酸度效应:确定了p K a与催化活性和立体选择性之间的相关性,并在meta ‐中的p K a -log(k)和p K a -log(R / S)相关性中观察到线性自由能关系(LFER)。和/或对位取代的芳族硫脲(见图)。这些结果为新催化剂的开发提供了基础,并且在我们最初的尝试中发现了几种改进的催化剂。
A simple alkylthiourea was found to be an effective catalyst for the Michaeladditionreaction of 3-substitutedoxindole to nitroolefins. A number of 3,3′-substituted oxindole derivatives, which have two vicinal quaternary-tertiary chiral centers were synthesized with up to 99% yield, 19:1 dr and 98% ee.