Aldehydes cross-dehydrogenative

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. 

The metal-free cross-dehydrogenative coupling between heterocycles and various aldehydes including sulfiir-containing heterocyclic aldehydes in benzene using... 

Efficient proeedures for the cross-dehydrogenative synthesis of aryl ketones have been introduced by complementing the radieal acylation with transition-metal-eatalyzed activation of aromatic C-H bonds. The first eross-dehydrogenative Pd-eatalyzed acylation of 2-phenylpyridines was developed independently by the groups of Chengf and Li. The latter demonstrated that various aliphatie, alicyclic and some aromatie aldehydes are smoothly converted in the presenee of 5 mol% of Pd(OAe)2 in combination with 1.5 equiv. of TBHP at 120 °C under an air atmosphere (Scheme 1.38). 

Scheme 17.21 Synthesis of epoxide hydrolase inhibitor via copper bromide catalysed cross dehydrogenative coupling of aldehydes and...

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. ... 

Piers et have completed the synthesis of eremophilenolide (347), using the hydroxymethylene derivative of (336). Thus, dehydrogenation of this compound gave the cross-conjugated keto-aldehyde (348) which was converted in four... 

The dehydrogenative cross-coupling of primary alcohols in die presence of an amine has been further extended to the synthesis of a,p-unsaturated aldehydes via the formation of imine intermediates. 

Good functional group tolerance was observed halides, esters, aldehydes, and vinyl and nitro groups were all viable substituents. Benzothiazoles can also undergo Cu-catalyzed dehydrogenative cross-coupling with silver(I) as an oxidant (eq 43). ... 

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