Patent GB-775060-A (GB)
Title: Unsaturated compounds and the manufacture thereof
Filed: 1955-08-16
Abstract: The invention comprises 2-[21,61,61-trimethylcyclohexen - (11) - yl] - 1 - acyloxy - ethylenes, 4 - [21,61,61 - trimethyl - cyclohexen - (11) - yl] - 1 - acyloxy - 2 - methyl - butadiene - (1,3)s and [2,6,6 - trimethyl - cyclohexen - (1) - yl] - acetaldehyde, and the corresponding compounds having a double bond also in the 3,4-position.  It also comprises a process for the manufacture of the enol-esters specified and their conversion into unsaturated aldehydes by converting [2,6,6 - trimethyl - cyclohexylidene - (1)] - acetaldehyde or 4-[21,61,61-trimethyl-cyclohexylidene - (11)] - 2 - methyl - butene - (2) - al - (1) or the corresponding compounds having a double bond in the 2,3- or 21,31-position as the case may be (referred to respectively as iso-C11-aldehyde, iso - C14 - aldehyde, retrodehydro - C11 - aldehyde and retrodehydro-C14-aldehyde) in a manner known per se for the preparation of enol-esters from unsaturated aldehydes, and, if desired, hydrolysing the resulting enol-esters under mild conditions.  The enol-ester may be obtained by treating the specified aldehydes with an aliphatic carboxylic acid anhydride containing up to 4 carbon atoms in each of its acyl groups in the presence of an acidic agent such as p-toluene-sulphonic acid or zinc chloride or of an alkali or alkaline earth metal salt of the corresponding acid.  Alternatively the aldehyde is heated in the presence of an acid condensing agent with an enol-ester of a lower boiling ketone, e.g. isopropenyl acetate, while distilling off the ketone formed.  The hydrolysis may be effected with an alkali-metal or alkaline earth metal carbonate, bicarbonate or hydroxide in aqueous medium preferably also containing methanol, phenol or dioxane.  In examples: (1) iso-C11-aldehyde is heated with acetic anhydride to give 2-[21,61,61-trimethyl -(11)-yl]-1-acetoxy-ethylene which on hydrolysis with aqueous methanolic sodium bicarbonate gives b -C11-aldehyde; (2) retrodehydro-C11-aldehyde is converted to the enol-acetate, reaction of which with potassium hydroxide at 20 DEG to 25 DEG  C. gives b  - dehydro - C11 - aldehyde; (3) iso - C14 -aldehyde is converted to the enol-acetate by heating with isopropenyl acetate and p-toluene sulphonic acid and the product is hydrolysed to b -C14-aldehyde; (4) retrodehydro-C14-aldehyde is converted to the enol-acetate by reaction with isopropenyl acetate and the product on hydrolysis with aqueous methanolic bicarbonate to give b -dehydro-C14-aldehyde.  The aldehydes are characterized as their phenyl semicarbazones.  The iso-C11-aldehyde can be prepared by condensation of ethoxy-acetylene with 2,6,6-trimethyl-cyclohexanone-(1), hydrogenation of the acetylenic carbinol obtained to the olefinic compound and treatment of the latter with an acid. Retrodehydro-C11-aldehyde is similarly obtained, starting from 2,6,6-trimethyl-cyclohexen-(2)-one-(1).  These compounds by conversion to acetals by condensation with a propenyl ether and treatment with acid give the other two compounds employed as starting materials.  iso-C14-Aldehyde can also be obtained by the method described in Specification 719,450. Retrodehydro-C14-aldehyde can also be prepared by condensing b -ionone with ethyl chloroacetate, hydrolysing the resulting glycidic-ester with alkali, treating the 4-[21,61,61-trimethylcyclohexen - (11) - yl] - 2 - methyl - buten-(2)-al-(1) obtained with N-bromo-succinimide and splitting off hydrogen bromide from the resulting product.