title: Synthesis of C2-symmetric bisamidines: a new type of chiral metal-free Lewis acid analogue interacting with carbonyl groups.
abstract: The chiral bisamidine 5 has been prepared in just two steps from malonodinitrile. In the monocationic form this compound adopts a planar conformation with an almost convergent orientation of two N-H groups. Ketones, aldehydes, and nitro compounds are assumed to bind to this strongly polar cleft via hydrogen bonds, resulting in a Lewis-acid-like activation of the carbonyl groups. A broad scope of reactions (Diels-Alder, hetero-Diels-Alder, Friedel-Crafts) can be catalyzed. The observed accelerations surpass the rate effects of neutral hydrogen-bond donors such as thioureas or TADDOLs.
authors.affiliation: Johann Wolfgang Goethe University Frankfurt, Institute of Organic Chemistry and Chemical Biology, Max-von-Laue-Str. 7, D-60438 Frankfurt am Main, Germany.
authors.forename: Deniz
authors.initials: D
authors.lastname: Akalay
authors.forename: Gerd
authors.initials: G
authors.lastname: Dürner
authors.forename: Jan W
authors.initials: JW
authors.lastname: Bats
authors.forename: Michael
authors.initials: M
authors.lastname: Bolte
authors.forename: Michael W
authors.initials: MW
authors.lastname: Göbel