61844-15-3Relevant academic research and scientific papers
Electrophilic Substitution in Indoles. Part 15. The Reaction between Methylenedi-indoles and p-Nitrobenzenediazonium Fluoroborate.
Jackson, Anthony H.,Prasitpan, Noojaree,Shannon, Patrick V. R.,Tinker, Alan C.
, p. 2543 - 2552 (2007/10/02)
p-Nitrobenzenediazonium fluoroborate (2 mol equiv.) reacts under aqueous conditions with 3,3'-methylenedi-indole (9a) and N,N-dimethyl-3,3'-methylenedi-indole (9c) to give, in each instance, high yields of the corresponding 3-p-nitrophenylazoindoles (13a) and (13c).When 1 mol equiv. of diazonium salt is used, the methylenedi-indole (9a) gives 1 mol equiv. of the 3-(p-nitrophenylazo)indole (13a) and some methylenedi-indole is recovered.In dry acetonitrile, 3,3'-methylenedi-indol gives, with 1 mol equiv. of diazonium salt, a mixture of 3-(p-nitrophenylazo)indole (13a) (0.45 mol equiv.) and the unstable 3-(p-nitrophenylazo)-2,3'-methylenedi-indole (16a) (0.42 mol equiv.).The latter was also synthesized from indole-2,3-dione and chloroacetylindole via indol-2-yl, indol-3-yl, and 2,3'-methylenedi-indole.Essentially similar results were obtained with N,N-dimethyl-3,3'-methylenedi-indole (9c) and the diazonium salt.The unsymmetrical compounds 3-indol-3-ylmethyl-1,2-dimethylindole (9d) and 3-indol-3-ylmethyl-2-methylindole (9e), with 2 mol equiv. of diazonium salt in aqueous solution, each give high yields of the two possible 3-p-nitrophenylazoindoles.With 1 mol equiv. of the diazonium salt only the 2-methyl-3-p-nitrophenylazo derivatives are obtained, together with 3,3'-methylenedi-indole.In dry acetonitrile, with either 1 or 2 mol equiv. of diazonium salt, the unsymmetrical methylenedi-indoles each give only the 2-methyl-3-p-nitrophenylazoindoles.The displacement of an indolylmethyl residue from methylenedi-indoles by the diazonium salt, and the formation of the azo coupled rearrangement product (16a) provides firm evidence that azo coupling of 3-alkylindoles to give the 2,3-disubstituted indoles proceeds by initial attack at the 3-position followed by rearrangement, rather than by direct substitution at the 2-position.
Electrophilic Substitution in Indoles. Part 14. Azo-coupling of Indoles with p-Nitrobenzenediazonium Fluoroborate
Jackson, Anthony H.,Lynch, Patrick P.
, p. 1483 - 1488 (2007/10/02)
Indole and its 1- and 2-methyl derivatives undergo second-order azo-coupling reactions with p-nitrobenzenediazonium tetrafluoroborate to afford the corresponding indole-3-azo-(4'-nitrobenzenes).Kinetic studies with related 3-deutrioindoles showed that there is no isotope effect, thus confirming that the initial attack of the electrophile is the rate-determining step, as in the majority of electrophilic aromatic substitutions.In contrast, 3-methylindole afforded 3-methylindole-2-azo-(4'-nitrobenzene) and the reaction not only showed a small deuterium isotope effect (ca. 2) but was also affected by case catalysis by water added to the acetonitrile.The difference in behaviour of the 3-methylindole from indole and its 1- and 2-methyl derivatives could be accounted for by a mechanism involving primary attack of the diazonium salt at the 3-position followed by rearrangement; further evidence for this mechanism was provided by the straight line plot obtained in comparisons of the rates of reactions for the four indoles with acidity functions (which reflect protonation at the 3-position).
