzene was used to couple the acid and the thiol.Treatment of 1-acylimidazoles with thiols in the presence of a catalytic amount of Mg(OEt)2 furnishes thioesters in good yields. Diphenyl-2-oxo-3-oxazolinylphosphonate brings about effective reaction between acids and thiols. Thiolacetates are efficiently prepared using the reaction of an alcohol with triphenylphosphine and di-isopropyl azodicarboxylate in the presence of thiolacetic acid/ A synthesis of some amino-acid derivatives containing the thioester functional group is achieved by the reaction of a vinyloxyborane with a Schiffs base (Scheme 56). ... 

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