GB802568A - Polyene aldehydes and a process for the manufacture thereof - Google Patents

Abstract

8 - Substituted - 2,6 - dimethyloctatrien - (2,4,6)-al-(1)s in which the 8-substituent (R) is a 21,61,61 - trimethyl - cyclohexylidene or a 21,61,61 - trimethyl - cyclohexen - (21) - ylidene, or a 21,61,61 - trimethyl - cyclohexen - (1) - y radical, which contains an oxo, hydroxy or esterified hydroxy group in the 41-position, are prepared. The process comprises acetalizing a 6 - substituted - 4 - methyl - hexadiene - (2,4)-al-(1) of general formula <FORM:0802568/IV (b)/1> condensing the resulting 1-acetal with a propenyl ether in the presence of an acidic condensing agent and treating the resulting 3-ether-1-acetal with an acid in order to hydrolyse the acetal group and split off the elements of an alcohol from 2,3-position. The acetalization step may be carried out using an aliphatic orthocarboxylic acid ester, e.g. methyl, ethyl or butyl esters of orthoformic acid, in the presence of an alcohol, boron trifluoride etherate, zinc chloride, phosphoric acid and/or p-toluene sulphonic acid and the starting material as defined. The resulting acetals, viz. 6[21,61,61 - trimethyl - cyclohexen - (11) - yl]-4 - methyl - hexadiene - (2,4) - acetal - (1)s, 6 - [21,61,61 - trimethyl - cyclohexylidene] - 4 - methyl - hexadiene - (2,4) - acetal - (1)s, 6 - [21,61,61 - trimethyl - cyclohexen - (21 - ylidene]-4 - methyl - hexadiene - (2,4) - acetal - (1)s containing an oxo, hydroxy, or esterified hydroxy group in 41-position are then condensed with a propenyl ether in the presence of e.g. boron trifluoride etherate, zinc chloride, titanium tetrachloride, aluminium chloride, ferric chloride or tin tetrachloride. Suitable propenyl ethers are methyl ether or butyl propenyl ethers. The reaction is preferably carried out between 0 DEG and 50 DEG C. with approximately molar proportions of the reactants. The 3-ether-1-acetals, viz. 8 - [21,61,61 - trimethyl cyclohexen - (11)-yl], 2 - 6 - dimethyl - 3 - alkoxy - octadiene - (4,6)-acetal-(1)s and the corresponding cyclohexylidene, and cyclohexyl-21-ylidene compounds containing an oxo, hydroxy, or esterified hydroxy group in 41-position, are then hydrolysed, preferably in the presence of e.g. p-toluene sulphonic acid, acetic acid, propionic acid, zinc chloride, or sodium hydrogen sulphate, and also with the addition of an anti-oxidant, e.g. hydroquinone, and in the absence of oxygen. A solvent, e.g. dioxan, tetrahydrofuran, or ethylene glycol dimethyl ether may also be present. The hydrolysis is preferably carried out by heating the 3-ether-1-acetals with acetic acid containing an alkali metal acetate, and a little water at about 100 DEG C. in a carbon dioxide atmosphere. The product may be purified by distillation or chromatographed on an aluminium oxide column. The temperature should be kept below 120 DEG C. throughout the process. Examples are given of the preparation of (1) 8-[21,61,61-trimethyl - 41 - acetoxy-cyclohexylidene] - 2,6 - dimethyl - octatrien - (2,4,6) - al - (1); (2) 8[21,61,61 - trimethyl - 41 - oxo - cyclohexylidene] - 2,6 - dimethyl - octatrien - (2,4,6) - al - (1); (3) 8 - [21,61,61 - trimethyl - 41 - oxo - cyclohexen - (21) - ylidene]-2,6 - dimethyl - octatrien - (2,4,6) - al - (1); (4) 8 - [21,61,61 - trimethyl - 41 - acetoxy - cyclohexen - (11) - yl] - 2,6 - dimethyl - octatrien - (2,4,6) - al - (1); (5) 8 - [21,61,61 - trimethyl - 41-acetoxy - cyclohexen - (21) - ylidene] - 2,6 - dimethyl - octatrien (2,4,6) - al - (1). Specification 802,567 is referred to.