Synthesis of (E)-6-alkenylpurines via Pd-catalyzed stannation/protodestannation tandem process of alkynylpurines

Abstract

A methodology for the synthesis of (E)-6-alkenylpurines, starting from 6-iodopurines, based on a Pd-catalyzed stannation/protodestannation protocol, is described. The alkynylation reactions were catalyzed by Pd(OAc)2/PPh3 in acetonitrile. The Pd-catalyzed stannation itself provided a mixture of Z regioisomers but following protodestannation using TFA induces Z to E isomerization giving (E)-6-alkenylpurines. The reactivity of other 2- and 8-alkynyl purines has also been studied.

Pd-catalyzed allylic substitution of purin-8-yl(allyl) acetate: Route to (E)-alkenylpurines

“…It is worth mentioning, that the 5a was formed in other cases as the by-product usually in less than 5% yield. The ability of various alkenylpurines to readily undergo E/Z-isomerization has been re- cently reported 25,28 . However, in our case, compounds 3a and 4a have not isomerized neither in the presence of Pd(OAc) 2 , PCy 3 nor with TsOH 28 .…”