216. Regiodivergent synthesis of pyrazino-indolines vs. triazocines via α-imino carbenes addition to imidazolidines
     Alejandro Guarnieri-Ibáñez, Adiran de Aguirre Fondevila, Céline Besnard, Amalia I. Poblador Bahamonde, Jérôme Lacour
     Chem. Sci. 2021, 12, 1479-1485

Hexahydropyrazinoindoles were prepared in a single step from N-sulfonyl triazoles and imidazolidines. Under dirhodium catalysis, α-imino carbenes were generated and formed nitrogen ylide intermediates that, after subsequent aminal opening, afforded the pyrazinoindoles predominantly via formal [1,2]-Stevens and tandem Friedel-Crafts cyclizations. Of mechanistic importance, a regiodivergent reactivity was engineered through the use of a specific unsymmetrically substituted imidazolidine that promoted the exclusive formation of 8-membered ring 1,3,6-triazocines. Based on DFT calculations, an original Curtin-Hammett-like situation was demonstrated for the mechanism. Further derivatizations led to functionalized tetrahydropyrazinoindoles in high yields.

For a highlight in the Swiss Science Concentrates of CHIMIA, see: https://doi.org/10.2533/chimia.2021.208

DOI: 10.1039/D0SC05725H 

open archive unige:148588