Lewis Acid Catalyzed Enantioselective Reactions Using Highly Coordinating Nucleophiles. Conjugate Additions of Thiols, Thiocarboxylic acids, and O-Benzylhydroxylamine

Studies of chiral Lewis acid catalyzed enantioselective reactions using strongly coordinating nucleophiles, as a rather unexplored categoly of catalyzed enantioselective reactions, are described. Selection of a proper chiral catalyst should be essential. The author has employed complexes of two chiral ligands, (R,R)-4,6-dibenzofurandiyl-2,2'-bis(4-phenyloxazoline) and (R,R)-isopropylidene-2,2'-bis[4-(o-hydroxybenzyl)oxazoline)], designated R,RDBFOX/Ph and R,R-BOX/o-HOBn, respectively. The complex catalyst derived from R,R-DBFOX/Ph and Ni(ClO4)2 . 3H2O works as a powerful catalyst in the enantioselective thiol conjugate additions to 3-(2-alkenoyl)-2-oxazolines, and the complex derived from R,R-BOX/o-HOBn and Cu(OTf)2 catalyzes the reactions of O-benzylhydroxylamine to 1-alkyl-3-(2-alkenoyl)-2-imidazolidinones. Internal delivery of nucleophiles to the activated acceptors is proposed as a powerful principle for the development of the titled reactions