Acid Assistance Protons are quite versatile catalysts of organic reactions, but because they achiral, cannot induce stereoselectivity on their own. One productive way around this problem has been to use chiral conjugate bases and perform reactions in media where the remain tightly attracted protonated substrates. Xu et al. (p. 986 ; see Perspective by Schreiner ) thoroughly explored mechanism an alternative approach, which achiral acid was used conjunction with a second, molecule (a urea...

An experimental and computational investigation of amido-thiourea promoted imine hydrocyanation has revealed a new unexpected mechanism catalysis. Rather than direct activation the by thiourea, as had been proposed previously in related systems, data are consistent with involving catalyst-promoted proton transfer from hydrogen isocyanide to generate diastereomeric iminium/cyanide ion pairs that bound catalyst through multiple noncovalent interactions; these collapse form enantiomeric...

The mechanism of the enantioselective cyanosilylation ketones catalyzed by tertiary amino-thiourea derivatives was investigated using a combination experimental and theoretical methods. kinetic analysis is consistent with cooperative in which both thiourea amine catalyst are involved productively rate-limiting cyanide addition step. Density functional theory calculations were used to distinguish between mechanisms involving activation ketone or enantioselectivity-determining strong...

The total synthesis of (+)-yohimbine was achieved in 11 steps and 14% overall yield. absolute configuration established through a highly enantioselective thiourea-catalyzed acyl-Pictet-Spengler reaction, the remaining 4 stereocenters were set simultaneously substrate-controlled intramolecular Diels-Alder reaction.

In the (salen)Co(III)-catalyzed hydrolytic kinetic resolution (HKR) of terminal epoxides, rate- and stereoselectivity-determining epoxide ring-opening step occurs by a cooperative bimetallic mechanism with one Co(III) complex acting as Lewis acid another serving to deliver hydroxide nucleophile. this paper, we analyze basis for extraordinarily high stereoselectivity broad substrate scope observed in HKR. We demonstrate that stereochemistry each two (salen)Co(III) complexes rate-determining...

The development of a system for the operationally simple, scalable conversion polyhydroxylated biomass into industrially relevant feedstock chemicals is described. This includes bimetallic Pd/Re catalyst in combination with hydrogen gas as terminal reductant and enables high-yielding reduction sugar acids. procedure has been applied to synthesis adipate esters, precursors production Nylon-6,6, excellent yield from biomass-derived sources.

The (salen)Co(III)-catalyzed hydrolytic kinetic resolution (HKR) of terminal epoxides is a bimetallic process with rate controlled by partitioning between nucleophilic (salen)Co-OH catalyst and Lewis acidic (salen)Co-X catalyst. commonly used (salen)Co-OAc (salen)Co-Cl precatalysts undergo complete irreversible counterion addition to epoxide during the course hydrolysis reaction, resulting in quantitative formation weakly severely diminished reaction rates late stages HKR reactions. In...

Site-selective functionalizations of C–H bonds are often achieved with a directing group that leads to five- or six-membered metallacyclic intermediates. Analogous reactions occur through four-membered metallacycles rare. We report challenging palladium-catalyzed oxidation primary β nitrogen in an imine aliphatic amine, process occurs palladacyclc intermediate. The success the reaction relies on identification, by H/D exchange, simple (salicylaldehyde) capable inducing formation this small...

Reported here is the Pd-catalyzed C-N coupling of hydrazine with (hetero)aryl chlorides and bromides to form aryl hydrazines catalyst loadings as low 100 ppm Pd KOH base. Mechanistic studies revealed two resting states: an arylpalladium(II) hydroxide chloride. These compounds are present in interconnected catalytic cycles react base or alone give product. The selectivity complex over diaryl was lower than that chloride complex, well reaction. In contrast, closely matched reaction, indicating...

Mit Uran auf neuen Wegen: Uran(III)-Komplexe mit sechszähnigen makrocyclischen Triazacyclononan-Liganden L1 ermöglichen Di- und Triketonen Reaktionswege zur Ein- Zwei-Elektronen-Reduktion. Der zweikernige Enolatkomplex, der über einen dieser Wege erzeugt wird, reagiert CO2 unter Bildung einer C-C-Bindung (siehe Schema).

We describe efforts to understand the structure and reactivity of lithiated cyclohexanone N-cyclohexylimine. The lithioimine affords complex solvent-dependent distributions monomers, dimers, trimers in a number ethereal solvents. Careful selection solvent provides exclusively monosolvated dimers. Rate studies on C-alkylations reveal chronic mixtures monomer- dimer-based pathways. explore factors influencing reactants alkylation transition structures marked differences between lithioimines...

An enantioselective Diels–Alder (DA) reaction of α-acyloxy enones has been developed to synthesize chiral oxidized cyclohexenes. Yttrium(III) triflate, in conjunction with a pyridinebisimidazoline (PyBim) ligand, was found catalyze the asymmetric [4 + 2] cycloaddition variety dienes and enone dienophiles. Using this method, terpinene-4-ol, key intermediate synthesis commercial herbicide cinmethylin, can be prepared four steps from isoprene. A combination kinetic data NMR studies support...

Abstract Reported here is the Pd‐catalyzed C–N coupling of hydrazine with (hetero)aryl chlorides and bromides to form aryl hydrazines catalyst loadings as low 100 ppm Pd KOH base. Mechanistic studies revealed two resting states: an arylpalladium(II) hydroxide chloride. These compounds are present in interconnected catalytic cycles react base or alone give product. The selectivity complex over diaryl was lower than that chloride complex, well reaction. In contrast, closely matched reaction,...

Jacobsen and co-workers report an asymmetric [4+2] cycloaddition of imines 2 with electron-rich alkenes (Povarov reaction) catalyzed by chiral urea-sulfinamide catalyst 1 ortho-nitrobenzenesulfonic acid ­(NBSA) as achiral co-catalyst. Detailed kinetic computational studies strongly supported a cationic reaction intermediate. Cooperative catalysis urea Brønsted rendered broad substrate scope reasonable yield, dia­stereoselectivity, high enantioselectivity. In particular, glyoxylate ester...

The authors report a scalable Strecker synthesis of unnatural amino acids, using thiourea catalyst (4) and KCN as cyanide source. 4 is simplified from their first generation catalysts 5 which contain diamino-cyclohexane moiety. In the presence 0.5 mol% 4, two equivalents 1.2 AcOH at 0 ˚C, different aliphatic imines undergo modified reaction with high enantioselectivity. conditions are mild practical (without purification by chromatography), 25-100 mmol scale reactions were exemplified for...

A very concise synthesis of (+)-yohimbine features creation the single stereogenic center at C3 in tetrahydro-β-carboline D via an organocatalytic asymmetric Pictet-Spengler reaction. This then controls simultaneous formation rings and E as well four contiguous centers by intramolecular Diels-Alder annulation (G → I).