Thiopyridyl Chloroformate

Handling, Storage, and Precautions very unstable to water and silica gel however, it can be handled in air. It is stable for one month if stored at —25 °C. Since phosgene is used in preparing this reagent, preparation should be in a working fume hood and extreme caution is required. 

Form Supplied in colorless oil main irqiuiity is bis(thiopyridyl) carbonate not commercially available. 

Lactone Formation. There are several exan5)les of the synthesis of lactones with 2-pyridylthiol esters. Since this is a facile reaction, reasonable yields of complex macrocycles are obtained (eq 2). The pyridine nitrogen may provide anchimeric assistance for the approaching nucleophile, thus facilitating the acylation.  

Ester Formation. 2-Pyridylthiol esters acylate lysophospha-tidylcholines rapidly when catalyzed by silver ion, giving mixed-chain phosphatidylcholines in high yields and isomeric purity (eq 3). The main advantages of this procedure over the usual 4-dimethylaminopyridine catalyzed acylation with acid anhydrides are that less acylating reagent is required to give high 

A list of General Abbreviations appears on the front Endpapers 

This imidazole transfer reaction occurs readily with o-hydroxybenzyl alcohols, giving the imidazole from a primary or secondary alcohol (eq 8). It is thought that the o-hydroxy group contributes to the facile transfer of the imidazole. Similarly, o-amines promote the transfer of the imidazole. Carbonyl dlimida-zole also works in this imidazole transfer reaction, but it usually gives lower yields of the desired product.  

This imidazole transfer reaction works with ketones as well however, in this case two products, the mono- and diimidazoles, are obtained (eq 9). Increasing the temperature does not change the product ratio or yield. Some examples contain hydrogenbonding groups on the ring, but this does not modify the product ratio or yield either. CDI gives similar results in most cases. This imidazole transfer reaction does not work with aldehydes under these conditions.  

Analysis of Reagent Purity IR(CH2C 2) 1765 cm (C=0) main impurity IR(CH2Cl2) 1715cm (C=0). 

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Pummerer rearrangements leading to thiolesters are discussed in the later sections on sulphoxides. A superficially related Arbuzov-type reaction, with a 1,2-shift of sulphur, through the intermediate (5), has a similar outcome. 2-Thiopyridyl chloroformate has been advocated as a reagent for the conversion of carboxylic acids into their pyridine-2-thiolesters under mild conditions. 

Some preliminary studies indicate that non-enolizable thioketones react with acid chlorides in the presence of Na2pe(CO)4 to give thioesters whereas enoliz-able thioketones lead to unsaturated thioesters i.e. 5-acyl enol thioethers). A new, readily-available reagent, 2-thiopyridyl chloroformate, has been found to be highly suited to the preparation of versatile 2-pyridinethioesters directly from carboxylic acids. ... 

Related Reagents. 2-Chloro-l-methylpyridinium Iodide 1,3-Dicyclohexylcarbodiimide 2-Thiopyridyl Chloroformate Trimethylacetyl Chloride. 

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