Dehydrogenative Coupling Reactions

The heterocoupling of hydrosilanes with olefins occurs, formally, via two pathways yielding an unsaturated product as well as either hydrogen or a hydrogenated olefin (DS-1, DS-2) as presented in eqs. (6), and is usually accompanied 

The number of examples of highly selective dehydrogenative silylation is still limited. The most convincing examples are Ru3(CO)i2- and Fe3(CO)i2-cata-lyzed reactions of styrene [106, 114] and vinylsilane [115] with HSiEts, RuH2(H2)2PCy3)2-catalyzed reaction of ethylene with HSiEt3 [116], and cationic rhodium complex-catalyzed dehydrogenative silylation, e.g., [117], as well as the nickel equivalent of the Karstedt catalyst [105]. 

Dehydrogenative silylation of alkynes also may become a predominant route under the optimum conditions [1-5, 102, 120]. According to the Crabtree concept, in the presence of (for example) the cationic iridium complex, [IrH-(H20)(bq)L2]SbF6 (L = PPh3, bq = [7, 8]benzoquinolinato), the above process 

Using a commercially available AC ( 50wt%), various secondary benzylic alcohols were dehydrogenated aerobically to the corresponding ketones [62, 63]. 

The preparative relevance of this method is illustrated by the synthesis of ketones from substrates containing functional groups prone to undergo oxidation with other methods, such as pyridine and phenol groups. It also allowed the preparation of complex 4-O-P-Af-acetylchitooligosyl lactones from the corresponding chitoohgosaccharides [64]. 

Various benzylic alcohols, as well as cinnamyl alcohol and cyclohexanol, were dehydrogenated using large amounts of GiO under sonication [71] or GeO [72]. Despite the high GeO loadings (200 wt%), the material acted as an aerobic oxidation catalyst, since hardly any reaction occurred under nitrogen and the material could be recycled many times. Interestingly, GiO acted as a multifunctional tandem alcohol oxidation-alkyne hydration-aldol condensation catalyst for chal-cone formation directly from phenylacetylenes and benzyl alcohols [73]. 

With GiO as carbocatalyst, oxidative cross condensations of various anihnes and ahphatic amines with benzyl amine to the corresponding Af-benzylidene derivatives have also been achieved by suppressing homocondensation of benzyl amine by using an excess of the cross-coupling partner [77]. Reduced GeO served as a reusable aerobic dehydrogenation catalyst for the preparation of azo compounds from their hydrazo precursors [79]. 

A diverse range of carbocycles and heterocycles has been aromatized by aerobic dehydrogenation under AC catalysis [80]. Substrates include 9,10-dihydroanthracenes [81], a l,8-diaza-9,10-dihydroanthracene [82], Hantzsch 1,4-dihydropyridines [83], pyrazolines [83], 2-arylimidazolines [84, 85], indolines [86], 3,4-dihydropyrimidin-2(l//)-ones [87, 88], and various 

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The unsymmetrical silyl-hydrido zirconium dimer, Cp2Zr(SiPhMeH) (p-H)2(SiPhMe2) ZrCp2, similar to the above-mentioned complex 6, was isolated from the dehydrogenative coupling reaction of phenylmethylsilane with dimethylzirconocene. The X-ray analysis of the dimer shows a disorder which is produced by the ordered superposition of two... 

A photoinduced intramolecolar dehydrogenative-coupling reaction of stable semiquinone radicals 296 yielded 6H-pyrido[2,l-c][l,4]benzoxazi-nium inner salts 297 (090L5530). 

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

Similar dehydrogenative coupling reactions of the dihydrides R2SnH2 gives oligo-stannanes (R2Sn) (see Section 18.2.1.3 and 18.4). 

Cross-Dehydrogenative Coupling Reactions of sp3-Hybridized C-H Bonds... 

Su W, Yu J, Li Z, Jiang Z. Solvent-free cross-dehydrogenative coupling reactions under high speed ball-milling conditions applied to the synthesis of functionahzed tetrahy-droisoquinolines. J Org Chem 2011 76 9144-50. 

Scheme 4.21. Proposed reaction mechanism of the TFB-catalyzed dehydrogenative coupling reaction.

Dehydrogenative coupling reactions of POSS silanes with POSS silanols were carried out in the presence of TFB. The reaction scheme and the structure of the compounds are shown in Scheme 4.25. 

Scheme 4.25. Dehydrogenative coupling reaction of POSS silane with POSS silanol.

Stereoselective cross-dehydrogenative coupling reactions based on sp C—H activation to give chiral heterocycHc compounds 12JHC721. Suzuki—Miyaura cross-coupHng in acylation reactions, scope and recent developments 13MOL1188. 

Recently, Su used terminal alkynes direcdy in a cross-dehydrogenative coupling reaction (100 108) with heterocycles including... 

Substrate Controlled Directing Groups in Cross-Dehydrogenative Coupling Reactions... 

Scheuermann CJ (2010) Beyond traditional cross couplings the scope of the cross dehydrogenative coupling reaction. Chem Asian J 5 436-451. doi 10.1002/asia.200900487... 

A method for the B-arylation of boron heterocycle 89 has been developed and used to synthesize the BN for C=C analog 90 of the nonsteroidal anti-inflammatory drug (NSAID) felbinac (Scheme 28) (2013AG(I)9316). An X-ray crystal structure of the immediate precursor to the acid 90 was determined. The synthesis of the B-N for C=C analog 91 of 4-methoxy-ira s-stilbene has been accompHshed in a similar Rh-catalyzed dehydrogenative coupling reaction (20140L3340). An X-ray crystal structure of the N-benzylated derivative of product 91 was reported. 

Polysubstituted 2E/-pyran-2-ones are available through rhodium(III)-medi-ated decarboxylative and dehydrogenative coupling reactions of maleic acid derivatives with alkynes, in moderate to excellent yields (Scheme 45) (13JOC11427). 

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