Total Syntheses of (+)-α-Allokainic Acid and (−)-2-<i>epi</i>-α-Allokainic Acid Employing Ketopinic Amide as a Chiral Auxiliary

Asymmetric Michael reaction of iminoglycinate 4 to α,β-unsaturated esters had been developed with >98:<2 diastereoselectivity. A reverse of diastereoselectivity for Michael reaction could be achieved by the replacement of lithium enolate with magnesium enolate. This methodology was applied to the total syntheses of (+)-α-allokainic acid 1 and (−)-2-epi-α-allokainic acid 6 each in 11 synthetic steps starting from 4 in 17.8 and 18.0% yields, respectively.