New Diene Formation from 1,3-Dienes

Functionalized dienes can be obtained by C-C bond formation between 1,3-dienes and alkenes via oxidative coupling with electron-rich ruthenium catalysts but also via insertion into Ru-H and then Ru-C bonds. For example, Ru(COD)(COT) catalyzed the selective codimerization of 1,3-dienes with acrylic compounds to give 3,5-dienoic acid derivatives [18] (Eq. 13). -coordination of 1,3-diene to a hydridoruthenium leads to a 7r-allylruthenium species to selectively give, after coupling with the C=C bond and isomerization, the functionalized conjugated 1,3-dienes. 

A 7r-allylruthenium complex, formed from 1,3-diene and a preformed Ru-H complex, was also postulated to be an intermediate for the regioselective hy-drovinylation of unsymmetrically substituted 1,3-dienes to afford 3-methyl-1,4-dienes as products [19] (Eq. 14). Isomerization of the initially formed 1,4-diene, such as 33, to the stabler conjugated 1,3-diene did not occur. 

This reaction was applied to a steroid and was shown to be stereospecific, giving a product with a (S) configuration at carbon 20 (Eq. 15). 

Functional 1,5-dienes were also synthesized in good yields by ruthenium-catalyzed regioselective codimerization of enol esters with 2-substituted-l,3-bu-tadienes [20] (Eq. 16). A ruthenacycle intermediate formed by oxidative coupling was proposed followed by intracyclic /1-hydride elimination. The (Z)-selectivity is thought to result from the configurational inhibition for the /1-hydride elimination in the intermediate ruthenacyclopentane. 

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