l!he use of isoprene for conf&ruction of terpenoids is one of the moat challensing problem6 of 4&hetlo chemlstq. Thermal? and oatalyt~ic~~~ ieopreno oligo-and telomerisation into terpenolds or related oompormdr, is well documented in literature (most4 in patent form). This way, aa a rule, allows one to obtain monoterpenoida, and for the 6ynthee3.s of more oompllcated substances some preUminaqy functionalization of ls.oprene Itself is nedeed4.
We wish to report here a new approach in utilization of lsoprene for atereospeoific 4nthesie of 7,Fpolyenic terpenoide by means of the selective tran8formatio.n of ieoprene c~loollgomers with regular ("head-to-tail") structure. The approach is exemplified by transformation of available3 dimer 3 and trimer 2 into the corresponding keto aldelyClee 2 6 and their dimethyl acetale -8, a,2 (Scheme). These compounda, which alternatively could be obtained by oxidative cleavage of the reepective unsaturated ketones of type s,$s6 are ddely used in the eyntheela of varioae acyclic and cyclic i6oprenoids.
The most natural way to deeirable transformation of the isoprene qelooligomers under consideratim consIsta of their partial osonolysie. Such osoaol;reis ie lmoar for some polyolefins7 s but compound6 1 and 2 are not involved, to our knowledge, in this reaction.8