A series of eight novel bis(oxazoline) ligands incorporating gem-disubstitution on one of the oxazoline rings were prepared from (S)-valine. These ligands are designed as a cost-effective alternative to similar ligands possessing an oxazolinyl C(5)-tert-butyl group derived from expensive (S)-tert-leucine. Four of the ligands possess a C(4)-gem-dimethyl group and four a C(4)-gem-diphenyl group adjacent to the C(5)-isopropyl substituent. Zinc complexes of ligands 11a-h, along with non-C(4)-gem-disubstituted analogues 1a-g, were effective in the Friedel-Crafts alkylation of both indole (up to 74% ee) and 2-methoxyfuran (up to 95% ee) with a series of nitroalkenes. Three of the ligands (11a-c), an iron dichloride complex of ligand 11d and two zinc dichloride complexes, were characterized by X-ray crystallography, one with ligand 11d and the second a bis-tert-butyl-substituted N-methylamine ligand. A direct comparison of the latter structures clearly illustrates the gem-dimethyl effect.

High levels of enantioselectivities are obtained for the conversion of compound (I) with the C5 gem-disubstituted ligand (BOX), whereas for the conversion of compound (IV) the best enantioselectivity is achieved with ligand (BXB). -(O'REILLY, S.; AYLWARD, M.; KEOGH-HANSEN, C.; FITZPATRICK, B.; MCMANUS, H. A.; MUELLER-BUNZ, H.; GUIRY*, P. J.; J. Org. Chem. 80 (2015) 20, 10177-10186, http://dx.doi.org/10.1021/acs.joc.5b01767 ; Cent. Synth. Chem. Biol., Univ. Coll., Dublin 4, Ire.; Eng.) -F. Berndt 09-025