Construction of NH-Unprotected Spiropyrrolidines and Spiroisoindolines by [4+1] Cyclizations of γ-Azidoboronic Acids with Cyclic N-Sulfonylhydrazones.

The reactions of N-sulfonylhydrazones derived from cyclic ketones with γ-azidopropylboronic acid and 2-(azidomethyl)phenylboronic acid give rise to spirocyclic pyrrolidines and spiroisoindolines, respectively. The reactions proceed without the need of any transition-metal catalyst through a domino process that comprises the formation of a Csp -C and a Csp -N bond of the former hydrazonic carbon. The scope of the reaction has been explored by the preparation of over 50 examples of NH-unprotected spirocyclic derivatives. Importantly, this methodology could be applied for the preparation of alkaloid steroids from steroid N-tosylhydrazones.