The [2 + 2 + 2] cyclotrimerization of diynes and nitrile provides an efficient method for the synthesis of pyridine and its derivatives which can be extended in the total synthesis of natural products. Use of Grubbs type ruthenium catalysts in the cyclotrimerization reaction expands the applicability of Ru(II) catalysts. Two plausible pathways, viz. metathesis and non-metathesis for the cyclotrimerization reaction between a diyne and a nitrile are elucidated with Grubbs second generation and Hoveyda-Grubbs catalysts using DFT techniques. A ruthenacyclobutene like complex is obtained as a stable intermediate in the metathesis pathway while the formation of a five membered metallacycle is invoked to explain the non-metathesis pathway using a decomposed catalyst. The study reveals the influence of N-substituents on N-heterocyclic ligands (NHC) as well as substituent on carbene ligand in controlling the energetic of both metathesis and non-metathesis pathways. Incorporating NHC ligand with reduced steric influence in catalyst design is desirable for improving the efficiency of cyclotrimerization reaction of alkynes with nitriles. If the catalyst is not decomposed, metathesis is the reaction route and the preferred product will be a benzene derivative. The heterocycle formation observed by Pérez-Castells et al. (Org. Lett.,14, 2012, 4982–4985) in presence of excess activated nitriles can only be described using the decomposed catalyst through a non-metathesis pathway.

二炔和腈的[2 + 2 + 2]环三聚化为吡啶及其衍生物的合成提供了一种有效的方法，该方法可以扩展到天然产物的总合成中。在环三聚反应中使用Grubbs型钌催化剂扩大了Ru（II）催化剂的适用性。两条合理的途径，即。使用DFT技术使用第二代Grubbs和Hoveyda-Grubbs催化剂阐明了二炔与腈之间环三聚反应的复分解和非复分解反应。在复分解途径中获得了类似钌烷基环丁烯的络合物作为稳定的中间体，同时调用了五元金属环的形成来解释使用分解催化剂的非复分解途径。该研究揭示了N-取代基对N-杂环配体（NHC）以及卡宾配体上的取代基在控制复分解和非复分解途径的能量方面的影响。为了提高炔烃与腈的环三聚反应的效率，在催化剂设计中引入具有减少的空间影响的NHC配体是合乎需要的。如果催化剂没有分解，复分解是反应途径，优选的产物是苯衍生物。Pérez-Castells等人观察到的杂环形成。（单位 快报。，14，2012，4982-4985）在过量活化腈的存在只能通过非复分解途径使用分解的催化剂进行说明。