Catalytic intramolecular hydroamination of aminoallenes using titanium and tantalum complexes of sterically encumbered chiral sulfonamides
Abstract
Catalysis using earth abundant metals is an important goal due to the relative scarcity and expense of precious metal catalysts. It would be even more beneficial to use earth abundant catalysts for the synthesis of common pharmaceutical structural motifs such as pyrrolidine and pyridine. Thus, developing titanium catalysts for asymmetric ring closing hydroamination is a valuable goal. In this work, four sterically encumbered chiral sulfonamides derived from naturally occurring amino acids were prepared. These compounds undergo protonolysis reactions with Ti(NMe₂)₄ or Ta(NMe₂)₅ to give monomeric complexes as determined by both DOSY NMR and X-ray crystallography. The resulting complexes are active for the ring closing hydroamination hepta-4,5-dienylamine to give a mixture of tetrahydropyridine and pyrrolidine products. However, the titanium complexes convert 6-methylhepta-4,5-dienylamine exclusively to 2-(2-methylpropenyl)pyrrolidine in higher enantioselectivity than those previously reported, with enantiomeric excesses ranging from 18–24%. The corresponding tantalum complexes were more selective with enantiomeric excesses ranging from 33–39%.
Additional Information
© 2020 The Royal Society of Chemistry. Submitted 20 Jul 2020; Accepted 21 Aug 2020; First published 21 Aug 2020. Financial support for this project was received from the National Science Foundation, NSF-MRI-1725142, the John Stauffer Fund for Summer Research in Chemistry, and Harvey Mudd College. We gratefully acknowledge NSF support for quantum mechanics calculations through the award CHE-1565743 (Robert J. Cave). The authors thank the Beckman Institute for their support of the X-Ray Crystallography Facility at Caltech and the Dow Next Generation Instrumentation Grant. There are no conflicts of interest to declare.Attached Files
Supplemental Material - d0dt02557g1.pdf
Supplemental Material - d0dt02557g2.cif
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Additional details
- Eprint ID
- 105168
- DOI
- 10.1039/d0dt02557g
- Resolver ID
- CaltechAUTHORS:20200831-110816175
- MRI-1725142
- NSF
- John Stauffer Charitable Trust
- Harvey Mudd College
- CHE-1565743
- NSF
- Caltech Beckman Institute
- Dow Next Generation Educator Fund
- Created
-
2020-09-08Created from EPrint's datestamp field
- Updated
-
2021-11-16Created from EPrint's last_modified field