A new access to 3,5-disubstituted piperazinones via Pd(0)-catalyzed amination

An original synthetic route toward 3,5-disubstituted piperazinones has been developed. The method relies upon a 6-exo intramolecular process between a sulfonylated nitrogen atom of amino acid derivation and an η3-allyl-palladium moiety. This cyclization process generates the two possible (cis and trans) diastereoisomers whose ratio depends on the amino acid employed. The bulkier the amino acid residue, the higher the observed cis:trans ratio. Convincing evidence for reversible intramolecular addition of the nitrogen nucleophile to the η3-allyl-palladium complex is put forward.