GB802567A - Novel polyene aldehydes and a process for the manufacture thereof - Google Patents

Abstract

6-Substituted-4-methyl-hexadien (2,4)-al-(1)s in which the 6-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)yl radical which contains an oxo or hydroxy or esterified hydroxy group in the 41-position, are prepared. The process comprises acetalizing a 4-substituted-2-methyl-buten-(2)-al-(1) of general formula <FORM:0802567/IV (b)/1> condensing the resulting 1-acetal with a vinyl ether in the presence of an acidic condensing agent, and hydrolysing and eliminating the elements of an alcohol from the 2,3-position of the resulting 6-substituted-4-methyl-hexen (4)-ether-(3)acetal-(1) by treatment with an acid, the 4- and 6-substituents being as defined above. 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. 4-[21,61,61-trimethyl cyclohexylidene] - 2 - methyl - buten (2) - acetal - (1)s, 4[21,61,61 - trimethyl - cyclohex - en - (11)-yl] - 2 - methyl - buten - (2) - acetal - (1)s, 4[21,61,61 - trimethyl - cyclohexen - (21) - ylidene] - 2 - methyl - buten - (2) - acetal - (1)s containing an oxo, hydroxy or esterified hydroxy group in 41-position, are then condensed with a vinyl ether in the presence of e.g. boron trifluoride etherate, zinc chloride, ferric chloride, or tin tetrachloride. Suitable vinyl ethers are e.g. methyl vinyl ether, ethyl vinyl ether, butyl vinyl ether. The condensation is carried out between 0 DEG and 50 DEG C. with preferably approximately molar proportions of the reactants. The 3-ether-1-acetals, viz. 6[2,61,61-trimethyl cyclohexen-(11)-yl]-4-methyl 3-alkoxy-hexene-(4)-acetal-(1)s, and the corresponding cyclohexylidene, and cyclohexen-(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, oxalic acid, sulphuric acid, phosphoric acid, zinc chloride or sodium hydrogen sulphate, and also with the addition of an antioxidant, e.g. hydroquinone and in the absence of oxygen. A solvent, e.g. dioxan, tetrahydro furan 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. 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 some of the starting materials: (a) 4,[21,61,61-trimethyl - 41 - oxo - cyclohexylidene] - 2 - methylbuten - (2) - al - (1) by ketalizing 2,6,6 - trimethyl - cyclohexanedione - (1,4) with ethylene glycol in the presence of p-toluene sulphonic acid and reacting the resulting monoketal with the lithium derivative of 3-methyl-3-hydroxy-4-methyl-butine-(1) (prepared by adding the corresponding methoxy compound to lithium amide), partially hydrogenating the resulting compound, and then heating with formic acid and finally treating with acetic acid and sodium acetate; (b) 4-[21,61,61-trimethyl-41-hydroxy cyclohexylidene] - 2 - methyl - buten - (2) - al-(1); (c) 4-[21,61,61 - trimethyl - 41 - acetoxy cyclohexylidene] - 2 - methyl - buten - (2) - al-(1); (d) 4-[21,61, 61-trimethyl-41-hydroxy-cyclohexen - (11) - yl] - 2 - methyl - buten - (2) - al-(1); (e) 4-[21,61, 61-trimethyl-41-acetoxy-cyclohexen - (11) - yl] - 2 - methyl - buten - (2) - al - (1); (f) 4-[21,61, 61-trimethyl-41-oxo-cyclohexen-(21) - ylidene] - 2 - methyl - buten - (2) - al - (1); (g) 4 - [21,61,61 - trimethyl - 41 - hydroxy - cyclohexen - (21) - ylidene] - 2 - methyl - buten - (2)-al-(1); (h) 4[21,61, 61-trimethyl-41-acetoxy-cyclohexen - (21) - ylidene] - 2 - methyl - buten - (2)-al-(1). Examples are also given of the preparation of (I) 6-[21,61, 61-trimethyl-41-acetoxy-cyclohexylidene] - 4 - methyl - hexadiene - (2,4) - al - (1); (II) 6-[2,61,61-trimethyl-41-oxo-cyclohexylidene] - 4 - methyl - hexadien - (2,4) - al - (1); (III) 6 - [21,61,61 - trimethyl - 41 - oxo - cyclohexen - (21) - ylidine] - 4 - methyl - hexadien - (2,4)-al-(1); (IV) 6-[21,61,61-trimethyl-41-acetoxy - cyclohexen - (11) - yl] - 4 - methyl - hexadien - (1,4) - al - (1), and 6 - [21,61,61 - trimethyl - 41 - acetoxy - cyclohexen - (21) - ylidene] - 4 - methyl - hexadien - (2,4) - al - (1). Specification 802,136 is referred to.