BOROX Catalysis: Self-assembled AMINO-BOROX and IMINO-BOROX Chiral Br?nsted Acids in a Five Component Catalyst Assembly/ Catalytic Asymmetric Aziridination

摘要

A five-component catalyst assembly/aziridinationnreaction is described starting from an aldehyde, an amine,nethyl diazoacetate, B(OPh)3, and a molecule of a vaulted biarylnligand (VAPOL or VANOL). A remarkable level of chemoselectivitynwas observed since, while 10 different productsncould have resulted from various reactions between the fivencomponents, an aziridine was formed in 85% yield and 98% eenand only two other products could be detected in 3% yield.nStudies reveal that the first in a sequence of three reactions isnan exceedingly rapid amine-induced assembly of an AMINOBOROXnchiral Brønsted acid species from VAPOL andnB(OPh)3, which is followed by imine formation from thenamine and aldehyde and the concomitant formation of annIMINO-BOROX chiral Brønsted acid and finally the reaction of the imine with ethyl diazoacetate mediated by the IMINO-BOROXncatalyst to give aziridine-2-carboxylic esters with very high diastereo- and enantioselectivity.