C-C cross-coupling reactions of O6-alkyl-2-haloinosine derivatives and a one-pot cross-coupling/O6-deprotection procedure.

Reaction conditions for the CC cross-coupling of O(6)-alkyl-2-bromo- and 2-chloroinosine derivatives with aryl-, hetaryl-, and alkylboronic acids were studied. Optimization experiments with silyl-protected 2-bromo-O(6)-methylinosine led to the identification of [PdCl(2)(dcpf)]/K(3)PO(4) in 1,4-dioxane as the best conditions for these reactions (dcpf=1,1'-bis(dicyclohexylphosphino)ferrocene). Attempted O(6)-demethylation, as well as the replacement of the C-6 methoxy group by amines, was unsuccessful, which led to the consideration of Pd-cleavable groups such that C-C cross-coupling and O(6)-deprotection could be accomplished in a single step. Thus, inosine 2-chloro-O(6)-allylinosine was chosen as the substrate and, after re-evaluation of the cross-coupling conditions with 2-chloro-O(6)-methylinosine as a model substrate, one-step C-C cross-coupling/deprotection reactions were performed with the O(6)-allyl analogue. These reactions are the first such examples of a one-pot procedure for the modification and deprotection of purine nucleosides under C-C cross-coupling conditions.