Postdoctoral fellow at ETH Zürich 2011/12, partially financed by Swiss National Science Foundation (SNF-No. 200020-126693). All the isolations of intermediates and preparations of single crystals, described herein, have been carried out by X. S.
Stoichiometric Reactions of Enamines Derived from Diphenylprolinol Silyl Ethers with Nitro Olefins and Lessons for the Corresponding Organocatalytic Conversions – a Survey†
Article first published online: 17 MAY 2013
Copyright © 2013 Verlag Helvetica Chimica Acta AG, Zürich
Helvetica Chimica Acta
Volume 96, Issue 5, pages 799–852, May 2013
How to Cite
Seebach, D., Sun, X., Ebert, M.-O., Schweizer, W. B., Purkayastha, N., Beck, A. K., Duschmalé, J., Wennemers, H., Mukaiyama, T., Benohoud, M., Hayashi, Y. and Reiher, M. (2013), Stoichiometric Reactions of Enamines Derived from Diphenylprolinol Silyl Ethers with Nitro Olefins and Lessons for the Corresponding Organocatalytic Conversions – a Survey . HCA, 96: 799–852. doi: 10.1002/hlca.201300079
Part of the results described herein had been reported in a preliminary communication .
- Issue published online: 17 MAY 2013
- Article first published online: 17 MAY 2013
- Manuscript Received: 7 FEB 2013
- Nitro olefins;
- Oxazine N-oxides;
- Density-functional theory (DFT)
The stoichiometric reactions of enamines prepared from aldehydes and diphenyl-prolinol silyl ethers (intermediates of numerous organocatalytic processes) with nitro olefins have been investigated. As reported in the last century for simple achiral and chiral enamines, the products are cyclobutanes (4 with monosubstituted nitro-ethenes), dihydro-oxazine N-oxide derivatives (5 with disubstituted nitro-ethenes), and nitro enamines derived from γ-nitro aldehydes (6, often formed after longer reaction times). The same types of products were shown to be formed, when the reactions were carried out with peptides H-Pro-Pro-Xaa-OMe that lack an acidic H-atom. Functionalized components such as alkoxy enamines, nitro-acrylates, acetamido-nitro-ethylene, or hydroxylated nitro olefins also form products carrying the diphenyl-prolinol silyl ether as a substituent. All of these products must be considered intermediates in the corresponding catalytic reactions; the investigation of their chemical properties provided useful hints about the rates, the conditions, the catalyst resting states or irreversible traps, and/or the limitations of the corresponding organocatalytic processes. High-level DFT and MP2 computations of the structures of alkoxy enamines and thermodynamic data of a cyclobutane dissociation are also described. Some results obtained with the stoichiometrically prepared intermediates are not compatible with previous mechanistic proposals and assumptions.