Intramolecular, addition cyclotrimerization

Intermolecular cyclotrimerization of alkynes using Wilkinson s catalyst has also afforded substituted carbazole derivatives. This reaction was extended to an intramolecular version by offering the possibility for a six-membered ring annotation that cannot be achieved easily in the corresponding intermolecular version. Intramolecular cyclotrimerization is completely regioselective due to an additional tether. 

The cyclotrimerization of alkynes to give benzene derivatives is perhaps the most general reaction of these compounds in the presence of transition metal complexes. Practically any mono- or di-substituted alkyne, in addition to acetylene itself, may be cyclotrimerized. In addition, cocycloadditions involving more than one different alkyne are possible with some degree of selectivity, and intramolecular versions of the reaction have seen sophisticated development. 

In addition to 6, different ruthenium complexes have been investigated as catalysts for alkyne cyclotrimerizations and cyclocotrimerization of alkynes with nitriles. Among them, Grubbs-type carbene complexes are of particular importance since they catalyze inter- and intramolecular metathesis-cascade cyclotrimerizations under mild conditions. In addition, they have good tolerance toward a variety of functional groups. 

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