A new class of bis-oxazoline ligands for the Cu-catalysed asymmetric cyclopropanation of olefins

• Published in: Tetrahedron letters Vol. 37; no. 23; pp. 4073 - 4076
• Main Authors: Bedekar, Ashutosh V., Andersson, Pher G.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 03-06-1996
• ISSN: 0040-4039; 1873-3581
• DOI: 10.1016/0040-4039(96)00736-8

A set of new chiral bis-oxazolines,
5a-b and
6a-c, has been syntheised from
D and
L-diethyl 2,3-
O-isopropylidene tartrates and chiral amino alcohols. These ligands were found to be efficient in the Cu(I)-catalysed asymmetric cyclopropanation of olefins. Bis-oxazolines of this type based on readily available valine were found comparable with previous ligands based on the more expensive
tert-leucine.
A set of new chiral bis-oxazolines,
5 and
6, were synthesised from
D and
L diethyl 2,3-
O-isopropylidene tartrates and chiral amino alcohols. Asymmetric cyclopropanation of styrene with ethyldiazoacetate in the presence of 1 % Cu(I)OTf and 1.05 % ligand was achieved with 39 – 84 % ee. This could be raised to 96 % ee with other diazoacetates.