It was demonstrated that α-hydroxycarboxamide is an excellent boron-protecting group. The reaction between α-hydroxycarboxamide and organoboronic acids produced stable oxazaborolidinones (OxBs), in which the -hybridized boron atom was sterically protected by α-hydroxycarboxamide. The alkyl groups of the α-hydroxycarboxamide moiety can dynamically cover the p-orbital of the -hybridized boron center, creating a small space around the boron atom, allowing for smooth transmetalation by a Pd catalyst and easy deprotection by water. This protecting phenomenon is effective for readily purification, Suzuki-Miyaura coupling reactions with unstable boronic acids and iterative cross-couplings.
Keywords: boron; coupling reactions; oxazaborolidinone; protecting groups.
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