A decarboxylative cross-coupling reaction of α-aminoacids with nitrones via visible-light-induced photoredox catalysis has been established for easy access to β-amino hydroxylamines and vicinal diamines with structural diversity, which is featured with simple operation, mild conditions, readily available α-aminoacids, and a broad scope of nitrone substrates. The application of this protocol can furnish
Meldrum’sacid has turned out to be a useful ketene equivalent when faced to nitrone dipoles to form various isoxazolidin‐5‐one derivatives under very mild Brønsted base organocatalytic conditions. The first asymmetric version of this original domino anionic formal [3+2] cycloaddition–decarboxylation reaction was demonstrated by means of quinine‐based organocatalysts.
Asymmetric 1,3-Dipolar Cycloaddition Reaction of Nitrones and Acrolein with a Bis-Titanium Catalyst as Chiral Lewis Acid
作者:Taichi Kano、Takuya Hashimoto、Keiji Maruoka
DOI:10.1021/ja0523284
日期:2005.8.1
A mu-oxo-type chiral bis-Ti(IV) oxide (S,S)-1 can be successfully utilized in the asymmetric 1,3-dipolar cycloaddition reactions between various nitrones 2 and acrolein to give the corresponding isoxazolidines with high to excellent enantioselectivities. For instance, the reaction between nitrone 2 (R = t-Bu) and acrolein in the presence of 10 mol % of bis-Ti(IV) catalyst (S,S)-1 in dichloromethane at -40 degrees C gave the corresponding endo cycloadduct with 97% ee.
We have developed a novel method for accessing exo adducts with high enantioselectivity in nitrone cycloadditions to enoates. Pyrazolidinones proved to be effective achiral templates in the cycloadditions, providing exo adducts typically in >15:1 selectivity and 90-98% ee. The use of Lewis acids that form square planar complexes, such as copper triflate, was important for obtaining high exo selectivity.
Lewis Acid Catalyzed Asymmetric Cycloadditions of Nitrones: α′-Hydroxy Enones as Efficient Reaction Partners
作者:Claudio Palomo、Mikel Oiarbide、Elena Arceo、Jesús M. García、Rosa López、Alberto González、Anthony Linden