Cuprous salts, reaction with alkynes

Some years later, Sonogashira and coworkers (1975) showed that both bromo-and iodoarenes and alkenes could be brought into reaction with terminal alkynes (in a direct extension of the Suzuki and Stephens-Castro reactions) in the presence of catalytic quantities of palladium(ll) (e.g., bis(triphenylphosphine)paUadium dichloride, ([C6H5]3P)2PdCl2, copper(l), e.g., cuprous iodide [Cul]), salts, and a primary (e.g., n-butylamine [CH3CH2CH2CH2NH2]) or secondary (e.g., diethyl-amine [(CH3CH2)2NH]) amine (Chapter 10). The details (Scheme 7.18) of this mild process (which are beyond the scope of this work) are thought to resemble the Heck (Chapter 6, Scheme 6.54) reaction in that a 7i-cloud-metal complex may play an intimate role. 

Copper tends to form more stable organocopper compounds with acetylene compounds than with aryl compounds. The synthetic reaction of acetylenic compounds with copper or copper salt, e.g., the Cadiot-Chodkiewics and Glaser reactions are well known. The Cadiot-Chodkiewics reaction is a reaction where I-bromoalkyne easily reacts with a terminal alkyne in the presence of a catalytic amount of a cuprous salt or amines to afford conjugate diacetylene compounds in high yield [43]. For example, polyacetylene is easily synthesized as shown in eq. (22.19) [43],... 

As already mentioned, the nature of the copper counter ion also has a dramatic effect on the rate and efficiency of the reaction. For example, the cuprous iodide-catalyzed reaction takes nearly 40 min to reach the maximum rate and over 100 min to reach full conversion (0.1 M in [azide] = [alkyne] = 0.1 M, [CuI/TTTA] = 0.005 M), whereas the replacement of the iodide with much weaker coordinating tetrafluor-oborate (by treating the reaction solution with 0.005 M of silver tetrafluoroborate salt) propels the reaction to completion within minutes (with v ax t least 10 times higher than for the Cul system). 

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