The synthesis of five chiral DBFOX (dibenzofuran-oxazoline) ligands with either aryl or benzyl substituents will be presented. The requisite amino alcohols were obtained with high enantioselectivity either commercially (DBFOX/Bn), via Sharpless asymmetric aminohydroxylation (DBFOX/Nap, DBFOX/t-BuPh, DBFOX/Pip), or via phase-transfer catalyzed asymmetric alkylation (DBFOX/MeNap). These ligands, complexed with Mg(NTf2)2, were used as Lewis acid promoters of enantioselective radical conjugate additions to α/β-unsaturated nitro-amides/esters. A summary of these results is presented and discussed. These findings led us to believe that our initial binding model between metal, ligand, and substrate was flawed. Thus, we figured that if we started with a functionality known to bind to both nitro groups and carbonyls, and then introduced a chiral element for control, we may be able to improve the beta-carbon enantioselectivity. We have tried to accomplish this via hydrogen-bonding ligands (ureas and thioureas). Initial studies on achiral versions of this concept are discussed.
College and Department
Physical and Mathematical Sciences; Chemistry and Biochemistry
BYU ScholarsArchive Citation
Capps, Steven G., "A Radical Conjugate Addition Approach to the Total Synthesis of Celogentin C" (2008). Theses and Dissertations. 1831.
radical, RCA, Celogentin C, DBFOX