Is it possible to use TMP (trimethyl phosphate) for a two step methylation (to substitute two hydroxyl-groups with two methoxy-groups)? I thought about a methylation of 5-hydroxyvannilin to 3,4,5-trimethoxybenzaldehyde (TMBA). US Pat 4,453,004 describes a way to methylate syringaldehyde to TMBA, but I couldn't find anything about the direct way 5-OH-vanillin --> TMBA.
I think, it would be a good choice to run it analogue to US Pat 3,855,306 (3,4,5-trimethoxybenzaldehyde from 5-hydroxyvanillin), just with TMP instead of the DMS (acetone as solvent). What do you think?