Tetrahedron Vol. 50, No. 23, pp. 6727-6758, 1994 Copyright 0 1994 Elsevier Science Ltd F’rinted in Great Britain. All rights reserved 0040402Oi94 $7.00+0.00 Selective Nitration versus Oxidative Dealkylation of Hydroquinone Ethers with Nitrogen Dioxide zyxwvutsrqponmlkjihgfedc R. Rathore, E. Bosch and J.K. Kochi* Chemistry Department, University of Houston, Houston, TX 772044641. Absbact: Various alkyl-substituted p-dialkoxybenxenes(AM) react readily with nitrogendioxide (NO$ in dichlommethane solution via either nitration (ArNm or oxidative tkalkylation to quinones ((2). Spectral transients indicate thatthesecoupled pnxesses proceed fromthe dialkoxybenzene radical cation(ArEI+.) formed as the commonreactive intermedia& fromelectron-transfer in the disproportionated precursor [ArH. NO+]NO3-. In fast subsequent steps, ArH+. undergoes homolytic coupling with N@ (which leads to aromatic nitration) and nucleophilic attack of NO3- (which results in oxidative dealkylation). As such, the competition between nitration andoxidative deakylation is effectively modulated by solvent polarity andad&d nitrate. Introduction Aromatic nitration is conventionally carried out with nitric acid either alone or in combination with either Bmnsted or Lewis acids.1 Different types of aromatic compounds, including various anthracenes, naphthalenes, (poly)methylbenzenes, and alkoxybenxenes, also react readily with nitrogen dioxide (Noz) in nonpolar solvents such as chloroform, dichloromethane, nitromethane, etc.2 Aromatic nitration with this (gaseous) reagent under such aprotic conditions thus represents a potentially useful synthetic methodology, especially for acid-sensitive functionalities. However, the ambiguous behavior of some types of aromatic donors toward nitrogen dioxide is particularly intriguing, and we believe it could provide the key to our understanding of this simple, yet versatile reagent.3 For example, there is an early report 4 that p-dimethoxybenzene is quantitatively nitrated by nitrogen dioxide in carbon tetracbloride at 25 Oc. On the other hand, we recently showed5 that the tetramethyl analogue is oxidatively demethylated by nitrogen dioxide under essentially the same reaction conditions to form duroquinone, also in quantitative yield. In order to examine the dichotomy between aromatic nitration and quinone formation, we prepared three homologous series of dialkoxybenzene derivatives for study, viz. Ohle R,VLJG OMe A. I w R2 ’ R4 OMe I II where Rt. R2, R3 and Rq are either methyl or hydrogen and R and R’ and R” are hydrogen or alkyl groups. 6727