| I. Magnesium halide-catalyzed anti-aldol reactions of chiral N-acyloxazolidinones. The magnesium halide-catalyzed anti-aldol reaction of chiral N-acyloxazolidinones has been extended to include certain saturated and polymerizable aldehydes. The reactions proceed in the presence of 20–100 mol% MgBr2·OEt2, which displays significantly more reactivity than MgCl2 with these aldehyde acceptors. In contrast with the originally reported conditions, i -Pr2NEt was found to be the optimal amine base. The potent silylating agent TMSBr was often necessary to induce conversion in cases where TMSCl was unreactive.; II. Magnesium halide-catalyzed anti-aldol reactions of chiral N-acylthiazolidinethiones. Magnesium halides catalyze the anti-aldol addition of chiral N-acylthiazolidinethiones to aromatic and unsaturated aldehydes in the presence of Et3N and TMSCl. The anti configuration of the aldol adducts is complementary to that observed in the analogous reactions of chiral N-acylthiazolidinethiones. The origin of this turnover in selectivity may derive from reaction through a dipole-minimized, boat-like transition state.; III. Nickel(II)-catalyzed enantioselective syn-aldol reactions of N-acylthiazolidinethiones. The enantioselective syn-aldol addition of N-acylthiazolidinethiones to various aromatic, saturated, and unsaturated aldehydes is catalyzed by Ni(OTf)2(t-BuBox) in the presence of 2,6-lutidine and silyl triflates. The silyl triflate is necessary for the reaction to occur, acting as either as a Lewis acid or an aldolate-capping agent. |
