On that site there are several synthesis (wich does not work), my choice would be this:
A mixture of 2,5-dimetoxybenzaldehyde (5.10g, 30.7 mmol), silver nitrate (5.60g, 33 mmol), and iodine (8.10 g, 32 mmol) in 125
mL of methanol was stirred under nitrogen for seven hours. The yellow precipitate was filtered and
washed with methanol. The filtrate was treated dropwise with just enough saturated sodium bisulfite
solution to reduce the remaining iodine, and the solvent was removed on a rotary evaporator. The solid
was suspended with 50 mL of water, filtered, and recrystallized from 95% ethanol to yield 7.62g
(84.9%) of 4, mp 137-139°C, lit.3 mp 136-137°C.
And from this a normal amphetamine synthesis would be done, just insted benzaldehyde the 4-iodo-2,5-dimethoxy-benzaldehyde would be used. My only problem: the catalyst for the condensation of the aldehyde and the nitroethane buthylamine is used. This would react with the iodine on the phenyl ring, so I have to look for another catalyst.
Under the hydrogenation of the nitrostyrene what is the product of the condensation the iodine atom on the phenyl ring could be hydrogenated off. ArI + H2 = ArH + HI. So, this is also a little problem.
There is another recipe where the iodination is made on the 2,5 dimethoxy amphetamine. Here the yields are not so good, but in this case there will be no such problems, like "the iodine just disappeared from the aromatic ring".
To a solution of (R)-2,5-dimethoxyamphetamine (R)
(5.42 g, 0.028 mol) in EtOH (100 mL) was added
I2 (14.10 g, 0.066 mol) and Ag2SO4 (17.32 g, 0.066
mol) and the reaction mixture was allowed to stir
overnight. The precipitated yellow solid was collected
by filtration and the EtOH evaporated. The solid
residue was dissolved in CHCl3 and washed with
aqueous 5% NaOH (250 mL). The aqueous layer was
extracted with CHCl3 (2×300 mL) and the organic
layers were combined and washed with H2O. The
organic layer was then dried over Na2SO4, filtered,
and evaporated down to a purplish brown solid (8.45
g). Column chromatography (SiO2, 8% EtOH/CHCl3)
gave (4.31 g, 48% yield) as an off white solid.
Treatment of a CHCl3 solution of the previous compound
(6.29 g, 0.020 mol) with HCl/MeOH, followed by evaporation
of the solvent gave a solid that was recrystallized
using MeOH/Et2O. The white crystals were collected
and washed with Et2O giving R-5d hydrochloride
(5.50 g, 0.015 mol, 79% yield)
As everybody can se, the firsle obtained colored compound is just 50% pure. So this is a bit messy synthesis, but actually there is no better idea. But the yield is better than that one what is described in the PiHKAL
Just an idea, but I think, that a 4-halo-2,5-dimethoxy-amphetamine thead would be useful for the forum, what do you think?