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Hazra S., Hirano K., Miura M.. Rhodium-Catalyzed C4-Selective C-H Alkenylation of 2-Pyridones by Traceless Directing Group Strategy. Organic Letters. 23(4), 1388-1393, (2021), 19 February 2021; © 2021 American Chemical Society. https://doi.org/10.1021/acs.orglett.1c00050., A rhodium-catalyzed C4-selective C-H alkenylation of 3-carboxy-2-pyridones with styrenes has been developed. The carboxylic group at the C3 position works as the traceless directing group, and the corresponding C4-alkenylated 2-pyridones are obtained exclusively with concomitant decarboxylation. Unlike the reported procedures, the exclusive C4 selectivity is uniformly observed even in the presence of potentially more reactive C-H bonds at the C5 and C6 positions. By using this strategy, the multiply substituted 2-pyridone can be prepared via sequential C-H functionalization reactions.

This is the accepted version of the following article:Hazra S., Hirano K., Miura M.. Solvent-Controlled Rhodium-Catalyzed C6-Selective C−H Alkenylation and Alkylation of 2-Pyridones with Acrylates. Asian Journal of Organic Chemistry 8, 1097 (2019), which has been published in final form at https://doi.org/10.1002/ajoc.201900190. This article may be used for non-commercialpurposes in accordance with the Wiley Self-ArchivingPolicy [https://authorservices.wiley.com/author-resources/Journal-Authors/licensing/self-archiving.html], A solvent-controlled rhodium-catalyzed C6-selective alkenylation and alkylation of 2-pyridones with acrylates via a pyridine-directed C−H cleavage was developed. Using DMF as solvent, the C−H alkenylation with acrylates selectively occurs to deliver the corresponding C6-alkenylated 2-pyridones in good yields. On the other hand, the C6-alkylated products are predominantly formed in a more polar and protic solvent, HFIP. Thus, a single set of starting substrates can be divergently transformed to C6-functionalized 2-pyridones, which are of potent interest in medicinal and pharmaceutical chemistry.

Hazra S., Hirano K., Miura M.. Pyridine-directed Rh-catalyzed C6-selective C–H acetoxylation of 2-pyridones. Heterocycles 101, 223 (2020); https://doi.org/10.3987/com-19-s(f)16., A Rh(III)-catalyzed C-H acetoxylation of 2-pyridones with phenyliodine(III) diacetate (PIDA) in a DCE/AcOH mixed solvent system has been developed using N-2-pyridyl function as directing group. The reaction occurs under mild conditions, typically in air at 40 oC, to selectively produce the corresponding C6-acetoxylated 2-pyridones in moderate to good yields.

Hazra S., Hoshimoto Y., Ogoshi S.. N-Phosphine Oxide-Substituted Imidazolylidenes (PoxIms): Multifunctional Multipurpose Carbenes. Chemistry - A European Journal 23, 15238 (2017); https://doi.org/10.1002/chem.201703644., This article discusses the concept of N-heterocyclic carbenes (NHCs) equipped with more than one functional moiety, which allows using these NHCs for multiple purposes. A pioneering example for such NHCs is N-phosphine oxide-substituted imidazolylidenes (PoxIms), and their synthesis and strategic use are highlighted. The utility of PoxIms by far exceeds the conventional use as multidentate ligands for metal complexes on account of the synergetic functions of the carbene and the N-phosphine oxide group(s).

Hoshimoto Y., Asada T., Hazra S., et al. Strategic Utilization of Multifunctional Carbene for Direct Synthesis of Carboxylic–Phosphinic Mixed Anhydride from CO2. Angewandte Chemie - International Edition 55, 16075 (2016); https://doi.org/10.1002/anie.201609710., Direct synthesis of carboxylic–phosphinic mixed anhydrides has been achieved by treating carbon dioxide with N-phosphine oxide-substituted imidazolylidenes (PoxIms) that contain both nucleophilic carbene and electrophilic phosphorus moieties. This novel mixed anhydride was efficiently derivatized into an ester, an amide, and an unsymmetrical ketone via transformation into its corresponding imidazolium salt followed by a dual substitution reaction. The presented work used well-designed multifunctional carbene reagents to establish a novel utility for carbon dioxide in organic synthesis.