| 摘要 |
<p>Pyridine compounds of the formula <FORM:1034483/C2/1> wherein the symbols R1 and R2 collectively designate an oxygen atom or together represent a grouping of the formula <FORM:1034483/C2/2> wherein each of R3 and R4 represent a hydrogen atom or an alkyl, aryl or acyl group or R3 and R4 together represent an alkylene group, are produced (a) by heating 4-methyl-oxazole with a dienophile of the formula <FORM:1034483/C2/3> in the presence of a dehydrogenating agent or (b) by heating 4-methyl-oxazole with a dienophile of said formula and treating the product thus obtained with a dehydrogenating agent. The preparations are preferably effected under pressure, at 150 DEG to 200 DEG C. in the presence of an antioxidant or in the atmosphere of an inert gas. Solvents, e.g. acetic acid, propionic acid, methanol, dioxane, triethylamine and N,N-dimethyl-formamide, may be employed or the reactions may be effected with excess dienophile as solvent. Specified dehydrogenation agents are nitro-benzene and halogenated and/or alkylated derivatives thereof; nitro-anilines and other specified nitro-aromatics; halogenated ketones; certain salts; quinonoid compounds and palladium/charcoal in pseudocumene. Pyridoxin and acid addition salts thereof may be prepared by acid hydrolysis of the pyridine compound products of the invention, with or without isolation of said products, and, where required, transformation of the hydrolysis product into an acid-addition salt.</p> |
