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  • Title: Synthesis of Cyclobutane-Fused Tetracyclic Scaffolds via Visible-Light Photocatalysis for Building Molecular Complexity.
    Author: Oderinde MS, Mao E, Ramirez A, Pawluczyk J, Jorge C, Cornelius LAM, Kempson J, Vetrichelvan M, Pitchai M, Gupta A, Gupta AK, Meanwell NA, Mathur A, Dhar TGM.
    Journal: J Am Chem Soc; 2020 Feb 12; 142(6):3094-3103. PubMed ID: 31927959.
    Abstract:
    We describe the synthesis through visible-light photocatalysis of novel functionalized tetracyclic scaffolds that incorporate a fused azabicyclo[3.2.0]heptan-2-one motif, which are structurally interesting cores with potential in natural product synthesis and drug discovery. The synthetic approach involves an intramolecular [2 + 2] cycloaddition with concomitant dearomatization of the heterocycle via an energy transfer process promoted by an iridium-based photosensitizer, to build a complex molecular architecture with at least three stereogenic centers from relatively simple, achiral precursors. These fused azabicyclo[3.2.0]heptan-2-one-based tetracycles were obtained in high yield (generally >99%) and with excellent diastereoselectivity (>99:1). The late-stage derivatization of a bromine-substituted, tetracyclic indoline derivative with alkyl groups, employing a mild Negishi C-C bond forming protocol as a means of increasing structural diversity, provides additional modularity that will enable the delivery of valuable building blocks for medicinal chemistry. Density functional theory calculations were used to compute the T1-S0 free energy gap of the olefin-tethered precursors and also to predict their reactivities based on triplet state energy transfer and transition state energy feasibility.
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