Patent GB-791202-A (GB)
Title: Polyene aldehydes and the manufacture thereof
IPC: C07C33/02
Filed: 1956-07-20
Abstract: 2,6 - Dimethyl - 2,5 - dihydroxy - octaen - (6)-in-(3)-al-(1) acetals where the 8-position is substituted by a 2,6,6-trimethyl hexenyl, a 2,6,6 trimethyl hexylidene, or a 2,6,6-trimethyl hexenylidene radical, are prepared by bilaterally condensing acetylene with a C14 aldehyde of general formula <FORM:0791202/IV (b)/1> (where R is a group mentioned above) and an acetal of pyruvic aldehyde in an organo metallic condensation.  The acetals of pyruvic aldehyde may be prepared by warming pyruvic aldehydes or glycols in an inert solvent in the presence of an acidic condensing agent under conditions which allow the water formed in the condensation to distil off.  The bilateral condensation of acetylene with a C14 aldehyde and an acetal of pyruvic aldehyde may be carried out by first reacting the C14 aldehyde in liquid ammonia with an alkali metal or alkaline earth metal acetylide and then condensing the reaction product, preferably after hydrolysis to the C1-(acetylenic carbinols), i.e. the corresponding 6 - R - 4 - methyl - hexen - 4 - in - (1) - ol - (3), in an organo metallic reaction with the acetal of pyruvic aldehyde. The reaction in liquid ammonia may be carried out at normal temperatures, e.g. 20 DEG  C. under elevated pressure or at the boiling point of the liquid ammonia under atmospheric pressure. Suitable acetylides are those of sodium, lithium or calcium. Preferably the reaction is carried out in the same reaction vessel and in the same liquid ammonia as used for the preparation of the particular acetylide used.  The C14 aldehyde may be added to the ammoniacal acetylide in the form of a solution in an inert organic solvent, e.g. diethyl ether.  The reaction product can be hydrolysed while in the liquid ammonia by adding an ammonium salt or it can be hydrolysed by distilling off the ammonia and adding an acid to the residue.  The resulting C16 (acetylenic carbinol) may then be condensed with two mols. of an alkyl magnesium halide or lithium phenyl, in an inert solvent, e.g. diethyl ether and the resulting organo-metallic compound reacted without isolation or purification with one mol. of the pyruvic aldehyde acetal.  The product is then hydrolysed, preferably without purification, e.g. by pouring into a mixture of ice and dilute sulphuric acid, and the C19 (dihydroxy acetal) obtained.  Alternatively the process may be carried out by first reacting the pyruvic aldehyde acetal in liquid ammonia with an alkali metal or an alkaline earth metal acetylide and then condensing the reaction product, preferably after hydrolysis to the corresponding 2-methyl-2-hydroxybutin-(3)-al-(1) acetal.  Suitable pyruvic aldehyde acetals are e.g. the dimethyl, diethyl, dibutyl or cyclic acetals (1,1-ethylenedioxy propanone (2)).  The C19 (dihydroxy acetals) so formed are converted into the corresponding C19 aldehydes, i.e. 8-R-2,6-dimethyl-octatrien-(2,4,6)-al-(1 by treating with lithium aluminium hydride, and then hydrolysing in an acid medium.  The lithium aluminium hydride is used in excess and the reaction preferably carried out in an inert solvent at room or elevated temperatures.  Suitable inert solvents are aliphatic or cyclic ethers or tertiary amines, e.g. diethyl ether, ethylene glycol dimethyl ether, dioxane, N, N-diethyl aniline or N-ethyl morpholine. Preferably the C19 (dihydroxy acetal is stirred in N,N-diethyl aniline with two to four mols. of lithium aluminium hydride at 60-120 DEG  C. in an atmosphere of nitrogen. The resulting C19 acetal, that is, the corresponding 8-R-2,6-dimethyl-octatrien (2,4,6)-al-(1) acetal is hydrolysed, e.g. by stirring in a water-miscible solvent in the presence of water with an acid such as sulphuric, acetic or p-toluene sulphonic acid at room or elevated temperature.  The resulting C19 aldehydes are used as intermediates for the synthesis of betacarotene or carotenoids.  Examples are given of the preparation of the C16 (acetylenic carbinols), C19 (dihydroxy acetals), C19 (acetals) and C19 aldehydes.