Dehydrogenative cross-coupling reactions

Copper-catalyzed dehydrogenative cross-coupling reactions of (benzo) thiazoles with cychc ethers 106 to give the products 107 have been developed by Jiang and Chen (Scheme 51) (20120L4950, 20130L4600). A radical pathway was proposed for the reaction with cyclic ethers initiated... 

Dehydrogenative Cross-Coupling Reactions Induced by NHC-Ni Complexes... 

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.

A silver-catalysed dehydrogenative cross-coupling reaction of substituted furans, thiophene, thioazole, and pyrrole (221) with diall l phosphites... 

Doi and Mori made excellent use of dihydroindole triflate 189 in Pd-catalyzed cross-coupling reactions. This compound was discussed earlier in the Suzuki section, and it also undergoes Stille couplings as illustrated below [140]. A final dehydrogenation completes the sequence to indoles. 

Abstract Applications of five-membered ring products as catalysts in cyclometalation reactions inclnde chiral reactions, metathesis reactions, cross-coupling reactions, and polymerization reactions. Other reactions include reductions, Michael addition reactions, dehydrogenations, Diels-Alder reactions, and hydrogenations. 

Suzuki cross-coupling reactions have also been applied for the synthesis of graphene ribbons (Scheme 44) [108]. In the example shown the para-bisboronic ester 171 is polymerized to the intermediate 172. Final dehydrogenation yielded the graphene ribbon 173. 

Since the biaryl structures are prevalent cores in pharmaceutical targets and functional materials [28, 29], the dehydrogenative biaryl coupling of nonfunctionalized simple arenes has been extensively studied in recent years. Early successful examples with copper salts alone involve the cross-coupling reaction of relatively acidic 1,3-azoles and polyfluoroarenes (Eqs. 10-13) [30-33]. 

Dehydrogenative Alcohol-Alcohol Cross-Coupling Reactions... 

For example, Porcheddu and co-workers recently reported the synthesis of a series of a,p-unsaturated aldehydes by the dehydrogenative cross-coupling of primary alcohols, which reacted with an amine to form the corresponding imine, followed by a Mannich-type condensation reaction (Scheme 39) [193]. 

Various transition metal catalysts of Pt, Pd, and Rh were not effective in this dehydrogenative cross-coupling condensation reaction, even though some of them had been reported as efficient catalysts for linear hydrosilanes and silanols in our previous paper [95,115]. 

The cross-coupling reaction of the ketoxime ester 179 with the alkenylboronic acid leads to the 3-azahexa-l,3,5-triene 181 67t-electrocyclization of the triene 181 affords the 3,4-dihydropyridine 182, whose dehydrogenation by O2 aromatizes to the pyridine 180. Notably, this approach allows flexible control over the substitution pattern of the pyridine system to be synthesized. 

Heteroaryl phosphonates are common motifs in biological compounds and have stimulated the development of transition metal-catalyzed methodologies for C-P bond formation [68]. Phosphonated thiophenes 43 are accessible via silver-catalyzed dehydrogenative cross-coupling of thiophene 1 with dialkyl phosphites 42 (Scheme 19) [69]. The reaction is performed in aqueous dichloromethane, proceeds regioselectively at the a-position, and utilizes silver(l) nitrate as catalyst and the oxidant potassium persulfate. 

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. ... 

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