GB598080A - Process for the preparation of halogenated pyran compounds - Google Patents

Abstract

Compounds of the general formula <FORM:0598080/IV/1> wherein X represents chlorine or bromine and R is an aliphatic group, and substitution derivatives thereof, are prepared by reacting 2 : 3-dihydropyran, or substitution derivatives thereof, with bromine or chlorine or a compound which will yield halogen under the conditions of the reaction, e.g. tertiary butyl hypochlorite or bromonitromethane, and a monohydroxy compound of the general formula ROH, where R has the above significance, or the corresponding metal alcoholate in which case it is preferred to conduct the reaction in the presence of a solvent. The reaction is preferably conducted in substantially anhydrous conditions, in the presence of a sufficient quantity of a basic substance to neutralize hydrogen halide formed and the temperature maintained below 100 DEG C. An organic solvent which is substantially inert to the action of chlorine and/or bromine and a pressure greater than atmospheric may be employed. In examples: (1) 2-methoxy-3-chlorotetrahydropyran is prepared by reacting 2 : 3-dihydropyran, chlorine and methanol in the presence of calcium carbonate at a temperature below 10 DEG C.; (2) similarly 5-chlor-2 : 3-dihydropyran is reacted in the presence of sodium carbonate to yield 2 - methoxy - 3 : 3 - dichlortetrahydropyran; (3) 2-methoxy-3-brom-3-carbmethoxytetrahydropyran is prepared by reacting methyl-2 : 3-dihydro-5-pyroate, bromine and methanol in the presence of calcium carbonate. 5-Methyl-2-methoxy-3-chlortetrahydropyran may also be prepared from 3-methyl-2 : 3-dihydropyran and methanol.