Sterically Congested Protecting Group for a Boronyl Group in Iterative Aminations

The reaction of α-hydroxycarboxamide and aryl boronic acid produces aryl-oxazaborolidinone (Ar-OxB). In Ar-OxB, the α-hydroxycarboxamide-moiety was found to be a good protecting group for the boronyl group. This Ar-OxB is effective for Iterative aminations including Chan-Evans-Lam couplings.

Abstract

In this study, we found that the sterically bulky α-hydroxycarboxamide moiety is a suitable framework for protecting the boronyl group of boron reagents during aminations. Condensation of α-hydroxycarboxamide with ArB(OH)₂ produced aryloxazaborolidinone (ArOxB). The reactivity of the C-B bond in ArOxB is easily controlled by the steric and weak electronic effects of the backbone. H₂N-(or Br−)ArOxB underwent Chan-Evans-Lam (C-E-L) or Buchwald-Hartwig (B-H) amination with retaining the C−B bond. On the other hand, direct C-E-L amination of ArOxB was also possible in an oxidative atmosphere, in which the C−B bond was activated by Cu^II species. Our methodology is effective for the precise synthesis of two or more arylamino group substituted arenes.

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