STUDIES IN TERPENE SYNTHESIS - REGIOSELECTIVE AND STEREOSELECTIVE COUPLING OF 2 TERPENYL SUBSTRATES

An easy method for the preparation of new terpenoids containing two te rpenyl (pinenyl) units is reported. Thus, eta(3)-allyltitanium (III) c omplex generated in situ from nopadiene has been reacted regiospecific ally with aldehydes such as (-)-citronellal, (-)-nopal or (-)-myrtenal to afford homoallylic alcohols. Especially, the reaction employing (- )-myrtenal occurred in a highly stereoselective way, leading to a uniq ue optically active carbinol (Z-Cram, d.s. greater than or equal to 95 %) among the four possible isomers. The selective dehydration of this compound led to a hydrocarbon bearing both alpha- and beta-pinenyl fra gments, which can be then considered as a promising new chiron.