1,6-Hydride Transfer-Enabled [6 + 1] Annulation to Access Polycyclic 3,4-Fused Azepinoindoles.

A [6 + 1] annulation reaction via cascade 1,6-hydride transfer/cyclization is reported to construct a polycyclic 3,4-fused azepinoindole skeleton. The newly designed 4-amino-indole-3-carbaldehyde is applied as a novel six-atom synthon, interacting with arylamines and malononitrile to achieve the [6 + 1] annulation. Notably, the reaction proceeds smoothly under redox-neutral and metal-free conditions, providing a wide range of azepinoindoles in up to 94% yields, with water as the only byproduct. Besides, the advantage of high step- and atom-economy further highlights the practicality of this methodology.

Fluorinated Alcohols: Magic Reaction Medium and Promoters for Organic Synthesis.

Fluorinated alcohols have been widely used in the synthetic organic chemistry over the past decades. The unique properties such as the strong hydrogen-bonding donor ability and low nucleophilicity allow them to promote organic reactions in the absence of any catalyst. These approaches have distinct advantages in terms of operational simplicity, practicability and environmental friendliness. Reactions promoted by fluorinated alcohols, including nucleophilic substitution reactions, annulation reactions, electrophilic reactions, dearomatization reactions, functionalization of multiple bond, epoxidation reactions and miscellaneous reactions have been summarized in this account.

Photoredox-Enabled Synthesis of ß-Substituted Pyrroles from Pyrrolidines.

The merger of photoredox-initiated enamine-imine tautomerization and nucleophilic addition processes to access ß-substituted pyrroles from pyrrolidines has been achieved. The significant advantage of this method is suppressing the Friedel-Crafts reaction, which usually occurs between N-aryl pyrrolidines and the highly electrophilic ketoesters. The good functional group tolerance, high atom economy, and high regioselectivity as well as easy handling conditions make it an appealing alternative to synthesize ß-substituted pyrroles.

Synthesis of Tetrahydro[1,3,4]triazepines via Redox-Neutral α-C(sp3)-H Amination of Cyclic Amines.

A Brønsted acid-catalyzed α-C(sp3)-H amination of cyclic amines using hydrazines as coupling partners has been reported. This methodology provides a unique protocol to the one-step assembly of tetrahydro[1,3,4]triazepines via [1,5]-hydride transfer-initiated C(sp3)-H amination. This reaction features mild conditions, good yields, and high atom economy.

Discovery of potent 1H-imidazo[4,5-b]pyridine-based c-Met kinase inhibitors via mechanism-directed structural optimization.

Starting from our previously identified novel c-Met kinase inhibitors bearing 1H-imidazo[4,5-h][1,6]naphthyridin-2(3H)-one scaffold, a global structural exploration was conducted to furnish an optimal binding motif for further development, directed by the enzyme inhibitory mechanism. First round SAR study picked two imidazonaphthyridinone frameworks with 1,8- and 3,5-disubstitution pattern as class I and class II c-Met kinase inhibitors, respectively. Further structural optimization on type II inhibitors by truncation of the imidazonaphthyridinone core and incorporation of an N-phenyl cyclopropane-1,1-dicarboxamide pharmacophore led to the discovery of novel imidazopyridine-based c-Met kinase inhibitors, displaying nanomolar enzyme inhibitory activity and improved Met kinase selectivity. More significantly, the new chemotype c-Met kinase inhibitors effectively inhibited Met phosphorylation and its downstream signaling as well as the proliferation of Met-dependent EBC-1 human lung cancer cells at submicromolar concentrations.

Hydride Transfer-Initiated Cross-Dehydrogenative Coupling Reaction to Access Nine-Membered Rings.

An unprecedented hydride transfer-triggered cross-dehydrogenative coupling of two C(sp3)-H bonds to target nine-membered rings has been developed. Salient features of this methodology include atom and step economy and metal-free and redox-neutral conditions, with water as the byproduct and proceeding well even with decomposed aldehydes.

Access to Polycyclic Indole-3,4-Fused Nine-Membered Ring via Cascade 1,6-Hydride Transfer/Cyclization.

A cascade aldimine condensation/1,6-hydride transfer/Mannich-type cyclization of indole-derived phenylenediamine with aldehydes was developed for one-step construction of a polycyclic indole-3,4-fused skeleton. Aldehyde serves as a key to start the whole process, including 1,6-hydride transfer enabled δ-C(sp3)-H activation of the secondary amine. The challenges of construction of medium-sized rings are addressed via hydride transfer chemistry.

Organocatalytic Cascade ß-Functionalization/Aromatization of Pyrrolidines via Double Hydride Transfer.

An unprecedented cascade ß-functionalization/aromatization reaction of N-arylpyrrolidines was established. A series of ß-substituted arylpyrroles embedded with trifluoromethyl groups are provided directly from N-arylpyrrolidines. The deuterium-labeling experiments indicate that sequential double hydride transfer processes serve as the key steps in this transformation.

Hydride Transfer Initiated Redox-Neutral Cascade Cyclizations of Aurones: Facile Access to [6,5] Spirocycles.

Reported herein is the hydride transfer initiated redox-neutral cascade cyclizations of aurones, providing a variety of [6,5] spiro-heterocycles in satisfactory yields and good diastereoselectivities.

Redox-Neutral ß-C(sp3)-H Functionalization of Cyclic Amines via Intermolecular Hydride Transfer.

Herein, we report the first redox-neutral and transition-metal-free ß-C(sp3)-H functionalization of cyclic amines via a consecutive intermolecular hydride transfer process. A series of N-aryl pyrrolidines and N-aryl 1,2,3,4-tetrahydropyridines decorated with CF3 and carboxylic ester functionalities are directly accessed in good yields from pyrrolidines and piperidines. This work pushes forward the application of the intermolecular hydride transfer strategy in one-step assembly of molecular complexity.

Photoredox-Induced Radical Relay toward Functionalized ß-Amino Alcohol Derivatives.

A radical relay strategy is described to synthesize functionalized ß-amino alcohols. This strategy is enabled by photoredox-catalyzed and nitrogen-centered radical-triggered cascade reactions of styrenes (or phenylacetylenes), enol derivatives, and O-acyl hydroxylamines in DMSO. The broad synthetic application of this method is demonstrated by the reaction of structurally diverse reaction components, including complex molecular scaffolds. Multiple functional groups of the resultant highly functionalized ß-amino alcohol derivatives facilitate their further transformations.

Organocatalytic Dearomative [4 + 2] Cycloadditions of Biomass-Derived 2,5-Dimethylfuran with ortho-Quinone Methides: Access to Multisubstituted Chromanes.

The organocatalytic dearomative [4 + 2] cycloadditions of biomass-derived 2,5-dimethylfuran with ortho-quinone methides were developed, affording two diffferent types of multisubstituted chromanes in high yields and excellent diastereoselectivities. The controllable synthesis of these two types of multisubstituted chromanes could be achieved by succinctly varying the reaction conditions.

Hydride transfer initiated ring expansion of pyrrolidines toward highly functionalized tetrahydro-1-benzazepines.

A novel hydride transfer initiated ring expansion of 4-pyrrolidinyl isatins to synthesize tetrahydro-1-benzazepines has been developed. This methodology represents an atom- and step-economical protocol to assemble seven-membered polycyclic amines from pyrrolidine derivatives in one step.

Direct Synthesis of Nitriles from Aldehydes Using an O-Benzoyl Hydroxylamine (BHA) as the Nitrogen Source.

The direct synthesis of nitriles from commercially available or easily prepared aldehydes has been achieved. O-(4-CF3-benzoyl)-hydroxylamine (CF3-BHA) was utilized as the nitrogen source to generate O-acyl oximes in situ with aldehydes, which can be converted to a nitrile with the assistance of a Brønsted acid. Several aliphatic, aromatic, and α,ß-unsaturated nitriles that contain different functional groups were prepared in high yields (up to 94% yield). This method has notable advantages, such as simple and mild conditions, high yields, and good functional group tolerance.

Visible-light-promoted and one-pot synthesis of phenanthridines and quinolines from aldehydes and O-acyl hydroxylamine.

A one-pot synthesis of phenanthridines and quinolines from commercially available or easily prepared aldehydes has been reported. O-(4-Cyanobenzoyl)hydroxylamine was utilized as the nitrogen source to generate O-acyl oximes in situ with aldehydes catalyzed by Brønsted acid. O-Acyl oximes were then subjected to visible light photoredox catalyzed cyclization via iminyl radicals to furnish aza-arenes. A variety of phenanthridines and quinolines have been prepared assisted by Brønsted acid and photocatalyst under visible light at room temperature with satisfactory yields.