The Photochemical Reaction of Vinylaziridines and Vinylazetidines with Chromium(0) and Molybdenum(0) (Fischer) Carbene Complexes

• Published in: Chemistry : a European journal Vol. 20; no. 5; pp. 1359 - 1366
• Main Authors: Rivero, Alexandra R., Fernández, Israel, Sierra, Miguel A.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 27.01.2014; WILEY‐VCH Verlag; Wiley; Wiley Subscription Services, Inc
• Subjects: aziridines; Chemistry; Chemistry, Multidisciplinary; Chromium; cycloaddition; DFT calculations; metal-carbenes; Molybdenum; photochemistry; Physical Sciences; Science & Technology; aziridines; VINYL AZIRIDINES; MECHANISM; ISOMERIZATION; DFT calculations; REARRANGEMENT; cycloaddition; metal-carbenes; photochemistry; 2-VINYLAZIRIDINES; ISOCYANATES; CYCLOADDITION REACTION; VALENCE
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201302029

The [5+2] and [6+2] cycloaddition reactions of vinylaziridines and vinylazetidines with ketenes generated photochemically from chromium(0) and molybdenum(0) Fischer carbene complexes have been investigated. These processes constitute a straightforward and efficient route to azepanones and azocinones, respectively. The peculiar electronic properties of the metalated ketenes allow for the introduction of electron‐rich substituents in the final cycloadducts, a difficult task using conventional organic chemistry procedures. The versatility of the process is demonstrated by using Cr0 Fischer bis(carbene) complexes as metalated bis(ketene) precursors. These species produce tethered bis(azepanone)s in a single step under mild reaction conditions. Density functional theory calculations point to a stepwise reaction pathway through the initial nucleophilic attack of the nitrogen atom of the aziridine on the metalated ketene, followed by ring closure of the zwitterionic intermediate formed. Carbene complexes at work: The [5+2] or [6+2] cycloaddition reactions between metalated ketenes, photochemically generated from Cr0 or Mo0 Fischer carbene complexes, and vinylaziridines or vinylazetidines efficiently produce azepanones or azocinones, respectively. The use of biscarbene complexes leads to more structurally complex tethered bis(azepanone)s in a double cycloaddition process. DFT calculations are consistent with a stepwise mechanism involving a zwitterionic intermediate for these processes (see figure).