5 years ago

Synthesis of ortho-Azophenols by Formal Dehydrogenative Coupling of Phenols and Hydrazines or Hydrazides

Synthesis of ortho-Azophenols by Formal Dehydrogenative Coupling of Phenols and Hydrazines or Hydrazides
Kenneth Virgel N. Esguerra, Jean-Philip Lumb
Azophenols are important chromophores and reagents in organic synthesis, with applications as pigments and molecular switches. Here, we describe a catalytic aerobic process that couples phenols and hydrazines or hydrazides for their synthesis. The key aromatic C−N bond is formed by condensation between the hydrazine or hydrazide and an ortho-quinone, which triggers a redox-isomerization to install the azo-functionality. Notable features include rapid access to highly functionalized azophenols with a range of electronic configurations, including “push–pull” systems, conditions that employ simple, unactivated substrates, occurrence at room temperature using an earth-abundant and commercially available copper catalyst, and production of water as the only stoichiometric byproduct. A bio-inspired coupling of phenols and hydrazines or hydrazides that draws inspiration from melanogenesis and collagen biosynthesis is developed for the mild and efficient synthesis of ortho-azo phenols. The method hinges on the catalytic aerobic dearomatization of phenols to ortho-quinones, which are versatile coupling partners for C−N bond formation.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/chem.201701226

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