Oxidative cross-dehydrogenative coupling

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. 

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... 

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... 

Scheme 50 Cu-catalyzed cross-dehydrogenative coupling of (hetero)arenes using iodine as an oxidant.

The synthesis of a-acyloxy ethers (formation of C—O bonds) was achieved by the TBHP oxidation of a mixture of a carboxylic acid (R C02H, R =aryl, heteroaryl, alkyl) and an ether (R, R = alkyl, alkyl halide) in the presence of BU4NI as the catalyst. The transformation involved a cross-dehydrogenative coupling (CDC) reaction of the C-H bond. ... 

A large number of cross-dehydrogenative couplings using iron catalysis under oxidative conditions have been reported [89,90]. The coupling of sp -sp, sp -sp, and sp -sp bonds has been achieved. These reactions proceed through iron-mediated electron-transfer processes and are outside the scope of this review. 

Zhao and Du s group [63] developed a metal-free cross-dehydrogenative coupling (CDC) of various 2-(A -arylamino)aldehydes 79 for direct aryl-aldehyde C (sp )-C(sp ) bond formation to provide a convenient approach for the synthesis of biologically important acridone derivatives 80 (Scheme 19). PIDA was used in combination with a substoichiometric amount of benzoyl peroxide as radical initiator for this oxidative intramolecular annulation reaction which presumably proceeds via the intermediacy of acyl radicals 81. 

SCHEME 5.47 Nickel-catalyzed enantioselective oxidative cross-dehydrogenative coupling of (3-ketoesters with xanthenes. 

SCHEME 7. 26 Copper-catalyzed oxidative cross-dehydrogenative-coupling of 3-ketoesters or 2-carbonyl-substituted phenols with ethers. 

An intramolecular cross-dehydrogenative coupling of 1,2,3-triazoles with arenes was reported in the presence of Cu(OAc)2 as the oxidant and pivalic acid as the additive (eq 172). ... 

Duan et al. developed a Cu20-catalyzed synthesis of highly functionalized dihydroquinolinones through tandem oxidative cyclization of cinnamamides with benzyl hydrocarbons (Scheme 8.96). The reaction proceeds smoothly via the direct cross-dehydrogenative coupling of C(sp )-H and C(sp )-H bonds using tert-butylperoxy benzoate (TBPB) as oxidant. This is the first example... 

---