Alkynylcopper reagents

The reaction of aryl halides 1 with alkynylcopper(I) 2 under reflux in pyridine to prepare internal arylacetylenes is known as the Stephens-Castro reaction [Eq. (1)] [2], The reaction has proved to be particularly important in the synthesis of a wide range of tolan and heteroaromatic alkynes [3]. Vinyl and allenic halides can also be used and several reviews 

The nature of the amine is critical for the efficiency of the coupling [9, 10]. From 1-iodoacetylene and less acidic alkylacetylenes, various unsymmetrical diacetylenes can be prepared in good yields in pyrrolidine. In the case of 1 -bromoalkynes, the Pd catalyst improved the yield of coupling products [9]. 

Very recently, a general method for the synthesis of pure samples of unsymmetrically disubstituted diacetylenes of the type CH3(CH2) —C C—C C—CH OH (n = 2, 3, 4, 5) 11 was reported in detail [11]. 

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Lastly, for organocopper reagents, in a rather surprising reaction, 2,2 -diiodobiphenyls react with alkynylcopper reagents to give 78% yield of a cyclized product (equation 62)476. 

More recently, the stereoselective formation of 1,3-enynes has been reported, via a new carbon-carbon bond-forming reaction, involving the direct coupling of alkenyliodinium tosylates (1) with alkenylcop-per(I) reagents. A wide variety of alkynylcopper reagents (2) are easily made by addition of alkylcop-... 

A similar coupling is possible between 11 and alkynylcopper reagents (106) resulting in conjugated diynes (107) (equation 49). ... 

Table 9.13 Selection of cross-couplings between alkynylcopper reagents and haloalkynes.

Oxidative addition of alkenyl halides, triflates, and other esters to zerovalent palladium compounds has been long known as a viable route to palladium(ii)-alkenyl complexes. Stereospecific coupling reactions involving mono- and (E)- or (Z)-dihalo-alkenes with palladium-copper catalysis under modified Sonogashira conditions are quite versatile and useful. These proceed through oxidative addition of the alkenyl halide via palladium(ii) alkenyl complexes, followed by coupling with a nucleophile (usually an alkynylcopper reagent obtained in situ with co-catalytic copper(i) from terminal alkynes in the presence of, in this case, a base like piperidine instead of diethylamine). ... 

Introduction. (lodoethynyl)trimethylsilane has been largely confined to aryl- and vinylcopper coupling, where it serves well since the reverse procedure, i.e. coupling with alkynylcopper reagents, is not straightforward due to the lack of reactivity of alkynyl moieties bound to copper. 

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