Alkynes synthesis from

In the context of pyridin synthesis from alkynes and nitriles homogeneously catalyzed by (cyclopentadienyl)cobalt complexes (Eq. 13), it was found that electron-withdrawing groups on the cyclopentadienyl ring significantly increase the activity [63]. During the screening of various cobalt half-sandwich complexes... 

Scheme 11. 1,3-Diene synthesis from alkyne and ethylene...

In a similar context Amdtsen developed a new pyrrole synthesis from alkynes, acid chlorides either imines or isoquinolines, based on the reactivity of isocyanides (Scheme 35a) [197]. Although all atoms from the isocyanide are excluded from the final structure, its role in the reaction mechanism is crucial. The process takes place through the activation of the imine (isoquinoline) by the acid chloride to generate the reactive M-acyliminium salt, which is then attacked by the isocyanide to furnish a nitrilium ion. This cationic intermediate coordinates with the neighboring carbonyl group to form a miinchnone derivative, which undergoes a [3+2] cycloaddition followed by subsequent cycloelimination of the isocyanate unit, to afford the pentasubstituted pyrrole adducts 243 and 244 (Scheme 35a, b). 

Co arene chemistry has been expanded by the preparation of a number of (arene)Co(j7" -diene)+ and (arene)Co( , -enyl) complexes starting from (10). Hydrogenation of (10) in the presence of an arene and a base (piperidine or quinuclidine for obvious stabilization of coordinatively unsaturated cobalt intermediates) gives cyclooctenyl complexes (37) (equation 53). This reaction occurs with a large niunber of arenes even CeFg gives an j -arene complex. The resulting complexes (37) are moderately active catalysts in the pyridine synthesis from alkynes and nitriles (Section 5.1.4). 

In contrast to carbocyclic alkyne cyclotrimerizations, the catalytic pyridine synthesis from alkynes and nitriles relies exclusively on cobalt catalysts with a few exceptions where rhodium [16] and iron complexes [17] could be applied. The cobalt-catalyzed pyridine synthesis can even be carried out in a one-potreac-tion generating the catalyst from C0CI2 6 H20/NaBH4 -1- nitrile/alkyne in situ [18]. 

This behaviour correponds to the observation that other unsaturated hydrocarbons, e.g. alkynes, allenes or 1,3-butadienes, which readily undergo transition metal catalyzed cyclooligomerizations, do also incorporate CX multiple bonds in such cycloadditions only with difficulty in most cases 207 208). Besides the well known cobalt-catalyzed pyridin synthesis from alkynes and nitriles98 cocyclooligomerizations have been achieved with alkynes on one side and isocyanates 209), carbodiimides210) and carbondioxide 211) on the other side as well as with 1,3-butadienes and aldehydes 212), carbondioxide213 and 2-aza- or 2,3-diaza- 1,3-butadiene214. ... 

Cobalt-catalyzed synthesis from alkynes and nitriles 85AG264 86MI13 ... 

Efficiency of pyridine synthesis from alkynes and nitriles is improved with light (Scheme 3) <93AOC(7)641>. 

Synthesis from alkynes has been touched on in the foregoing discussion, and brief details of points of interest are included as part of ref. 319 (see also ref. 365). 

H. Bonnemann, Cobalt-Catalysed Pyridine Synthesis from Alkynes and Nitriles , Angew. Chem. Internat. Edn., 1978,17, 505. 

Kinoshita A, Sakakibara N, Mori M. Novel 1,3-diene synthesis from alkyne and ethylene by ruthenium-catalyzed enyne metathesis. 7. Aw. Chem. Soc. 1997 119 12388-12389. 

Tonogaki K, Mori, M. An improved 1,3-diene synthesis from alkyne and ethylene using cross-enyne metathesis. Tetrahedron Lett. 2002 43 2235-2238. 

The few examples of catalytic cyclopentenone formation from alkyne, alkene, and CO are discussed below, as is the bifuryli-denedione synthesis from alkyne and CO. It should also be noted that Co4(CO)i2, obtained by heating the dinuclear carbonyl, can probably replace the latter in most of the above catalytic reactions, but without obvious advantage. 

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