Dehydrogenation intermolecular oxidative

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. 

Using a similar Pt-catalyzed intermolecular oxidative dehydrogenation hydroamination followed by intramolecular aryl C(sp )—H fuctionalization process, Poli and coworkers developed a simple protocol for the synthesis of quinaldine 78 from readily available aniline and ethylene (Scheme 12.36) [41]. It was found that the selectivity of the catalytic reaction between aniline and ethylene in the presence of the Brunet catalyst (PtBr2/Br ) shifts from the hydroamination product Af-ethylaniline to the heterocyclization product... 

M-butane proceeds via an intermolecular mechanism with 2-butene involved intermediately.300-303 The role of the transition metal promoters such as Fe and Mn was shown to increase the surface concentration of the intermediate butene 304 The formation of butene is speculated to occur through an oxidative dehydrogenation on the metal site305 or by one-electron oxidation.306... 

Here hydrocarbon conversion reactions occur wholly or at least partly on the carbonaceous overlayer on the metal and oxide surfaces, as reported by others (13,15-20). Poly-condensed EDA complexes may behave as giant alkenes in which by reversible catalytic hydrogenation/dehydrogenation occurs. This mechanism is similar to the intermolecular hydrogen transfer mechanism proposed (IS) for hydrogenation of unsaturated hydrocarbons. 

Intermolecular dehydrogenative oxidative homocouplings of (hetero)arenes turned out to be among the most important methods for the synthesis of symmetrically substituted biaryls [122]. A recent illustrative example is oxidative coupling reactions of 2-naphthols, which were accomplished in an asymmetric fashion employing an inexpensive iron catalyst (Scheme 9.47) [123]. 

A series of reactions pertinent to quinoxaline fused 2,3-dihydro-l.ff-l,2-diazepines (77) has been published <90jhc819, 90JHC2I97). These involve intermolecular displacement of the 5-cyano group of C77) by alkoxides, a reaction that proceeds with spontaneous tautomerism to yield diazepinones (78) (Equation (15)) (see Section 9.04.3.2). When the aryl group, R, bears an ortho hydroxyl moiety, the resultant intramolecular reaction yielded compounds, such as (79) <90JHC2209,9i JHC787). Treatment of (79) with dead leads to dehydrogenation however, attempted oxidation of (78 ... 

Several examples of intermolecular C-H bond functionalization have appeared during the past decade. In addition to the oxidations reported above in Shilov-type systems, and the dehydrogenation of alkanes to make alkenes, catalytic systems have been developed to introduce functional groups into hydrocarbons. 

In the Absence of Oxygen Methanol, Ethanol, 2-Propanol, and t-Butyl Alcohol Alcohols such as methanol, ethanol, and 2-propanol are converted with Pt/Ti02 to the corresponding dehydrogenation products such as formaldehyde, acetaldehyde, and acetone, respectively, with the formation of equimolar H2. t-Butyl alcohol is converted into 2,5-dimethyl-2,5-hexanediol with the formation of H2 through intermolecular dimerization since t-butyl alcohol has no alpha-hydrogen. In these oxidative reactions, alcohols are oxidized by photoformed holes, while photoexcited electrons reduce water (or H" ) to form H2 [4]. 

Scheme 7.51 Intermolecular dehydrogenative nitrogen atom incorporation for the synthesis of quinoxaline N-oxides from imines...

Second, 1,4-diols undergo intermolecular hydrogen transfer, giving lactones efficiently in acetone containing Cp Ru(P-N) catalysts the TOF of this reaction at 30 C exceeds 1,000 h (Fig. 21) [67]. The catalytic oxidative lactonization of diols is characterized by its unique chemo- and regioselectivity. The significant rate difference between primary and secondary alcohols in dehydrogenation, and the rate difference between 1,4-diols and 1,5- or 1,6-diols enable unique oxidative lactonization of triols. 

Intermolecular direct C(3)-alkenylation of indoles using palladium(II) as catalyst and oxygen as the oxidant has been achieved. The reaction shows complete regio- and stereo-selectivity all products are ii-isomers at the C(3)-position, and no Z-isomers or 2-substituted products are detected. Aerobic a, -dehydrogenation of aldehydes and ketones is catalysed by Pd(TFA)2/4,5-diazafluorenone. The cleavage of a-C-H bond of the ketone has been identified as the turnover-limiting step of the catalytic mechanism. ... 

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