Asymmetric Isothiourea-Catalysed Formal [3+2] Cycloadditions of Ammonium Enolates with Oxaziridines
作者:Siobhan R. Smith、Charlene Fallan、James E. Taylor、Ross McLennan、David S. B. Daniels、Louis C. Morrill、Alexandra M. Z. Slawin、Andrew D. Smith
DOI:10.1002/chem.201501271
日期:2015.7.13
A highly enantioselective Lewis base‐catalysed formal [3+2] cycloaddition of ammonium enolates and oxaziridines to give stereodefined oxazolidin‐4‐ones in high yield is described. Employing an enantioenriched oxaziridine in this process leads to a matched/mis‐matched effect with the isothiourea catalyst and allowed the synthesis of either syn‐ or anti‐stereodefined oxazolidin‐4‐ones in high d.r., yield
incorporate fluxional groups provide enhanced selectivity in asymmetric transformations? To address this issue, we have designed chiral 4‐dimethylaminopyridine (DMAP) catalysts with fluxional chirality. These catalysts were found to be efficient in promoting the acylative kineticresolution of secondary alcohols and axially chiral biaryl compounds with selectivityfactors of up to 37 and 51, respectively.
Isothiourea-Catalyzed Asymmetric Synthesis of β-Lactams and β-Amino Esters from Arylacetic Acid Derivatives and <i>N</i>-Sulfonylaldimines
作者:Siobhan R. Smith、James Douglas、Hugues Prevet、Peter Shapland、Alexandra M. Z. Slawin、Andrew D. Smith
DOI:10.1021/jo402590m
日期:2014.2.21
The isothiourea HBTM-2.1 (5 mol %) catalyzes the asymmetric formal [2 + 2] cycloaddition of both arylacetic acids (following activation with tosyl chloride) and preformed 2-arylacetic anhydrides with N-sulfonylaldimines, generating stereo-defined 2,3-diaryl-beta-amino esters (after ring-opening) and 3,4-diaryl-anti-beta-lactams, respectively, with high diastereocontrol (up to >95:5 dr) and good to excellent enantiocontrol. Deprotection of the N-tosyl substituent within the beta-lactam framework was possible without racemization by treatment with SmI2.