Yuya Hu

Herein we report a transition metal-free procedure for the base-promoted 1,2-addition of polyfluorophenylboronates to aldehydes and ketones to generate organofluorine-containing alcohols in yields up to 93 %.

Abstract

A novel protocol for the transition metal-free 1,2-addition of polyfluoroaryl boronate esters to aldehydes and ketones is reported, which provides secondary alcohols, tertiary alcohols, and ketones. Control experiments and DFT calculations indicate that both the ortho-F substituents on the polyfluorophenyl boronates and the counterion K⁺ in the carbonate base are critical. The distinguishing features of this procedure include the employment of commercially available starting materials and the broad scope of the reaction with a wide variety of carbonyl compounds giving moderate to excellent yields. Intriguing structural features involving O−H⋅⋅⋅O and O−H⋅⋅⋅N hydrogen bonding, as well as arene-perfluoroarene interactions, in this series of racemic polyfluoroaryl carbinols have also been addressed.

Co/organophotoredox dual catalysis allows the stereocontrolled synthesis of 1,3-diol products featuring quaternary carbon centers using vinyl cyclic carbonates and aldehydes as reaction partners. This streamlined method offers a wide scope of syn-configured products obtained under mild operating conditions, and control reactions suggest that diastereocontrol is exerted within a Zimmerman–Traxler type transition state.

Abstract

An efficient and attractive Co/organophotoredox dual catalysis protocol has been developed allowing the stereoselective access to a wide variety of syn-configured 1,3-diols featuring quaternary carbon centers. The synthesis of the target molecules is achieved under ambient reaction conditions using modular and accessible reagents, substituted vinyl cyclic carbonates and aldehydes, and in short reaction times. Mechanistic control experiments suggest that the stereoselectivity can be rationalized via a preferred Zimmerman–Traxler transition state comprising a Co(allyl) species and an activated aldehyde. This newly developed process thus expands the use of base metal catalysis in the construction of challenging quaternary carbon stereocenters.

Metal-free dearomatization of N-heteroarenes is a well-known and powerful method to yield partially saturated N-heterocyclic building blocks. Yet, the use of sensitive reagents restricts the applicability in synthetic laboratories. Herein, we present a very mild and selective reduction of N-heteroarenes by amine borane to synthesize a broad variety of N-substituted 1,4- and 1,2-dihydropyridines.

Abstract

Dearomatization is an effective method to transform readily available N-heterocycles into partially saturated motifs. Manipulation of dihydro-derivatives holds great potential and provides access to a variety of semi-saturated N-heterocyclic building blocks. However, current strategies are limited in scope and the use of sensitive reagents restricts the applicability in synthetic laboratories. Herein, we report the synthesis of a broad variety of N-substituted 1,4- and 1,2-dihydropyridines by very mild and selective reduction with amine borane for the first time.

The first successful example of catalytic nitrogen fixation using a rhenium-dinitrogen complex as a catalyst under mild reaction conditions is described in this paper. The dinitrogen-bridged dirhenium complex worked as an effective catalyst for the formation of ammonia and silylamine, where up to 8.4 equiv of ammonia and 11.7 equiv of silylamine were produced based on the Re atom of the catalyst.

Abstract

A series of rhenium complexes bearing a pyridine-based PNP-type pincer ligand are synthesized from rhenium phosphine complexes as precursors. A dinitrogen-bridged dirhenium complex bearing the PNP-type pincer ligands catalytically converts dinitrogen into ammonia during the reaction with KC₈ as a reductant and [HPCy₃]BAr^F ₄ (Cy=cyclohexyl, Ar^F=3,5-(CF₃)₂C₆H₃) as a proton source at −78 °C to afford 8.4 equiv of ammonia based on the rhenium atom of the catalyst. The rhenium-dinitrogen complex also catalyzes silylation of dinitrogen in the reaction with KC₈ as a reductant and Me₃SiCl as a silylating reagent under ambient reaction conditions to afford 11.7 equiv of tris(trimethylsilyl)amine based on the rhenium atom of the catalyst. These results demonstrate the first successful example of catalytic nitrogen fixation under mild reaction conditions using rhenium-dinitrogen complexes as catalysts.

Publication date: 13 May 2021

Source: Chem, Volume 7, Issue 5

Author(s): Yujie Wang, Mingyang Wang, Yibiao Li, Qiang Liu

Abstract

Herein, we report the manganese catalyzed coupling of alcohols with phosphorus ylides. The selectivity in the coupling of primary alcohols with phosphorus ylides to form carbon‐carbon single (C−C) and carbon‐carbon double (C=C) bonds can be controlled by the ligands. In the conversion of more challenging secondary alcohols with phosphorus ylides the selectivity towards the formation of C−C vs. C=C bonds can be controlled by the reaction conditions, namely the amount of base. The scope and limitations of the coupling reactions were thoroughly evaluated by the conversion of 21 alcohols and 15 ylides. Notably, compared to existing methods, which are based on precious metal complexes as catalysts, the present catalytic system is based on earth abundant manganese catalysts. The reaction can also be performed in a sequential one‐pot reaction generating the phosphorus ylide in situ followed manganese catalyzed C−C and C=C bond formation. Mechanistic studies suggest that the C−C bond was generated via a borrowing hydrogen pathway and the C=C bond formation followed an acceptorless dehydrogenative coupling pathway.

CO₂ fixation by halogen‐bonding catalysis: A halogen bond is introduced into the catalytic cycloaddition of CO₂ into epoxide (CCE) reactions. N‐iodopyridinium halide salts are used as cationic halogen‐bond donor catalyst to activate the epoxides under ambient pressure to produce quantitative yields. This methodology could be a supplementary approach to classical hydrogen bonds to promote CCE reactions.

Abstract

Halogen bonding, parallel to hydrogen bonding, was introduced into the catalytic cycloaddition of carbon dioxide into epoxide (CCE) reactions. A series of halogen‐bond donor (XBD) catalysts of N‐iodopyridinium halide featured with N−I bond were synthesized and evaluated in CCE reactions. The optimal XBD catalyst, 4‐(dimethylamino)‐N‐iodopyridinium bromide ([DMAPI]Br), under screened conditions at 100 °C, ambient pressure, and 1 mol % catalyst loading, realized 93 % conversion of styrene oxide into cyclic carbonate in 6 h. The substrate scope was successfully extended with excellent yields (mostly ≥93 %) and quantitative selectivity (more than 99 %). ¹H NMR spectroscopy of the catalyst [DMAPI]Br on substrate epoxide certified that the N−I bond directly coordinated with the epoxide oxygen. A plausible mechanism of halogen‐bonding catalysis was proposed, in which the DMAPI cation functioned as halogen‐bond donor to activate the epoxide, and the counter anion bromide attacked the methylene carbon to initiate the ring‐opening of the epoxide. CCE reactions promoted by N‐iodopyridinium halide, exemplify a first case of halogen‐bonding catalysis in epoxide activation and CO₂ transformation.

Abstract

Nitroarenes are stable, low‐cost, and readily available starting materials. The directly utilize nitroarenes in synthetically valuable C−N bond formation is of great significance, because the pre‐reduction step to corresponding amines can be avoided. Previously, phosphines and carbon monoxide (CO) are the most widely used reductants in the reductive cyclization or/and carbonylation of nitroarenes. Currently, much attention has been attracted to organosilanes as new potential reducing agents, not only because they are inexpensive, easy‐to‐handle, and mild reagents, but also various novel reaction models of nitroarenes have been explored. In this review, we mainly summarize the recent progress on the reductive coupling of nitroarenes by using organosilanes as the end reductants. We hope that a deep understanding of the reaction model and underlying working mechanism can provide a timely guideline for researchers who are interested in this fantastic area, leading to further exploration of practical and efficient reductive coupling of nitroarenes for C−N bond formation and N‐heterocycle synthesis.

Synlett
DOI: 10.1055/s-0040-1707263

A highly efficient nucleophilic addition–O-acylation–intramolecular Wittig reaction of β-trifluoromethyl α,β-enones is disclosed. This strategy features mild reaction conditions and provides a practical transition-metal-free method to a set of biologically significant trifluoromethylated furans in high yields with diverse functional groups.
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

Article in Thieme eJournals:
Table of contents  |  Abstract  |  Full text

A highly active bifunctional organoboron catalyst with the advantages of scalable preparation, thermostability, and recyclability was reported for the cyclization of CO₂ and epoxides. An intramolecular cooperative mechanism was substantiated by investigations into the crystal structure of the catalysts, structure– performance relationships, kinetic studies, and the key reaction intermediates.

Abstract

A series of highly active organoboron catalysts for the coupling of CO₂ and epoxides with the advantages of scalable preparation, thermostability, and recyclability is reported. The metal‐free catalysts show high reactivity towards a wide scope of cyclic carbonates (14 examples) and can withstand a high temperature up to 150 °C. Compared with the current metal‐free catalytic systems that use mol % catalyst loading, the catalytic capacity of the catalyst described herein can be enhanced by three orders of magnitude (epoxide/cat.=200 000/1, mole ratio) in the presence of a cocatalyst. This feature greatly narrows the gap between metal‐free catalysts and state‐of‐the‐art metallic systems. An intramolecular cooperative mechanism is proposed and certified on the basis of investigations on crystal structures, structure–performance relationships, kinetic studies, and key reaction intermediates.

Publication date: Available online 31 August 2020

Source: Chem

Author(s): Heidar Darmandeh, Viktoria H. Gessner

Nature, Published online: 03 August 2020; doi:10.1038/d41586-020-02275-8

Resins to be cheerful: A series of heterogeneous bifunctional catalysts, based on a thiourea and quaternary ammonium salt system, is prepared by using a convenient and low‐cost method involving a thiol‐ene click reaction under ultraviolet light. Owing to synergistic interactions of the electrophilic center and the nucleophilic site, the catalysts exhibit excellent selectivity for the cycloaddition of carbon dioxide with a diverse range of epoxides under mild conditions.

Abstract

The development of solvent‐free, metal‐free, recyclable organic catalysts is required for the current chemical fixation of carbon dioxide converted into cyclic carbonates. With the goal of reducing the cost, time, and energy consumption for the coupling reaction of CO₂ and epoxides, a series of highly active heterogeneous catalysts, based on a thiourea and quaternary ammonium salt system, are synthesized by using a thiol‐ene click reaction under ultraviolet light. Benefitting from synergistic interactions of the electrophilic center (thiourea) and the nucleophilic site (ammonium bromide), the catalysts exhibit excellent catalytic selectivity (99 %) for the cycloaddition of carbon dioxide with a diverse range of epoxides under mild conditions (1.2 MPa, 100 °C). Moreover, the catalyst can be easily recycled by facile filtration and reused for 5 times without noticeable loss of activity and selectivity. This work provides a potential heterogeneous catalyst for the conversion of carbon dioxide into high value‐added chemicals with the combined advantages of low cost, easy recovery, and satisfactory catalytic properties.