Cassar-Heck-Sonogashira coupling

The Heck-Cassar-Sonogashira-Hagihara system, which couples terminal alkynes and vinylic or aromatic halides in an amine solvent, typically piperi-... 

A. Dondoni, A. Marra, and M. G. Zampolli, Synthesis of all carbon linked glycoside clusters round benzene scaffold via Sonogashira-Heck-Cassar cross coupling of iodobenzenes with ethynyl C-glycosides, Synlett, 11 (2002) 1850-1854. 

Direct introduction of sp carbon to alkynes by the reaction of Cu acetylides with aryl and alkenyl halides to form arylalkynes and alkenylalkynes is known as the Castro reaction [1]. Later it was found that coupling of terminal alkynes (1-alkynes) with halides proceeds more smoothly by using Pd catalysts. There are two methods of Pd-catalyzed coupling, hi 1975 direct coupling of 1-alkynes catalyzed by a phosphine-Pd(O) complex in the presence of amines was reported by Heck and Cassar as an extension of the Heck reaction to 1-alkynes [2,3]. In the same year, Sonogashira and Hagihara found that the addition of Cul as a co-catalyst gave better results, and the Pd(0)-CuI-catalyzed reaction is called the... 

Scheme 9.7 Proposed mechanism of the Cu-free Sonogashira reaction (the so-called Heck-Cassar coupling) [25].

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