grandpa>
In my post
Post 422844
(Bandil: "Verification of Bariums research", Methods Discourse), 2,5-dimethoxybenzaldehyde was used as the substrate. This is highly activate compared to 4-fluorobenzaldehyde, and gives much higher yields in the condensation reactions. That is most likely the reason that methylamine failed with 4-fluorobenzaldehyde.
Generally speaking its a good idea to use a N-alkylamine (-propyl or -butyl) in a small excess of GAA (compared to the catalst) for the condensation, if you are working with the not so activated substrates.
Kind regards
Bandil