Nickel-Catalyzed Enantioselective Hydrothiocarbonylation of Cyclopropenes.

Hydrothiocarbonylation of olefins using carbon monoxide and thiols is a powerful method to synthesize thioesters from simple building blocks. Owing to the intrinsic challenges of catalyst poisoning, transition-metal-catalyzed asymmetric thiocarbonylation, particularly when utilizing earth abundant metals, remains rare in the literature. Herein, we report a nickel-catalyzed enantioselective hydrothiocarbonylation of cyclopropenes for the synthesis of a diverse collection of functionalized thioesters in good to excellent yields with high stereoselectivity. This new method employs an inexpensive, air-stable nickel(II) precursor, which provides enhanced catalyst fidelity against CO poisoning compared to nickel(0) catalysts.

Controlling Selectivity in Shuttle Hetero-difunctionalization Reactions: Electrochemical Transfer Halo-thiolation of Alkynes.

Shuttle hetero-difunctionalization reaction, in which two chemically distinct functional groups are transferred between two molecules, has long been an unmet goal due to the daunting challenges in controlling the chemo-, regio-, and stereoselectivity. Herein, we disclose an electrochemistry enabled shuttle reaction (e-shuttle) to selectively transfer one RS- and one X- group between ß-halosulfides and unsaturated hydrocarbons via a consecutive paired electrolysis mechanism. The preferential anodic oxidation of one anion over the other, which is controlled by their distinct redox potentials, plays a pivotal role in controlling the high chemoselectivity of the process. This easily scalable methodology enables the construction of a myriad of densely functionalized ß-halo alkenyl sulfides in unprecedented chemo-, regio-, and stereoselectivity using benign surrogates, e.g., 2-bromoethyl sulfide, avoiding the handling of corrosive and oxidative RS-Br reagents. In a broader context, these results open up new strategies for selective shuttle difunctionalization reactions.

Merging shuttle reactions and paired electrolysis for reversible vicinal dihalogenations.

Vicinal dibromides and dichlorides are important commodity chemicals and indispensable synthetic intermediates in modern chemistry that are traditionally synthesized using hazardous elemental chlorine and bromine. Meanwhile, the environmental persistence of halogenated pollutants necessitates improved approaches to accelerate their remediation. Here, we introduce an electrochemically assisted shuttle (e-shuttle) paradigm for the facile and scalable interconversion of alkenes and vicinal dihalides, a class of reactions that can be used both to synthesize useful dihalogenated molecules from simple alkenes and to recycle waste material through retro-dihalogenation. The reaction is demonstrated using 1,2-dibromoethane, as well as 1,1,1,2-tetrachloroethane or 1,2-dichloroethane, to dibrominate or dichlorinate, respectively, a wide range of alkenes in a simple setup with inexpensive graphite electrodes. Conversely, the hexachlorinated persistent pollutant lindane could be fully dechlorinated to benzene in soil samples using simple alkene acceptors.

Kinetic Resolution of Tertiary Propargylic Alcohols by Enantioselective Cu-H-Catalyzed Si-O Coupling.

A broad range of tertiary propargylic alcohols were kinetically resolved by catalyst-controlled enantioselective silylation. This non-enzymatic kinetic resolution is catalyzed by a Cu-H species and makes use of the commercially available precatalyst MesCu/(R,R)-Ph-BPE and a simple hydrosilane as the resolving reagent. Both alkyl,aryl- as well as dialkyl-substituted propargylic alcohols participate, and especially high selectivity factors are achieved when the alkyne terminus carries a TIPS group, which also enables facile post-functionalization in this position (s up to 207).

Kinetic Resolution of α-Hydroxy-Substituted Oxime Ethers by Enantioselective Cu-H-Catalyzed Si-O Coupling.

A catalyst-controlled enantioselective alcohol silylation by Cu-H-catalyzed dehydrogenative Si-O coupling of hydroxy groups α to an oxime ether and simple hydrosilanes is reported. The selectivity factors reached in this kinetic resolution are generally high (s≈50), and these reactions thereby provide reliable access to highly enantioenriched α-hydroxy-substituted oxime ethers. The synthetic usefulness of these compounds is also demonstrated.

Broad-spectrum kinetic resolution of alcohols enabled by Cu-H-catalysed dehydrogenative coupling with hydrosilanes.

The enantioselective silylation of racemic alcohols, where one enantiomer reacts faster than the other, is an alternative approach to established enzymatic and non-enzymatic acylation techniques. The existing art is either limited to structurally biased alcohols or requires elaborate catalysts. Simple substrates, such as benzylic and allylic alcohols, with no coordinating functionality in the proximity of the hydroxy group have been challenging in these kinetic resolutions. We report here the identification of a broadly applicable chiral catalyst for the enantioselective dehydrogenative coupling of alcohols and hydrosilanes with both the chiral ligand and the hydrosilane being commercially available. The efficiency of kinetic resolutions is characterized by the selectivity factor, that is, the ratio of the reaction rates of the fast-reacting over the slow-reacting enantiomer. The selectivity factors achieved with the new method are good for acyclic benzylic alcohols (≤170) and high for synthetically usefully cyclic benzylic (≤40.1) and allylic alcohols (≤159).

Synthesis of 3-acylindoles by visible-light induced intramolecular oxidative cyclization of o-alkynylated N,N-dialkylamines.

A visible-light photoredox synthesis of 3-acylindoles through intramolecular oxidative cyclization of o-alkynylated N,N-dialkylamines is developed. The reaction proceeds effectively under mild reaction conditions using air as the oxidant, and only water is generated as a side product. A plausible mechanism involving the addition of α-amino alkyl radicals to alkynes, followed by C-O bond formation, is proposed.

PhI(OAc)2-mediated synthesis of 6-(trifluoromethyl)phenanthridines by oxidative cyclization of 2-isocyanobiphenyls with CF3SiMe3 under metal-free conditions.

A mild and efficient method for the synthesis of 6-(trifluoromethyl)phenanthridines through oxidative cyclization of 2-isocyanobiphenyls with CF3SiMe3 under metal-free conditions was developed. The reaction allows the direct formation of C-CF3 bonds and rapid access to phenanthridine ring systems in one catalytic cycle.

Benzofuran and indole synthesis via Cu(I)-catalyzed coupling of N-tosylhydrazone and o-hydroxy or o-amino phenylacetylene.

A general and practical method to synthesize 2-substituted benzofurans and indoles is described. This method employs easily accessible N-tosylhydrazones and o-hydroxy or o-amino phenylacetylenes as substrates. The reaction proceeds through a CuBr-catalyzed coupling-allenylation-cyclization sequence under ligand-free conditions.

Isolation and structure determination of anti-influenza component from Mahonia bealei.

The fraction possessing anti-influenza activity, which is obtained from the roots of Mahonia bealei (Fort), has been studied regarding its chemical compositions and molecular structure. The previous experiment on this fraction in vitro suggested that the anti-influenza effect was due to the existence of alkaloids in M. bealei (Fort), and mainly from one bisbenzylisoquinoline alkaloid. In this paper the structure of this bisbenzylisoquinoline alkaloid has been determined as 1R, 1'S-(+)-isotetrandrine by means of MS, 1H NMR, 13C NMR, FT-IR and HPLC analyses.

[Study on anti-influenza effect of alkaloids from roots of Mahonia bealei in vitro].

Anti-influenza effect of alkaloids from roots of Mahonia bealei (Fort.) Carr. was studied in vitro. The experiment in embryo indicated that the alkaloids at concentration of 0.25 mg/ml obviously inhibited the proliferation of influenza virus Al, and at concentration of 20 mg/ml showed no side-effect on embryo.