A Modular Access to 1, 2‐ and 1, 3‐Disubstituted Cyclobutylboronic Esters by Consecutive Radical Additions. (3rd December 2021)

• Record Type: Journal Article
• Authors: Michalland, Jean; Casaretto, Nicolas; Zard, Samir Z.
• Is Part Of: Angewandte Chemie. Volume 134:Number 3(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-12-03
• Subjects: cyclobutylboronic esters -- cyclopropylboronic esters -- radical addition -- radical stabilities -- xanthates; Chemistry -- Periodicals; 540
• DOI: 10.1002/ange.202113333
• Languages: English
• ISSNs: 0044-8249

Abstract

Abstract: A modular approach to substituted cyclobutylboronic esters is described. It proceeds by successive intermolecular radical additions of xanthates to pinacolato 1‐cyclobutenylboronate and to pinacolato bicyclo[1.1.0]but‐1‐ylboronate. Success hinges on tuning the stability of the α‐boryl radical by exploiting the stabilizing influence of the trivalent boronic ester and the slightly destabilizing cyclobutane, which increases the σ‐character of the radical. Reductive removal of the xanthate group finally provides a range of 1, 2‐ and 1, 3‐disubstituted cyclobutylboronic esters. The contrast with cyclopropylboronic esters is striking, since the strong destabilization by the highly strained cyclopropane ring allows the first radical addition to take place but not the second. Furthermore, the first adducts are geminal xanthyl boronic esters that can be converted into cyclobutanones. This chemistry furnishes cyclobutylboronic esters that would be quite difficult to obtain otherwise and thus complements existing methods. Abstract : Using the strain inherent in a cyclobutyl ring to counteract the stabilization of a radical adjacent to a boronic ester allows the synthesis of a broad variety of 1, 2‐ and 1, 3‐disubstituted cyclobutylboronic esters.