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1. Electrocatalytic redox neutral [3 + 2] annulation of N -cyclopropylanilines and alkenes

   https://doi.org/10.1039/d0sc05665k  

   Wang, Qi; Wang, Qile; Zhang, Yuexiang; Mohamed, Yasmine M.; Pacheco, Carlos; Zheng, Nan; Zare, Richard N.; Chen, Hao (January 2021, Chemical Science)

   null (Ed.)

   Although synthetic organic electrochemistry (EC) has advanced significantly, net redox neutral electrosynthesis is quite rare. Two approaches have been employed to achieve this type of electrosynthesis. One relies on turnover of the product by the reactant in a chain mechanism. The other involves both oxidation on the anode and reduction on the cathode in which the radical cation or the radical anion of the product has to migrate between two electrodes. Herein, a home-built electrochemistry/mass spectrometry (EC/MS) platform was used to generate an N -cyclopropylaniline radical cation electrochemically and to monitor its reactivity toward alkenes by mass spectrometry (MS), which led to the discovery of a new redox neutral reaction of intermolecular [3 + 2] annulation of N -cyclopropylanilines and alkenes to provide an aniline-substituted 5-membered carbocycle via direct electrolysis (yield up to 81%). A chain mechanism, involving the regeneration of the substrate radical cation and the formation of the neutral product, is shown to be responsible for promoting such a redox neutral annulation reaction, as supported by experimental evidence of EC/MS. 

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2. Anion mediated, tunable isoguanosine self-assemblies: decoding the conformation influence and solvent effects

   https://doi.org/10.1039/d1sc00988e  

   Liu, Mengjia; He, Ying; Shan, Chuan; Wojtas, Lukasz; Ghiviriga, Ion; Fathalla, Omar; Yan, Yu; Li, Xiaopeng; Shi, Xiaodong (June 2021, Chemical Science)

   null (Ed.)

   Systematic investigations were performed with various substituted groups at C8 purine and ribose. A series of isoG analogs, C8-phenyl substituted isoG were synthesized and applied for Cs + coordination. The structural proximity between purine and ribose limited pentaplex formation for C8-phenyl substituted isoG derivatives. Based on this observation, deoxy isoG derivative with modification on ribose ( tert -butyldimethylsilyl ether) was applied to assemble with the Cs + cation. Critical solvent (CDCl 3 and CD 3 CN) and anion (BPh 4 − , BARF − , and PF 6 − ) effects were revealed, leading to the controllable formation of various stable isoG pentaplexes, including singly charged decamer, doubly charged decamer, and 15-mer, etc. Finally, the X-ray crystal structure of [isoG 20 Cs 3 ] 3+ (BARF − ) 3 was successfully obtained, which is the first example of multiple-layer deoxy isoG binding with the Cs + cation, providing solid evidence of this new isoG ionophore beyond two-layer sandwich self-assembly. 

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3. Formal oxo- and aza-[3 + 2] reactions of α-enaminones and quinones: a double divergent process and the roles of chiral phosphoric acid and molecular sieves

   https://doi.org/10.1039/d0sc02078h  

   Luo, Weiwei; Sun, Zhicheng; Fernando, E. H.; Nesterov, Vladimir N.; Cundari, Thomas R.; Wang, Hong (September 2020, Chemical Science)

   null (Ed.)

   A double divergent process has been developed for the reaction of α-enaminones with quinones through facile manipulation of catalyst and additive, leading to structurally completely different products. The two divergent processes, which involve formal aza- and oxo-[3 + 2] cycloaddition reactions, are mediated by chiral phosphoric acid and molecular sieves, respectively. While inclusion of phosphoric acid in the reaction switched the reaction pathway to favor the efficient formation of a wide range of N -substituted indoles, addition of 4 Å molecular sieves to the reaction switched the reaction pathway again, leading to enantioselective synthesis of 2,3-dihydrobenzofurans in excellent yields and enantioselectivities under mild conditions. Studies in this work suggest that the chiral phosphoric acid acts to lower the transition state energy and promote the formation of amide intermediate for the formal aza-[3 + 2] cycloaddition and the molecular sieves serve to facilitate proton transfer for oxo-[3 + 2] cycloaddition. The reactivity of α-enaminones is also disclosed in this work. 

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4. Synthesis of Heterocycles by HNTf2-Catalyzed C–H Functionalization of Vinyldiazo Compounds with 3-Phenyl-3-hydroxyisoindolinone

   https://doi.org/10.1055/a-2360-8359  

   Bao, Ming; Arman, Hadi; Doyle, Michael P (July 2024, Synthesis)

   Abstract A Brønsted acid catalyzed C–H functionalization of vinyldiazoacetates with 3-hydroxyisoindolinone is developed. This methodology provides a general access to E-substituted isoindolinone vinyldiazo compounds in good yields and excellent diastereoselectivities with broad substrate generality under mild conditions, and with 4-substituted 2-diazo-3-butenoates produces fused bicyclic pyrrolidines. The reaction generally involves addition of the N-acyl ketiminium electrophile, formed from the 3-hydroxyisoindolinone, to the vinylogous position of the vinyldiazo compound resulting in vinyldiazonium ion intermediates that undergo deprotonation to new vinyldiazo compounds or ring closure to fused bicyclic pyrrolidines. 

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5. Photochemical Decarbonylation of Oxetanone and Azetidinone: Spectroscopy, Computational Models, and Synthetic Applications**

   https://doi.org/10.1002/anie.202215856  

   Singh, Manvendra; Dhote, Pawan; Johnson, Daniel R.; Figueroa‐Lazú, Samuel; Elles, Christopher G.; Boskovic, Zarko (January 2023, Angewandte Chemie International Edition)

   Abstract Photoexcitation of cyclic ketones leads to the expulsion of carbon monoxide and a mixture of products derived from diradical intermediates. Here we show that synthetic utility of this process is improved if strained heterocyclic ketones are used. Photochemistry of 3‐oxetanone and N ‐Boc‐3‐azetidinone has not been previously described. Decarbonylation of these 4‐membered rings proceeds through a step‐wise Norrish type I cleavage of the C−C bond from the singlet excited state. Ylides derived from both compounds are high‐energy species that are kinetically stable long enough to undergo [3+2] cycloaddition with a variety of alkenes and produce substituted tetrahydrofurans and pyrrolidines. The reaction has a sufficiently wide scope to produce scaffolds that were either previously inaccessible or difficult to synthesize, thereby providing experimental access to new chemical space. 

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