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1. Copper( i )-catalyzed highly enantioselective [3 + 3]-cycloaddition of γ-alkyl enoldiazoacetates with nitrones

   https://doi.org/10.1039/D0QO00539H  

   Dong, Kuiyong; Xu, Xinfang; Doyle, Michael P. (June 2020, Organic Chemistry Frontiers)

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   Chiral copper( i ) catalysts are preferred over chiral dirhodium( ii ) catalysts for [3 + 3]-cycloaddition reactions of γ-alkyl-substituted enoldiazoacetates compounds with nitrones. Using the In-SaBox ligand these reactions effectively produce cis -3,6-dihydro-1,2-oxazine derivatives under mild conditions in high yield and with exceptional stereocontrol, and enantioselectivity increases with the size of the γ-substituent. Mechanistic studies show that cycloaddition occurs solely through the formation of ( Z )-γ-substituted metallo-enolcarbene intermediates that are catalytically gennerated from both ( Z )- and ( E )-γ-substituted enoldiazoactates via donor–acceptor cyclopropene intermediates. 

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2. Converting Strain Release into Aromaticity Loss for Activation of Donor–Acceptor Cyclopropanes: Generation of Quinone Methide Traps for C-Nucleophiles

   https://doi.org/10.1021/acs.orglett.4c03106  

   Shorokhov, Vitaly V; Chabuka, Beauty K; Tikhonov, Timur P; Filippova, Anastasia V; Zhokhov, Sergey S; Tafeenko, Victor A; Andreev, Ivan A; Ratmanova, Nina K; Uchuskin, Maxim G; Trushkov, Igor V; et al (September 2024, Organic Letters)

   Here, we present a new approach for the activation of donor–acceptor cyclopropanes in ring-opening reactions, which does not require the use of a Lewis or Brønsted acid as a catalyst. Donor–acceptor cyclopropanes containing a phenolic group as the donor undergo deprotonation and isomerization to form the corresponding quinone methides. This innovative strategy was applied to achieve (4 + 1)-annulation of cyclopropanes with sulfur ylides, affording functionalized dihydrobenzofurans. Additionally, the generated ortho- and para-(aza)quinone methides can be trapped by various CH-acids. 

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3. Catalytic asymmetric cycloaddition reactions of enoldiazo compounds

   https://doi.org/10.1039/C9OB00478E  

   Marichev, Kostiantyn O.; Doyle, Michael P. (April 2019, Organic & Biomolecular Chemistry)

   This review describes catalytic asymmetric cycloaddition reactions of silyl-protected enoldiazo compounds for the construction of highly functionalized carbo- and heterocycles which possess one or more chiral center(s). The enoldiazo compound or its derivative, donor–acceptor cyclopropene, form electrophilic vinylogous metal carbene intermediates that combine stepwise with nucleophilic dipolar reactants to form products from [3 + 1]-, [3 + 2]-, [3 + 3]-, [3 + 4]-, and [3 + 5]-cycloaddition, generally in high yield and with exceptional stereocontrol and regioselectivity. 

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4. Photo-cycloaddition reactions of vinyldiazo compounds

   https://doi.org/10.1038/s41467-024-48274-5  

   Bao, Ming; Łuczak, Klaudia; Chaładaj, Wojciech; Baird, Marriah; Gryko, Dorota; Doyle, Michael_P (May 2024, Nature Communications)

   Abstract Heterocyclic rings are important structural scaffolds encountered in both natural and synthetic compounds, and their biological activity often depends on these motifs. They are predominantly accessible via cycloaddition reactions, realized by either thermal, photochemical, or catalytic means. Various starting materials are utilized for this purpose, and, among them, diazo compounds are often encountered, especially vinyldiazo compounds that give access to donor-acceptor cyclopropenes which engage in [2+n] cycloaddition reactions. Herein, we describe the development of photochemical processes that produce diverse heterocyclic scaffolds from multisubstituted oximidovinyldiazo compounds. High chemoselectivity, good functional group tolerance, and excellent scalability characterize this methodology, thus predisposing it for broader applications. Experimental and computational studies reveal that under light irradiation these diazo reagents selectively transform into cyclopropenes which engage in cycloaddition reactions with various dipoles, while under thermal conditions the formation of pyrazole from vinyldiazo compounds is favored. 

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5. Asymmetric reactions induced by electron spin polarization

   https://doi.org/10.1039/d0cp03129a  

   Bloom, B. P.; Lu, Y.; Metzger, Tzuriel; Yochelis, Shira; Paltiel, Yossi; Fontanesi, Claudio; Mishra, Suryakant; Tassinari, Francesco; Naaman, Ron; Waldeck, D. H. (January 2020, Physical Chemistry Chemical Physics)

   Essential aspects of the chiral induced spin selectivity (CISS) effect and their implications for spin-controlled chemistry and asymmetric electrochemical reactions are described. The generation of oxygen through electrolysis is discussed as an example in which chirality-based spin-filtering and spin selection rules can be used to improve the reaction's efficiency and selectivity. Next the discussion shifts to illustrate how the spin selectivity of chiral molecules (CISS properties) allows one to use the electron spin as a chiral bias for inducing asymmetric reactions and promoting enantiospecific processes. Two enantioselective electrochemical reactions that have used polarized electron spins as a chiral reagent are described; enantioselective electroreduction to resolve an enantiomer from a racemic mixture and an oxidative electropolymerization to generate a chiral polymer from achiral monomers. A complementary approach that has used spin-polarized, but otherwise achiral, molecular films to enantiospecifically associate with one enantiomer from a racemic mixture is also discussed. Each of these reaction types use magnetized films to generate the spin polarized electrons and the enantiospecificity can be selected by choice of the magnetization direction, North pole versus South pole. Possible paths for future research in this area and its compatibility with existing methods based on chiral electrodes are discussed. 

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