3,4-Dihydroxy-6-fluoro-benzaldehyde synthesis

Yield:71144-36-0 96%

Reaction Conditions:

with boron tribromide in dichloromethane at -78 - 20; for 18 h;Inert atmosphere;

Steps:

2-Fluoro-4,5-bis(methoxymethoxy)benzaldehyde (3)

A 1 M solution of BBr3 in CH2Cl2 (45 mL) was added dropwise toa solution of 2-fluoro-4,5-bis(methoxy)benzaldehyde (3 g, 1.6?10-2 mol) in anhydrous CH2Cl2 (20 mL) cooled to -78 °C,then the reaction mixture was warmedup to 20 °C and stirredunder these conditions for 18 h.
Then, MeOH (20 mL) was added dropwise to the reaction mixture, a resulting solution was concentrated, the residue was diluted with MeOH (25 mL) and concentrated once more.
This procedure was repeated two times.
The product was purified by column chromatography on silica gel (11×3 cm) in the system CH2Cl2-AcOEt, 5 : 1 to obtain 2-fluoro-4,5-dihydroxybenzaldehyde (2.4 g, 96%) as a light yellow oil-very easy oxidizable in air.
To avoid losses, it was immediately used in the subsequent step without additional purification and crystallization, thus alternating procedure described in thework [35].
The oil obtained was dissolved in anhydrous acetonitrile (120 mL), followed by a sequential addition of MOMCl (1.2 mL, 1.28 g, 1.6?10-2 mol) and ButOK (1.8 g, 1.6?10-2 mol). The reaction mixture was stirred for 2 h at ~20 °C, then, MOMCl (1.2 mL, 1.28 g, 1.6?10-2 mol) and ButOK (1.8 g, 1.6?10-2 mol) were add and the stirring was continued for 16 h.
The reaction progress was monitored by TLC on silica gel in the the system hexane-ethyl acetate, 1 : 1, observing the disappearance of the spot of the starting compound with Rf 0.13 and the appearance of the spot of the product with Rf 0.54.
The intermediate monomethoxymethoxy product has Rf 0.20.
The product (3.5 g, 89%) was obtained as a colorless oil.

References:

Fedorova;Orlovskaya;Maleev;Belokon';Savel'Eva;Chang;Chen;Liu;Krasikova [Russian Chemical Bulletin,2014,vol. 63,# 5,p. 1169 - 1177][Izv. Akad. Nauk, Ser. Khim.,2014,# 5,p. 1169 - 1177,9]