Patent GB-816819-A (GB)
Title: A process for the preparation of ª‡,ª‰-unsaturated aldehydes
IPC: C07C47/20
Filed: 1958-04-01
Abstract: The invention comprises a process for the preparation of alpha, beta-unsaturated aldehydes by treating a 1,1-disubstituted propyn-(2)-yl-(1) ester with an acidic agent in the presence of a metal or metal compound of Group Ib of the Periodic System and hydrolysing the product.  Suitable starting materials are those of general formula <FORM:0816819/IV (b)/1> where R1 is acyl, and R2 and R3 each stand for a saturated or unsaturated aliphatic, alicyclic, or aromatic group, or, together a polymethylene bridge, and may contain one or more oxygencontaining radicals, e.g. hydroxyl, ester, carboxyl, ether, carbonyl or enol radicals, as substituents.  Amongst the many starting materials specified are esters of the following acetylenic carbinols, 3-phenyl-butyn-(1)-ol-(3); 3 - methyl - penten - (4) - yn - (1) - ol - (3); 5 - [21,61,61 - trimethyl - cyclohexen - (11) - yl] - 3 - methyl - pentyn - (1) - ol - (3); 3 - methyl - 3,4 - dihydroxy - butyne - (1), 3 - methyl - 5 - ethoxycarbonyl - pentyn - (1) - ol - (3); 5 - [21,61,61 - trimethyl - 41 - oxo - cyclohexen - (21) - yl] - 3 - methyl - pentyn - (1) - ol - (3); and 17-ethynyl testosterone.  Esters specified are the formates, acetates, thioacetates and benzoates.  The esters may be prepared in the same reaction vessel as used to carry out the process of the invention. The first step of the process of the invention is carried out in the presence of copper, silver or gold compounds, e.g. the acetates, carbonates, oxalates, nitrates and sulphates of copper and of silver or mixtures thereof.  If copper is used, it may be added as such, e.g. in a finely-divided form, or on a carrier, so that the copper salts are formed during the course of the reaction.  The catalysts may also be employed in the form of their oxides, or in combination with another metal, e.g. copper-chromium oxide.  The acidic media may be provided by, e.g., acetic, propionic, butyric, sulphuric or phosphoric acids. When strong mineral acids are used an inert solvent such as benzene, toluene, carbon tetrachloride, ethyl acetate or acetone may also be present.  The starting materials of propynyl esters may be used in an emulsion or suspension and the treatment in acidic medium conducted in the liquid or vapour phase.  During the first step of the process one or more of the following types of compounds may be formed <FORM:0816819/IV (b)/2> where R20 is a bivalent group obtained by eliminating one hydrogen atom from R2. The hydrolysis of the product so formed may be carried out in alkaline or in acidic medium, preferably under mild conditions such as heating with soda in, e.g., aqueous methanol, treating with alcoholic potassium hydroxide at low temperature, heating with dilute acetic acid or treating with dilute sulphuric acid in acetone at ordinary temperatures.  If the acidic medium used in the first stage contains water, the second stage of the reaction occurs immediately after the first one.  Preferred embodiments of the invention are (1) heating the 1,1-disubstituted-propyn-(2)-yl-(1) acetate with anhydrous acetic acid in the presence of silver carbonate and isolating and hydrolysing the product so formed by heating with soda in aqueous methanol; (2) heating the 1,1-disubstituted propyn-(2)-yl-(1) acetate in aqueous acetic acid.  The aldehydes produced may be isolated by known methods, e.g. by formation of their bisulphite addition products.  Examples are given of the preparation of 2-methyl-buten-(2)-al-(1); cyclohexylidene acetaldehyde, cyclopentylidene acetaldehyde; citral; e -methyl citral, 3-methyl-7-phenyl - heptadien - (2,6) - al - (1); 3,7,11 - trimethyl - dodecyn - (2) - al - (1); 3,7,11 - trimethyl-dodecatrien-(2,6,10)-al-(1); 3,7,11,15-tetramethyl - hexadecen - (2) - al - (1); 3,7 - dimethyl - 8 - methoxy - octadien - (2,6) al - (1), the cyclohexyl ester of 4-methyl-hexen-(4)-al-(6) carboxylic acid, (2,6,6 - trimethyl - cyclohexylidene) - acetaldehyde, 3b  - acetoxy - pregnadien - (5,17,20) - al - (21), and of the following intermediates, 2 - methyl - buten - (2) - al - (1), 3 - methyl - 1,1 - diacetoxy - butene - (2), 2 - [cyclohexen - (11) - yl] - vinyl - (1) acetate, 3,7 - dimethyl - 1 - acetoxy - octatriene - (1,2,6), 3,7 - dimethyl - 1,1 - diacetoxy - octadiene - (2,6), and 1 - (21,61,61 - trimethyl - cyclohexylidene) - 2-acetoxy ethylene.