Design, Synthesis, and Application of Enantioselective Coupling Reagent with a Traceless Chiral Auxiliary
摘要:
Stable chiral N-triazinylbrucinium tetrafluoroborate enantioselectively activates racemic carboxylic acids yielding enantiomerically enriched amides, esters, and dipeptides with er from 8:92 to 0.5:99.5. Due to the departure of a chiral auxiliary after the activation of the carboxylic function, all of the subsequent stages of the coupling reaction proceed without any perturbation caused by a chirality discriminator (traceless). Therefore, the advantageous coupling conditions, configuration, and enantiomeric purity of the final product are entirely predictable from the model experiment.
The highly enantioselective synthesis of chiral amides was achieved by an asymmetric Wolff rearrangement. A bifunctional phosphoric acid catalyst not only expedited the transformation but also controlled the enantioselectivity. The developed method enables the asymmetric addition between potent nucleophilic reagents and ketene species and provides a new approach to chiral amides.