Abstract
A highly efficient organocatalytic Michael addition/I2‐mediated cyclization reaction sequence between 1,3‐diketones and unsaturated pyrazolones was achieved in the presence of a chiral cinchonidine‐derived squaramide catalyst and I2 under mild reaction conditions. A variety of optically active spiro‐dihydrofuran pyrazolones were obtained in good to high yields (71–97 %) with excellent diastereoselectivities and high to excellent enantioselectivities (up to >99:1 dr and 99 % ee). A gram‐scale synthesis of chiral spiro‐dihydrofuran pyrazolones was also successfully realized.
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