Cycloisomerization of 1,6-diynes

A mechanism which involved the allylic carbon-hydrogen bond activation of the alkene moiety was proposed for the cycloisomerization of 1,6-diyne to alkylidenecy-cloheptene on the basis of stereochemical consideration and deuterium labeling experiment (Scheme 12.7). 

The cycloisomerization of 1,6-diyne 171 in the presence of AcOH is terminated by reduction of the alkenylpalladium 172 with hydride such as H-SiEt3 to afford the conjugated diene 173. 

A gold(I)-catalysed cycloisomerization of 1,6-diynes containing propargylic esters and arenynes is reported for the synthesis of 3-pyrrolines or pyrroles (Scheme 111). ... 

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