Did you measure any analytical data to support your findings, such as melting point or mass spectrometrical information?
I have tried to synthesize DMT for the first time, following your route. The synthesis of indole-3-carboxyaldehyde via DMF/POCl3 was no problem, and MS indicated the aldehyde as only substance (minor indole impurity, less then 1%). However, once I subject the aldehyde to an aqueous MeNH2-catalyzed Henry reaction, I run into problems.
Dissolving indole-3-carboxaldehyde and MeNO2 in IPA gives a yellow solution; once I add MeNH2, the solution turns dark brownish/black. When I add an alkaline KBH4 solution, I notice yellow solids being formed. Drying the formed solids and subjecting them to GC/MS results in alot of crap. Alot of indole-3-carboxaldehyde, a major high MW impurity (M+ = 282) and also a substance with M+ = 156, which I tentatively identified as the condensation product of indole-3-carboxaldehyde and MeNH2. I'm pretty sure the high MW impurity is formed due to the presence of the aldehyde-MeNH2 condensation product.
But why is this? I don't think that I added to much MeNH2 (50 mmol indole-3-carboxaldehyde and 1.55 mL aq MeNH2 20%), and I allowed the reactions to proceed long enough. The aq MeNH2 was not freshly prepared, but it is properly stored so I don't see why that could form a problem. Any suggestions?