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Synthesis of Bis(oxazoline) Ligands Possessing C-5 gem-Disubstitution and Their Application in Asymmetric Friedel-Crafts Alkylations.
- Source :
-
The Journal of organic chemistry [J Org Chem] 2015 Oct 16; Vol. 80 (20), pp. 10177-86. Date of Electronic Publication: 2015 Oct 02. - Publication Year :
- 2015
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Abstract
- 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.
Details
- Language :
- English
- ISSN :
- 1520-6904
- Volume :
- 80
- Issue :
- 20
- Database :
- MEDLINE
- Journal :
- The Journal of organic chemistry
- Publication Type :
- Academic Journal
- Accession number :
- 26406290
- Full Text :
- https://doi.org/10.1021/acs.joc.5b01767