Precursor: 2,5-Dimethoxy-4-ethylbenzaldehyde

[Rhodium]

2,5-Dimethoxy-4-ethylbenzaldehyde

2,5-Dimethoxyethylbenzene (66.4 g, 0.4 mol) was dissolved in 250 ml of dry CH₂Cl₂ and cooled to 10°C and 208 g (0.8 mol) of anhydrous SnCl₄ was added. Cl₂CHOCH₃ (45.9 g, 0.4 mol) was then added over 40 min, maintaining the temperature at 5-10°C. The solution was allowed to warm to room temperature over 45 min, heated under reflux for 1 hr, cooled, and poured over 500 g of ice-H₂O. The aqueous layer was discarded. The CH₂Cl₂ layer was washed with 3 N HCl and H₂O and dried (Na₂SO₄). After removal of the solvent the residue was triturated with saturated NaHSO₃ solution. The addition product was dissolved in H₂O; the aqueous solution was washed with Et₂O and then decomposed with Na2CO2 solution. On cooling, the aldehyde solidified, was collected by filtration, and recrystallized from MeOH-H₂O: yield 42g (54%); mp 46-47°C.

1-(2,5-Dimethoxy-4-ethylphenyl)-2-nitropropene

This nitrostyrene was prepared by condensation of the above aldehyde with EtNO₂ in AcOH containing NH₄OAc. The yellow product was recrystallized from MeOH: yield 60.8%; mp 63-64°C.

1-(2,5-Dimethoxy-4-ethylphenyl)-2-propanone

This substituted phenylacetone was prepared by Fe-HCl reduction of the above nitro compound: yield 60%; by 131-132°C (0.1mm); oxime, mp 79.5-80.5°C

[terbium]

Cl2CHOCH3 (45.9 g, 0.4 mol) was then added
This is not a typo? This is not supposed to be bis(chloromethyl)ether e.g. (CH₂Cl)₂O  ?

[Rhodium]

Definitely not, the sought after compound is dichloromethyl methyl ether, which together with a mild Lewis acid is a common way of introducing a formyl function to an aromatic ring, especially moderately activated ones.

It is a simple friedel-crafts alkylation (using a masked formyl equivalent), the intermediate product being Ph-CHCl-OMe, which upon aqueous hydrolysis splits off HCl and MeOH, giving PhCHO (benzaldehyde).