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Stereochemical Control of the Triflate Mediated Intramolecular Schmidt Reaction

preprint
submitted on 01.07.2020 and posted on 03.07.2020 by Lars Gnägi, Florence Giornal, Harish Jangra, Ajoy Kapat, Erich Nyfeler, Hendrik Zipse, Robin Marc Schärer, Philippe Renaud
The stereoselectivity of the triflate mediated intramolecular Schmidt reaction of substituted 3-(1-azidocyclohexyl)propanol derivatives leading to octahydro-1H-pyrrolo[1,2-a]azepine, the structural skeleton of several important families of alkaloids such as the Stemona alkaloids, has been examined. The reaction involves an initial intramolecular SN2 reaction between the azide moiety and the triflate affording an intermediate spirocyclic aminodiazonoium salt that undergoes the expected 1,2-shift/N2-elimination followed by hydride mediated iminium salt reduction. Remarkably, chiral alcohols are converted to the azabicylic derivative with no or limited racemization. The initial asymmetric alcohol center controls the diastereoselectivity of the whole process leading to the formation of one out of the four possible diastereoisomers of disubstituted octahydro-1H-pyrrolo[1,2-a]azepine. The origin of the stereoselectivity of is rationalized based on theoretical calculations.

Funding

National Science Foundation (Project 200020_172621)

History

Email Address of Submitting Author

philippe.renaud@dcb.unibe.ch

Institution

University of Bern

Country

Switzerland

ORCID For Submitting Author

0000-0002-9069-7109

Declaration of Conflict of Interest

No conflict of interest

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