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Creators/Authors contains: "Duan, Shengzu"

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  1. α-Branched amines are fundamental building blocks in a variety of natural products and pharmaceuticals. Herein is reported a unique cascade reaction that enables the preparation of α-branched amines bearing aryl or alkyl groups at the β- or γ-positions. The cascade is initiated by reduction of redox active esters to alkyl radicals. The resulting alkyl radicals are trapped by styrene derivatives, leading to benzylic radicals. The persistent 2-azaallyl radicals and benzylic radicals are proposed to undergo a radical–radical coupling leading to functionalized amine products. Evidence is provided that the role of the nickel catalyst is to promote formation of the alkyl radical from the redox active ester and not promote the C–C bond formation. The synthetic method introduced herein tolerates a variety of imines and redox active esters, allowing for efficient construction of amine building blocks. 
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  2. Abstract Allylation of nucleophiles with highly reactive electrophiles like allyl halides can be conducted without metal catalysts. Less reactive electrophiles, such as allyl esters and carbonates, usually require a transition metal catalyst to facilitate the allylation. Herein, we report a unique transition-metal-free allylation strategy with allyl ether electrophiles. Reaction of a host of allyl ethers with 2-azaallyl anions delivers valuable homoallylic amine derivatives (up to 92%), which are significant in the pharmaceutical industry. Interestingly, no deprotonative isomerization or cyclization of the products were observed. The potential synthetic utility and ease of operation is demonstrated by a gram scale telescoped preparation of a homoallylic amine. In addition, mechanistic studies provide insight into these C(sp 3 )–C(sp 3 ) bond-forming reactions. 
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  3. null (Ed.)
    A unique enantioselective nickel-catalyzed vinylation of 2-azaallyl anions is advanced for the first time. This method affords diverse vinyl aryl methyl amines with high enantioselectivities, which are frequently occurring scaffolds in natural products and medications. This C–H functionalization method can also be extended to the synthesis of enantioenriched 1,3-diamine derivatives by employing suitably elaborated vinyl bromides. Key to the success of this process is the identification of a Ni/chiraphos catalyst system and a less reducing 2-azaallyl anion, all of which favor an anionic vinylation route over a background radical reaction. A telescoped gram scale synthesis and a product derivatization study confirmed the scalability and synthetic potential of this method. 
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  4. Abstract

    α‐Amino nitriles are versatile structural motifs in a variety of biologically active compounds and pharmaceuticals and they serve as valuable building blocks in synthesis. The preparation of α‐ and β‐functionalized α‐amino nitriles from readily available scaffolds, however, remains challenging. Herein is reported a novel dual catalytic photoredox/copper‐catalyzed chemo‐ and regioselective radical carbocyanation of 2‐azadienes to access functionalized α‐amino nitriles by using redox‐active esters (RAEs) and trimethylsilyl cyanide. This cascade process employs a broad scope of RAEs and provides the corresponding α‐amino nitrile building blocks in 50–95 % yields (51 examples, regioselectivity >95 : 5). The products were transformed into prized α‐amino nitriles and α‐amino acids. Mechanistic studies suggest a radical cascade coupling process.

     
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  5. Abstract

    α‐Amino nitriles are versatile structural motifs in a variety of biologically active compounds and pharmaceuticals and they serve as valuable building blocks in synthesis. The preparation of α‐ and β‐functionalized α‐amino nitriles from readily available scaffolds, however, remains challenging. Herein is reported a novel dual catalytic photoredox/copper‐catalyzed chemo‐ and regioselective radical carbocyanation of 2‐azadienes to access functionalized α‐amino nitriles by using redox‐active esters (RAEs) and trimethylsilyl cyanide. This cascade process employs a broad scope of RAEs and provides the corresponding α‐amino nitrile building blocks in 50–95 % yields (51 examples, regioselectivity >95 : 5). The products were transformed into prized α‐amino nitriles and α‐amino acids. Mechanistic studies suggest a radical cascade coupling process.

     
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  6. Abstract

    Benzofused lactams, especially indolin‐2‐one and dihydroquinolin‐2‐one are popular structural motives in durgs and natural products. Herein, we developed a room temperature and robust synthesis of benzofused lactams through cobalt(III)‐catalyzed C(sp2)−H amidation. In this protocol, in‐situ formation of Cp*Co(III)(ligand) catalyst from Cp*Co(CO)I2and ligand simplify the synthetic effort of cobalt complexes. Simple and readily synthesized 1,4,2‐dioxazol‐5‐ones underwent room temperature intramolecular C−H amidation and afforded a wide variety of functionalized benzofused lactams in up to 86% yield. The scalability of the reaction is also be demonstrated.

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  7. Abstract

    A general and versatile alkenylation protocol for the synthesis of vinyl‐azaarylmethylamines has been developed. Enabled by a palladium/NIXANTPHOS catalyst, this protocol provides efficient access to a large variety ofN‐heterocycles bearing allylic amines in up to 98% yield. A wide variety of azaarylmethylamines bearing 2‐pyridylmethyl, 4‐pyridylmethyl, 2‐(aminomethyl)quinoline aryl motifs and diverse 5 to 7 membered cyclic amines were well tolerated. A gram scale reaction was also used to demonstrate the scalability. This method can be readily adopted by medicinal chemists to prepare valuable scaffolds that were previously difficult to access.

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