Synthesis of Pyrrolidines by a Csp3 -Csp3 /Csp3 -N Transition-Metal-Free Domino Reaction of Boronic Acids with γ-Azido-N-Tosylhydrazones.

The reaction between γ-azido-N-tosylhydrazones and boronic acids leads to the obtention of 2,2-disubstituted pyrrolidines in a domino process that includes 1) diazoalkane formation, 2) intermolecular carboborylation of the diazocompound, and 3) intramolecular carborylation of the azide, and comprises the formation of a Csp3 -Csp3 and a Csp3 -N bonds on the same carbon atom. The reaction proceeds without the need of any transition-metal catalyst under microwave activation and features wide scope in both reaction partners. It can be applied to both alkyl and arylboronic acids with equal efficiency. With N-tosylhydrazones derived from 2-(2-azidoethyl)-cyclopentanone and cyclohexanone the reactions are highly diastereoselective leading to the cis-fused bicyclic systems as unique diastereoisomers. The scope of the process is illustrated by over sixty examples, including scaffolds present in natural alkaloids, and the mechanistic proposal is suppported by DFT-based computations.