Bromination of 2,5-dimethoxybenzaldehyde in GAA gives 87% yield of the 4-bromo- and 5% of the 6-bromo isomer, the former of which is easily purified by recrystallization from ethanol:
Bromination of 2,5-Dimethoxybenzaldehyde
Org. Prep. Proc. Int. 23(4), 419-424 (1991) (https://www.thevespiary.org/rhodium/Rhodium/chemistry/bromodimethoxybenzaldehyde.html)
(https://www.thevespiary.org/rhodium/Rhodium/chemistry/bromodimethoxybenzaldehyde.html)
A cold solution of 20.0 g (0.12 mol) of 2,5-dimethoxybenzaldehyde in glacial acetic acid (115 mL) was treated with 20.0 g of bromine in glacial acetic acid (60 mL). The solution was stirred at room temperature for 2-3 days and diluted with ice water. The yellow precipitate was collected by filtration and dried (28 g, 95%), mp. 118-126°C (lit. mp 125-126°C). Recrystallization from ethanol gave 15.20 g of 2, mp 132-133°C (lit. mp 132-133°C). Ethanol was removed from the mother liquor in vacuo and the residue was subjected to column chromatography (silica gel, benzene). The solid (10.4 g) collected in initial fractions was 4-bromo-2,5-dimethoxybenzaldehyde (2), total yield 25.6g (87%), mp 132-133°C. Subsequent fractions gave 1.5g (5%) of 6-bromo-2,5-dimethoxybenzaldehyde (3), mp 102-103°C (EtOH).
Acid-catalyzed dehydration of a phenylpropanolamine does not stop at any 'aminopropene' stage, that intermediate immediately rearranges to the phenyl-2-propanone imine, which in the presence of water hydrolyzes to the free phenyl-2-propanone.
For details, see Phenyl-2-propanone from Ephedrine Derivatives (https://www.thevespiary.org/rhodium/Rhodium/chemistry/phenylacetone.html#ephedrine)
(https://www.thevespiary.org/rhodium/Rhodium/chemistry/phenylacetone.html#ephedrine).
As you can see, pretty vigorous reaction conditions are needed (the reaction also happens to a varying degree in the hydriodic acid reduction of (pseudo)ephedrine, lowering the yield of methamphetamine, and creating a veritable Zoo of byproducts from condensations of the formed P2P with both unreacted starting material and product, as well as with itself, forming various non-polar hydrocarbon dimers.
I would say that dehydration is more likely to occur with the nitro alcohol, forming the phenyl-2-nitropropene, which in turn reduces to unknown products.