Abstract
Many natural terpenic compounds are known to have skeltons of 1-4 addition of isoprene. But few terpenic compounds have been synthesized hitherto.
We shall now report the synthesis of citronellol VII-a natural monoterpene alcohol-from isoprene.
The reaction consists of the f olloouing four steps ;
(1) Catalytic dimerization and alcohol addition of isoprene in the presence of (π-allyl PdCI) 2, phos-phine, and NaOMe.
The yield of II is up to 97.5% when PPh3 : (π-allyl PdCI) 2=2 : 1 and 2 days reaction at room temperature.
(2) Dealcohol reaction of If or V is carried out in the presence of [P (η-Bu) 3] 2 NiCl2 and NaOMe as catalytic system,
(3) Selective 1-4 hydrogenation of conjugated diene is carried out in the presence of Cr (CO) 3 (C6H, -COOMe) as a catalyst under hydrogen atmosphere to form IV or VI.
(4) Terminal hydration of terminal double bond is carried out by hydroboration and following alkaline hydrolysis to obtain V or VII.
Two synthetic routes are practically possible and the overall yield of citronellol is ca. 40% in each case.
