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

Abstract

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.

Alkenyl Boronates: Synthesis and Applications

“…[116] The ozonolysis of alkenyl MIDA boronates has also been achieved by Bode and Ito et al to afford acyl boronates,w hicha re intermediates in the synthesis of a-aminoa cylborons. [117] Acylboronates are also accessible by ad ihydroxylation/meta-periodate cleavage process described by Perrin (Scheme27d). [118] Very recently,t he reactivity of tetracoordinate alkenyl boronate complexes by means of 1,2-migration rearrangement has been exploited by several authors (Scheme 28).…”

Concise Synthesis of Potassium Acyltrifluoroborates from Aldehydes through Copper(I)‐Catalyzed Borylation/Oxidation

“…Recently, our group and that of Perrin reported ozonolysis and dihydroxylation/oxidative cleavage of alkenyl MIDA boronates, respectively, which afford acyl MIDA boronates (Scheme B, a) ,. These approaches are conducted under relatively mild conditions and are suitable for the preparation of highly functionalized acylboronates including the first examples of enantioenriched α‐amino acylboron compounds.…”

Direct Access to MIDA Acylboronates through Mild Oxidation of MIDA Vinylboronates

“…Yudin et al employed a3-step radical decarboxylation of a-carboxy MIDAb oronates, [11] which were obtained in 3steps from the corresponding vinylboronates. [15] ever,t he latter method requires air-sensitive glove-box techniques.Surprisingly,nomention of subsequent oxidation was made in either of these antecedent studies.I ns ummary, methods for preparing acylboronates have so far required multistep procedures,o fw hich several rely on the use of highly basic boryl or carbon anions,w hich restricts the reaction scope to as mall number of base-tolerant functional groups and substrates. [13] Additionally, Molander et al described diborylation of aldehydes to afford a-hydroxy alkyltrifluoroborate precursors.…”

“…[12] Alternatively, a-hydroxy boronate esters might be accessed through the Matteson homologation by reaction with CHCl 2 Li at very low temperature. [15] To simplify access to acylboronate MIDAe sters,w e imagined at wo-step pathway that exploits classic olefin reactivity,w hereby an alkenyl-2-boronate MIDAe ster (1) undergoes successive dihydroxylation and oxidative diol cleavage (Scheme 1, bottom) under air-a nd water-tolerant conditions. [14] How-Scheme 1.…”