Dong-Dong Guo

Palladium-Catalyzed C–H Homocoupling of Furans and Thiophenes Using Oxygen as the Oxidant

A general and efficient palladium-catalyzed intermolecular direct C-H homocoupling of furans and thiophenes has been developed. The reaction is characterized by using molecular oxygen as the sole oxidant and complete C5-position regioselectivity. Both C2- and C3-substituted furans or thiophenes are appropriate substrates. The approach provides a straightforward, facile, and economical route to bifurans and bithiophenes under mild reaction conditions.

Copper-Catalyzed Radical Reaction of N-Tosylhydrazones: Stereoselective Synthesis of (E)-Vinyl Sulfones

A new chemistry of hydrazines that is a copper-catalyzed radical reaction to synthesize vinyl sulfones from readily available N-tosylhydrazones has been described. The protocol provides a novel strategy for the synthesis of various vinyl sulfones including α, β-disubstituted ones and terminal ones. The advantages of the transformation include excellent E stereoselectivity, broad substrate scope, low cost of reagents, and convenient operation. A novel and efficient one-pot synthesis of alkynes from N-tosylhydrazones has been achieved. The studies provide important complementary approaches for the syntheses of vinyl sulfones and alkynes.

Wacker-type oxidation and dehydrogenation of terminal olefins using molecular oxygen as the sole oxidant without adding ligand.

An efficient and economical palladium-catalyzed oxidation system has been identified. The oxidation system, characterized by not adding ligand and using molecular oxygen as the sole oxidant, can realize the Tsuji-Wacker oxidation of terminal olefins and especially styrenes to methyl ketones; in addition, this system can achieve tandem Wacker oxidation-dehydrogenation of terminal olefins to α,β-unsaturated ketones.

Silver‐Catalyzed Coupling of Two C sp 3H Groups and One‐Pot Synthesis of Tetrasubstituted Furans, Thiophenes, and Pyrroles

Silver-catalyzed coupling of two C sp(3)-H groups to form 1,4-diketones have been developed for the first time. The resultant ketones then undergo cyclization to synthesize tetrasubstituted furans, thiophenes, and pyrroles from benzyl ketone derivatives in a one-pot reaction process. This highly-efficient synthetic method, which utilizes air as the terminal oxidant and readily accessible starting materials, displays a wide substrate scope and broad functional-group tolerance.

Palladium-catalyzed C-7 alkenylation of indolines using molecular oxygen as the sole oxidant

A general and efficient method for the intermolecular direct C-7-selective C–H alkenylation of indolines using palladium(II) as the catalyst and molecular oxygen as the sole oxidant has been developed. The reaction showed complete regio- and stereoselectivity. All products were E-isomers at the C-7 position, and no Z-isomers or other position substituted products could be detected. The approach also presented an efficient route for the synthesis of C-7 alkenylated indoles.

Synthesis of 6H-Benzo[c]chromenes via Palladium-Catalyzed Intramolecular Dehydrogenative Coupling of Two Aryl C–H Bonds

The palladium-catalyzed intramolecular C-H/C-H coupling reaction of two simple arenes to generate 6H-benzo[c]chromenes has been reported for the first time. The approach features broad substrate scope and good tolerance of functional groups and uses molecular oxygen as the terminal oxidant. The high efficiency of the approach is verified by concise total synthesis of natural product cannabinol.

Palladium-Catalyzed C-H Functionalization of Phenyl 2-Pyridylsulfonates.

An efficient palladium(II)-catalyzed intermolecular direct ortho-alkenylation and acetoxylation of phenols has been developed. The reaction proceeded via a seven-membered cyclopalladated intermediate and showed complete regio- and diastereoselectivity. The approach also provided an efficient route for the synthesis of coumarins and benzofurans.

Palladium-Catalyzed Direct Monoarylation of Aryl C−H Bonds with Iodoarenes

The transition‐metal‐catalyzed direct arylation of nonactivated aryl C−H bonds with iodoarenes has emerged as an important method for the construction of biaryls. Generally, the direct arylation reaction proceeds in the presence of stoichiometric Ag additives; moreover, the diarylation product is often unavoidable if there are two identical aromatic C−H bonds in the substrate. Herein we disclose an efficient Pd(OAc)2/trifluoroacetic acid/O2 catalytic system that promotes direct arylation reactions of a variety of aromatic C−H bonds with diverse iodoarenes under Ag‐free conditions. The coupling reaction possesses a complete monoarylation selectivity. This approach provides a straightforward, facile, and economical route to biaryls.

CCDC 1518522: Experimental Crystal Structure Determination

Related Article: Dong-Dong Guo, Bin Li, Da-Yu Wang, Ya-Ru Gao, Shi-Huan Guo, Gao-Fei Pan, Yong-Qiang Wang|2017|Org.Lett.|19|798|doi:10.1021/acs.orglett.6b03763

Copper-Catalyzed Isomerization and Cyclization of E/Z-o-Haloaryl N-Sulfonylhydrazones: Convenient Access to of 1H-Indazoles

The isomerization of the C=N double bond in hydrazones has drawn considerable attention because of its potential for application in a broad range of chemical transformations. Generally, this isomerization can be realized either photochemically or thermally. A new isomerization approach is presented, namely a copper‐catalyzed C=N double bond isomerization of hydrazones, which is followed by an efficient intramolecular C−N coupling reaction, providing an unprecedented catalytic approach for the synthesis of 1H‐indazoles from readily accessible Z/E mixture of o‐haloaryl N‐sulfonylhydrazones.