Evidence for the protiocatalytic nature of the diacetoxylation of alkenes using PhI(OAc)(2) as oxidant is presented. Systematic studies into the catalytic activity in the presence of proton-trapping and metal-complexing agents indicate that protons act as catalysts in the reaction. Using triflic acid as catalyst, the selectivity and reaction rate of the conversion is similar or superior to most efficient metal-based catalysts. Metal cations, such as Pd(II) and Cu(II), may interact with the oxidant in the initiation phase of the catalytic transformation; however, 1 equiv of strong acid is produced in the first cycle which then functions as the active catalyst. Based on a kinetic study as well as in situ mass spectrometry, a mechanistic cycle for the proton-catalyzed reaction, which is consistent with all experimental data presented in this work, is proposed.

Monolayer Ru atoms covered highly ordered porous Pd octahedra have been synthesized via the underpotential deposition and thermodynamic control. Shape evolution from concave nanocube to octahedron with six hollow cavities was observed. Using aberration-corrected high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy, we provide quantitative evidence to prove that only a monolayer of Ru atoms was deposited on the surface of porous Pd octahedra. The as-prepared monolayer Ru atoms covered Pd nanostructures exhibited excellent catalytic property in terms of semihydrogenation of alkynes.

The first example organocatalyzed aerobic oxidation of aldehydes to carboxylic acids in both organic solvent and water under mild conditions is developed. As low as 5 mol % N-hydroxyphthalimide was used as the organocatalyst, and molecular O 2 was used as the sole oxidant. No transition metals or hazardous oxidants or cocatalysts were involved. A wide range of carboxylic acids bearing diverse functional groups were obtained from aldehydes, even from alcohols, in high yields.

An enantioselective formal [3+3] annulation reaction of cyclic ketones with enones has been developed. In the presence of 20 mol % of pyrrolidine-thiourea 1a or N-(pyrrolidin-2-ylmethyl)trifluoromethanesulfonamide 1i, the reactions afford bicyclo [3.3.1] adducts in moderate to good yields with good to high enantioselectivities under mild conditions.

Trisoxazolines [1] have been applied widely in asymmetric catalysis [2] and molecular recognition. [3] In our efforts to develop superior catalysts that are cheap, readily accessible, air stable, and water tolerant, we designed and synthesized the pseudo-C 3 -symmetric trisoxazoline 1 b (Scheme 1) by the sidearm approach, and found that 1 b/Cu II promoted smoothly the highly enantioselective Friedel-Crafts reaction of indoles with arylidene malonates [4] and the Kinugasa reaction.[5] We also described tox/Co II -catalyzed [3+2] cycloaddition reactions between nitrones and alkylidene malonates in which the endo/exo selectivity could be controlled well by the reaction temperature. Thus, both cis and trans isoxazolidines could be prepared enantioselectively.[6] Herein, we report that the system tox/Ni II catalyzes the [3+3] cycloaddition of racemic 2-substituted cyclopropane-1,1-dicarboxylates with nitrones to provide ready access to optically active tetrahydro-1,2-oxazine derivatives with high diastereoselectivity and enantioselectivity. Furthermore, this reaction can be employed for the kinetic resolution [7] of 2-substituted cyclopropane-1,1-dicarboxylates to furnish these compounds in optically active form with excellent ee values.Tetrahydro-1,2-oxazine derivatives occur frequently in biologically active compounds [8] and are valuable synthetic intermediates.[9] Among the methods developed for the preparation of such compounds, [10] the [3+3] cycloaddition of donor-acceptor cyclopropanes with nitrones, pioneered by Kerr and co-workers, [11] is a particularly elegant approach. They found that nitrones 3 react smoothly with cyclopropanes 2 in the presence of Yb(OTf) 3 ·x H 2 O to give the cis isomers 4 diastereospecifically (see Table 1). Recently, Sibi et al. developed a highly efficient asymmetric version of this reaction. [12] They reported that nitrones react with cyclopropane-1,1-dicarboxylates to afford tetrahydro-1,2-oxazine derivatives with high enantioselectivity in the presence of dbfox/Ni II (10 mol %; dbfox = 4,6-dibenzofurandiyl-2,2-bisoxazoline). When 2-substituted cyclopropane-1,1-dicarboxylates were used as substrates, and the quantity of the catalyst was increased to 30 mol %, the reactions proceeded smoothly to give the products with high ee values but with low diastereoselectivities (the cis/trans ratio ranged from 1.0:1.4 to 1.0:0.8).Gratifyingly, we found that diethyl 2-phenylcyclopropane-1,1-dicarboxylate (2 a) reacted smoothly with nitrone 3 a to furnish the cycloaddition adduct in 99 % yield with excellent diastereoselectivity (d.r. > 99:1) in the presence of a catalytic amount of 1 b/Ni(ClO 4 ) 2 ·6 H 2 O. Further studies showed that ligands derived from iPr-box (box = bisoxazoline) influenced strongly both the enantioselectivity and diastereoselectivity of the reaction. The bisoxazoline 1 a without a pendant group gave the desired product with good diastereoselectivity (d.r. 97:3) but only 20 % ee (Table 1, entry 1). However, when a pyrid-2-yl or oxazolinyl group was introduced as a pend...

A palladium-catalyzed asymmetric synthesis of planar chiral metallocene compounds is reported. The reaction stereoselectively functionalized one of the ortho C-H bonds of Cp rings by intramolecular cyclization to form indenone derivatives in high yields with excellent enantioselectivity. The mild set of reaction conditions allowed a wide variety of chiral metallocene compounds to be synthesized with broad functional group tolerance. The influences of preinstalled chiralities on the other Cp-ring were also investigated.

A metal‐free aerobic autoxidative nitrooxylation of alkenyl oximes mediated by tert‐butyl nitrite is described. Molecular oxygen is used as the oxidizing reagent, avoiding use of organic trapping reagents such as 2,2,6,6‐tetramethylpiperidine 1‐oxyl (TEMPO). The desired products were obtained in generally high yields.magnified image

Trisoxazoline 1/Co(ClO(4))(2).6H(2)O catalyzed the 1,3-cycloaddition between nitrones 3 with alkylidene malonates 2 at 0 degrees C to give the isoxazolidines with both high enantioselectivity and high exo selectivity. However, when the temperature was lowered from 0 to -40 degrees C, the same cycloaddition afforded endo isomers as the major products with good to high enantioselectivity. A mechanism is provided.