Totalsynthese des ß-Carotins

A total synthesis of ß-carotene is described. First a C19-aldehyde was built up by condensation of ß-C14-aldehyde with a C5-ethinyl-oxy-ether. Then two molecules of the partially hydrogenated C19-aldehyde were condensed with acetylene-dimagnesiumbromide resulting in a C4o-acetylene-diol, which was dehydrated, giving rise to a ß-carotene-9,9'-ine or 9,9'-dehydro-ß-carotene. The last step consisted in the adding of two hydrogen atoms to the triple bond of the compound C40H54 furnishing a mixture of cis-trans-ß-carotene-isomers. From this mixture dark-red-violet crystals could be isolated which after recrystallisation melted at 178-179° and gave no depression of the melting point when mixed with natural ß-carotene, F. 179°.