Oxidative coupling terminal alkynes

Benzo[ ] [l,4]thiazine-4-carbonitrile derivatives could be synthesized by a Cul-catalyzed coupling of 2-aminobenzothiazoles and terminal alkynes under ambient air (Scheme 8.124). Various benzo[ ][l,4]thiazine-4-carbonitriles which are not readily accessible by conventional methods could be obtained in moderate to good yields. Preliminary mechanistic studies indicate that the reaction possibly proceeds through the ring opening of thiazole moiety followed by sequential oxidative coupling with alkyne and intramolecular cyclization to afford the products [198]. 

The Glaser reaction is an oxidative coupling of terminal alkynes 1 to yield a symmetrical Z -acetylene 2 the coupling step is catalyzed by a copper salt. Closely related is the Eglinton reaction, which differs from the Glaser reaction mainly by the use of stoichiometric amounts of copper salt as oxidizing agent. 

The coupling of terminal alkynes with aryl or alkenyl halides catalysed by palladium and a copper co-catalyst in a basic medium is known as the Sonogashira reaction. A Cu(I)-acetylide complex is formed in situ and transmetallates to the Pd(II) complex obtained after oxidative addition of the halide. Through a reductive elimination pathway the reaction delivers substituted alkynes as products. 

There are a number of procedures for coupling of terminal alkynes with halides and sulfonates, a reaction that is known as the Sonogashira reaction.161 A combination of Pd(PPh3)4 and Cu(I) effects coupling of terminal alkynes with vinyl or aryl halides.162 The reaction can be carried out directly with the alkyne, using amines for deprotonation. The alkyne is presumably converted to the copper acetylide, and the halide reacts with Pd(0) by oxidative addition. Transfer of the acetylide group to Pd results in reductive elimination and formation of the observed product. 

Oxidative homo-coupling of terminal alkynes using copper catalyst in the presence of oxygen. 

Eastmond, R. Johnson, T. R. Walton, D. R. M. Silylation as a Protective Method for Terminal Alkynes in Oxidative Couplings, Tetrahedron 1972,28, 4601. 

Oxidative coupling of a terminal alkyne is a particularly easily performed carbon-carbon bond forming reaction, which results in a good yield of the symmetrical diacetylene. A widely used procedure involves the oxidation of the alkyne with air or oxygen in aqueous ammonium chloride in the presence of a copper(i) chloride catalyst (Glaser oxidative coupling). 

The Eglinton Reaction is an oxidative coupling of terminal alkynes, and allows the synthesis of symmetric or cyclic bisacetylenes via reaction of the terminal alkyne with a stoichiometric amount of a copper(II) salt in pyridine. 

Whereas Glaser-type oxidative coupling opens efficient synthetic pathways toward symmetrical diynes, its performance in heterocoupling is poor. The latter may be accomplished by Cadiot-Chodkiewicz coupling of terminal alkynes with 1-haloalkynes (usually 1-bromoalkynes). The reaction is conducted in the presence of an amine and catalytic amounts of a copper(I) salt. Because, in contrast with the Glaser-type reactions described above, it follows a nonoxidative reaction mechanism, oxygen is not necessary - but needs often not to be excluded (Scheme 4) [9]. 

Conditions based on stoichiometric amounts of silver oxide have been developed by Mori et al. for the synthesis of arylated alkynes from terminal alkynes and aryl iodides. Under such conditions, neither silylated alkynes nor aryl bromides or triflates did not undergo coupling (Scheme 10.78).129,130... 

The oxidative coupling of two terminal alkynes via their copper acetylide complexes to form a 1,3-butadiyne function is known variously as Glaser, Eglinton, or Hay... 

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