On the reaction of 3-bromo-2-nitrobenzo[b]thiophene with some ortho-substituted anilines:: an analysis of the products of reaction and of their NMR and MS properties

The title reaction, carried out in DMF in the presence of triethylamine or potassium carbonate, has furnished the 'expected' 3-amino-2-nitrobenzo[b]thiophenes 2o together with the 'unexpected' 2-amino-3-nitrobenzo[b]thiophenes 3o, thus recalling the situation observed with other weak nucleophiles in the presence of non-nucleophilic bases. The effects (electronic as well as steric) of the ortho-substituent (OH, NH2, OMe, Me, Et, F, Cl and Br) on the course of the reaction have been investigated, determining their influence on yields and product ratios (2o/3o). An analysis of C-13 NMR and MS spectra of 2o and 3o has been carried out. Ab initio computations on 2of, 2oi, 3of and 3oi at DFT level have furnished informations on their geometry and stability in the gas phase, thus allowing to assign a role to their stability on the course of the reaction as well as on some EI-MS results. (C) 2003 Elsevier Ltd. All rights reserved.