Issue in Honor of Prof. Alfred Hassner ARKIVOC 2001 (iv) 29-42
A novel synthesis of polysubstituted phenols using the SnAr reaction
of 2,5-dinitrofuran Albert Padwa* and Alex G. Waterson
Department of Chemistry, Emory University, Atlanta, GA 30322, USA E-mail:
[email protected]
Dedicated to Prof. Alfred Hassner on the occasion of his 70th birthday (received 06 Feb 01; accepted 15 Oct 01; published on the web 23 Oct 01)
Abstract
2,5-Dinitrofuran is readily available from 2-nitrofuran by treatment with concentrated nitric acid. The reaction of this compound with various nucleophilic reagents proceeds by an addition/elimination sequence (SNAr) to furnish substituted 5-nitrofurans in good yield. Diels— Alder cycloaddition of the resulting activated furans with various p-systems affords transient [4+2]-cycloadducts that undergo nitro group elimination and subsequent aromatization to produce polysubstituted phenols.
Keywords: SnAr, nitro, dinitro, furan, nucleophilic, substitution, Diels-Alder, phenol
Introduction
Nucleophilic substitutions using benzenoid aromatics have been proposed to proceed through an addition-elimination mechanism (SNAr). This proposal is consistent with the available kinetic data.1,2 Molecular orbital calculations have been performed on the suspected intermediate Meisenheimer complex,3 theories have been advanced to explain attack-site preferences,4 and some theoretical work using bond energies have been carried out.5 In contrast to this situation, nucleophilic aromatic substitution on the furan ring has been little studied. Monographs dealing with the chemistry of furans either ignore the subject entirely or sometimes present just a few
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