Xiu-Long Yang

CuCl/DABCO/4-HO-TEMPO-catalyzed aerobic oxidative synthesis of 2-substituted quinazolines and 4H-3,1-benzoxazines.

The Cu/N-ligand/TEMPO catalytic system was first applied to the aerobic oxidative synthesis of heterocycles. As demonstrated, 2-substituted quinazolines and 4H-3,1-benzoxazines were synthesized efficiently from the one-pot reaction of aldehydes with 2-aminobenzylamines and 2-aminobenzyl alcohols, respectively, by employing CuCl/DABCO/4-HO-TEMPO as the catalysts and oxygen as the terminal oxidant.

Efficient aerobic oxidative synthesis of 2-aryl quinazolines via benzyl C-H bond amination catalyzed by 4-hydroxy-TEMPO.

A novel and efficient aerobic protocol for the oxidative synthesis of 2-aryl quinazolines via benzyl C-H bond amination by a one-pot reaction of arylmethanamines with 2-aminobenzoketones and 2-aminobenzaldehydes has been carried out using the 4-hydroxy-TEMPO radical as the catalyst, without any metals or additives.

Iminoxyl Radical-Promoted Dichotomous Cyclizations: Efficient Oxyoximation and Aminooximation of Alkenes

A novel iminoxyl radical-involved metal-free approach to vicinal oxyoximation and aminooximation of unactivated alkenes is developed. This method utilizes the dichotomous reactivity of the iminoxyl radical to furnish a general difunctionalization on alkenes using simple tert-butyl nitrite (TBN) as the iminoxyl radical initiator as well the carbon radical trap. By using this protocol, oxime featured 4,5-dihydroisoxazoles and cyclic nitrones were facilely prepared from β,γ- and γ,δ-unsaturated ketoximes, respectively.

Synthesis of Isoxazoline-Functionalized Phenanthridines via Iminoxyl Radical-Participated Cascade Sequence

Readily accessible β,γ-unsaturated ketoximes reacted with 2-arylphenylisonitriles under the conditions of t-BuOOH and n-Bu4NI to give isoxazoline functionalized phenanthridines via tandem intramolecular/intermolecular C-O/C-C/C-C bond formation. The reaction involves the initial generation of iminoxyl radicals from the oxidation of β,γ-unsaturated ketoximes by t-BuOOH and n-Bu4NI followed a cascade radical cyclization/addition/cyclization sequence.

Hydrazone Radical Promoted Vicinal Difunctionalization of Alkenes and Trifunctionalization of Allyls: Synthesis of Pyrazolines and Tetrahydropyridazines

The intramolecular addition of hydrazone radicals to carbon-carbon double bonds was achieved by using TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy) or DIAD (diisopropyl azodicarboxylate) as the hydrazone radical initiator as well as the carbon radical scavenger. Consequently, alkenes were difunctionalized to afford pyrazolines and tetrahydropyridazines via C-N forming 5-exo-trig and 6-exo-trig cyclizations, respectively, and allyls were trifunctionalized to afford pyrazolines via C-N forming tandem 1,5-H-shift/5-exo-trig cyclizations under metal-free neutral conditions.

TEMPO-Mediated Aza-Diels–Alder Reaction: Synthesis of Tetrahydropyridazines Using Ketohydrazones and Olefins

A novel, facile, and efficient method for the synthesis of tetrahydropyridazines by a one-pot tandem reaction of easily accessible ketohydrazones and olefins in the presence of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) has been successfully developed. The reaction involves the initial generation of azoalkenes from direct oxidative dehydrogenation of ketohydrazones using TEMPO as the commercially available oxidant, followed by a subsequent aza-Diels-Alder reaction with olefins.

Hydrazonyl Radical-Participated Tandem Reaction: A Strategy for the Synthesis of Pyrazoline-Functionalized Oxindoles.

An efficient and practical tandem cyclization/addition/cyclization strategy is developed for the initial generated hydrazonyl radicals derived from the oxidation of β,γ-unsaturated hydrazones. By using this protocol, structurally novel pyrazoline-functionalized oxindoles are prepared by the reaction of easily accessible β,γ-unsaturated hydrazones with N-aryl acrylamides under the metal- and solvent-free conditions of DTBP (di-tert-butyl peroxide) via a tandem intra/intermolecular C-N/C-C/C-C bond formation.

Synthesis of Isoxazoline/Cyclic Nitrone-Featured Methylenes Using Unsaturated Ketoximes: A Dual Role of TEMPO

A novel, metal-free, and regioselective approach for the synthesis of isoxazoline/cyclic nitrone-featured methylenes has been developed by the reaction of readily accessible β,γ- and γ,δ-unsaturated ketoximes with TEMPO via tandem iminoxyl radical-promoted cyclization/TEMPO-mediated Cope-like elimination, respectively. This protocol utilizes commercially available TEMPO as the iminoxyl radical initiator as well as the β-hydrogen acceptor in the Cope-like elimination.

Synthesis of isoxazoline-featured oxindoles by iminoxyl radical-promoted cascade oxyalkylation/alkylarylation of alkenes

A novel, selective and metal-free iminoxyl radical-promoted cascade oxyalkylation/alkylarylation of unactivated alkenes and activated alkenes via tandem O–C/C–C/C–C bond formation was developed. By using this protocol, isoxazoline-featured oxindoles were successfully synthesized by a one-pot reaction using β,γ-unsaturated ketoximes and N-arylacrylamides as readily accessible substrates and TBHP as the commercially available oxidant.