Organic Letters
Letter
open product.56,57 However, for the reaction of substrate 1r
with a cyclopropyl substituent, we found that no ring-open
product could be observed.
which involves both C−Cl and C−O bond formation, has the
advantages of mild reaction conditions, simple operation, fast,
easy purification, large-scale preparation, and metal-free
features. Further investigation of the reaction mechanism is
still ongoing in our lab.
On the basis of these results, we tentatively proposed an
ionic pathway for this reaction.37,58 First, the alkyne triple
bond coordinates with PhICl2 to give intermediate A. Next, a
concerted process involving the nucleophilc attack of the
carbonyl oxygen atom of the ester group on the triple bond
and the triple bond on the iodine center to PhICl2 occurs
affording the oxonium ion intermediate B, with the formation
of a C−I bond and release of a chloride anion. Next, chloride
nucleophilically attacks the methyl carbon center in B, leading
to the formation of intermediate C. While in the case of tert-
butyl ester 1d, the removal of the tert-butyl group should occur
by an SN1 mechanistic pathway. Finally, reductive elimination
of PhI in C affords the title product (Scheme 6). We
ASSOCIATED CONTENT
* Supporting Information
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S
The Supporting Information is available free of charge on the
Experimental procedures and compound characteriza-
AUTHOR INFORMATION
Corresponding Author
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Scheme 6. Proposed Pathway for the Halocyclization of
Methyl o-Alkynylbenzoates
ORCID
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
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The authors acknowledge the National Natural Science
Foundation of China (21472136) and the Tianjin Research
Program of Application Foundation and Advanced Technology
(15JCZDJC32900) for financial support.
tentatively proposed that the failure of substrate 1t might be
attributed to unstable intermediate B with an n-butyl R group,
which might easily undergo a β-H elimination to give some
unstable allene byproduct.
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The alternative outcome of the reaction of substrate 1v
might also support an ionic pathway: because of the presence
of the MeO substituent at the para position of the alkyne
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allene intermediate E. Then the nucleophilic attack of the
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In conclusion, we have developed a novel and efficient
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Scheme 7. Proposed Alternative Pathway for the Reaction
of 1v
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