Diynes polycyclic cyclohexadienes

The cascade process reported by Varela et al. [14] involved a Ru-catalyzed addition of alkenes 15 to 1,6-diynes 16 and a thermal 6ji electrocycUzation (Scheme 5.7). A reaction producing polycyclic cyclohexadienes 17 is performed under a catalytic mixture of 10% [Cp Ru(CH3CN)3]PF and 10% Et NCl at 80°C. 

Formation of Polycyclic Cyclohexadienes by Ru-catalyzed Cascade Reactions of 1,6-Diynes and Alkenes... 

Varela, J.A., Rubin, S.G., Gonzalez-Rodriguez, C., Castedo, L. and Saa, C. (2006) A new Ru-catalyzed cascade reaction forming polycyclic cyclohexadienes from 1,6-diynes and aJkenes. J ournal of the American Chemical Society, 128(29), 9262-9263. 

It is not quite clear which step takes place first - the Co-catalyzed [2+2+1] cycloaddition of the outer alkyne moiety, or the Diels-Alder reaction of the diene with the inner alkyne to form a 1,4-cyclohexadiene, which then undergoes a Pauson-Khand reaction with the remaining alkyne. Recently, it has been shown that a domino reaction can also be performed using 1 mol of a 1,7-diphenyl-1,6-diyne 6/4-20 and a 1,3-diene 6/4-21 in the presence of Co/C at 150 °C under 30 atm CO, to give the polycyclic compounds 6/4-22 as sole product (Scheme 6/4.7) [282]. 

Various cyclohexadienes can be obtained through the rhodium-catalyzed cyclotrimerization of 1,6-diynes with alkenes [12] or 1,6-enynes with alkynes [13], Valorization of these cyclohexadienes was reported with the development of original tandem [2-I-2-I-2] cycloaddition/[4-l-2] Diels-Alder cascades. For example, Tanaka and coworkers recently achieved the construction of bridged polycyclic lactam products, by performing a [2-1-2-1-2] cycloaddition/[4-l-2] Diels-Alder cascade between... 

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