Highly Stereoselective Synthesis of Spiropyrazolones

The synthesis of spiro compounds through a Michael–Michael–aldol reaction is reported. The reaction affords spiropyrazolone derivatives in good yields, in almost diastereo‐ and enantiopure form, and is catalyzed by diphenylprolinol derivatives. The reaction showed strong nonlinear effects. Remarkably, when a catalyst with 70 % ee is used, the reaction still affords the final spiro compound in almost diastereo‐ and enantiopure form.