Iridium-catalysed asymmetric allylic substitutions.
Ir-catalysed allylic substitution is supplementing the traditional Pd-catalysed variant. With simple, easily available monosubstituted allylic acetates and carbonates as substrates, Ir catalysts generally favour chiral, branched products, while Pd catalysts typically give rise to linear, achiral products. With phosphorus amidites as ligands, regioselectivities >10 : 1 and enantiomeric excess in the range 95-99 %ee are currently routinely achieved. A broad range of nucleophiles can be employed: for example stabilised carbanions, amines including their sulfonyl- and diacyl-derivatives, phenolates and alkoxides. A few applications, based on combinations of the allylic substitution and ring closing metathesis, indicate considerable potential of the method for the synthesis of biologically active compounds.
Helmchen
Günter
G
Organisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 270. D-69120 Heidelberg, Germany. g.helmchen@oci.uni-heidelberg.de
Dahnz
Axel
A
Dübon
Pierre
P
Schelwies
Mathias
M
Weihofen
Robert
R