- Electrophilic tetraalkylammonium nitrate nitration. II. Improved anhydrous aromatic and heteroaromatic mononitration with tetramethylammonium nitrate and triflic anhydride, including selected microwave examples
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A new one-pot nitration employing tetramethylammonium nitrate and trifluoromethanesulfonic anhydride in dichloromethane to provide a ready source of the nitronium triflate nitrating agent is presented. Rapid and selective nitration with a variety of aromatic and heteroaromatic substrates is achieved resulting in the synthesis of several novel organic compounds. A distinct advantage is the removal of undesired byproducts by aqueous workup. This very mild nitration permits large-scale syntheses and gives high isolated product yields that often require no further purification. This tetramethylammonium nitrate-based nitration also has been applied to microwave-assisted conditions, and the results with several compounds are outlined.
- Shackelford, Scott A.,Anderson, Mark B.,Christie, Lance C.,Goetzen, Thomas,Guzman, Mark C.,Hananel, Martha A.,Kornreich, Wayne D.,Li, Haitao,Pathak, Ved P.,Rabinovich, Alex K.,Rajapakse, Ranjan J.,Truesdale, Larry K.,Tsank, Stella M.,Vazir, Haresh N.
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p. 267 - 275
(2007/10/03)
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- Factors controlling the Selectivity of ipso-Attack in Homolytic Aromatic Substitutions. Reactions of Alkyl Radicals with Nitrothiophen Derivatives
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The reactions of the nearly electroneutral methyl and of the nucleophilic 1-adamantyl radical with some selected nitrothiophen derivatives have been investigated in order to elucidate the factors which control the positional selectivity of radical addition to an aromatic substrate.With 5-nitro-2-X-thiophens (II), (V), and (VI) and 3,5-dinitro-2-methoxycarbonylthiophen (III) the adamantyl radical gave exclusively the products of ipso-attack, whereas the methyl radical selectively added at the unsubstituted 4-position.On the other hand, with 4-nitro-2-methoxycarbonylthiophen (I) both radicals added at the 5-position and with 4,5-dinitro-2-methoxycarbonylthiophen (IV) both radicals gave the products of ipso-substitution by displacing the nitro-group from the 5-position.These changes in positional selectivity are explained by assuming that the nature of the transition state of the addition step changes as a function of the polar character of the radical and of the electron deficiency of the aromatic substrates.
- Cogolli, Pietro,Maiolo, Filippo,Testaferri, Lorenzo,Tiecco, Marcello,Tingoli, Marco
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p. 1331 - 1335
(2007/10/02)
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