Regioselective Oxidation of Tetrahydronaphthalenes to α-Tetralone Derivatives Using DDQ as Oxidizing Agent: Synthesis and Evaluation of Antibacterial and Antifungal Activities

An easy and efficient approach for the synthesis of highly regioselective functionalized dihydronaphthalen-1(2H)-one family of α-tetralones from functionalized tetralone precursors which derived from Morita-Baylis-Hillman (MBH) adducts as starting substrates has been developed. The target dihydronaphthalen-1(2H)-ones are obtained through the oxidation of tetrahydronaphthalenes (THN) using DDQ as the oxidizing agent, conducted in aqueous acetic acid at reflux conditions. The yields obtained ranged from 90 to 98%. The resulting dihydronaphthalen-1(2H)-ones were evaluated for their in vitro antibacterial activity against nine Gram-positive and six Gram-negative strains. Additionally, their antifungal properties were assessed against three fungal pathogens by using the microdilution method and Biolog Phenotype Microarrays technology. Remarkably, the synthesized dihydronaphthalen-1(2H)-ones exhibited good antibacterial activity when compared to reference drugs such as vancomycin and ampicillin. Similarly, their antifungal activity is comparable to the effectiveness of the reference drugs cycloheximide and fluconazole.

Divergent Reactivity of Iminyl Radicals in Four Interrupted Pathways for the Synthesis of Cyclic/Acyclic Ketones and N-Heterocycles from Vinyl Azides and Phenylacetic Acids

Herein, we report the Ag-catalyzed substrate-controlled interrupted radical pathways of the iminyl radical. The benzylic groups played a crucial role in pathway selection involving a series of dimerization and hydrolysis, a 1,5-H shift followed by cascade radical cyclization, and direct N-(sp2)/aromatization reactions that provide access to diverse cyclic/acyclic ketones, quinolines, and phenanthridine derivatives. Contrary to previous reports, mechanistic investigations with high-resolution mass spectrometry analysis uncovered the involvement of rare azine, oxime, and β-functionalized vinyl azide intermediates.

Synthesis of Indenones via Persulfate Promoted Radical Alkylation/Cyclization of Biaryl Ynones with 1,4-Dihydropyridines

The oxidative radical cascade cyclization of alkynes has emerged as a versatile strategy for the efficient construction of diverse structural units and complex molecules in organic chemistry. This work reports an alkyl radical initiated 5-exo-trig cyclization of biaryl ynones with 1,4-dihydropyridines to selectively synthesize indenones.

Silver-catalyzed cyclization of α-imino-oxy acids to fused tetralone derivatives

A silver-catalyzed intramolecular radical relay cyclization of α-imino-oxy acids under mild conditions has been described. This reaction offers facile access to a diverse range of fused tetralone derivatives with exquisite stereoselectivity in moderate to good yields (40-98%). Experimental studies show that the reaction undergoes a decarboxylation and acetone fragmentation/1,5-hydrogen atom transfer (HAT)/cyclization process.

Radical annulation using a radical reagent as a two-carbon unit

Radical annulation has emerged as one of the most efficient and straightforward methods for synthesizing cyclic/polycyclic compounds as the core structures can be constructed through a single procedure comprising multiple bond-forming steps. Particularly, radical annulation using a radical reagent as a cyclization partner and two-carbon unit greatly expands the diversity of cyclic skeletons and the functionality of radical reagents. We herein have highlighted the representative processes reported in the past decade for radical annulation using a radical reagent as a two-carbon unit, including [2 + 2 + 2], [3 + 2], [4 + 2], and [5 + 2] modes, with an emphasis on their reaction mechanisms. These studies not only pave the way toward annulation but also provide insight into the exploration of a new reaction mode for radical chemistry.

Chemodivergent photocatalytic access to 1-pyrrolines and 1-tetralones involving switchable C(sp3)–H functionalization

A chemodivergent photocatalytic approach to 1-pyrrolines and 1-tetralones from alkyl bromides and vinyl azides has been developed through chemoselectively controllable intermolecular [3 + 2] and [4 + 2] cyclization. This photoredox-neutral two-component protocol involves intermolecular radical addition and switchable distal C(sp³)–H functionalization enabled by iminyl radical-mediated 1,5-hydrogen atom transfer. Meanwhile, chemoselectivity between C(sp³)–N bond formation and C(sp³)–C(sp²) bond formation is precisely switched by photocatalysts (Ru(bpy)₃(PF₆)₂ vs. fac-Ir(ppy)₃) and additives (base vs. acid).

Synthesis of gem-Disulfonyl Enamines via an Iminyl-Radical-Mediated Formal 1,3-HAT/Radical Coupling Cascade

We herein report the first example of an iminyl-radical-mediated formal 1,3-HAT/radical coupling cascade of vinyl azides leading to the synthesis of tetrasubstituted gem-disulfonyl enamines. It is possible to employ a variety of vinyl azides and sulfinate salt coupling elements without sacrificing effectiveness and scalability. The combination of experimental studies and DFT calculations showed that this reaction proceeds via a radical addition/formal 1,3-HAT/radical coupling mechanism.

Radical borylation of vinyl azides with NHC-boranes: divergent synthesis of α-boryl ketones and borylated triazoles

A divergent radical borylation of vinyl azides with N-heterocyclic carbene (NHC) boranes in the presence of ^tBuSH is described. The protocol enables the divergent synthesis of α-boryl ketones and borylated triazoles with excellent functional group tolerance and a broad substrate scope. Remarkably, this work shows that vinyl azides can serve as unprecedented five-atom synthons for the construction of 1,2,3-triazoles without N₂ extrusion.

Alkylation/Ipso-cyclization of Active Alkynes Leading to 3-Alkylated Aza- and Oxa-spiro[4,5]-trienones

A method for the preparation of 3-alkylated spiro[4.5]trienones via alkylation/ipso-cyclization of activated alkynes with 4-alkyl-DHPs under transition-metal-free conditions is proposed. This alkylation successively undergoes the generation of alkyl radicals, addition of alkyl radicals to the alkynes, and intramolecular ipso-cyclization. The mechanism studies suggest that the alkylation/ipso-cyclization involves a radical process. This ipso-cyclization procedure shows a series of advantages, such as accessibility, mild conditions, high efficiency, greater safety, and an environmentally friendly method.

CuCl2·2H2O/TBHP mediated synthesis of β-enaminones via coupling reaction of vinyl azides with aldehydes

A facile and efficient oxidative functionalization of vinyl azides with aldehydes furnishing a diverse array of β-acylated enaminones was developed. The cross coupling was accomplished in the presence of CuCl₂·2H₂O/TBHP and produced the desired β-acylated enaminones in a (Z)-stereo-selective and atom-economic manner, which make this protocol particularly attractive. In the transformation, the new C-C and C-N bonds were formed via a one-pot strategy including the process of radical addition and recombination.

Transition-Metal-Free Alkylation Strategy: A Facile Access of Alkylated Oxindoles via Alkyl Transfer

An efficient transition-metal-free alkylation/cyclization of activated alkenes using Hantzsch ester derivatives as effective alkyl reagents was described. A wide variety of valuable oxindoles were constructed in a single step with...

Visible-Light-Promoted Multistep Tandem Reaction of Vinyl Azides toward the Formation of 1-Tetralones

A visible-light-driven multistep tandem reaction between vinyl azides and alkyl bromides has been developed leading to the formation of tetralone skeletons under mild conditions, which can be easily scaled up to the gram scale. Various 1-tetralone derivatives are synthesized and transformed into desired products in good to high yields.

Photocatalytic Decarboxylative [3 + 2] and [4 + 2] Annulation of Enynals and γ,σ-Unsaturated N-(Acyloxy)phthalimides by NaI/PPh3 Catalysis

A practical and eco-friendly strategy for the radical-mediated decarboxylative [3 + 2] and [4 + 2] annulation of enynals and γ,σ-unsaturated N-(acyloxy)phthalimides through the photoactivation of an electron donor-acceptor (EDA) complex has been developed. A wide range of primary, secondary, and tertiary alkyl N-hydroxyphthalimide (NHP) esters can be used as suitable substrates for the synthesis of fused ketones without any transition-metal catalysts or oxidants. This protocol features a broad substrate scope, excellent selectivity, and clean reaction conditions.