1,721,273 research outputs found
Rate-accelerated nonconventional amide synthesis in water: A practical catalytic aldol-surrogate reaction
No full textX119793sciescopu
Recent Developments in the Direct Methylation of Electron Deficient N-Heteroarenes
No full textThe direct introduction of methyl groups into electron-deficient N-heteroarenes has recently emerged as an efficient and promising strategy to afford methylated N-heteroarenes, which are important motifs in a variety of pharmaceuticals and biologically active molecules. Herein, three general state-of-the-art approaches including radical-mediated, transition-metal-catalyzed, or transition-metal-free direct C-H methylations of electron-deficient N-heteroarenes are highlighted.111310sciescopu
Iridium-catalyzed diborylation of benzylic C-H bonds directed by a hydrosilyl group: Synthesis of 1,1-benzyldiboronate esters
No full textWe describe a regioselective diborylation of primary benzylic C-H bonds catalyzed by [Ir(COD)OMe](2) and 4,4'-di-tert-butyl-2,2'-bipyridine (dtbpy). The hydrosilyl group acts as a traceless directing group, providing access to a range of 1,1-benzyldiboronate esters in good yields. Transformations of the 1,1-benzyldiboronate ester products include chemoselective Suzuki-Miyaura cross-couplings and synthesis of tetrasubstituted alkenyl boronate esters.open115354sciescopu
Room temperature copper-catalyzed 2-functionalization of pyrrole rings by a three-component coupling reaction
No full textX11108106sciescopu
Iridium-catalyzed borylation of secondary benzylic C-H bonds directed by a hydrosilane
No full textMost functionalizations of C-H bonds by main-group reagents occur at aryl or methyl groups. We describe a highly regioselective borylation of secondary benzylic C-H bonds catalyzed by an iridium precursor and 3,4,7,8-tetramethyl-1,10-phenanthroline as the ligand. The reaction is directed to the benzylic position by a hydrosilyl substituent. This hydrosilyl directing group is readily deprotected or transformed to other functional groups after the borylation reaction, providing access to a diverse set of secondary benzylboronate esters by C-H borylation chemistry.X115852sciescopu
Steady and unsteady computation of a two-dimensional upwash jet
No full textComputational procedures and results of an upwash jet arising from two opposing plane wall jets based on the Reynolds averaged Navier-Stokes equations are discussed. For the calculation of the flow, a steady and an unsteady numerical approach were taken. For the steady computation, we adopted various eddy viscosity models(the standard k-epsilon model, the RNG k-epsilon model and the Bardina's model) and the Reynolds stress transport model with various diffusion term closures. Results of the steady computation indicated that the jet halfwidth was very much underpredicted, and hence the velocity profiles of the upwash jet were in very poor agreement with the experimental data. We found, however, that the velocity profiles nondimensionalized by the jet half width and the maximum velocity appeared to be in good agreement with the experimental data, which could be misleading. When an unsteady approach with an unsteady version of the standard k-epsilon eddy viscosity model was taken, a periodic oscillation of the jet was observed. The jet half-width distribution obtained by taking the time average of the periodic velocity profiles was found to be in much better agreement with the experimental data
Intramolecular oxidative C-N bond formation for the synthesis of carbazoles: Comparison of reactivity between the copper-catalyzed and metal-free conditions
No full textNew synthetic procedures for intramolecular oxidative C-N bond formation have been developed for the preparation of carbazoles starting from N-substituted amidobiphenyls under either Cu-catalyzed or metal-free conditions using hypervalent iodine(III) as an oxidant. Whereas iodobenzene diacetate or bis(trifluoroacetoxy)iodobenzene alone undergoes the reaction to provide carbazole products in moderate to low yields, combined use of copper(II) triflate and the iodine(III) species significantly improves the reaction efficiency, giving a more diverse range of products in good to excellent yields. On the basis of mechanistic studies including kinetic profile, isotope effects, and radical inhibition experiments, the copper species is proposed to catalytically activate the hypervalent iodine(III) oxidants. The synthetic utility of the present approach was nicely demonstrated in a direct synthesis of indolo[3,2-b]carbazole utilizing a double C-N bond formation.X11331314sciescopu
Intramolecular oxidative diamination and aminohydroxylation of olefins under metal-free conditions
No full textA metal-free procedure that is simple to operate and convenient to handle was developed for the facile intramolecular oxidative diamination of olefins using an iodobenzene diacetate oxidant and a halide additive to furnish bisindolines at room temperature. The present reaction is featured by mild conditions, a broad substrate scope, and excellent functional group tolerance. The same protocol was successfully extended to the aminohydroxylation.X117171sciescopu
A versatile rhodium(I) catalyst system for the addition of heteroarenes to both alkenes and alkynes by a C-H bond activation
No full textX119382sciescopu
Iridium-Catalyzed, Hydrosilyl-Directed Borylation of Unactivated Alkyl C–H Bonds
No full textWe report the iridium-catalyzed borylation of primary and secondary alkyl C-H bonds directed by a Si-H group to form alkylboronate esters site selectively. The reactions occur with high selectivity at primary C-H bonds gamma to the hydrosilyl group to form primary alkyl bisboronate esters. In the absence of such primary C-H bonds, the borylation occurs selectively at a secondary C-H bond gamma to the hydrosilyl group, and these reactions of secondary C-H bonds occur with high diastereoselectivity. The hydrosilyl-containing alkyl boronate esters formed by this method undergo transformations selectively at the carbon-boron or carbon-silicon bonds of these products under distinct conditions to give the products of amination, oxidation, and arylation.112318sciescopu
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