Patent GB-920915-A (GB)
Title: Carotenoids and intermediates therefor
Inventor: WEEDON BASIL CHARLES LEICES TE
IPC: C07C403/00
Filed: 1958-03-27
Abstract: The invention comprises keto-alkylidene alkapolyenes of the general formula R7=R6=R8 in which R6 represents the acylic hydrocarbon residue of a conjugated polyenic monoor di-aldehyde or the corresponding radical in which ethylenic linkage is replaced by an acetylenic linkage, R7 is a group of the general formula <FORM:0920915/IV(a)/1> in which Q is a carbonyl group, a hydroxymethylene group, an acyloxymethylene group or a ketalised carbonyl group, R1 and R2 are alkyl groups, each of which contains 1-4 carbon atoms, R3 is an alkyl or a hydrogen atom and R4 is an alkyl group or a hydrogen atom; and R8 is a group of the general formula <FORM:0920915/IV(a)/2> (where R1, R2, R3 and R4 are as defined above), or an analogue thereof in which the keto group is replaced by a methylene group e.g. a 2,6,6-trimethylcyclohexenyl methine group or a group of the general formula XVIII.  The keto-alkylidene alkapolyenes in which Q represents a carbonyl group may be cyclized directly in the presence of an alkaline condensing agent to give carotenoids.  The compounds may be prepared by condensing a ketone of the general formula <FORM:0920915/IV(a)/3> with an aldehyde of the formula O=R6=O or O=R6=X1, (where Q1 is an acyloxymethylene, a hydroxymethylene or a ketalised carbonyl group and X1 is a group of the formula VI or an analogue thereof in which the keto group is replaced by a methylene group), the condensation being carried out in the presence of an alkaline agent such as alcoholic alkali.  For the production of a carotenoid by cyclization the group Q1 may be converted to a keto group by (1) where Q1 is a hydroxymethylene group, oxidation, (2) where Q1 is an acyloxymethylene group, hydrolysis followed by oxidation, (3) where Q1 is a ketalised carbonyl group, hydrolysis.  The keto-alkylidene alkapolyenes may also be prepared by condensing a polyunsaturated ketone of the formula Y=R6=Y1 Y=R6=Y1 VII where Y is a group of the general formula R1R2CH.CO.CR4= VIII and Y1 is a group of the general formula VI or an analogue thereof in which the keto group is replaced by a methylene group or a group of the general formula XVIII in which Q represents a carbonyl group or a group of the general formula VIII, with a vinyl ketone of the general formula R3CH2COCH=CH2 XIII in the presence of an alkaline condensation agent.  In this latter method the keto-alkylidene alkapolyene intermediate may be obtained in a transitory form and cyclized in situ to the carotenoid by the action of the alkaline condensation agent used in the condensation of the ketone VII with the vinyl ketone XIII.  The vinyl ketone XIII may be prepared in situ by the action of an alkali metal hydroxide or alkoxide on a quaternary ammonium compound of the formula R3CH2COCH2CH2(Z+A-) where Z+A- represents the quaternary ammonium residue.  In examples :- (1) crocetin dialdehyde is condensed with 3,3-dimethyl-6-ethylenedioxy-octanone-2 to give 3,30-bis (ethylenedioxy) - 6,6,10,14,19,23,27,27 - octamethyl - dotriacontanonaene - 8,10,12,14,16,18, 20,22,24-dione-7,26 which is hydrolysed to the 3,7,26,30-tetra-one and cyclized to canthaxanthin; (2) apo-carotinal is condensed with 3,3-dimethyl-6-ethylenedioxy-octanone-2 to give 3 - ethylenedioxy - 25 - (2,6,6-trimethyl-cyclohexen-1-yl)-6,6,10,14,19,23-hexamethyl - pentacosanonaene - 8,10,12,14,16,18,20,22,24 - one-7 which is hydrolysed to the 3,7-dione and cyclized to echinenone; (3)-(5) 2,9-dimethyldeca-2,4,6,8-tetraene-1,10-dial is condensed with 3,3-dimethyl-6-ethylenedioxy-octanone-2 to give 3,24-di(ethylenedioxy)-6,6,10,17,21,21-hexamethyl - hexacosa-8,10,12,14,16,18-hexaene-7,20-dione which is hydrolysed to the 3,7,20, 24-tetra-one and cyclized to give 1,12-di(3-keto - 2,6,6 - trimethyl-cyclohexen-1-yl)-3,10-dimethyl-dodeca-1,3,5,7,9, 11-hexaene; (6) 2,6, 10,15,19,23 - hexamethyl - tetracosa - 4,6,8,10, 12,14,16,18,20-nonaene-3,32-dione, (prepared by condensing crocetin dial with 3-methyl-butanone-2) is condensed with an ethyl vinyl ketone precursor in the presence of potassium ethoxide to give canthaxanthin directly; (7)-(11) echinenone, 15,151-dehydro-echinenone and 15,151-dehydro-canthaxanthin are similarly prepared; (12) 15,151-dehydro-echinenone is hydrogenated over a Lindler catalyst to give echinenone. 1-diethylamino-pentane-3-one is prepared by reacting propionyl chloride with ethylene to give 1-chloro-pentane-3-one and treating the chloroketone with diethylamine.  A general reference is made in the earlier Provisional Specification to keto-alkylidene alkapolyenes in which R7 represents the group XVIII in which the -(CH2)2- link is replaced by a -CH2- link and which, on cyclization, give carotenoids containing cyclopentenyl rings.  Specification 920,914 is referred to.