Synthesis of Chiral Tetrahydrofurans and Pyrrolidines by Visible-Light-Mediated Deoxygenation
作者:Daniel Rackl、Viktor Kais、Eugen Lutsker、and Oliver Reiser
DOI:10.1002/ejoc.201700014
日期:2017.4.18
The synthesis of chiral tetrahydrofurans and pyrrolidines starting from 1,2‐diols or β‐amino alcohols, respectively, by visible‐light‐mediated deoxygenation is described. Easily accessible monoallylated/propargylated substrates were activated either as inexpensive ethyl oxalates or as recyclable 3,5‐bis(trifluoromethyl)benzoates to generate alkyl radicals suitable for 5‐exo‐trig/5‐exo‐dig cyclizations
Highly diastereoselective intramolecular cycloaddition of nitrones 5–7 and 16, as well as oximes 11–13 that are easily accessible from diethyl (R,R)-tartrate, affords bicyclic compounds 8–10 and 17. The tetracyclic compound 14 is formed as the main product by an intramolecular domino reaction of dioxime 11. Some of the bicyclic compounds and the tetracyclic compound 14 are tested as chiral ligands in the enantioselective addition of diethylzinc to benzaldehyde. An ee of 93% was achieved in the presence of the best ligand.