| 摘要 |
The invention comprises di-esters of monoallyl acetone dicarboxylic acid, the free acid and its alkali-metal and alkaline-earth metal salts. The esters may be prepared by reacting a diester of acetone carboxylic acid with an allyl halide in the presence of an alkaline condensing agent and an inert organic solvent, under anhydrous conditions. Reaction may be effected at raised temperature and if desired under pressure. The esters used as reagents are preferably those having up to 5 carbon atoms, such as the methyl, ethyl and propyl esters, and the condensing agent is suitably an alkali metal alcoholate. When allyl chloride is used as reagent it is preferably present in excess. The resulting allyl acetone carboxylic acid esters may be saponified with an aqueous solution of a basic alkali metal or alkaline earth metal compound, e.g. sodium or lithium carbonate or an hydroxide of sodium, potassium, lithium or barium to give the corresponding salts of allyl-acetone dicarboxylic acid which may be isolated, e.g. by addition of a lower aliphatic alcohol. Aqueous solutions of the salts may be acidified to liberate the free acid which is then recoverable, e.g. by acetone extraction. Alternatively the aqueous solutions of the salts may be reacted with pyruvaldehyde at a pH from about 6.5 to 9.5 to form the corresponding salts of 1-allyl-2,5-diketo-4-hydroxyheptanoic acid which may be isolated by precipitation with a non-solvent, e.g. methanol or by drying the solution in the frozen state under vacuum. The free acid may be obtained by cooling an aqueous solution of the salt to near its freezing point, adding dilute acid with agitation and freeze drying the acidified solution. The free acid decarboxylates at room temperature to nona-8-ene - 2,5 - dione - 3 - ol, which may be cyclized with dilute alkali to allethrolone. The acyclic ketonic alcohol may be obtained direct by acidifying the aqueous solution of the metal salt of the heptanoic acid to a pH of about 1.0-2.5 with a mineral acid, followed by extraction with a water-immiscible solvent, preferably in the presence of a neutral water-soluble solvent. In examples: (1) allyl bromide is reacted with a methanolic solution of dimethyl acetone dicarboxylate and sodium methoxide under reflux and the resulting mono-allyl dimethyl acetone dicarboxylate is isolated; the ester is then saponified with aqueous KOH, the product neutralized with sulphuric acid, pyruvaldehyde is added, the pH adjusted to 7.5-8.0 and the mixture stirred at room temperature; the resulting aqueous solution of 1-allyl-2,5-diketo-4-hydroxy heptanoic acid sodium salt is acidified with HCl to pH 2 with evolution of CO2; the resulting nona-8-ene-2,5-dione-3-ol is isolated. (2) Allyl chloride (3 molar proportions) is reacted with dimethyl acetone dicarboxylate and sodium methoxide as in (1) to give dimethyl mono-allyl acetone dicarboxylate. |
