Enantioselective 1,4-Addition Reactions of Malonic Acid Half-Thioesters to Nitroolefins

Significance

An organocatalytic decarboxy­lative 1,4-addition of malonic acid half-thioesters (MAHTs) to nitroolefins is reported. Several urea-functionalized cinchona alkaloids were screened and epiquinineurea 1 proved to be the most active and selective catalyst. Moreover, different solvents were tested and THF gave the best chemical yields. Electron-deficient aromatic nitroolefins gave better results (yields up to 99%) than their electron-rich counterparts (78% yield). Higher enantioselectivities were obtained when the reactions were performed in ethyl vinyl ether; however, the reaction rate is lower. Nevertheless, in two cases it is shown that after a single recrystallization of the solid 1,4-addition product enantiomeric enrichment with an er of 99.5:0.5 was achieved.