Verfahren zur Herstellung von Pyridinderivaten

摘要

Compounds of formula (wherein R1 is an alkyl group and R2 and R3 each represent a hydroxyl group or together are an epoxy group or a methylenedioxy or substituted-methylenedioxy group of formula where R4 and R5 are hydrogen atoms or alkyl, alkenyl, phenylalkyl or phenyl groups or together are an alkylene group) are obtained by additively reacting an oxazole of formula (where R1 is as above and R6 is an alkyl group) with a compound of formula (where R20 and R30 together are an epoxide group or a methylenedioxy or substitutedmethylenedioxy group as above) to form a Diels-Alder type adduct of formula isolating the adduct and breaking the oxide bridge at the 2,5-position (with concomittant removal of the alkoxy group at the 5-position and aromatization) in a weakly acid medium at a temperature lower than that at which the addition reaction is effected and where a 4,5-di-(hydroxy-methyl) product is required, hydrolysing the product and, where an acid addition salt is required, reacting the resulting compound with an acid. In examples adducts are obtained by reacting 4-methyl-5-ethoxy-oxazole with 2 - isopropyl - 4,7 - dihydro - 1,3 - dioxepin, with 4,7-dihydro-1,3-dioxepin and with 2,5-dihydro-furan, the adducts are reacted with solutions of pyridoxin hydrochloride to break the oxide bridges and then hydrolysed with hydrochloric acid to obtain pyridoxin hydrochloride.