Augmented indoles

Issue ICHC-20 ARKIVOC 2006 (vii) 67-75 2.6. Formation of 5,7-dimethoxyindoles Finally, we present some examples of reactions involving 5,7-dimethoxyindoles. These examples use 5,7-dimethoxyindole and methyl 5,7-dimethoxyindole-2-carboxylate as the starting materials. 11-13 Their modified synthetic routes are straightforward and effective (Scheme 10). NO2 NO2 MeO CHO MeO MeO Cu(NO3)2 / Ac2O CH3NO2 / NH4OAc NO2 65% 81% MeO MeO MeO N H MeO Fe / HOAc 53% MeO CO2Me MeO MeO CHO MeO o-dichlorobenzene N3CH2CO2Et reflux CO2Me N3 N NaOMe/MeOH 87% H MeO MeO MeO 87% Scheme 10 2.7. Cyclisation between C3 and C4 on the indole ring Formylation of 5,7-dimethoxyindole gives a mixture of the 3- and 4-carbaldehydes, but ways have been found to achieve selective reaction.14 However, the 3,4-dicarbaldehyde can be formed easily using excess Vilsmeier reagent, and reacts readily with nitromethane or ammonia, to give augmented indoles with a fused benzene or pyridine ring respectively (Scheme 11).14 NO2 NO2 H H CHO CHO HO OH MeO MeO MeO CH3NO2 N KOH / MeOH N N H H MeO 63% MeO MeO H H N CHO H CHO N HO OH MeO NH3 MeO MeO N 100% N H N H MeO MeO MeO Scheme 11 ISSN 1424-6376 Page 73 ©ARKAT