Catalytic Asymmetric Synthesis of Vicinal Quaternary Stereocenters Enabled by Alkylation of α,α-Disubstituted Aldehydes with 3-Bromooxindoles.

An organocatalytic enantioselective alkylation of α,α-disubstituted aldehydes with 3-bromooxindoles is reported. Enantioenriched oxindoles with vicinal quaternary stereocenters are accessed by an asymmetric conjugate addition process of branched aldehydes with o-azaxylylene intermediates (indol-2-ones). Key to the success of highly diastereo- and enantioselective transformations is the combined use of a triphenylsilyl-protected ß-amino alcohol catalyst derived from the spiropyrrolidine scaffold and 3,5-dinitrobenzoic acid. This study also presents a rare example of aldehyde alkylation with the formation of consecutive quaternary stereocenters.

Iridium-catalyzed selective arylation of B(6)-H of 3-aryl-o-carboranes with arylboronic acid via direct B-H activation.

This work discloses an iridium-catalyzed selective arylation of B(6)-H of 3-Ar-o-carboranes with arylboronic acid via direct B-H activation for the first time. A series of unsymmetric and symmetric 3,6-diaryl-o-carboranes decorated with diverse active groups have been synthesized with moderate to excellent yields under mild conditions. This work offers an efficient approach for selective arylation of B(6)-H with arylboronic acid and has important value for selective functionalization of o-carboranes.

Au-Catalyzed Asymmetric Polyene Cyclization and Its Application in the Total Synthesis of (+)-2-Ketoferruginol, (+)-Fleuryinol B, (+)-Salviol, and (-)-Erythroxylisin A.

A catalytic asymmetric 1,3-acyloxy shift/polyene cyclization cascade has been achieved with good enantioselectivities under the catalysis of the chiral Au(I) reagent. The synthetic utility of this method has been showcased by the catalytic asymmetric total syntheses of (+)-2-ketoferruginol, (+)-fleuryinol B, and (+)-salviol. Notably, the first enantioselective total synthesis of (-)-erythroxylisin A has also been realized in 15 steps.

Enantiocontrolled Total Synthesis of (-)-Retigeranic Acid A.

The asymmetric total synthesis of (-)-retigeranic acid A has been realized. The key features of the current synthesis include (1) a Pt-catalyzed Conia-ene 5-exo-dig cyclization of enolyne to establish the key quaternary stereochemical center of C-10 (D/E ring), (2) an intramolecular diastereoselective Prins cyclization to construct the trans-hydrindane backbone (A/B ring), and (3) a late-stage intramolecular Fe-mediated hydrogen atom transfer (HAT) Baldwin-disfavored 5-endo-trig radical cyclization to rapidly assemble vicinal quaternary centers and the core structure of (-)-retigeranic acid A (C ring).

Rh(I)-Catalyzed [5 + 2]/[2 + 2] Cycloaddition Cascade to Access a Cyclobutane-Fused [4-5-6-7] Tetracyclic Framework.

A Rh(I)-catalyzed [5 + 2]/[2 + 2] cycloaddition cascade has been developed to afford a complex and highly strained [4-5-6-7] tetracyclic framework in good yields and excellent diastereoselectivities. During this transformation, three rings, three C-C bonds, and four contiguous stereocenters were formed efficiently. Mechanistically, the rare sterically congested multisubstituted cyclobutanes are constructed readily through Michael addition and a Mannich reaction cascade.

InI3-catalyzed polyene cyclization of allenes and its application in the total synthesis of seven abietane-type diterpenoids.

A novel polyene cyclization using the allene group as the initiator has been successfully developed. This methodology provides an efficient strategy for the construction of an abietane-type tricyclic skeleton with a functionalizable C2-C3 double bond and features a wide substrate scope and excellent stereoselectivities. Potential utility of this approach has been well demonstrated by the collective total synthesis of seven abietane-type diterpenoids. Specifically, (±)-2,3-dihydroxyferruginol and (±)-2,3-dihydroxy-15,16-dinor-ent-pimar-8,11,13-triene were synthesized for the first time.

Synthesis and Biological Activity Evaluation of 2-Cyanopyrrole Derivatives as Potential Tyrosinase Inhibitors.

In order to find potential inhibitors of tyrosinase, two series of pyrrole derivatives A (1-17) and B (1-8) were synthesized and screened for their inhibitory activities on tyrosinase. Most of the 2-cyanopyrrole derivatives exhibited effective inhibitory activities. In particular, A12 exhibited the strongest inhibitory activities, with the IC50 values of 0.97 µM, which is ∼30 times stronger than the reference inhibitor kojic acid (IC50: 28.72 µM). The inhibitory mechanism analysis results revealed that A12 was a reversible and mixed-type inhibitor. Molecular docking experiments clarified the interaction between A12 with tyrosinase. Furthermore, A12 (100 µM) presented effective inhibitory effect on tyrosinase in B16 melanoma cells with inhibition of 33.48%, which was equivalent to that of Kojic acid (39.81%). Accordingly, compound A12 may serve as the lead structure for the further design of potent tyrosinase inhibitors. Molecular docking studies confirmed the interaction between the compound and tyrosinase.

Copper-Catalyzed Asymmetric Ring-Opening Reaction of Cyclic Diaryliodonium Salts with Imides.

An efficient copper-catalyzed asymmetric ring-opening reaction of diaryliodonium salts with imides has been developed, affording a wide range of axially chiral 2-imidobiaryl compounds with excellent enantioselectivities and better convertibility. The potential utility of the current method has been supported by the synthesis of two known chiral ligands with better efficiency, which would be of great significance to the development of other catalytic asymmetric reactions.

Total Synthesis of (±)-Furanether A.

The first total synthesis of (±)-furanether A, which exhibits good antifeedant activity, has been concisely achieved in 13 linear steps. Notably, the key rigid tetracyclic skeleton containing a 1-methyl-8-oxabicyclo[3.2.1]octane moiety with two vicinal quaternary carbon centers was rapidly constructed in one step through a unique tandem C-H oxidation/oxa-[3,3] Cope rearrangement/aldol cyclization sequence.

Transition-Metal-Free Reductive Deoxygenative Olefination with CO2.

A new transition-metal-free reductive deoxygenative olefination of phosphorus ylides with CO2, an abundant and sustainable C1 chemical feedstock, is described. This catalytic CO2 fixation afforded ß-unsubstituted acrylates and vinyl ketones in good yields with broad scope and good functional group tolerance under mild reaction conditions. Cost-effective and easily handled polymethylhydrosiloxane was used as a reductant. Bis(silyl)acetal was proved to be the key intermediate in this reductive functionalization of CO2.

Reductive CO2 Fixation via Tandem C-C and C-N Bond Formation: Synthesis of Spiro-indolepyrrolidines.

We describe herein a tandem C-C and C-N bond-forming reaction in the reductive functionalization of CO2, an abundant and cheap C1 chemical feedstock. This catalytic metal-free CO2 fixation afforded spiro-indolepyrrolidines by dearomatization of tryptamine derivatives with broad scope and good functional group tolerance under mild conditions.

Catalytic Asymmetric Construction of α-Quaternary Cyclopentanones and Its Application to the Syntheses of (-)-1,14-Herbertenediol and (-)-Aphanorphine.

A novel and efficient strategy to build α-benzylic quaternary cyclopentanones with excellent enantioselectivities (up to 96 % ee) and high yields (up to 99 % yield) has been developed, and its application demonstrated by the first catalytic asymmetric total synthesis of (-)-1,14-herbertenediol and the formal synthesis of (-)-aphanorphine.

An Au(I)-catalyzed rearrangement/cyclization cascade toward the synthesis of 2-substituted-1,4,5,6-tetrahydrocyclopenta[b]pyrrole.

An Au(I)-catalyzed tandem reaction for the synthesis of 2-phenyl-1,4,5,6-tetrahydrocyclopenta[b]pyrrole derivatives from 1-(1-hydroxy-3-phenylprop-2-yn-1-yl)cyclobutanol and primary amines or NH4OAc has been developed to afford a series of polysubstituted pyrroles in moderate to good yields.

Efficient oxa-Diels-Alder/semipinacol rearrangement/aldol cascade reaction: short approach to polycyclic architectures.

A novel carbon electrophile induced intermolecular oxa-Diels-Alder/semipinacol rearrangement/aldol cascade reaction of allylic silyl ether with ß,γ-unsaturated α-ketoester has been developed under the promotion of SnCl4. This highly efficient transformation enables the quick construction of polycyclic architectures with up to five contiguous stereogenic centers in a single operation with moderate to good yields as well as high diastereoselectivity and would provide versatile short approaches to frameworks and/or analogues of numerous biologically important polycyclic natural products.

A nickel-mediated oxidative α-C(sp(3))-H functionalization of amides with allylic alcohols terminated by radical 1,2-aryl migration.

A Ni-mediated oxidative C(sp(3))-H functionalization of N,N-substituted amides with α,α-diaryl allylic alcohols through a radical 1,2-aryl migration process has been developed. This process features a broad substrate scope and excellent functional group tolerance. Notably, γ-amino ketones containing an all-carbon quaternary center were synthesized under these conditions in moderate to good yields.

Palladium-catalyzed cascade process to construct 1,2,5-trisubstituted pyrroles.

A novel palladium-catalyzed cascade allylic amination/intramolecular hydroamination/isomerization process of protected enynol 1 and primary amine 2 has been explored, which constructs the important 1,2,5-trisubstituted pyrroles. This transformation offers an alternative synthetic methodology capable of generating substituted pyrroles in a straightforward way.

Regiodivergent annulation of alkynyl indoles to construct spiro-pseudoindoxyl and tetrahydro-ß-carbolines.

Regiodivergent annulations of 3-phenoxy alkynyl indoles have been developed and tuned by protective groups through gold catalysis. With electron-donating protective groups, the substrate followed a C3-selective annulation and gave structurally interesting tetrahydro-ß-carboline derivatives possessing potential bioactivity. Using electron-withdrawing protective groups, the substrate underwent a C2-selective annulation and afforded the structurally useful spiro-pseudoindoxyl found in natural indole alkaloids. Notably, an interesting and unusual 1, 2-migration of the phenoxy group was found in the C3-selective process.