Asymmetric cooperative catalysis of strong Brønsted acid-promoted reactions using chiral ureas.
Cationic organic intermediates participate in a wide variety of useful synthetic transformations, but their high reactivity can render selectivity in competing pathways difficult to control. Here, we describe a strategy for inducing enantioselectivity in reactions of protio-iminium ions, wherein a chiral catalyst interacts with the highly reactive intermediate through a network of noncovalent interactions. This interaction leads to an attenuation of the reactivity of the iminium ion and allows high enantioselectivity in cycloadditions with electron-rich alkenes (the Povarov reaction). A detailed experimental and computational analysis of this catalyst system has revealed the precise nature of the catalyst-substrate interactions and the likely basis for enantioinduction.
Xu
Hao
H
Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, USA.
Zuend
Stephan J
SJ
Woll
Matthew G
MG
Tao
Ye
Y
Jacobsen
Eric N
EN
D000143:Acids / Q000737:chemistry*; D000475:Alkenes / Q000737:chemistry*; D001557:Benzenesulfonates / Q000737:chemistry*; D002384:Catalysis; D055598:Chemical Phenomena; D007097:Imines / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D011522:Protons; D013237:Stereoisomerism; D013890:Thiourea / Q000031:analogs & derivatives / Q000737:chemistry; D014508:Urea / Q000031:analogs & derivatives* / Q000737:chemistry*
D000143:Acids; D000475:Alkenes; D001557:Benzenesulfonates; D007097:Imines; D011522:Protons; D014508:Urea; C448313:3-nitrobenzenesulfonic acid; D013890:Thiourea