The synthesis of several acyclic nucleosides 5 and 6, analogs of penciclovir, was achieved by Michael addition as the key step. This reaction worked not only for the protected natural bases but even for the less nucleophilic deaza purine and deaza pyrimidine. ... Michael addition proved to be efficient to introduce natural and deaza purine and pyrimidine bases. ... In a previous work, we obtained good results for the conjugate nucleophilic addition of alcohols, ...