Transition metal-mediated cross-coupling

For some applications, it is useful to put a substrate on a solid support. Linkers that can be converted directly to desired functionality ( traceless ) are particularly valuable. Andrew M. Cammidge of the University of East Anglia and A. Ganesan of the University of Southampton independently (Chem. Commun. 2004, 1914, 1916) developed the polymeric sulfonyl chloride 9. The derived phenyl sulfonates are useful partners for transition-metal mediated cross coupling. 

Transition Metal-Mediated Cross-Coupling Reactions. Ill... 

Reactions of alkynyliodonium salts 119 with nucleophiles proceed via an addition-elimination mechanism involving alkylidenecarbenes 120 as key intermediates. Depending on the structure of the alkynyliodonium salt, specific reaction conditions, and the nucleophile employed, this process can lead to a substituted alkyne 121 due to the carbene rearrangement, or to a cyclic product 122 via intramolecular 1,5-carbene insertion (Scheme 50). Both of these reaction pathways have been widely utilized as a synthetic tool for the formation of new C-C bonds. In addition, the transition metal mediated cross-coupling reactions of alkynyliodonium salts are increasingly used in organic synthesis. 

Transition metal mediated cross couplings of epoxides have remained relatively unexplored, with only a few examples of this potentially useful reaction reported in the literature. A recent report details the Suzuki-Miyaura cross-coupling of epoxides <07JOC3253>. The reaction of aryl epoxides with arylboronic acids under Suzuki-Miyaura coupling conditions provides the coupled product in good yields. Careful monitoring of the reaction is essential to avoid Pd-catalyzed rearrangement of the epoxides. 

Diaryliodonium salts represent the most stable and well-investigated class of iodonium salts. Their chemistry was extensively covered in several reviews [854,855,860]. The most important and synthetically useful reactions of diaryliodonium salts include the following the direct electrophilic arylation of various nucleophiles, transition metal mediated cross-coupling reactions and reactions involving generation and trapping of the benzyne intermediates. 

Van der Eycken and coworkers have demonstrated an interesting solid-phase synthesis of 2(l//)-pyrazinones " based on the Strecker reaction" of the resin-bound amine with an appropriate aldehyde and a cyanide, allowing a wide diversity at the C6 position of the pyrazinone ring (Scheme 8.29). The authors investigated a number of interesting decorations on the resin-bound 2(lJ/)-pyrazinones, using a variety of microwave-assisted, transition metal-mediated cross-coupling reactions (Scheme 8.29). 

The Stille reaction involves the transition-metal-mediated cross-coupling of organostannanes with organic electrophiles. Generally, it is a mild and efficient way for the creation of C—C bonds, especially between Csp or Csp centers. The most significant disadvantage of the method is... 

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