New Reactions of Thallium Compounds: A Simple Synthesis of 4- and 7-Substituted Indoles Bearing a Nitro or an Azido Group

Abstract

New reactions far converting thallium compounds to nitro and azido compounds are elaborated.Applying these reactions.4-nitroindole-3-carboxaldehyde and 1-acetyl-2.3-dihydro-7-nitroindoleare now readily available in one pot reaction from indole-3-carboxaldehyde and 1-acetyl-2.3-dihydroindole.respectively.4-Azidoindole-3-carboxaldehyde and 1-acetyl-7-azido-2,3dihydroindole are similarly produced.Preparation of methyl 4nitroindole-3-ca~boxylate is also reported.Recently, indoles bearing nitrogen containing functional group, such as 4-nitro-, 2-5 4-amin0-,~'~ and 4-a~idoindoles,~ have been much interested because they are suitable building blocks for biologically interesting teleocidines7 and 4-azidoindole-3acetic acid,6d which is a plant growth regulator and an important tool for the study of active site of auxin.6dVarious reactions have been developed for the syntheses of 4-amino-and 4-nitroindole derivatives and they are classified into three categories: direct nitration method of indoles,' construction method of indoles from an appropriately substituted benzene d e r i ~a t i v e s , ~-~ and ring transformation method.5However, these reactions are still not satisfactory due to the lack of regioselectivity and low overall yield.Thus far we have engaged in the regioselective syntheses of 4-4r8 and 7-substituted indoles,' and developed a three step synthetic method of 4-nitroind0le~'~ (7-1 in 67% overall yield from 2.6-dinitratoluene (6).In this report, we describe a new " convenient two step or one pot synthesis of 4-nitro-(3) and 4-azidoindole-3-car-boxaldehyde (13).Syntheses of 7-11itro-'~ (12).7-azido-1-acetyl-2,3-dihydroindole .-. ,(5), and methyl 4-nitroindole-3-carboxylate (8) are also reported.--