Synthesis of Acylborons by Ozonolysis of Alkenylboronates: Preparation of an Enantioenriched Amino-Acid Acylboronate.

A concise synthesis of acylborons was achieved by ozonolysis of alkenyl MIDA (N-methyliminodiacetic acid) boronates. This reaction exhibits excellent functional-group tolerance and is applicable to various acyl MIDA boronates and potassium acyltrifluroborates (KATs) which could not be synthesized by previous methods. In addition, α-amino acylborons, which would be essential for peptide ligations, were prepared for the first time. The acylboron of l-alanine was obtained in high enantiopurity and found to be configurationally stable. Oligopeptide synthesis between the α-amino KATs and amino acid in dilute aqueous media was studied.