Cross dehydrogenative couplings

Anilides react in a general way as arenes in the presence of Pd(OAc)2/DMSO catalyst and TFA in an atmosphere of O2 to give products of ortho-arylation [149]. In this reaction, arenes with electron-withdrawing substituents, such as fluoroben-zene derivatives, gave only poor conversions, which suggests that this reaction does not proceed via a proton-abstraction mechanism. 

A palladium-catalyzed cross-dehydrogenative coupling of benzo[h]quinoline (117) and related substrates with substituted arenes takes place in the presence of benzoquinone [150]. In this reaction, the initiaUy formed palladacycle (as in 

The direct arylation of arenes with stannaries ArSnCls is similarly catalyzed by PdCl2 and proceeds with CuCh as oxidant [152]. In this instance, a different mechanism was suggested based on the transmetallation between the stannane and a Pd(lV) salt, followed by an electrophilic aromatic substitution and reductive elimination. Arylzinc reagents also arylate 2-arylpyridines in the presence of iron catalysts [153]. 

It is important that, whilst mechanisms that occur via the Pd(ll)/Pd(lV) catalytic cycle have been excluded from Heck and cross-coupling reactions, this type of catalytic system may well be found in arylation reactions with [Ar2l]Bp4, or in those reactions which occur under oxidative conditions. 

51 Leading references on the palladium-catalyzed arylation of furans (a) McClure, M.S., Glover, B., McSorley, E., Millar, A., Osterhout, M.H. and Roschangar, F. (2001) Org. Lett., 3,1677-88  

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Mannich-type chemistry and cross-dehydrogenative couplings between t/i3-C-H and t/i-G-H bonds can be mediated by copper catalysis (Equations (43) and (44)).49,49a It is to be noted that the nitrogen atom mediates the... 

The same catalytic system as described for the CDC of amines and ni-troalkanes, complemented with C0CI2 as a co-catalyst, also proved efficient for the allylic alkylation via cross-dehydrogenative coupling between various cycloalkenes and diketones (Eq. 9). Again, the exact mechanism or role of the organic peroxide are not known to date, but the formation of water probably provides the thermodynamic driving force for these reactions [121,122]. 

Li, Z. and Li, C.-J. 2005. CuBr-catalyzed direct indolation of tetrahydroisoquinolines via cross-dehydrogenative coupling between sp3 C-H and sp2 C-H bonds. Journal of the American Chemical Society, 127 6968-69. 

Cross-Dehydrogenative Coupling Reactions of sp3-Hybridized C-H Bonds... 

As illustrated in this chapter, oxidative cross-dehydrogenative coupling (CDC) has provided the opportunity to simplify organic synthesis by presenting an alternative to the separate steps of prefunctionalization and defunctionalization that have traditionally been part of synthetic design. In the near future, we anticipate the development of CDC reactions that will be more efficient and effective to provide a positive economical and ecological impact on the next generation of C-C bond formation processes. 

Scheme 9.1 Copper-catalyzed cross-dehydrogenative coupling.

Scheme 9.2 Ruthenium-catalyzed cross-dehydrogenative coupling between the 2-arylpyridine 4...

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... 

By building their own vibration ball mill, Shayesteh and coworkers obtained 100% conversion in just 12 min at 30 Hz for cross-dehydrogenative coupling (CDC) of 2-naphthol [62]. In comparison, the Toda s mortar grinding and above described method by Rasmussen et al. needed 2 and 1 h, respectively. On operation condition of 30 Hz vibration ball mill gives better performance in comparison to other commonly used methods such as ball mill and mortar and pestle, due to higher mechanical... 

Su W, Yu J, Li Z, Jiang Z. Solvent-free cross-dehydrogenative coupling reactions under high speed ball-milling conditions applied to the synthesis of functionahzed tetrahy-droisoquinolines. J Org Chem 2011 76 9144-50. 

CAN Cerium ammonium nitrate CDC Cross-dehydrogenative coupling CDI Carbonyl diimidazole CPD Cyclopentadiene... 

From C-H to C-C Bonds Cross-Dehydrogenative-Coupling 27 Renewable Resources for Biorefineries 28 Transition Metal Catalysis in Aerobic Alcohol Oxidation 29 Green Materials from Plant Oils... 

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