Dialkoxy Derivatives of 1,3-Dihydroxy Compounds

The reactions in this group comprise ring substitution and dealkylation of benzenoid compounds and syntheses with 1,3-dimethoxy compounds in the bicyclic and polycyclic series. The monosubstitution of polyalkoxy benzenes is generally not facile. Monobromination of 1,3-dimethoxybenzene in carbon tetrachloride was effected at 30°C during 2 hours with N-bromosuccinimide in the presence of acidic silica gel (type microbead 3A) in 99% yield without formation of dibromo compounds (ref.141). The evolution of HBr is avoided. 

Mild monoformylation of 1,3-dimethoxybenzene took place in dichloromethane containing tris(phenylthio)methane by subsequent treatment over 1.5 hours at ambient temperature with dimethyl methylthiosulphonium fluoroborate and work-up by quenching with water to afford 2,4-dimethoxybenzaldehyde in 70% yield (ref. 142). 

3-Dimethoxybenzene, magnesium monoperoxyphthalate and iron(lll) meso-tetrakis-(2,3,5,6-tetrafluorophenyl)tetrasulphonatoporphyrin in the proportions (1 3 0.01) in acetonitrile/tartrate buffer (pH3) when kept at 20°C for 1 hour afforded 2-methoxybenzo-1,4-quinone in 95% yield (ref.143). 

In dealkylation experiments although removal of methyl groups can be achieved readily by reagents such as lithium iodide in hot collidine (ref. 144) milder conditions are frequently obligatory. 

The iso-pentenyidimethoxy compound shown by treatment in dimethylformamide with bromomagnesium ethyl mercaptide was converted in 53% yield to the natural resorcinolpolletochlorin2-(3-methylbut-3-enyl)-3-chloro-5-formyl-4-methylresorcinol (ref. 145). 

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