Yuya Hu

B,B bicycles: A series of C ₂‐symmetric spiro‐bicyclic bisboranes has been prepared. These bisboranes demonstrate highly effective and selective asymmetric hydrogenation of quinolines. The exceedingly broad functional‐group tolerance allows access to various enantioenriched and functionalized tetrahydroquinilines, which are inaccessible by previous methods using either borane or transition‐metal catalysts.

Abstract

A new series of spiro‐bicyclic bisborane catalysts has been prepared by means of hydroboration reactions of C ₂‐symmetric spiro‐bicyclic dienes with HB(C₆F₅)₂ and HB(p‐C₆F₄H)₂. When used for hydrogenation of quinolines, these catalysts give excellent yields and enantiomeric excesses, and show turnover numbers of up to 460. The most attractive feature of these metal‐free hydrogenation reactions was the broad functional‐group tolerance, making this method complementary to existing methods for quinoline hydrogenation.

What 50 principal investigators taught me about my failure to land tenure

What 50 principal investigators taught me about my failure to land tenure, Published online: 12 February 2019; doi:10.1038/d41586-019-00560-9

Mix and match: New protocols for controlled reduction of carboxamides to either alcohols or amines were established using a combination of sodium hydride (NaH) and zinc halides (ZnX₂). Use of a different halide on ZnX₂ dictates the selectivity, where the NaH‐ZnI₂ system delivers alcohols and NaH‐ZnCl₂ gives amines.

Abstract

New protocols for controlled reduction of carboxamides to either alcohols or amines were established using a combination of sodium hydride (NaH) and zinc halides (ZnX₂). Use of a different halide on ZnX₂ dictates the selectivity, wherein the NaH‐ZnI₂ system delivers alcohols and NaH‐ZnCl₂ gives amines. Extensive mechanistic studies by experimental and theoretical approaches imply that polymeric zinc hydride (ZnH₂)_∞ is responsible for alcohol formation, whereas dimeric zinc chloride hydride (H−Zn−Cl)₂ is the key species for the production of amines.

Synlett
DOI: 10.1055/s-0037-1612230

An efficient method has been developed for the 1,2-hydro(cyanomethylation) of alkenes, in which a cyanomethyl radical species is generated from a cyanomethylphosphonium ylide by irradiation with visible light in the presence of an iridium complex, a thiol, and ascorbic acid. The cyanomethyl radical species then adds across the C=C double bond of an alkene to form an elongated alkyl radical species that accepts a hydrogen atom from the thiol to produce an elongated aliphatic nitrile. The ascorbic acid acts as the reductant to complete the catalytic cycle.
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Georg Thieme Verlag Stuttgart · New York

Article in Thieme eJournals:
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Walk along! Sequential formation of distant bonds within a catalytic cycle was achieved for palladium‐catalyzed hydrosilylation/cyclization of various 1,n‐dienes by a nondissociative chain‐walking pathway. The reaction was applicable to various 1,n‐dienes, including a 1,13‐diene, to form a cyclopentane ring as well as a carbon–silicon bond at a remote site.

Abstract

Sequential formation of distant bonds in organic molecules was achieved for the palladium‐catalyzed hydrosilylation/cyclization of various 1,n‐dienes by chain walking of the metal catalyst. The reaction was applicable to various 1,n‐dienes, including a 1,13‐diene, to form a cyclopentane ring as well as a carbon–silicon bond at a remote site. The use of “nondissociative” chain walking provides a fascinating strategy in organic synthesis to functionalize distant parts of organic molecules, in a particular order, within a catalytic cycle by effectively moving the reactive center from a remote position.

Abstract

The synthesis of different metal pincer complexes coordinating to the chiral PNP ligand bis(2‐((2R,5R)‐2,5‐dimethyl‐phospholanoethyl))amine is described in detail. The characterized complexes with Mn, Fe, Re and Ru as metal centers showed good activities regarding the reduction of several prochiral ketones. Comparing these catalysts, the non‐noble metal complexes produced best selectivities not only for aromatic substrates, but also for different kinds of aliphatic ones leading to enantioselectivities up to 99% ee. Theoretical investigations elucidated the mechanism and rationalized the selectivity.

Strategic move: The phosphine‐catalyzed enantioselective (3+2) annulation reaction between allenes and isoindigos is introduced as a powerful strategy for the construction of structural motifs containing two vicinal quaternary stereogenic centers. The reactions feature high yields, enantioselectivities, and regioselectivities, and are highly useful for creating structurally challenging hexahydropyrroloindoles (HPIs).

Abstract

Construction of contiguous all‐carbon quaternary stereogenic centers is a long‐standing challenge in synthetic organic chemistry. In this report, a phosphine‐catalyzed enantioselective (3+2) annulation reaction between allenes and isoindigos, containing either two identical or different oxindole moieties, is introduced as a powerful strategy for the construction of spirocyclic bisindoline alkaloid core structures. The reported reactions feature high chemical yields, excellent enantioselectivities, and very good regioselectivities, and are highly useful for creating structurally challenging bisindoline natural products.

The first example of phosphine‐catalyzed asymmetric dearomative [3+2]‐cycloaddition of 3‐nitroindoles and 2‐nitrobenzofurans was realized, which provides a new, facile, and efficient protocol for the synthesis of chiral 2,3‐fused cyclopentannulated indolines and dihydrobenzofurans by reacting with allenoates and MBH carbonates, respectively.

Abstract

Over the past years, the metal‐catalyzed dearomative cycloaddition of 3‐nitroindoles and 2‐nitrobenzofurans have emerged as a powerful protocol to construct chiral fused heterocyclic rings. However, organocatalytic dearomative reaction of these two classes of heteroarenes has become a long‐standing challenging task. Herein, we report the first example of phosphine‐catalyzed asymmetric dearomative [3+2]‐cycloadditio of 3‐nitroindoles and 2‐nitrobenzofurans, which provide a new, facile, and efficient protocol for the synthesis of chiral 2,3‐fused cyclopentannulated indolines and dihydrobenzofurans by reacting with allenoates and MBH carbonates, respectively through a dearomative [3+2]‐cycloaddition.

Synlett
DOI: 10.1055/s-0037-1611717

The first copper-catalyzed aziridination of olefins using re­cyclable magnetic nanoparticles is described. Magnetic nanoparticles were modified with dopamine and used as a support to coordinate copper. The methodology was optimized with styrene as olefin and using [N-(p-toluenesulfonyl)imino]phenyliodinane (PhI=NTs) as nitrene source. A microwave irradiation decreased the reaction time by 4-fold compared to conventional heating method. The catalyst was recovered by simple magnetic extraction and could be reused successfully up to five times without significant loss of activity. The methodology was ­applied to a range of different olefins leading to moderate to excellent yields in the formation of the expected aziridine.
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© Georg Thieme Verlag Stuttgart · New York

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

Isomerizing olefin metathesis is currently undergoing a transformation from laboratory curiosity to powerful synthetic concept at the heart of orthogonal tandem catalysis. In this process, an isomerization catalyst continuously moves double bonds along carbon chains, while a metathesis catalyst scrambles the residues at the C–C double bonds. This cooperative action of two catalysts can be used to access single, defined products from a complex mixture of compounds. Alternatively, it enables the transformation of uniform starting materials into complex product blends with defined, tunable properties. This concept article highlights recent developments and potential applications of this fascinating reaction concept.

Abstract

In the presence of catalytic amounts of elemental sulfur, dibenzyl disulfide/DMSO was found to be an excellent thiobenzoylating agent of amines to provide a wide range of thioamides. The reaction becomes autocatalytic when anilines substituted by an o‐cyclizable group were used as nucleophile, leading to the corresponding 2‐aryl aza heterocycles.