Synthesis of C2-symmetric bisamidines: a new type of chiral metal-free Lewis acid analogue interacting with carbonyl groups.
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.
Akalay
Deniz
D
Johann Wolfgang Goethe University Frankfurt, Institute of Organic Chemistry and Chemical Biology, Max-von-Laue-Str. 7, D-60438 Frankfurt am Main, Germany.
Dürner
Gerd
G
Bats
Jan W
JW
Bolte
Michael
M
Göbel
Michael W
MW