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.
The first highly diastereo- and enantioselective organocatalytic synthesis of 2,2-disubstituted-2H-oxazol-5-ones is described. The addition of oxazolones to maleimides is promoted by bifunctional thiourea catalysts, which afford the corresponding 2,2-disubstituted-2H-oxazol-5-ones with total regio- and stereocontrol.
The enantioselective synthesis of pyrazol-3-ones has not been extensively studied in organic synthesis. Here in we report the first asymmetric addition of pyrazolones to maleimides catalyzed by bifunctional thiourea catalysts.
The alkylation of oxazolones through an SN1 reaction by using stabilized carbocations is reported. The reaction (catalyzed by Brønsted acids, such as TFA or thioureas) affords the final compounds in excellent yields. Reaction with other heterocycles has also been studied, rendering pyrazolone or oxindole derivatives in good yields.
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