6, 10-Dimethyl-2-undecanone (10), a key intermediate for squalane and isophytol, was effectively synthesized from prenyl chloride (4a, b) via telomerization with isobutylene and hydroformylation with cobalt catalyst followed by aldol condensation with acetone.
Telomerization of (4a, b) with excess amount of isobutylene was carried out in the presence of zinc chloride catalyst to obtain 6-chloro-2, 6-dimethyl-2-heptene (5) in 63.5%. Dehydrochlorination of (5) was investigated under various conditions. A mixture of 2, 6-dimethyl-1-heptene (7a) and 2, 6-dimethyl-2-heptene (7b) was obtained from (5) by hydrogenation followed by dehydrochlorination. Hydroformylation of the mixed products (7a, b) with cobalt catalyst proceeded with migration of the double bond to yield 3, 7-dimethyloctanal (8) as the sole product which was converted to (10) by aldol condensation with acetone and by selective hydrogenation.