Abstract
Proline-catalyzed aldol addition of 2,2-dialkyl-1,3-dioxan-5-ones to aldehydes requires the presence of water, pyridinium p-toluenesulfonate or lithium chloride to proceed with high yield and high enantioselectivity. Acyclic amino acids such as alanine, phenylalanine, lysine and valine also catalyze the reaction but overall show yields and selectivities inferior to those of proline. An ester of a proline analogue shows catalytic activity in the presence of PPTS, suggesting that, in the presence of a Bronsted acid, a free carboxyl group on the catalyst might not be critical.
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