Abstract
A simple protocol yielding ortho-substituted nitrosophenols from phenols is demonstrated, in the form of copper(II) bis(nitrosophenolato) complexes. The developed methodology was applied to a range of substrates, confirming the role of the copper in both the formation and protection of the challenging 1, 2-substitution pattern. Using polymer supported thiourea, the Cu could be stripped from the complexes and thus enabled the isolation or identification of the uncoordinated ligands and their decomposition products, in yields generally low in line with the intrinsic high reactivity of 2-nitrosophenols. The product complexes are useful intermediates as demonstrated in revisiting a formal [4 + 2] cycloaddition with dimethylacetylene dicarboxylate to synthesise bicyclic products in variable yields, revealing the product has a novel structure different from those previously reported in the literature.
Highlights
Due to challenges in the synthesis and issues with stability including oxidation, dimerisation and condensation, ortho-substituted-nitrosophenol compounds are seldom reported in the literature [1]
Our specific contribution to the field starts with the synthesis and characterisation of a selection of copper complexes including isolating the free ligands from them, we address some confusion
After a series of basic scoping reactions, with the specific aim of creating simple and direct conditions for the formation of the copper-nitrosophenolato complexes and their isolation, we settled on the following protocol
Summary
Due to challenges in the synthesis and issues with stability including oxidation, dimerisation and condensation, ortho-substituted-nitrosophenol compounds are seldom reported in the literature [1]. While substrates with particular directing or blocking substituents can be used to force ortho- nitrosation to dominate, additional issues pertaining to the fact that 2-nitrosophenol compounds are generally unstable, and that highly functionalised substrates are often not reactive enough to undergo nitrosation [4], inhibit further investigation into this class of compounds. Metals such as copper can be used to lower the activation barrier of the nitrosation process via generation of a more powerful nitrosating agent, and act to protect the 2-nitrosophenol products from unwanted oxidation or decomposition pathways through complexation.
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