Quanbin Jiang

Highly Active Ruthenium(II) Complex Catalysts Bearing an Unsymmetrical NNN Ligand in the (Asymmetric) Transfer Hydrogenation of Ketones

N-Heterocylic ligands have recently become more and more attractive in homogeneous catalysis and organic synthesis because their organometallic complexes usually exhibit higher reactivity and better stability than those with phosphine ligands. Tridentate NNN ligands such as Pybox, 2,6-bis ACHTUNGTRENNUNG(imino)pyridines,[3] terpyridines, and other symmetrical NNN ligands have demonstrated their potential applications. However, examples of unsymmetrical tridentate NNN ligands and their transition-metal complexes are scarce. Transition-metal complexes bearing an unsymmetrical polydentate ligand are usually bestowed with good catalytic activity. Thus, unsymmetrical pyridyl-based NNN ligands are strongly desired for the construction of highly active transition-metal complex catalysts. Functional metal complexes were obtained with symmetrical bis(benzimidazol-2-yl)pyridines and bis(N-alkylbenzimidazol-2-yl)pyridines, and the electronic properties of the respective ruthenium complexes have been described. However, only a few of them have been applied as catalysts. We recently synthesized very efficient Ru pyridyl–pyrazolyl-based NNN complex catalysts for transfer hydrogenation of ketones. Ru-catalyzed transfer hydrogenation reactions with 2-propanol as the hydrogen source have been extensively studied by Noyori et al. Baratta’s group recently reported highly active Ru 2-(aminomethyl)pyridinylphosphane complex catalysts for the transfer hydrogenation of ketones. A few Ru complex catalysts featuring no N H functionality have also been documented for the same purpose. Herein, we report the construction of unsymmetrical (chiral) pyridyl– benzimidazolyl-based NNN ligands and their Ru complex catalysts for the (asymmetric) transfer hydrogenation of ketones by following the strategy shown in Scheme 1. The mono-N-alkyl derivative of bis(benzimidazol-2-yl)pyridine (1), that is, 2, and bis(N-propylbenzimidazol-2yl)pyridine (3) were obtained by reacting 1 with 1-bromopropane in the presence of NaH (Scheme 2). Reactions of ligands 1–3 with one equivalent of [Ru ACHTUNGTRENNUNG(PPh)3Cl2] in refluxing methanol afforded Ru complexes 4–6 in 76–91 % yields. Treatment of 5 with K2CO3 base in CH2Cl2 formed

Palladium-catalyzed, copper-mediated construction of benzene rings from the reactions of indoles with in situ generated enones†

Construction of the benzene ring in carbazoles was efficiently realized through a domino dehydrochlorination/alkenylation/cycloaddition–oxidation sequence by means of palladium(II)-catalyzed, copper(II)-mediated reactions of N-protected 2,3-unsubstituted indoles with 3-chloropropiophenones in the presence of a base. 3-Alkenylated indole was confirmed to be formed as the reaction intermediate which then underwent Diels–Alder cycloaddition to the initially in situ generated enone from a 3-chloropropiophenones substrate, and the subsequent dehydrogenative aromatization yielded the carbazole product. The strategy to employ in situ generated enones as the reactive species avoided the use of a large excess of labile substrates and lessened the side reactions.

Palladium-catalyzed oxidative annulation of in situ generated enones to pyrroles: a concise route to functionalized indoles

Palladium(II)-catalyzed, copper(II)-mediated indole synthesis was achieved from the reactions of N-substituted simple pyrroles with enones generated in situ from 3-chloropropiophenones. A benzene ring was thus constructed onto a pyrrole backbone, affording substituted indole derivatives. A domino dehydrochlorination/C–H olefination /Diels–Alder cycloaddition/dehydrogenative aromatization sequence was established as the reaction pathway. The present methodology provides a concise route to highly functionalized indole derivatives.

Copper-Catalyzed Asymmetric Borylation: Construction of a Stereogenic Carbon Center Bearing Both CF3 and Organoboron Functional Groups

Copper-catalyzed borylation of β-trifluoromethyl-α,β-unsaturated ketones was efficiently achieved by means of bis(pinacolato)diboron (B2pin2), affording the enantioenriched products in good yields with high enantioselectivities. CuI and (R,S)-Josiphos consist of the most efficient catalyst system under mild conditions. In the absence of the chiral ligand, the reactions could be performed more efficiently to form β-ketone derivatives which were directly borylated and indirectly trifluoromethylated at the β-carbon atom of the α,β-unsaturated ketone substrates. The present protocol provides a promising method to access a stereogenic carbon center bearing both CF3 and organoboron functional groups.

Copper‐Catalyzed Tandem Asymmetric Borylation of β‐Chloroalkyl Aryl Ketones and Related Compounds

The Cu‐catalyzed, one‐pot tandem (asymmetric) borylation of β‐chloroalkyl aryl ketones via the in situ generated acyclic enones with bis(pinacolato)diboron was achieved efficiently to reach up to 97 % yield and 99 % enantioselectivity for the formal sp3 CCl borylation products. The present methodology provides an efficient alternative route to (chiral) alkylboron compounds.

Synthesis of chalcones via domino dehydrochlorination/Pd(OAc)2-catalyzed Heck reaction

通过Domino脱HCl/Pd（OAc）2催化的Heck反应实现了β-氯代烷基芳基酮、酯和酰胺与卤代芳烃的交叉偶联反应,高效合成了查尔酮类化合物.利用原位生成烯酮为中间体进行反应的策略,减少副反应的发生,从而提高反应的效率.该方法对各种官能团的容忍性好,为从氯代烷烃出发直接合成查尔酮类化合物提供了一条新途径.Abstract A new method has been developed for the cross-coupling of aryl halides with β -chloroalkyl aryl ketones and their ester and amide analogs through a domino dehydrochlorination/Pd(OAc) 2 - catalyzed Heck reaction sequence. The enone intermediates generated in situ reduced the occurrence of side reactions and therefore enhanced the efficiency of the reaction. This reaction exhibited good tolerance to various functional groups on both substrates and provides rapid access to a wide range of chalcone derivatives.A new method has been developed for the cross-coupling of aryl halides with β-chloroalkyl aryl ketones and their ester and amide analogs through a domino dehydrochlorination/Pd(OAc)2- catalyzed Heck reaction sequence. The enone intermediates generated in situ reduced the occurrence of side reactions and therefore enhanced the efficiency of the reaction. This reaction exhibited good tolerance to various functional groups on both substrates and provides rapid access to a wide range of chalcone derivatives.

α,β-Unsaturated N-Acylindoles: An Alternative Class of Michael Acceptors and Their Application in Asymmetric Borylation

Copper(I)-catalyzed enantioselective borylation of α,β-unsaturated N-acylindoles as well as N-acylpyrroles was efficiently achieved by means of bis(pinacolato)diboron (B2pin2), affording the enantioenriched products in excellent yields with up to 99% ee. The present work provides an alternative class of Michael acceptors, that is, α,β-unsaturated N-acylindoles, for potential asymmetric transformations.

PIDA-Mediated Formal Olefinic C=C Bond Cleavage of α-Oxo-Ketene N,N-Acetals toward Substituted Oxazolines

The hypervalent iodine reagent PhI(OAc)2 (PIDA) mediated the formal oxidative C=C bond cleavage and subsequent cyclization of internal olefins, that is, α-oxo-ketene N,N-acetals, which afforded substituted oxazolines. Isothiazoline derivatives were obtained from the reactions of α-thioxo-ketene N,N-acetals with PIDA under the same conditions. Hydrolysis of the resultant oxazoline derivatives led to highly functionalized oxazolones. A plausible mechanism was proposed based upon the formation of isothiazoline-type intermediates.

Article (Special Issue on Catalysis in Organic Synthesis)Synthesis of chalcones via domino dehydrochlorination/Pd(OAc)2-catalyzed Heck reaction

通过Domino脱HCl/Pd（OAc）2催化的Heck反应实现了β-氯代烷基芳基酮、酯和酰胺与卤代芳烃的交叉偶联反应,高效合成了查尔酮类化合物.利用原位生成烯酮为中间体进行反应的策略,减少副反应的发生,从而提高反应的效率.该方法对各种官能团的容忍性好,为从氯代烷烃出发直接合成查尔酮类化合物提供了一条新途径.Abstract A new method has been developed for the cross-coupling of aryl halides with β -chloroalkyl aryl ketones and their ester and amide analogs through a domino dehydrochlorination/Pd(OAc) 2 - catalyzed Heck reaction sequence. The enone intermediates generated in situ reduced the occurrence of side reactions and therefore enhanced the efficiency of the reaction. This reaction exhibited good tolerance to various functional groups on both substrates and provides rapid access to a wide range of chalcone derivatives.A new method has been developed for the cross-coupling of aryl halides with β-chloroalkyl aryl ketones and their ester and amide analogs through a domino dehydrochlorination/Pd(OAc)2- catalyzed Heck reaction sequence. The enone intermediates generated in situ reduced the occurrence of side reactions and therefore enhanced the efficiency of the reaction. This reaction exhibited good tolerance to various functional groups on both substrates and provides rapid access to a wide range of chalcone derivatives.