Diethers From Dihalomethanes

Catechols likewise undergo 0-alkylation under phase transfer conditions, yielding methylenedioxy derivatives on reaction with methylene bromide [8]. This reaction constitutes a useful route to this commonly occurring oxygen heterocycle as well as providing a facile protection method for 1,2-dihydroxyarenes. Dibromo-methane rather than the more reactive diiodomethane was used in this reaction because the latter is a source of iodide ion which poisons the phase transfer catalyst by selectively ion-pairing with the quaternary ammonium cation. Phenoxide ion can apparently compete successfully with bromide but not iodide in the formation of an extractable ion pair under these conditions. 

It seems likely that dichloromethane could be used in this procedure instead of dibromomethane because after the first chlorine has been substituted, the second substitution should be extremely fast. Cyclization to form a five-membered ring is a favorable process and the alkylating reagent at this stage will be an alkoxymethyl halide. Substitution of the first chlorine in dichloromethane is not improbable, especially in light of the known reaction of both alkoxide and phenoxide anions with it under phase transfer conditions to yield symmetrical dialkyl or diaryl acetals of form- 

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