1309686-87-0Relevant academic research and scientific papers
Stoichiometric reactions of enamines derived from diphenylprolinol silyl ethers with nitro olefins and lessons for the corresponding organocatalytic conversions - A survey
Seebach, Dieter,Sun, Xiaoyu,Ebert, Marc-Olivier,Schweizer, W. Bernd,Purkayastha, Nirupam,Beck, Albert K.,Duschmale, Joerg,Wennemers, Helma,Mukaiyama, Takasuke,Benohoud, Meryem,Hayashi, Yujiro,Reiher, Markus
, p. 799 - 852 (2013/07/19)
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. Copyright
Mechanistic rationalization of organocatalyzed conjugate addition of linear aldehydes to nitro-olefins
Bures, Jordi,Armstrong, Alan,Blackmond, Donna G.
supporting information; experimental part, p. 8822 - 8825 (2011/08/04)
Kinetic studies of the conjugate addition of propanal to nitrostyrene catalyzed by diarylprolinol ethers reveal that formation of the product iminium species is rate-determining and is promoted by both the reaction product and acid additives. The beneficial role of a dominant cyclobutane intermediate in maintaining high stereoselectivity is highlighted. This mechanistic understanding led to the design of highly productive reaction protocols.
