Formal Carbene Insertion into C−O or C−N Bond: An Efficient Strategy for the Synthesis of 2-Substituted 2<i>H</i>
-Chromene Derivatives from Chromene Acetals or Hemiaminal Ethers
作者:Dan Zhang、Wenhao Hu
DOI:10.1002/adsc.201800179
日期:2018.7.4
We report the palladium/Brønsted acid co‐catalyzed formal insertion of carbene into the C−O or C−N bond of 2H‐chromene acetals or hemiaminal ethers. This transformation was initiated by the Brønsted acid‐promoted cleavage of the C−O or C−N bond, followed by modification of the leaving alcohol or amino fragments with palladium carbenes, and reassembly of the modified fragments. A variety of C‐2 functionalized
2-Substituted chromenes were obtained via combination of ring-closing metathesis of allylic acetals to the corresponding cyclic acetals, followed by Lewis acid-mediated functionalization of the resulting stable 1-benzopyrylium ion with suitable nucleophiles. (C) 2000 Elsevier Science Ltd. All rights reserved.