Premium
Catalytic Electrophilic C−H Borylation Using NHC⋅Boranes and Iodine Forms C2‐, not C3‐, Borylated Indoles
Author(s) -
McGough John S.,
Cid Jessica,
Ingleson Michael J.
Publication year - 2017
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201702060
Subject(s) - borylation , electrophile , chemistry , boranes , carbene , catalysis , medicinal chemistry , combinatorial chemistry , boron , stereochemistry , organic chemistry , aryl , alkyl
Activation of N‐heterocyclic carbene boranes (NHC⋅BH 3 ) by I 2 enables the metal‐free catalytic C−H borylation of heteroarenes with formation of H 2 as the by‐product in a process that uses only bench stable precursors. The borylation of indoles using NHC⋅BH 3 /I 2 produces C2‐borylated indoles exclusively in contrast to other catalytic electrophilic C−H borylation methods. Mechanistic studies indicate that this is due to C3 to C2 boron migration facilitated by the absence of exogenous Brønsted bases. Thus this C−H borylation methodology proceeds under sufficiently Brønsted acidic conditions to enable the thermodynamic C2‐borylated indole isomer to be formed instead of the C3 borylated‐isomer. This demonstrates that electrophilic C−H borylation can be used to access a wider range of borylated regioisomers than reported to date.