DIASTEREOSELECTIVE COPE REARRANGEMENTS, THE KEY STEP IN CONSTRUCTION OF TERPENOID CARBON-FRAMEWORKS

Ehsan Fereyduni, Alexander J. Grenning

University of Florida, Department of Chemistry, PO BOX 117200 Gainesville FL, 32611

The Cope rearrangement is a very useful synthetic organic transformation involving the [3,3]-sigmatropic rearrangement of 1,5-dienes. Since the [3,3]-sigmatropic rearrangement is a reversible reaction, researchers have focused more on the other types of Cope rearrangement like Claisen, oxy-Cope, Overman, aza-Cope and 1,2-divinyl-cycloalkane rearrangements. These types of [3,3]-sigmatropic rearrangements shift the equilibrium to the product because of the involved heteroatom or releasing of the ring strain. The originally reported Cope rearrangement using are 3,3-dicyano-1,5-dienes also rely on the right side of the equilibrium because of the conjugation of gem-dinitrile and the formed double bond. We took advantage of this transformation and designed a four-step strategy in which the key step is the Cope rearrangement. This method allows us to synthesis terpenoid-like polycycloalkane scaffolds from ketone-derived Knoevenagel adducts and allylic electrophiles. We studied the diastereoselectivity, ring strain and electronic effects of the original Cope rearrangement, as well as one-pot [3,3] rearrangement/alkylation sequence towards the synthesis of different polycycloalkanes which have three stereogenic centers.