Diene syntheses cyclopropenes

Cyclopropenes cycloaddition-ring opening with - 32, 630 diene synthesis with -30, 469s31... 

The ruthenium-catalyzed addition of diazo compounds to alkynes has led to the selective synthesis of functional 1,3-dienes by the combination of two molecules of diazoalkane and one of alkyne [106] (Eqs. 82,83). The stereoselective formation of these conjugated dienes results from the selective creation of two C=C double bonds rather than leading to the cyclopropene derivative. This is expected to be due to the possibility for the C5Me5RuCl moiety to accomodate two cis carbene ligands. 

A new synthesis of 1,4-dienes involves treatment of aa -dihydroxy-derivatives (455) of cyclopropenes with diphosphorus tetraiodide in the presence of pyridine in benzene. ... 

ROM-CM Sequence The ROM reaction of a cycloalkene engaged in the subsequent CM reaction with an olefinic partner provides the straightforward procedure for the synthesis of diene products having the isolated double bonds. This sequence is applicable not only to relatively strained cycloalkenes but also to unstrained compounds such as cyclohexene. The ROM-CM sequence of norbor-nene compounds or cyclopropene ketals with various olefins is reported for the preparations of natural products. 

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