Huawen Huang

Conversion of Pyridine to Imidazo[1,2-a]pyridines by Copper-Catalyzed Aerobic Dehydrogenative Cyclization with Oxime Esters

A rapid and environmentally friendly conversion of pyridine to imidazo[1,2-a]pyridines has been developed via copper-catalyzed aerobic dehydrogenative cyclization with ketone oxime esters.

Palladium-Catalyzed Intermolecular Dehydrogenative Aminohalogenation of Alkenes under Molecular Oxygen: An Approach to Brominated Enamines

A novel and efficient palladium-catalyzed dehydrogenative aminohalogenation of alkenes with molecular oxygen as the sole oxidant has been developed. This protocol provides a valuable synthetic tool for the assembly of a wide range of brominated enamines under mild conditions, with unprecedented stereoselectivity and exceptional functional group tolerance. This attractive route for the synthesis of brominated enamines is of great significance due to the products versatile reactivity for further transformations.

Palladium‐Catalyzed Sequential Formation of CC Bonds: Efficient Assembly of 2‐Substituted and 2,3‐Disubstituted Quinolines

A series of substituted quinolines was prepared from arylamines, aldehydes, and terminal olefins (see scheme). The palladium-catalyzed sequential formation of C-C bonds proceeds smoothly with both electron-deficient and electron-rich olefins. When acrylic acid is used as terminal olefin, decarboxylation occurs to provide 2-substituted quinolines.

Copper-catalyzed formal C-N bond cleavage of aromatic methylamines: assembly of pyridine derivatives.

An efficient copper-catalyzed C-N bond cleavage of aromatic methylamines was developed to construct pyridine derivatives. With neat conditions and facile operation, the fragment-assembling strategy affords a broad range of 2,4,6-trisubstituted pyridines in up to 95% yield from simple and readily available starting materials. Interestingly, when pyridin-2-yl methylamine was employed as the substrate, α-alkylation reaction of ketones readily occurred to give β-(pyridin-2-yl) ketones instead of the 2,4,6-trisubstituted pyridines.

Metal-Free Synthesis of 2-Aminobenzothiazoles via Aerobic Oxidative Cyclization/Dehydrogenation of Cyclohexanones and Thioureas

A metal-free process for the synthesis of 2-aminobenzothiazoles from cyclohexanones and thioureas has been developed using catalytic iodine and molecular oxygen as the oxidant under mild conditions. Various 2-aminobenzothiazoles, 2-aminonaphtho[2,1-d]thiazoles, and 2-aminonaphtho[1,2-d]thiazoles were prepared via this method in satisfactory yields.

Copper-catalyzed oxidative [2 + 2 + 1] cycloaddition: regioselective synthesis of 1,3-oxazoles from internal alkynes and nitriles

A robust and regioselective copper(II)-catalyzed cycloaddition of internal alkynes and nitriles providing an effective access to oxazole fragments is reported herein. Water substantially participated in this reaction. Control experiments proposed that this transformation may proceed via an enamide intermediate. This strategy enables the preparation of the core structure of a COX-2 inhibitor.

Palladium-Catalyzed Oxidative Coupling of Aromatic Primary Amines and Alkenes under Molecular Oxygen: Stereoselective Assembly of (Z)-Enamines

An efficient Pd-catalyzed oxidative coupling of aromatic primary amines and alkenes under molecular oxygen is disclosed. Under mild reaction conditions, it provides a rapid access to (Z)-enamine compounds with exceptional functional group tolerance and excellent regio- and stereoselectivity. This attractive route is of great significance due to its applicability to a wide range of aromatic primary amines, most of which could not be efficiently converted into enamines previously. Moreover, this protocol is scalable, and the resultant enamines could be conveniently transformed into a series of N-containing heterocyclics, thus illustrating its potential applications in synthetic and medicinal chemistry.

Palladium-Catalyzed Sequential C–N/C–O Bond Formations: Synthesis of Oxazole Derivatives from Amides and Ketones

A highly efficient method for the synthesis of oxazole derivatives from simple amides and ketones has been established via a Pd(II)-catalyzed sp(2) C-H activation pathway in one step. The reaction is supposed to proceed through a C-N bond formation followed by a C-O bond formation closing the ring. Because of the simple and readily available starting materials, easy operation, and high bioactivity of oxazoles, this strategy can be broadly applied to medical chemistry.

Copper-Catalyzed Oxidative C(sp3)–H Functionalization for Facile Synthesis of 1,2,4-Triazoles and 1,3,5-Triazines from Amidines

A facile and versatile catalytic system involving copper catalyst, K3PO4 as the base, and O2 as the oxidant has been developed to enable efficient synthesis of 2,4,6-trisubstituted and 2,6-disubstituted 1,3,5-triazines and 1,3-disubstituted 1,2,4-triazoles from amidines with trialkylamines, DMSO, and DMF as the reaction partners, respectively. This protocol features inexpensive metal catalyst, green oxidant, good functional group tolerance, and high regioselectivity, providing an efficient entry to those products that are challenging to prepare by traditional methods. A single-electron-transfer (SET) mechanism is proposed for these transformations.

A regio- and diastereoselective palladium-catalyzed cyclopropanation of norbornene derivatives with molecular oxygen as the sole oxidant

A mild and efficient Pd-catalyzed cyclopropanation of norbornene derivatives with tertiary propargylic alcohols using molecular oxygen as the sole oxidant is described. This process allows quick and atom-economical assembly of various 1,2,3-trisubstituted cyclopropanes bearing α,β-unsaturated ketone moieties in high yields as a single regio- and diastereoisomer.