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Please login or sign up for a free trial to access the full content. Variation 2: [2+2+2]-Cyclotrimerization Reactions of Nitriles and Alkynes

DOI: 10.1055/sos-SD-019-00272

Collier, S. J.; Langer, P.Science of Synthesis, (200419412.

The transition-metal catalyzed cyclotrimerization of a nitrile with two molecules of an alkyne is a powerful synthetic approach to substituted pyridines (Scheme 14); this chemistry has been reviewed in Science of Synthesis, Vol.15 (Six-Membered Hetarenes with One Nitrogen or Phosphorus Atom). A wide range of pyridines have been prepared using this method. Cobalt complexes are the most common compounds used to catalyze the reaction, and their use has been reviewed in Science of Synthesis, Vol.1 [Compounds with Transition MetalCarbon π-Bonds and Compounds of Groups 108 (Ni, Pd, Pt, Co, Rh, Ir, Fe, Ru, Os) (Section], as well as elsewhere;[‌44‌] these review articles are referenced extensively in this section. Alkyl and aryl cyanides react with acetylene to give 2-substituted pyridines in high yields, a few examples of which are given in Scheme 14. When symmetrically substituted alkynes are used, pentasubstituted pyridines can be prepared (Scheme 14).[‌44‌] However, with unsymmetrical alkynes, a mixture of products, 40 and 41, is obtained.[‌44‌,‌45‌] When pyridinecarbonitriles are used, bipyridine derivatives can be obtained (Scheme 14).[‌44‌] The cyclotrimerization is not limited to simple carbonitriles as heterosubstituted derivatives may also be used. Thus cyanamides lead to pyridin-2-amines and alkyl thiocyanates give 2-(alkylsulfanyl)pyridines.[‌44‌]

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