Wen-Xiong Zhang

Transition-Metal-Catalyzed Cleavage of C-N Single Bonds

Kunbing Ouyang,†,‡ Wei Hao,† Wen-Xiong Zhang,*,†,§ and Zhenfeng Xi† †Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Bioorganic Chemistry and Molecular Engineering of the Ministry of Education, College of Chemistry, Peking University, Beijing 100871, China ‡Institute of Chemistry, Chinese Academy of Sciences (CAS), Beijing 100190, China State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, China

Cyclopentadiene–Phosphine/Palladium-Catalyzed Cleavage of C–N Bonds in Secondary Amines: Synthesis of Pyrrole and Indole Derivatives from Secondary Amines and Alkenyl or Aryl Dibromides

An efficient Pd-catalyzed cleavage of C(sp(3))-N bonds in secondary amines and a consequent C(sp(2))-N and C(sp(3))-N coupling process was developed. Various secondary amines could be used to react with alkenyl or aryl dibromides, affording pyrroles and indoles in high yields. Cyclopentadiene-phosphine ligands, a new type of P-olefin ligand, were found to be able to promote the efficiency of this Pd-catalyzed process remarkably. A reactive Pd complex coordinated with a cyclopentadiene-phosphine ligand was successfully isolated and structurally characterized.

Zn(OTf)2-catalyzed addition of amines to carbodiimides: efficient synthesis of guanidines and unpredicted formation of Zn–N amido species

Zn(OTf)(2) acts as an excellent catalyst precursor for addition of various amine N-H bonds to carbodiimides under an atmosphere of air, offering a convenient synthesis of substituted guanidines with high functional-group tolerance. A Zn-N amido species is shown to act as the active species.

Efficient one-pot synthesis of 2,3-dihydropyrimidinthiones via multicomponent coupling of terminal alkynes, elemental sulfur, and carbodiimides.

An organolithium-promoted multicomponent reaction (MCR) involving readily available terminal alkynes, elemental sulfur, and carbodiimides has been achieved for the first time. This MCR offers an atom-economic route to 2,3-dihydropyrimidinthiones which are difficult to access by other means via an interesting and useful C=N double bond cleavage and an sp(3) C-H bond functionalization of carbodiimides.

Procedure-Controlled Selective Synthesis of 5-Acyl-2-iminothiazolines and their Selenium and Tellurium Derivatives by Convergent Tandem Annulation†

Concise and selective: the procedure-controlled synthesis of the title compounds has been achieved for the first time by an organolithium-promoted convergent tandem annulation involving readily available terminal alkynes, chalcogen elements (S, Se, and Te), carbodiimides, and acid chlorides. A novel 1,5-acyl migration is considered to be essential for this useful transformation.

Regioselective Ring Expansion of 2,4-Diiminoazetidines via Cleavage of C–N and C(sp3)–H Bonds: Efficient Construction of 2,3-Dihydropyrimidinesulfonamides

A highly regioselective base-mediated ring expansion of 2,4-diiminoazetidines via cleavage of C-N and C(sp(3))-H bonds is achieved for the first time to afford efficiently 2,3-dihydropyrimidinesulfonamides. The mechanism of the ring expansion via tandem 4π electrocyclic ring-opening/1,5-H shift/6π electrocyclic ring-closing is well confirmed by the trapping experiments of two key intermediates and deuterium labeling studies.

Efficient One-Pot Synthesis of N-Containing Heterocycles by Multicomponent Coupling of Silicon-Tethered Diynes, Nitriles, and Isocyanides through Intramolecular Cyclization of IminoacylZr Intermediates

An efficient multicomponent synthesis of 5-azaindoles and dihydropyrrolo[3,2-c]azepines was achieved by zirconocene-mediated coupling of silicon-tethered diynes, nitriles, and isocyanides. The synthesis, structures, and intramolecular cyclization of mono- and bis(iminoacyl)--Zr intermediates were investigated to elucidate the reaction process. Upon hydrolysis, the isolated mono(iminoacyl)--Zr intermediates underwent intramolecular cyclization to afford tetrasubstituted 5-azaindoles, whereas intramolecular cyclization of bis(iminoacyl)--Zr intermediates led to the formation of dihydropyrrolo[3,2-c]azepines. The structure of a bis(iminoacyl)--Zr intermediate, formed through insertion of two molecules of CyNC into the Zr--C bond, and structures of two dihydropyrrolo[3,2-c]azepines were characterized by single-crystal X-ray structural analysis.

Intramolecular C–F and C–H bond cleavage promoted by butadienyl heavy Grignard reagents

Organomagnesium compounds (Grignard reagents) are among the most useful organometallic reagents and have greatly accelerated the advancement of synthetic chemistry and related sciences. Nevertheless, heavy Grignard reagents based on the metals calcium, strontium or barium are not widely used, mainly due to their rather inert heavy alkaline-earth metals and extremely high reactivity of their corresponding Grignard-type reagents. Here we report the generation and reaction chemistry of butadienyl heavy Grignard reagents whose extremely high reactivity is successfully tamed. Facile synthesis of perfluoro-π-extended pentalene and naphthalene derivatives is realized by the in situ generated heavy Grignard reagents via intramolecular C-F/C-H bond cleavage. These obtained perfluorodibenzopentalene and perfluorodinaphthopentalene derivatives show low-lying LUMO levels, with one being the lowest value so far among all pentalene derivatives. Our results set an exciting example for the meaningful synthetic application of heavy Grignard reagents.

Diverse Reactions of 1,4-Dilithio-1,3-dienes with Nitriles: Facile Access to Tricyclic Δ1-Bipyrrolines, Multiply Substituted Pyridines, Siloles, and (Z,Z)-Dienylsilanes by Tuning of Substituents on the Butadienyl Skeleton

Addition cyclization of 1,2,3,4-tetrasubstituted 1,4-dilithio-1,3-dienes (Type I) with four equivalents of various aromatic nitriles in the presence of hexamethylphosphoramide (HMPA) gives exclusively fully substituted pyridines in moderate to good yields. Similarly, trisubstituted pyridines can be prepared by the reaction of 2,3-dialkyl- or diaryl-substituted 1,4-dilithio-1,3-dienes (Type II) with nitriles. However, five- or six-membered-ring fused 2,3-disubstituted 1,4-dilithio-1,3-dienes (Type III) reacted with various aromatic and aliphatic nitriles without alpha-hydrogen atoms to afford tricyclic Delta1-bipyrrolines in high yields. The reaction of six-membered-ring fused 2,3-disubstituted 1,4-dilithio-1,3-diene (Type III) with 2-cyanopyridine afforded the corresponding pyridine, and no tricyclic Delta1-bipyrroline was observed. Seven-membered-ring fused dilithiodienes reacted with PhCN or trimethylacetonitrile to afford the corresponding pyridines in good yield. When 1,2,3,4-tetrasubstituted dilithio reagents (Type I) were treated with Me3SiCN, a tandem silylation/intramolecular substitution process readily occurred to yield siloles, whereas the reaction of 2,3-disubstituted dilithio reagents (Types II and III) with Me3SiCN gave rise to (Z,Z)-dienylsilanes with high stereoselectivity. These results revealed that the formation of tricyclic Delta1-bipyrrolines, pyridines, siloles, and (Z,Z)-dienylsilanes are strongly dependent on the substitution patterns of the dilithio butadienes and the nature of the nitriles employed.

Cleavage and reorganization of Zr-C/Si-C bonds leading to Zr/Si-N organometallic and heterocyclic compounds.

The t-BuCN-stabilized zirconacyclopropene-azasilacyclopentadiene complexes 2 are generated in situ in high yields from the Si-tethered diynes, Cp(2)Zr(II) species, and 2 equiv of t-BuCN via a coordination-induced Zr-C/Si-C bond cleavage and reorganization. Complexes 2 have been demonstrated to be synthetically very useful. A variety of novel Zr/Si organo-bimetallic compounds and Si/N heterocyclic compounds, such as azasilacyclopentadienes, azasilacyclohexadienes, and allenylazazirconacycles, are obtained in high yields when complexes 2 are treated with ketones, carbodiimides, alkynes, elemental sulfur (S(8)), acid chlorides, or nitriles. In this chemistry, t-BuCN behaves as both an initiator and a brake/release handle to initiate and control the reaction process.