Diastereo- and Enantioselective Synthesis of Spiro-Pyrrolidine-Pyrazolones by Squaramide-Catalyzed Cascade Aza-Michael/Michael Reactions

A new method was developed to rapidly generate a series of spiro-pyrrolidine-pyrazolones by using a squaramide-catalyzed cascade aza-Michael/Michael addition of either tosyl-aminomethyl enones or enoates to unsaturated pyrazolones. This tandem reaction sequence proceeded well by using 5 mol-% of a chiral bifunctional tertiary amine squaramide catalyst to afford the desired products in good to excellent yields (up to 98 %) with excellent diastereoselectivities [up to >20:1 diastereomeric ratio (dr)] and high to excellent enantioselectivities (up to 98 % ee).