Cyclotrimerization cyclohexadienes

The transition metal-catalyzed [2 -i- 2 -i- 2] cyclocotrimerization of two molecules of an alkyne with an alkene has studied to a lesser degree compared to the parent alkyne cyclotrimerization [9], although the resultant cyclohexadiene is a valuable synthetic intermediate (e.g., a diene component for the Diels-Alder reaction). This is because a 2 1 coupling of an alkyne and an alkene is generally difficult to compete with the more facile alkyne cyclotrimerization. The success of the selective coupling depends on the electronic balance between the employed alkyne and alkene components the combinations of an electron-deficient alkene with a neutral alkyne [35] or an electron-deficient alkyne with a neutral alkene [36] were successful in the previous... 

Whereas the transition metal catalyzed cyclotrimerization and cyclotetramerization of alkynes leading to benzene or cyclooctatetraene and their derivatives is a rather common reaction, there exist only a few examples of cooligomerizations between alkynes and alkenes or 1,3-butadienes leading to 1,3- or 1,4-cyclohexadiene derivatives20S). It is therefore surprising that the [3+2]-cycloaddition between methylenecyclopropanes and alkynes, catalyzed by triarylphosphite modified Ni(0) compound, is a rather convenient method to synthesize 4-methylenecyclopentenes 206). A wide range of methylenecyclopropanes and alkynes, in the latter case mainly 1,2-disubstituted ones, can be used for these reactions (Eqs. 98-100, see p. 127-128). 

Ru3(CO)i2 coordinated with 2-(diphenylphosphino)benzonitrile catalysed the regioselective 2 + 2 + 2-cyclotrimerization of trifluoromethyl-substituted aryl alkynes in high yields and with a high regio-selectivity4 The alkyne 2 + 2 + 2-cyclotrimerization reaction has been applied to the synthesis of the central 4,5,6-tricyclic core (94) of 4,5,6-trinems (Scheme 30)4 The NbC /DMI-catalysed intermolecular 2 + 2 + 2-cycloadditions of terminal alkynes, internal alkynes, and alkenes produced 1,3,4,5-tetrasubstituted 1,3-cyclohexadienes in excellent yields and with high chemo- and regio-selectivities. ... 

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... 

Cycloadditions constitute a remarkable tool for the synthesis of 1,3-cyclohexadiene derivatives and related heterocyclic compounds. Surprisingly, no cyclotrimerization of alkynes (Reppe reaction) has been reported to date with NHC-Ni complexes. 

The cyclopentadienylcobalt complexes CpCo(L)n are also good catalysts for co-cyclotrimerization of diynes with alkenes [79a]. Recently, it has been shown that the similar catalytic activity is exhibited by the ruthenium complex 106, which efficiently catalyzed cycloaddition of diynes with cyclic alkenes to the conjugated cyclohexadienes 174 (Scheme 77) [112]. 

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