Controllable Synthesis of N-Heterocycles via Hydride Transfer Strategy-Enabled Formal [5 + 1] and [5 + 2] Cyclizations

The Brønsted acid-controlled switchable synthesis of indoline-fused tetrahydroquinolines and indole-fused benzazepines was developed through hydride transfer-enabled formal [5 + 1] and [5 + 2] cyclization reactions from indoles and N-alkyl o-aminobenzoketones. Indoline, furanone, and tetrahydroquinoline hybridized pentacyclic products were unprecedentedly accessed via a cascade condensation/hydride transfer/dearomatization-cyclization/deethylation/nucleophilic addition process. In addition, the undeveloped hydride transfer-involved [5 + 2] cyclizations were also realized for direct construction of indole-fused benzazepines.

Substrate Switchable Pathway for Selective Construction of Bridged Dibenzo[b,f][1,5]diazocines and Bridged Spiromethanodibenzo[b,e]azepines

An operationally simple method for the synthesis of bridged dibenzo[b,f][1,5]diazocines and bridged spiromethanodibenzo[b,e]azepines exhibiting bridged eight-membered and seven-membered molecular architecture is reported. This unique approach is based on substrate selective mechanistic pathway, including an unprecendented aerial oxidation-driven mechanism for the synthesis of bridged spiromethanodibenzo[b,e]azepines. The reaction is highly atom economic, and in addition, it allows the construction of two rings and four bonds in a single operation under metal-free condition. The easy availability of β enaminone and ortho phathalaldehyde as starting materials and the simple operation make this approach suitable for the preparation of important dibenzo[b,f][1,5]diazocine and spiromethanodibenzo[b,e]azepine cores.

I2-Mediated [6 + 1] Annulation of Alkynes with MsONH3OTf: Direct Synthesis of Benzo[b]azepines

The synthesis of benzo[b]azepines using protonated aminating reagent (MsONH₃OTf) and alkynes through I₂-mediated [6 + 1] annulation reaction has been developed. This protocol features excellent functional group tolerance and mild reaction conditions and affords the benzo[b]azepines in moderate to good yields under metal-free reaction conditions.

Concomitant Functionalization of Two Different Ketones by Merging Brønsted Acid Catalysis and Radical Relay Coupling

In previous literature, incorporation of functional groups at the α-position of unactivated carbonyl compounds was mainly restricted to one kind of corresponding precursors. Herein, we report the concomitant functionalization of...

Copper-catalyzed selective oxidation of hydrazones through C(sp3)-H functionalization

A simple and mild protocol for copper-catalyzed oxidation of hydrazones at the α-position has been reported. Various substrates are compatible, providing the corresponding products in moderate to good yields. This strategy provides an efficient and convenient solution for the synthesis of carbonyl hydrazone. A free radical pathway mechanism is suggested for the transformation.

A palladium-catalyzed ring-expansion reaction of cyclobutanols with 2-haloanilines leading to benzazepines and quinolines

A general synthesis of 2-aryl benzazepines has been developed through palladium-catalyzed ring-expansion reactions of cyclobutanols with 2-haloanilines; the further oxidative rearrangement reaction of benzazepines provided an efficient synthesis of 2-acyl quinolines. These transformations feature the efficient construction of six- and seven-membered N-containing heterocycles from easily obtained materials with excellent functional group tolerance.

I2 -Promoted Intramolecular Oxidative Cyclization of Butenyl Anilines: A Facile Route to Benzo[b]azepines

A metal-free approach for the synthesis of seven-membered N-heterocycles has been developed by the I₂ -promoted intramolecular cross-coupling/annulation of butenyl anilines. This cyclization reaction involves C-H activation and C-C bond formation and exhibits good functional group tolerance. A series of benzo[b]azepine derivatives are obtained in moderate to good yields.

Synthesis of Benzoazepine Derivatives via Azide Rearrangement and Evaluation of Their Antianxiety Activities

A new synthetic method for the construction of benzoazepine analogues has been developed employing ortho-arylmethylbenzyl azide derivatives as precursors using an azide rearrangement reaction. In this work, 14 benzoazepine compounds were successfully synthesized in moderate to excellent yields. All synthetic benzoazepines were evaluated for their cytotoxicity against normal human kidney cell line (HEK cell). The results showed that compound 18c had the lowest cytotoxicity (IC₅₀ = 65.68 μM) among tested compounds, which was comparable with the antianxiety drug diazepam (IC₅₀ = 87.90 μM). Based on the cytotoxicity results, five benzoazepine analogues (compounds 18c, 18h, 18j, 18n, and 18p) were selected to determine the antianxiety effect on stressed rats using elevated plus maze (EPM) and open field test (OFT) methods. Interestingly, compound 18c showed better anxiolytic activity than diazepam without a sedative effect by showing superior hyperlocomotor activity. Therefore, this discovery could pave the way for drug development to treat patients with anxiety disorder.

Copper-Catalyzed Trifluoromethylation/Cyclization of Alkynes for Synthesis of Dioxodibenzothiazepines

A facile and efficient approach for the synthesis of the CF₃-containing dioxodibenzothiazepines has been developed via copper-catalyzed trifluoromethylation/cyclization of alkynes utilizing a radical relay strategy. This method has demonstrated low catalyst loading, high regiocontrol, and broad scope under mild conditions. Good compatibility for the N-protecting group, gram-scale experiment, and further derivation of product prove the versatility of this transformation.

Copper-Catalyzed Intramolecular Amination of C(sp3)-H Bond of Secondary Amines to Access Azacycles

The cross-coupling of C-N bond directly from inert C-H bonds is an ideal approach to synthesize saturated azacycles due to its high efficiency and atom economy. In this article, a copper-catalyzed intramolecular amination via the cross coupling of C(sp³)-H and N-H bonds of secondary amine has been reported, which exhibit excellent chemo- and regioselectivity, extensive substrate scope, and functional group tolerance in good to excellent yield, offering an efficient pathway to build nitrogen-containing heterocycle skeletons.

Remote azidation of C(sp3)–H bonds to synthesize δ-azido sulfonamidesviairon-catalyzed radical relay

A selective remote C–H azidation was developed with an iron catalyst playing dual roles as a radical initiator and terminator.

Enantioselective Copper-Catalyzed Cyanation of Remote C(sp3)-H Bonds Enabled by 1,5-Hydrogen Atom Transfer

The direct functionalization of C(sp³)-H bonds has led to the development of methods to access molecules or intermediates from basic chemicals in an atom- and step-economic fashion. Nevertheless, achieving high levels of chemo-, regio-, and enantioselectivity in these reactions remains challenging due to the ubiquity and low reactivity of C(sp³)-H bonds. Herein, we report an unprecedented protocol for enantioselective cyanation of remote C(sp³)-H bonds. With chiral Box-Cu complex as the catalyst, the reaction of N-fluorosulfonamide furnishes the corresponding products in excellent yields and high enantiomeric excess (ee) under mild reaction conditions. A radical relay pathway involving 1,5-hydrogen atom transfer (1,5-HAT) of N-center radicals followed by enantioselective cyanation of the in situ-formed benzyl radicals is proposed. This enantioselective copper-catalyzed cyanation thus offers insights into an efficient way for the synthesis of bioactive molecules for drug discovery.

Mild, Metal-Free Oxidative Ring-Expansion Approach for the Synthesis of Benzo[ b]azepines

Benzo[ b]azepines are important structural motifs for the pharmaceutical industry. However, their syntheses are usually lengthy, involving several steps, transition-metal catalysts, and/or harsh conditions. A novel, general, mild, and metal-free oxidative ring expansion tandem reaction of hydroquinolines with TMSCHN₂ as a versatile soft nucleophile to gain access to these valuable compounds in a simple and straightforward manner is presented.

3d Transition Metals for C-H Activation

C-H activation has surfaced as an increasingly powerful tool for molecular sciences, with notable applications to material sciences, crop protection, drug discovery, and pharmaceutical industries, among others. Despite major advances, the vast majority of these C-H functionalizations required precious 4d or 5d transition metal catalysts. Given the cost-effective and sustainable nature of earth-abundant first row transition metals, the development of less toxic, inexpensive 3d metal catalysts for C-H activation has gained considerable recent momentum as a significantly more environmentally-benign and economically-attractive alternative. Herein, we provide a comprehensive overview on first row transition metal catalysts for C-H activation until summer 2018.

Modular Access to Azepines by Directed Carbonylative C-C Bond Activation of Aminocyclopropanes

A modular Rh-catalyzed entry to azepines is outlined. Under a CO atmosphere, protecting group directed C–C bond activation of aminocyclopropanes provides rhodacyclopentanones. These intermediates are effective for intramolecular C–H metalation of either an N-aryl or N-vinyl unit en route to azepine ring systems. Thus, byproduct-free heterocyclizations are enabled by sequential C–C activation and C–H functionalization steps.

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

The first example of ring expansion from a five-membered nitrogen-containing ring to a seven-membered heterocyclic ring has been developed.

Copper-catalyzed remote oxidation of alcohols initiated by radical difluoroalkylation of alkenes: facile access to difluoroalkylated carbonyl compounds

A Cu-catalyzed oxidation of alcohols triggered by the radical difluoroalkylation of alkenes has been developed.

Organocatalytic C(sp3)-H Functionalization via Carbocation-Initiated Cascade [1,5]-Hydride Transfer/Cyclization: Synthesis of Dihydrodibenzo[b,e]azepines

Carbocation-initiated cascade [1,5]-hydride transfer/cyclization and dimerization reactions were developed to synthesize dihydrodibenzo[b,e]azepine and octahydrodipyrroloquinoline derivatives in high yields. These redox-neutral C(sp³)-H functionalization-involving cascade reactions feature transition-metal-free, high atom- and step-economy, and environmental friendliness with water as the sole byproduct.