Thiols enyne derivatives

Thiols very readily add to diacetylene in the presence of bases, such as alkoxides, with formation of enyne sulfides HC=CCH=CHSR [175]. In strongly basic media, thiol can be eliminated from these enyne derivatives [2], Thus, functionalization of HChCCH=CHSR followed by treatment with an excess of sodium amide results in a derivative of butadiyne. This sequence of conversions permits the synthesis of some 1,3-diyne systems that are not otherwise easily accessible. 

Possibility of activation through conjugation the association of several unsaturated functions in conjugated position (dienes, enynes, enones, enolides, polyunsaturated derivatives) renders the corresponding molecules very reactive. It facilitates especially the addition of biological nucleophiles and notably of thiols. 

Heterocyclizations. Hemiacetals derived from 5-hydroxy-2-alkenoic esters under basic conditions can cyclize to form l,3-dioxanes. This method is suitable for the synthesis of iyn-1,3-diol units. The base-catalyzed reaction of 2-hydroxymethyl 1,3-enynes and the thiol analogs provide furans and thiophenes. 2,3-Disubstituted furans are accessible from isomeric enynes, by way of an 5 2 reaction. 

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