Chuanle Zhu

Csp3–P versus Csp2–P Bond Formation: Catalyst-Controlled Highly Regioselective Tandem Reaction of Ene-Yne-Ketones with H-Phosphonates

Under copper-catalyzed or base-promoted conditions, a wide range of ene-yne-ketones react with H-phosphonates to afford various phosphorylated furans in good yields. A copper carbene generation or a Michael addition is proposed as the key step in the selective construction of the Csp(3)-P or Csp(2)-P bond, which is supported by carbene capture reactions and interval (31)P NMR experiments. Furthermore, this method features inexpensive metal catalysts, no usage of oxidant, and high atom economy, which make it attractive and practical.

Copper-Mediated [3 + 2] Oxidative Cyclization Reaction of N-Tosylhydrazones and β-Ketoesters: Synthesis of 2,3,5-Trisubstituted Furans

The first attempt at utilizing N-tosylhydrazones as two-carbon synthons has been successfully achieved, which underwent a copper-mediated [3 + 2] oxidative cyclization reaction to afford 2,3,5-trisubstituted furans in moderate to good yields. The features of this method include inexpensive metal catalyst, readily available substrates, high regioselectivity, and convenient operation. The studies provide important approaches for further exploration of the powerful and diverse reaction abilities of N-tosylhydrazones.

Transition-Metal-Free Cyclopropanation of 2-Aminoacrylates with N-Tosylhydrazones: A General Route to Cyclopropane α-Amino Acid with Contiguous Quaternary Carbon Centers

Cyclopropanation of 2-aminoacrylates with N-tosylhydrazones could proceed smoothly under transition-metal-free conditions via a [3 + 2] cycloaddition process. This robust protocol exhibits excellent generality, delivering a wide spectrum of cyclopropane α-amino acid esters bearing contiguous quaternary carbon centers in high yields and diastereoselectivities. With these readily available products, the steric convergence of cyclopropane α-amino acids could be readily obtained.

Transition-Metal-Free Diastereoselective Epoxidation of Trifluoromethylketones with N-Tosylhydrazones: Access to Tetrasubstituted Trifluoromethylated Oxiranes

The first example of the epoxidation reaction of trifluoromethylketones with N-tosylhydrazones under transition-metal free conditions is reported. This epoxidation reaction provided tetrasubstituted trifluoromethylated oxiranes with excellent yields and diastereoselectivities. The salient features of this reaction include readily available starting materials, mild conditions, broad substrate scope, high efficiency, and valuable further applications. Remarkably, this reaction proceeded through an unprecedented nucleophilic addition process, and the ammonium O-anion intermediate was detected and characterized by NMR and HRMS analysis.

Synthesis of Polysubstituted 3-Amino Pyrroles via Palladium-Catalyzed Multicomponent Reaction

A novel approach for the synthesis of polysubstituted 3-amino pyrroles via palladium-catalyzed three-component tandem reaction was developed. The procedure constructs various polysubstituted 3-amino pyrroles with moderate to excellent yields under mild reaction conditions with assembly efficiency, readily available starting materials, and good functional group tolerance. Furthermore, this process was successfully applied to the synthesis of different 3-phenyl-1,4-dihydropyrrolo[3,2-b]indole derivatives via an intramolecular Buchwald-Hartwig cross-coupling reaction in two steps.

Palladium-Catalyzed Fluoroalkylative Cyclization of Olefins

A palladium-catalyzed fluoroalkylative cyclization of olefins with readily available Rf-I reagents to afford the corresponding fluoroalkylated 2,3-dihydrobenzofuran and indolin derivatives with moderate to excellent yields is reported. This novel procedure provides an efficient method for the construction of Csp3-CF2 and C-O/N bonds in one step. A wide range of functional groups are tolerated. It is proposed that a radical/SET (single electron transfer) pathway proceeding via the fluoroalkyl radical may be involved in the catalytic cycle.

Palladium-Catalyzed Sequential Nucleophilic Addition/Oxidative Annulation of Bromoalkynes with Benzoic Acids To Construct Functionalized Isocoumarins

An efficient and robust protocol for the preparation of 3-substituted isocoumarins via palladium-catalyzed nucleophilic addition/oxidative annulation of bromoalkynes with benzoic acids has been developed. Remarkably, preliminary mechanistic studies indicated that the transformation might proceed via a stereo- and regioselective nucleophilic addition and C-H functionalization procedure.

Copper-Catalyzed Cyanation of N-Tosylhydrazones with Thiocyanate Salt as the “CN” Source

A novel protocol for the synthesis of α-aryl nitriles has been successfully achieved via a copper-catalyzed cyanation of N-tosylhydrazones employing thiocyanate as the source of cyanide. The features of this method include a convenient operation, readily available substrates, low-toxicity thiocyanate salts, and a broad substrate scope.

MnO2-Promoted Oxidative Radical Sulfonylation of Haloalkynes with Sulfonyl Hydrazides: C(sp)–S Bond Formation towards Alkynyl Sulfones

A catalyst-free oxidative radical sulfonylation of haloalkynes with sulfonyl hydrazides is reported. It represents an example of C(sp)-S bond formation using sulfonyl hydrazides as sulfonyl radical sources. Various alkynyl sulfones were synthesized in moderate to good yields. Having MnO2 as the oxidant is very critical for this transformation. Remarkably, the self-coupling reaction of haloalkynes through C(sp)-C(sp) bond formation is significantly inhibited under the standard reaction conditions.

Copper-catalyzed coupling of oxime acetates and aryldiazonium salts: an azide-free strategy toward N-2-aryl-1,2,3-triazoles

An azide-free strategy for the synthesis of N-2-aryl-1,2,3-triazoles via copper-catalyzed coupling of oxime acetates and aryldiazonium tetrafluoroborates is reported. With the magic p-methoxyphenyldiazonium tetrafluoroborate as the reaction partner, this copper-catalyzed system favored the desired single electron transfer process via N–O bond cleavage of oxime acetates, while the classic single electron transfer process via C–N2 bond cleavage of aryldiazonium tetrafluoroborates was sufficiently inhibited. Significantly, various oxime acetates were suitable for this reaction, delivering the corresponding 4-substituted-N-2-aryl-1,2,3-triazoles and 4,5-disubstituted-N-2-aryl-1,2,3-triazoles in high yield. Primary mechanism studies indicated that this reaction involved a radical procedure. Furthermore, various novel and attractive tetraphenylethylene and carbazole based N-2-aryl-1,2,3-triazoles were synthesized smoothly.