Department of Chemistry, Occidental College, 1600 Campus Road M-5, Los Angeles, California 90041, United States.
J Org Chem. 2022 Mar 4;87(5):3498-3510. doi: 10.1021/acs.joc.1c03055. Epub 2022 Feb 8.
Photoredox catalysis has become a powerful method to generate free radical intermediates in organic synthesis. This report describes the use of photoredox catalysis to directly oxidize common nucleophilic anions to access electrophilic 1,3-dicarbonyl and amidyl radical intermediates. First, conjugate bases of 1,3-dicarbonyls were oxidized to neutral radical species for intramolecular hydro- and dialkylation of alkenes. This overall redox-neutral process provided cyclopentanone products in excellent yields (up to 96%). The scope included a variety of styrene radical acceptors and products with newly formed vicinal quaternary carbons. This process was then extended to the synthesis of pyrrolidinones by alkene amidoalkylation that proceeded via -aryl amidyl radical intermediates in good yield (up to 85%). These reactions were characterized by their mild conditions, high atom economy, and the absence of stoichiometric byproducts. Mechanistic and computational studies supported a stepwise proton-coupled electron transfer mechanism, where an "electron borrowing" photocatalyst oxidizes an anion and reduces a benzylic radical after bond formation.
光氧化还原催化已成为有机合成中生成自由基中间体的一种有力方法。本报告描述了用光氧化还原催化直接氧化常见亲核阴离子，以获得亲电的 1,3-二羰基和酰胺基自由基中间体。首先，1,3-二羰基的共轭碱被氧化为中性自由基物种，用于烯烃的分子内氢烷基化和二烷基化。这个整体氧化还原中性过程以优异的收率（高达 96%）提供了环戊酮产物。该范围包括各种苯乙烯自由基受体和具有新形成的偕季碳原子的产物。该过程随后通过烯键酰胺烷基化扩展到吡咯烷酮的合成，通过 -芳基酰胺基自由基中间体以良好的收率（高达 85%）进行。这些反应的特点是条件温和、原子经济性高且没有化学计量的副产物。机理和计算研究支持逐步质子耦合电子转移机理，其中“电子借贷”光催化剂氧化阴离子并在键形成后还原苄基自由基。
