Mercaptan, acidity acylation reactions

Hydrogen atom donors such as non-nucleophilic tertiary thiols or tri-n-butyltin hydride are extremely efficient traps for the capture of the alkyl radical R derived from O-acyl thiohydroxamates, thus providing a very efficient method for reductive decarboxylation (Scheme 3). In practical terms, the use of the mercaptan is preferred since the tertiary alkyl pyridyl disulfide can be easily removed during work up by a simple acid extraction. The reaction has been successfully applied to a very wide range of complex substrates [8] possessing primary, secondary, or tertiary aliphatic carboxylic acids, and reactions at room temperature or below require only photolysis from a simple tungsten lamp and often involve in situ O-acyl thiohy-droxamate derivatization. 

Reaction of the side chain hydroxyacetone in flumethasone (27-4) with periodic acid leads to cleavage of that function to give carboxylic acid (29-1) with the loss of the carbon atom at C-21. Further reaction of the very hindered acid group requires prior activation. Thus, acylation with diphenyl chlorophosphate leads to the mixed anhydride (29-2) this is not isolated, but treated immediately with methyl mercaptan. The product, tibecasone (29-3), is a quite effective topical anti-inflammatory agent [24]. Cleavage of the ester side chain would lead back to the inactive starting acid (29-1). 

Aromatic compounds are usually readily alkylated or acylated by a Friedel-Crafts reaction.150 The combination of reagents used most commonly for aromatic alkylation is an alkyl halide with a strong Lewis acid (Equation 7.65). However, alkenes, alcohols, mercaptans, and a number of other types of organic... 

Reactions of acetyl chloride that are formally analogous to hydrolysis occur with alcohols, mercaptans, and amines primary or secondary compounds form corresponding acetates or amides tertiary alcohols generally yield the tertiary alkyl chlorides. Acetyl chloride can split the ether linkages of many ordinary ethers and acetals. It equilibrates with fatty acids to provide measureable amounts of the mixed acetic—alkylcarboxylic anhydride or acyl chloride, either of which may be employed in esterifications. For example, lauric acid [143-07-7], and acetyl chloride undeigo the reactions... 

Thus far we have considered reactions in which there is a net synthesis of a thiol-ester bond. In addition to these, two different types of ester interchange reactions have been demonstrated by which one thiol ester can be used to synthesize another. One of these methods involves a transfer of the acyl group to other mercaptans, whereas the other involves a transfer of the thioalkyl group to various acids. 

Reactions.—Unsymmetrical dialkyl sulphides are obtained by the action of aqueous KOH, at 80 °C, on 05-dialkyl dithiocarbonates (with different alkyl groups) under phase-transfer conditions. The reaction depends on the liberation of a mercaptan and its alkylation by the 0-alkyl group of the diester. Ethoxythiocarbonyl derivatives of amino-acids are made by acylating the amino-acids with the stable reagent bis (ethoxythiocarbonyl) sulphide, (EtOCS)2S. This is prepared by an improved method from potassium ethylxanthate (2 mol) and ethyl chloroformate (1 mol). Esters of amino-acids are acylated by carboxymethyl... 

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