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DOI: 10.1055/s-0036-1591314
Borylketenimines in the Synthesis of Borylated Heterocycles
Publication History
Publication Date:
18 September 2017 (online)
Key words
copper catalysis - ketenimines - coumarins - boryl heterocycles - azetidimines - [2+2] cycloaddition
Significance
Incorporation of the N-methyliminodiacetate (MIDA) boron protecting group generally provides bench-stable compounds that can withstand a variety of reaction conditions, and can also participate in the Suzuki–Miyaura reaction (see Review below). The amphoteric nature of the BMIDA (B) moiety prevents undesired dative interactions with the boron atom.
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Review
J. J. Molloy, A. J. B. Watson B-Protected Boronic Acids: Methodology Development and Strategic Application, In Boron Reagents in Synthesis, ACS Symposium Series 1236: Washington, 2016, 379–413.
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Comment
Reported is the synthesis of borylazetidimines 1 and 3-boryliminocoumarins 5 through in situ trapping of borylketenimines with imine 2 or salicylaldehyde 4, respectively. The borylketenimines are prepared from ethynyl MIDA boronate (3) and an N-arylsulfonyl-protected azide. The synthesis of 1 shows tolerance to a heterocyclic substituent (1b). As the boryliminocoumarins 5a and 5b were found to be fluorescent, these compounds were submitted to Suzuki–Miyaura cross-coupling conditions to give fluorescently labeled cyclic peptides 6a and 6b.
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