Terminal dehydrogenative cross-coupling

Metal-mediated Reaction. The o -position of this inner salt can undergo dehydrogenative cross-coupling with terminal aUcynes, such as phenylacetylene, under Cu-mediated reaction conditions. The a-alkynyl derivative readily cyclizes in situ with the loss of the Ts group to afford 2-phenylpyrazolo[ l,5-a]pyridine in a 22% yield. This inner salt does not work as well as the analogous l-(benzoylamino)pyridinium inner salt in this reaction. ... 

Tertiary amines are coupled with terminal alkynes to give propargylamines in an iron-catalyzed dehydrogenative cross-coupling reaction. Iron(II) chloride is used as a catalyst and di-terr-butyl peroxide as oxidant. Unsymmetrical alkynes are obtained in a reaction sequence involving two cross-coupling steps (Scheme 4-259). ... 

Scheme 4-259. Double iron-catalyzed dehydrogenative cross-coupling reaction of tertiary amines and terminal alkynes.

The PPEs [14, 35, 36], which are dehydrogenated analogs of the poly(p-phenylene vinylene) s, display desirable optoelectronic properties that have found extensive use as emissive materials [37, 38]. PPE preparation is dominated by the Sonogashira Pd/Cu-catalyzed cross-coupling of aryl haUdes and terminal alkynes [39]. However, polymerizations under these conditions rarely achieve a high molecular weight, and defects such as diyne formation and alkyne crosshnking in the polymer backbone are endemic [14, 40]. Alkyne metathesis was envisioned as a complementary method to PPE synthesis, with much success. 

Copper Catalysts Direct oxidative functionalization of tertiary amines is of importance both enzymatically and synthetically. The combination of CuBr—TBHP has proved to be as an efficient system in the oxidative activation of sp3 C—H bonds adjacent to a nitrogen atom [10]. Various types of cross-dehydrogenative coupling (CDC) reactions have been developed, including compounds with activated methylene groups [11], indoles [12], and terminal alkynes (Scheme 11.2) [13]. Because 1,2,3,4-tetrahydroisoquinoline derivatives are important structure motifs of natural... 

The first cross-dehydrogenative intermolecular arylation of a heteroarene with an arene was reported by Fagnou in 2007. N-acetyl-lH-indoles were coupled with simple arenes and selective C3-arylation was obtained (88 89) in the presence of Pd(TFA)2 as catalyst in combination with superstoichiometric Cu(OAc)2 as terminal oxidant (Scheme 40) (2007SCI1172). The N-acetyl group proved to be crucial as no reaction product was achieved with IH-indoles, furthermore N-methyl-lH-indoles gave only self-dimerized products. 

Recently, Su used terminal alkynes direcdy in a cross-dehydrogenative coupling reaction (100 108) with heterocycles including... 

The proposed iminium intermediate in the CDC-type allgmylation implies that other C-H based pronueleophiles, besides terminal allqmes, can also couple with an a-sp C-H bond of a nitrogen in amines via the same process. Thus, we examined eleetron-rieh arenes as one such nucleophile via a cross-dehydrogenative Friedel-Crafts type arylation. Indole derivatives were coupled with N-aryl-THIQs under the CuBr/TBHP system to produce the desired CDC reaction product in good-to-excellent yields (Scheme 1.9). It is worth noting that the reaction was not sensitive to moisture or air, and that the desired product was obtained in reasonable yield even when the reaction was... 

Cross-Dehydrogenative-Coupling Reactions with Molecular Oxygen as the Terminal Oxidant... 

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