Communication
ChemComm
This work was supported by the Anhui Provincial Natural
Science Foundation (grant no. 2008085MB50), the Education
Bureau of Anhui Province (grant no. KJ2020ZD011 and
gxbjZD2020081), the Program for Science and Technology
Innovation Talents in Universities of Henan Province (grant
no. 20HASTIT037) and the Henan Youth Talent Support Project
(grant no. 2020HYTP046).
Conflicts of interest
There are no conflicts to declare.
Notes and references
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Based on previous reports9,10 and these control experiments, a
plausible mechanism is provided in Scheme 3. In this process, the
nucleophilic attack of iodide anions on a BAST molecule forms
the triiodide compound I, which then transforms into iodo-
intermediate II, accompanied by a loss of iodine. Subsequently,
the electrophilic attack of II on 1a (proceeding through III)
generates intermediate IV, which then reacts with 1a to afford
the sulphur-bridged imidazopyridine 3a and amine V. The for-
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an iodine radical to yield the iodosulfonium ion VII. This ion is
resonance stabilized because it can transition to VIII. The nucleo-
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In conclusion, we have developed a mild and highly efficient
strategy for C–S bond formation based on C–H bond functio-
nalization, to afford sulfur-bridged imidazopyridines under
metal-free conditions at room temperature. This is the first-
ever observation that BAST can act as a novel sulfur source to
construct C–S bonds. A mechanistically unique approach to the
synthesis of 1,2,4-thiadiazoles was also demonstrated based on
the reaction of imidazo[1,5-a]pyridines with BAST using NH4I
as both a promoter and nitrogen source at room temperature.
The present approach that avoids the use of high temperatures,
metal catalysts and oxidants, represents an interesting alter-
native to existing methods for the preparation of sulfur-bridged
imidazopyridines14 and 1,2,4-thiadiazoles.15 This research thus
provides a path to the development of BAST as a unique sulfur
source in organic synthesis.
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Chem. Commun.
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