Transition metal-mediated cross-coupling reactions

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. 

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). 

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