Enantioselective Cobalt-Catalyzed Remote Hydroboration of Alkenylboronates

Heteroatomic groups in alkenes typically direct thermodynamically favored chain walking of C═C bonds toward themselves, thereby facilitating C-H bond functionalization near the heteroatoms. We present herein an efficient cobalt-catalyzed contra-thermodynamic remote hydroboration of alkenylboronates with pinacolborane to synthesize chiral 1,n-diboronates. This protocol features a broad substrate scope, high functional group tolerance, and excellent enantioselectivity. Mechanistic studies indicate the involvement of a chain-walking process. Gram-scale reactions and various product derivatizations further highlight its practicality.

Copper-catalyzed asymmetric propargylic substitution with salicylaldehyde-derived imine esters

Copper-catalyzed asymmetric propargylic substitution with salicylaldehyde-derived imine esters and propargylic carbonates has been successfully realized, generating a wide range of chiral amino acid derivatives containing propargylic groups with excellent results (up to 95% yield and 94% ee). The ortho-hydroxy group of the salicylaldehyde-derived imine esters is crucial to increase the reactivity and stabilize the azomethine ylide, which may be due to the formation of an intramolecular hydrogen bond between the hydroxyl group and the imine group. A series of synthetic transformations were carried out to access other important chiral compounds, which displayed the synthetic versatility.

Cobalt-Catalyzed Migration Isomerization of Dienes

A cobalt-catalyzed multipositional isomerization of conjugated dienes has been reported for the first time using an 8-oxazoline iminoquinoline ligand. This reaction is operationally simple and atom-economical using readily available starting materials with an E/Z mixture to access disubstituted 1,3-dienes with excellent yields and good E,E stereoselectivity. The mechanism via alkene insertion of cobalt hydride species and β-H elimination of a π-allyl cobalt intermediate is proposed on the basis of deuterium labeling and control experiments and density functional theory calculations.

Exploiting the Chiral Ligands of Bis(imidazolinyl)- and Bis(oxazolinyl)thiophenes-Synthesis and Application in Cu-Catalyzed Friedel-Crafts Asymmetric Alkylation

Five new C2-symmetric chiral ligands of 2,5-bis(imidazolinyl)thiophene (L1-L3) and 2,5-bis(oxazolinyl)thiophene (L4 and L5) were synthesized from thiophene-2,5-dicarboxylic acid (1) with enantiopure amino alcohols (4a-c) in excellent optical purity and chemical yield. The utility of these new chiral ligands for Friedel-Crafts asymmetric alkylation was explored. Subsequently, the optimized tridentate ligand L5 and Cu(OTf)2 catalyst (15 mol%) in toluene for 48 h promoted Friedel-Crafts asymmetric alkylation in moderate to good yields (up to 76%) and with good enantioselectivity (up to 81% ee). The bis(oxazolinyl)thiophene ligands were more potent than bis(imidazolinyl)thiophene analogues for the asymmetric induction of the Friedel-Crafts asymmetric alkylation.

Heteroarene-tethered Functionalized Alkyne Metamorphosis

Heteroarene-tethered functionalized alkynes are multipotent synthons in organic chemistry. This detailed Review described herein offers a thorough discussion of the metamorphosis of heteroarene-tethered functionalized alkynes, an area which has earned much attention over the past decade in the straightforward synthesis of architecturally complex heterocyclic scaffolds in atom and step economic manner. Depending upon the variety of functionalized alkynes, this Review is divided into multiple sections. Amongst the vast array of synthetic transformations covered, dearomatizing spirocyclizations and cascade spirocyclization/rearrangement are of great interest. Synthetic transformations involving the heteroarene-tethered functionalized alkynes with scope, challenges, limitations, mechanism, their application in the total synthesis of natural products and future perceptions are surveyed.

Catalytic enantioselective synthesis of α-aryl α-hydrazino esters and amides

Asymmetric 1,2-addition of aryl boronic acids to N-carbamoyl (Cbz and Fmoc) protected glyoxylate-derived hydrazones affords α-aryl α-hydrazino esters/amides, key building blocks en route to artificial peptides.

Development of TsDPEN based imine-containing ligands for the copper-catalysed asymmetric Kinugasa reaction

A novel class of chiral N,N,N imine-containing ligands derived from TsDPEN (N-(p-tosyl)-1,2-diphenylethylene-1,2-diamine) has been developed and applied to the copper-catalyzed asymmetric Kinugasa reaction. The copper(ii) salt proved to be an efficient catalyst precursor, and it provides an efficient way to synthesize enantioenriched cis-β-lactam. The pathway is air-tolerant and easily manipulated, and the ligands are easy to synthesize. A working model is proposed in which the stereocontrolling step is the [2 + 2] cycloaddition between ketene and imine to explain the observed stereoselectivities.

A novel class of chiral N,N,N imine-containing ligands derived from TsDPEN has been developed and applied to the copper-catalyzed asymmetric Kinugasa reaction.

Catalytic Asymmetric Synthesis of Spiropyrazolones and their Application in Medicinal Chemistry

Chiral spiropyrazolones are unique frameworks widely found in a large family of medicinally relevant compounds with various biological activities. Substantial research efforts have been invested toward stereoselectively by constructing spiro-cyclic structures. Over the past years, remarkable progress has been made in the organo- and metal-catalyzed asymmetric synthesis of spiropyrazolones through the utilization of accessible simple pyrazolone derivatives as raw materials. This review is organized according to the size of the spiro-ring fused at the 4-position of the pyrazolone framework. In the last part, the bio-evaluations of chiral spiropyrazolones for drug discovery are summarized.

Chiral superstructures from homochiral Zn2+ , Co2+ , Fe2+ -2,6-bis (aryl ethylimine)pyridine complexes

We report the hierarchical supramolecular organization of metallosupramolecular homochiral complexes 1-Λ-(S,S,S,S)-M²⁺ /1-∆-(R,R,R,R)-M²⁺ and 2- Λ-(S,S,S,S)-M²⁺ /2-∆- (R,R,R,R)-M²⁺ of M²⁺ = Co²⁺ , Fe²⁺ , Zn²⁺ metal ions with chiral pseudo-terpyridine-type ligands: 1-(S,S) or 1-(R,R) = 2,6-bis (naphthyl ethylimine)pyridine and 2-(S,S) or 2-(R,R) = 2,6-bis (phenyl-ethylimine)pyridine. Circular dichroism measurements in solution were used to confirm the enantiomeric nature of all twelve complexes. For crystal structures of 1- Λ- (S,S,S,S)-M²⁺ or 1-∆- (R,R,R,R)-M²⁺ complexes, absolute configurations {∆ (or P), Λ (or M)} were confirmed by refinement of the Flack parameter x: -0.007 ≤ x ≤ 0.11 for the single crystals of 1-Λ-(S,S,S,S)-M²⁺ /1-∆- (R,R,R,R)-M²⁺ , 2- Λ- (S,S,S,S)-Fe²⁺ , and 2-∆- (R,R,R,R)-Co²⁺ .

10 gram-scale synthesis of a chiral oxazoline iminopyridine ligand and its applications

This method reports on the preparation of a chiral oxazoline iminopyridine (OIP) ligand and its applications on a scale of 10 grams.

Enantioselective magnesium-catalyzed transformations

This review updates the major progress in the field of enantioselective transformations promoted by chiral magnesium catalysts, covering the literature since 2007, illustrating the power of these green catalysts to promote many types of reactions.