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By replacing an α-hydrogen with a halogen, acid-catalyzed α-halogenation of aldehydes or ketones yields a monohalogenated product
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Rh-Catalyzed aldehydic C-H alkynylation and annulation.

Maddali L N Rao1, Boddu S Ramakrishna

  • 1Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, UP, India. maddali@iitk.ac.in.

Organic & Biomolecular Chemistry
|February 1, 2020
PubMed
Summary

This study introduces a new Rhodium-catalyzed method for synthesizing chromones and aurones. The process efficiently creates these compounds from salicylaldehyde and alkynes via C-H bond alkynylation and annulation.

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Area of Science:

  • Organic Chemistry
  • Catalysis
  • Synthetic Methodology

Background:

  • Chromones and aurones are important heterocyclic compounds with diverse biological activities.
  • Efficient synthesis of these scaffolds remains a challenge in organic chemistry.
  • Rhodium-catalyzed reactions offer powerful tools for C-H functionalization and heterocycle synthesis.

Purpose of the Study:

  • To develop a novel Rhodium-catalyzed protocol for the in situ synthesis of chromones and aurones.
  • To achieve sequential aldehydic C-H bond alkynylation and annulation starting from salicylaldehyde.
  • To explore the scope and limitations of the developed methodology.

Main Methods:

  • The study employs a Rhodium catalyst for the sequential C-H alkynylation of salicylaldehyde.
  • In situ generation of 1-bromoalkynes from 1,1-dibromoalkenes is utilized.
  • Base-mediated cyclization of intermediate o-hydroxyynones leads to the formation of aurones.

Main Results:

  • A novel Rh-catalyzed protocol for the synthesis of chromones and aurones was successfully developed.
  • The reaction involves sequential C-H alkynylation of salicylaldehyde followed by annulation.
  • The method demonstrates good functional group tolerance with various aryl, alkenyl, alkyl, and heteroaryl-1,1-dibromoalkenes.
  • Steric and electronic effects were investigated during the base-mediated cyclization to aurones.

Conclusions:

  • A new and efficient Rh-catalyzed method for the in situ synthesis of chromones and aurones has been established.
  • The protocol is versatile, accommodating a wide range of substrates and functional groups.
  • This work provides a valuable synthetic route to important heterocyclic compounds.