Organocatalyzed Diastereo- and Site-Selective Monoacylation of Acyclic Diarylpropanoid Stereotriads by Amplification Processes.

In the present article, we describe a simple method to perform selective monoacylation of diols in the diarylpropanoid series. First, the diastereoselective acylation of acyclic pseudo-C2-symmetrical 1,3-diols was realized with complete diastereoselectivity, leading to valuable acyclic building blocks bearing an additionally revealed stereocenter. Using a simple achiral organocatalyst and under mild conditions, this diastereoselective process resulted in the selective monoacylation of a wide array of 1,3-diols and anhydrides. This method was then successfully conducted on even more challenging unsymmetrical stereotriads, leading to a site-selective monoacylation. An experimental and theoretical mechanistic study was carried out to explain this high level of selectivity, resulting from a first highly selective catalyzed acylation in synergy with a second acylation of the minor monoester. As a consequence, this study demonstrated an unprecedented case of subtractive amplification by using an achiral catalyst.