1,199,012. Polyene compounds. F. HOFFMANN-LA ROCHE & CO. A.G., and B. C. L. WEEDON. 14 Feb., 1968 [14 Feb., 1967], No. 7094/67. Heading C2C. The invention comprises aldehydes of the general formula in which RSP1/SP is oxo, C 1 -C 7 alkylenedioxy or dialkoxy and RSP3/SP represents CHO. They may be prepared by reducing an acetylenic compound of formula in which RSP2/SP is a protecting group and RSP4/SP is C 1 -C 7 alkylenedioxy or dialkoxy, with an alkali metal (e.g. Li) aluminium hydride to yield an olefinic compound of formula removing the protecting groups RSP2/SP and RSP4/SP by acid hydrolysis, reintroducing the RSP4/SP group, if desired, and oxidizing the alcohol product, e.g. with manganese dioxide or chromic acid, to the desired aldehyde. Suitable protecting groups RSP2/SP are those of formula in which RSP5/SP is a C 1 -C 7 group and RSP6/SP and RSP7/SP each represent a C 1 -C 7 alkyl group or together form a trimethylene group. The acetylenic compound referred to above may be obtained by protecting the hydroxy group of cis-3- methyl - pent - 2 - en - 4 - yn - 1 - ol (e.g. by treating with isopropenyl methyl ether) and reacting the resisting alcohol of formula with a 2,6,6 - trimethyl - 4 - (C 1 -C 7 alkylenedioxy) - 2 - cyclohexen - 1 - one or a 2,6,6- trimethyl - 4,4 - dialkoxy - 2 - cyclohexen - 1 -one by means of a metal-organic reaction, e.g. by a Grignard reaction. Those aldehydes, in which RSP1/SP is an alkylenedioxy or dialkoxy group may also be prepared by reacting a 2,6,6-trimethyl- 4 - (alkylenedioxy) - cyclohex - 2 - en - 1 - one or a 2,6,6 - trimethyl - 4,4 - dialkoxy - cyclohex- 2-en-1-one with cis-3-methyl-pent-2-en-4-yrrl-ol by a Grignard reaction, oxidizing the hydroxymethyl group of the resulting acetylenic alcohol and reducing the triple bond to a double bond. Those aldehydes in which RSP1/SP is an oxo group may be prepared by this method with the additional step of hydrolysing with an acid the product at any stage. The aldehydes described above may be oxidized to give compounds of Formula (I) in which R is a C 1 -C 7 alkyl group. The oxidation may be carried out by means of silver oxide at 0-50‹ C. and the product may be converted to an ester by means of a diazoalkane, a C 1 -C 7 alkanol or an alkyl halide.
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