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The Thermal Rearrangement of an NHC‐Ligated 3‐Benzoborepin to an NHC‐Boranorcaradiene
Author(s) -
Shimoi Masaki,
Kevlishvili Ilia,
Watanabe Takashi,
Maeda Katsuhiro,
Geib Steven J.,
Curran Dennis P.,
Liu Peng,
Taniguchi Tsuyoshi
Publication year - 2020
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201912234
Subject(s) - carbene , diradical , chemistry , boranes , borane , boron , hydroboration , density functional theory , reaction mechanism , photochemistry , stereochemistry , computational chemistry , organic chemistry , singlet state , catalysis , physics , nuclear physics , excited state
An N‐heterocyclic‐carbene‐ligated 3‐benzoborepin with a bridged structure has been synthesized by double radical trans ‐hydroboration of benzo[3,4]cycloundec‐3‐ene‐1,5‐diyne with an N‐heterocyclic carbene borane. The thermal reaction of the NHC‐ligated borepin at 150 °C gives an isolable NHC‐boranorcaradiene. Experiments and density functional theory calculations support a mechanism whereby the borepin initially rearranges to a boranorcaradiene by a thermal 6π‐electrocyclic reaction. This is followed by 1,5‐boron shift to give a rearranged boranorcaradiene. This shift occurs with stereoinversion at boron through a transition state with open‐shell diradical character. This is the first example of the isolation of a boranorcaradiene from a thermal reaction of a borepin.