Thiolative Lactonization

Thiol carboxylic esters (1) are the most common compounds among the three types of thioester. They are activated derivatives of carboxylic acids and exhibit acylating properties similar to those of carboxylic acid anhydrides. They have therefore found widespread application in synthetic chemistry and have been used for preparing esters, amides and peptides, especially macrocyclic ketones and lactones. Several review articles concerning the chemistry of thiol carboxylic esters - - and thiol lactones have appeared. 

Finally, it should be mentioned that y- and 8-thiol lactones are in many cases formed simply by heating the corresponding mercaptocarboxylic acids or by treating them with phosphorus pentoxide. The P-thiolactone (20) has also been obtained by flash pyrolysis of 3-mercapto-2-naphthoic acid (equation IS). - ... 

Recently, cobalt carbonyl has been used in thiolative lactonization of alkynes with thiols with incorporation of two molecules of carbon monoxide which affords a,(3-xmsaturated y-thio y-lactones regioselectively in 50-70% yield, depending upon the type of thiol and acetylene used [44]. This reaction becomes relevant as sulphur compoimds are generally believed to be catalyst poison (Scheme 10.5). 

Scheme 10.5 Cobalt carbonyl catalyzed thiolative lactonization of alkynes (partially reproduced from Ref. [44]).

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