Dehydrogenative coupling aromatic

SiH-functional poly(silylated) aromatic hydrocarbons are important starting materials for the preparation of arene-bridged polysilanes through thermal or catalytic dehydrogenative coupling reactions. 

Sulfuric acid, H2SO4, rarely acts as an oxidant. It can be used for the dehydrogenative coupling of aromatic rings [595]. Equally rare is the oxidation of a sulfide to a sulfoxide with sulfuryl chloride, SO2CI2 [506]. 

The spectrum of applications of potassium permanganate is very broad. This reagent is used for dehydrogenative coupling [570], hydrox-ylates tertiary carbons to form hydroxy compounds [550,831], hydroxylates double bonds to form vicinal diols [707, 296, 555, 577], oxidizes alkenes to a-diketones [560, 567], cleaves double bonds to form carbonyl compounds [840, 842, 552] or carboxylic acids [765, 841, 843, 845, 852, 869, 872, 873, 874], and converts acetylenes into dicarbonyl compounds [848, 856, 864] or carboxylic acids [843, 864], Aromatic rings are degraded to carboxylic acids [575, 576], and side chains in aromatic compounds are oxidized to ketones [566, 577] or carboxylic acids [503, 878, 879, 880, 881, 882, 555]. Primary alcohols [884] and aldehydes [749, 868, 555] are converted into carboxylic acids, secondary alcohols into ketones [749, 839, 844, 863, 865, 886, 887], ketones into keto acids [555, 559, 590] or acids [559, 597], ethers into esters [555], and amines into amides [854, 555] or imines [557], Aromatic amines are oxidized to nitro compounds [755, 559, 592], aliphatic nitro compounds to ketones [562, 567], sulfides to sulfones [846], selenides to selenones [525], and iodo compounds to iodoso compounds [595]. 

Nickel peroxide, an undefined black oxide of nickel, is prepared from nickel sulfate hexahydrate by oxidation in alkaline medium with an ozone-oxygen mixture [929] or with sodium hypochlorite [930, 931, 932, 933]. Its main applications are the oxidation of aromatic side chains to carboxyls [933], of allylic and benzylic alcohols to aldehydes in organic solvents [929, 932] or to acids in aqueous alkaline solutions [929, 930, 932], and of aldehydes to acids [934, the conversion of aldehyde or ketone hydrazones into diazo compounds [935] the dehydrogenative coupling of ketones in the a positions with respect to carbonyl groups [931] and the dehydrogenation of primary amines to nitriles or azo compounds [936]. 

A alk aromatic alkylation DC dehydrogenative coupling trans transalkylation isom isomerization HT hydrogen transfer ol oligomerization alk alkylation cycl cyclization. 

Another possibility is the partial oxidation of methane to oxygen-containing compounds (methanol, higher alcohols, aldehydes) or synthesis gas and dehydrogenative coupling to give aromatic compounds. 

This poljunerization can be applied to a wide range of condensations between diethynyldiphenylsilane and aromatic halides including p3rridine and thiophene derivatives (13) (84). It was reported that dehydrogenative coupling of phenylsi-lane with m-diethynylbenzene in the presence of MgO to provide poly(silylene-m-diethynylenephenylene) (14) (eq. 14) (85,86). 

Styrene, the best known representatives of the aromatic olefin class, is readily obtained by cometathesis reaction of stilbene with ethene in the presence of alumina-supported molybdenum oxide catalysts. In a two-step process [27] stilbene is first produced from toluene by catalytic dehydrogenative coupling over Pb0/Al203, followed by codisproportionation to styrene, with ethene, over M0O3/AI2O3 ... 

Recently, an efficient CuBr-catalyzed aerobic intramolecular dehydrogenative cyclization reaction of AfAf-disubstituted hydrazones to pyrazoles by a double C(sp )-H bond functionalization was developed in Ge s group (Scheme 8.67). This transformation includes C(sp )-H oxidation, cyclization, and aromatization for the formation of pyrazole products. This is the first example of an intramolecular copper-catalyzed dehydrogenative coupling reaction via an iminium ion intermediate by a C(sp )-H bond functionalization process [113]. 

Kita et al. further developed PIFA-induced CDC reactions between phenyl ether derivatives and cyclic 1,3-dicarbonyl compounds as nucleophiles (Scheme 8.2). The reactions with 1 equiv. of PIFA in hexafluoro-2-propyl alcohol attach nucleophiles onto the ort/jo-position of para-substituted phenyl ethers to afford the dehydrogenative coupling products 8 in moderate yields. UV and electron spin resonance (ESR) spectroscopic studies support a reaction mechanism involving the formation of the charge-transfer complex 9 followed by the generation of the cation radical intermediate 10. This is the first example of the reaction of aromatic compounds with PIFA that involves the formation not of diatyliodonium(m) salt 11 but the cation radical intermediate 10 as a key intermediate. 

Similarly, Royo and co-workers proposed an interesting process of silyla-tion of aromatic thiols via a dehydrogenative coupling pathway induced by a half-sandwich Ni complex containing a Cp-NHC tethered ligand [eqn (10.5)]. Of note, this catalyst also mediated the hydrosilylation of aldehydes with PhSiHj in quantitative yields. ... 

In addition to protons, other electrofugic leaving groups such as SO3 (i. e., anions of sulfonic acids), Cl, Br, I, C02, and others can also be displaced in azo coupling reactions with aromatic substrates. The mechanism of such substitutions is in principle the same as that of dehydrogenation (see Fischer and Zollinger, 1972). 

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