title: Enantioselective organo-photocatalysis mediated by atropisomeric thiourea derivatives.
abstract: Can photocatalysis be performed without electron or energy transfer? To address this, organo-photocatalysts that are based on atropisomeric thioureas and display lower excited-state energies than the reactive substrates have been developed. These photocatalysts were found to be efficient in promoting the [2+2] photocycloaddition of 4-alkenyl-substituted coumarins, which led to the corresponding products with high enantioselectivity (77-96% ee) at low catalyst loading (1-10 mol%). The photocatalytic cycle proceeds by energy sharing via the formation of both static and dynamic complexes (exciplex formation), which is aided by hydrogen bonding.
authors.affiliation: Chemistry and Biochemistry, North Dakota State University, Fargo, ND 58103 (USA).
authors.forename: Nandini
authors.initials: N
authors.lastname: Vallavoju
authors.forename: Sermadurai
authors.initials: S
authors.lastname: Selvakumar
authors.forename: Steffen
authors.initials: S
authors.lastname: Jockusch
authors.forename: Mukund P
authors.initials: MP
authors.lastname: Sibi
authors.forename: Jayaraman
authors.initials: J
authors.lastname: Sivaguru
keywords: asymmetric catalysis; organocatalysis; photocatalysis; photochirogenesis; thioureas