Cross-dehydrogenative coupling arylation

Scheme 45 Cu-mediated cross-dehydrogenative coupling of 2-aryl di)azines and (benz)-l,3-azoles.

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. ... 

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. 

Addition of vinyl and aryl groups Cope rearrangement Cross-dehydrogenative coupling Cycloaddition reaction... 

Prior to the concept of cross-dehydrogenative-coupling (CDC), Moritani and Fujiwara developed the oxidative formation of Heck-type reaction products directly from arenes and alkenes, instead of aryl halides and... 

The ideal scenario would be to oxidatively couple two aryl C-H bonds and produce a new biaryl C-C bond. This coupling method, herein known as cross-dehydrogenative-coupling (CDC), requires no pre-functionalization steps and generates fewer by-products as waste (Scheme 6.1). 

Aryl-Aryl Coupling via Cross-Dehydrogenative-Coupling Reactions Crass-dehydrogenative-coupling... 

Activation by rhodium complexes has been used to achieve direct exchange of ketone methyl or aryl groups with an aryl group on ArB(OH)2, selective C(CO)-C bond cleavage on reaction of ketones with water, oxidative acylation between secondary benzamides and aryl aldehydes with subsequent intramolecular cyclization to 3-hydroxyisoindolin-l-ones, " cross dehydrogenative coupling to form xanthones from 2-aryloxybenzaldehydes, and activation of the aldehydic C-H bond to achieve hydroacylation of unactivated alkenes by salicylaldehyde derivatives and of vinylsilane by benzaldehyde. ... 

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. 

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