1.4- Dichloro-2,5-dimethoxybenzene

Dichloro-2,5-dimethoxybenzene Dichlorophene 2,6-Dichloro-p-phenylenediamine Dicloran Dihydroxyacetone... 

Captan Copper oxide (ous) 1,4-Dichloro-2,5-dimethoxybenzene Drazoxolon Mancozeb Metam-sodium Methoxyethylmercury acetate Paraformaldehyde Prochloraz Propamocarb hydrochloride... 

Whilst the majority of chromone syntheses from phenols involve cyclization y to the heteroatom and are discussed later, there are some instances where ring closure occurs at the heteroatom. For instance, 1,3-dimethoxybenzene is acylated by 2,3,3-trichloropropenoyl chloride in the presence of aluminum chloride to give 2,3-dichloro-7-methoxychromone (64CB80). 

The following chemicals were obtained from Aldrich Chemical Company, Inc. and used without further purification 1,3-dimethoxybenzene (99%) butyl lithium (1.6 M in hexanes) 1-formylpiperdine (99%) boron trifiuoride-diethyl ether (purified, redistilled) 2,3-dichloro-5,6-dicyano-l,4-benzo-quinone (98%), and pyridine hydrochloride (98%). All solvents were reagent grade and were obtained from Fisher Scientific and used without further purification except where noted. Silica gel (230-400 mesh) was obtained from EM Scientific. Chloroform was stored over activated, 4-A molecular sieves for at least 24 h prior to use. Tetrahydrofuran (optima grade) was distilled from sodium benzophenone. Pyrrole (99%) was obtained from Aldrich Chemical Company, Inc. and distilled from calcium hydride. 

The solubility of the components in the solvent must be sufficient. To improve the solubility, cosolvents can be used. Another possibility is the application of a two-phase system or an emulsion in the presence of phase-transfer catalysts. A two-phase system also has advantages in product isolation and continuous electrolysis procedures. A typical example is the synthesis of p-methoxy benzonitrile by anodic substitution of one methoxy group in 1,4-dimethoxybenzene by the cyanide ion (Eq. 22.21). The homogeneous cyanation system (acetonitrile, tetraethylammonium cyanide) [24] can be efficiently replaced by a phase-transfer system (dichloro-methane, water, sodium cyanide, tetrabutylammonium hydrogen sulfate) [71]. 

A fungicidal active substance of this group, also having moderate systemic effect, is chloroneb, l,4-dichloro-2,5-dimethoxybenzene (14). It is synthesised by the chlorination of p-dimethoxybenzene (15) (Plazek, 1930 Alvarez, 1968). 

The dichloro compound 137 undergoes Friedel-Crafts alkylation with 1,4-dimethoxybenzene in the presence of a catalytic amount of SnCU, to give 88% of 142a (Equation 34) <1997JOC2234>. 

Dichloro-3,6-dihydroxy-2,5-cyclohexadiene-l,4-dione l,4-Dichloro-2,5-dimethoxybenzene 2,4 -Dichlorodiphenyl ketone Dichlorodiphenyltrichloroethane... 

Preparation by demethylation of 2,3 -dichloro-4,5-di-methoxybenzophenone (SM) with pyri-dinium chloride for 2 h at 180-200°. SM was obtained by reaction of m-chlorobenzoic acid with l-chloro-3,4-dimethoxybenzene in the presence of phosphorous pentoxide in methane-suUbnic acid for 30 min at 70° [1199]. 

---