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Cobalt‐Catalyzed Annulation of Salicylaldehydes and Alkynes to Form Chromones and 4‐Chromanones
Authors:Dr Junfeng Yang  Prof Naohiko Yoshikai
Institution:Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, Singapore
Abstract:A unique cobalt(I)–diphosphine catalytic system has been identified for the coupling of salicylaldehyde (SA) and an internal alkyne affording a dehydrogenative annulation product (chromone) or a reductive annulation product (4‐chromanone) depending on the alkyne substituents. Distinct from related rhodium(I)‐ and rhodium(III)‐catalyzed reactions of SA and alkynes, these annulation reactions feature aldehyde C?H oxidative addition of SA and subsequent hydrometalation of the C=O bond of another SA molecule as common key steps. The reductive annulation to 4‐chromanones also involves the action of Zn as a stoichiometric reductant. In addition to these mechanistic features, the CoI catalysis described herein is complementary to the RhI‐ and RhIII‐catalyzed reactions of SA and internal alkynes, particularly in the context of chromone synthesis.
Keywords:aldehydes  alkynes  C-H functionalization  cobalt  heterocycles
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