10.1002/anie.201810204
Angewandte Chemie International Edition
COMMUNICATION
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boryl group activated the substrate as 1a showed higher
reactivity toward difluorination in comparison with its methyl- (28)
or ester-substituted (29) counterpart (Scheme 5b). Based on
these results and literature precedents,[4c,4e,11,18] the possible
reaction pathways were proposed and outlined in Scheme 5c.
Initially, the interaction between the double bond within styrenyl
MIDA boronate and (difluoroiodo)benzene generated in-situ from
the reaction of PIDA and Py·HF, triggers a regioselective vicinal
fluoroiodination to deliver an intermediate B. The capability of
the aryl group to stabilize the developing benzylic cation
accounts for the observed regioselectivity. Thereafter, the
intramolecular nucleophilic attack of phenyl ring on the C-I bond
leads to the formation of a phenonium ion species C. The
second regioselective fluoride attack results in the ring-opening
of C, which is accompanied by the homotopic 1,2-aryl migration,
providing a β-difluorinated alkylboron. This selectivity may result
from the more eletrophilicity of the carbon bound to a fluorine
atom. Likewise, the reaction of 1,1-disubstituted alkenyl MIDA
boronate first gives arenium cation intermediate D. An open
chain carbocation species E is likely formed before the attack of
fluoride due to the stabilization from both of the attached boron
and fluorine atoms (SN1-like mechanism).
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reactivity of sp3-MIDA boronates, we developed a regioselective
migratory difluorination reaction of alkenyl MIDA boronates with
Py·HF in the presence of stoichiometric amounts of the oxidant,
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Acknowledgements
Financial support from the National Natural Science Foundation
of China (21472250 and 21502242), the Key Project of Chinese
National Programs for Fundamental Research and Development
(2016YFA0602900) and the National Science and Technology
Major Project of the Ministry of Science and Technology of
China (2018ZX09735010) are gratefully acknowledged.
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Keywords: alkene • difluorination • migration • organoboron •
oxidation
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