Coupling iridium catalyzed

Scheme 15 Iridium-catalyzed hydrogen-mediated coupling of alkyl-substituted alkynes to activated ketones and aldehydes. Conditions a ligand = BIPHEP, solvent = toluene, T = 80 °C b ligand = DPPF, solvent = toluene, T = 60 °C c ligand = BIPHEP, solvent = DCE,...

Iridium-catalyzed transfer hydrogenation of aldehyde 73 in the presence of 1,1-dimethylallene promotes tert-prenylation [64] to form the secondary neopentyl alcohol 74. In this process, isopropanol serves as the hydrogen donor, and the isolated iridium complex prepared from [Ir(cod)Cl]2, allyl acetate, m-nitrobenzoic acid, and (S)-SEGPHOS is used as catalyst. Complete levels of catalyst-directed diastereoselectivity are observed. Exposure of neopentyl alcohol 74 to acetic anhydride followed by ozonolysis provides p-acetoxy aldehyde 75. Reductive coupling of aldehyde 75 with allyl acetate under transfer hydrogenation conditions results in the formation of homoallylic alcohol 76. As the stereochemistry of this addition is irrelevant, an achiral iridium complex derived from [Ir(cod)Cl]2, allyl acetate, m-nitrobenzoic acid, and BIPHEP was employed as catalyst (Scheme 5.9). 

Interestingly, the alkenylation of sp3 C-H bond is observed in the iridium-catalyzed coupling reaction of aldehydes, amines, and alkynes (Equation (56)).62... 

Secondary phosphine oxides are known to be excellent ligands in palladium-catalyzed coupling reactions and platinum-catalyzed nitrile hydrolysis. A series of chiral enantiopure secondary phosphine oxides 49 and 50 has been prepared and studied in the iridium-catalyzed enantioselective hydrogenation of imines [48] and in the rhodium- and iridium-catalyzed hydrogenation functionalized olefins [86]. Especially in benzyl substituted imine-hydrogenation, 49a ranks among the best ligands available in terms of ex. 

Under the conditions of iridium-catalyzed hydrogenation, alkyne-carbonyl and alkyne-imine reductive coupling occurs in the absence of stoichiometric byproducts. For example, iridium-catalyzed hydrogenation of nonconjugated alkynes in the presence of ot-ketoesters delivers the corresponding a-hydroxy esters in... 

Scheme 9 Catalytic carbonyl addition via iridium-catalyzed hydrogenative coupling of dimethy-lallene...

Scheme 10 Iridium-catalyzed reductive coupling of 1,1-dimethylallene to an aldehyde under an atmosphere of deuterium...

Scheme 12 Isotopic labeling and crossover experiments in iridium-catalyzed couplings of 1,1-dimethylallene under transfer hydrogenation conditions...

Under the conditions of iridium-catalyzed transfer hydrogenation employing isopropanol as reductant, 1,3-cyclohexadiene couples to aryl aldehydes to provide... 

Scheme 15 Iridium-catalyzed couplings of 1,3-cyclohexadiene under transfer hydrogenation conditions (ratio refers to 1,4-oIefinic versus 1,5-olefinic alcohols)...

Examples of catalytic formation of C-C bonds from sp C-H bonds are even more scarce than from sp C-H bonds and, in general, are limited to C-H bonds adjacent to heteroatoms. A remarkable iridium-catalyzed example was reported by the group of Lin [116] the intermolecular oxidative coupling of methyl ethers with TBE to form olefin complexes in the presence of (P Pr3)2lrH5 (29). In their proposed mechanism, the reactive 14e species 38 undergoes oxidative addition of the methyl C-H bond in methyl ethers followed by olefin insertion to generate the intermediate 39. p-hydride elimination affords 35, which can isomerize to products 36 and 37 (Scheme 10). The reaction proceeds under mild condition (50°C) but suffers from poor selectivity as well as low yield (TON of 12 after 24 h). 

A convenient direct route has recently been described for obtaining regioregular polyalkylthiophenes using a tandem iridium-catalyzed borylation to produce the monomer, and a palladium-mediated coupling to produce the polymer [68]. The treatment of substituted thiophenes with B2pin2 in the presence of [lrCl2(COD)]2/ 4,4 -di-tert-butyl-2,2 -bipyridine (DTBPY) provided the expected monomer in 97% yield (Scheme 7.35). 

Iridium-Catalyzed, Three-Component Coupling Reactions of Aldehydes,... 

The cationic iridium complex [Ir(cod)(PPh3)2]OTf, when activated by H2, catalyzes the aldol reaction of aldehydes 141 or acetal with silyl enol ethers 142 to afford 143 (Equation 10.37) [63]. The same Ir complex catalyzes the coupling of a, 5-enones with silyl enol ethers to give 1,5-dicarbonyl compounds [64]. Furthermore, the alkylation of propargylic esters 144 with silyl enol ethers 145 catalyzed by [Ir(cod)[P(OPh)3]2]OTf gives alkylated products 146 in high yields (Equation 10.38) [65]. An iridium-catalyzed enantioselective reductive aldol reaction has also been reported [66]. 

Iridium-catalyzed reductive coupling of acrilates and imines has been reported to provide trans (3-lactams with high diastereoselection [142], The use of electron-deficient aryl acrylates resulted in improved product yields. The mechanism, proposed by the authors, started from an in situ generated iridium hydride reacting with the acrilate to provide an iridium enolate that, then, reacted with the imine to give a (3-amido ester. Subsequent cyclization furnished the p-lactam and an iridium alcoxide. 

Iridium-catalyzed reductive coupling of acrylates and imines provides trans-P-lactams 22 bearing aromatic, alkenyl, and alkynyl side-chains, with high diastereoselection <02OL2537>. This reaction appears to proceed through a reductive Mannich addition-cyclization mechanism. 

Takagi, J., Sato, K., Hartwig, J. F., Ishiyama, T., Miyaura, N. Iridium-catalyzed C-H coupling reaction of heteroaromatic compounds with bis(pinacolato)diboron regioselective synthesis of heteroarylboronates. Tetrahedron Lett. 2002,43, 5649-5651. 

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