RESEARCH
| RESEARCH ARTICLE
mesitylene, were competent nucleophiles. Cyclo-
hexenyl triflates bearing substituents at the 4-
or 5-position could also be arylated, including
the enol triflate derived from 5a-cholestan-3-
one, which yielded an arylated steroid core in
90% yield and 8:1 d.r. Various ring sizes were
also competent under these reaction conditions,
with cyclopentenyl triflate and cycloheptenyl tri-
flate undergoing smooth reductive alkylation
with benzene reaction partners in 64 and 71%
yields, respectively. Cyclobutenyl triflate partici-
pated in this reductive Friedel-Crafts alkylation,
as did aromatic alkenes. The triflate derived from
a-tetralone was reductively arylated in 43% yield,
and acetophenone-derived acyclic triflates were
also arylated in 51 to 77% yield (Fig. 4, entries 15
and 16). Simple acyclic vinyl triflates were com-
petent electrophiles for arylation by both electron-
poor and electron-rich arenes, requiring as little
as 10 equivalents of arene in chloroform solvent
at −40°C (Fig. 4, entries 17 to 20).
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ACKNOWLEDGMENTS
H.M.N. thanks M. Jung for reagents and advice. Funding: Support was
generously provided by the David and Lucile Packard Foundation
(to H.M.N.), the Alfred P. Sloan Foundation (to H.M.N.), the National
Science Foundation (CHE-1361104 to K.N.H.), and the National Natural
Science Foundation of China (grant nos. 11504130, 51673164, and
21501169 to L.Z.). A.L.B. thanks the Christopher S. Foote Fellowship
for funding. The authors thank the UCLA Molecular Instrumentation
Center for NMR instrumentation, x-ray crystallography, and the Mass
Spectrometry facility at the University of California, Irvine. Author
contributions: S.P., B.S., and A.L.B. designed and conducted
experiments. T.R.B., L.Z., and Z.Y. designed and conducted
computations. H.M.N., K.N.H., S.P., B.S., A.L.B., and T.R.B. prepared
the manuscript. Competing interests: The authors declare no
competing financial interests. Data and materials availability:
Crystallographic data are available free of charge from the
Cambridge Crystallographic Data Centre under CCDC 1838441.
Additional experimental procedures and characterization data are
provided in the supplementary materials.
Outlook
We have shown that vinyl cations, the subject
of numerous computational and experimental
studies, are now accessible synthetically from
simple vinyl triflates using WCA salts under mild
conditions. The nonnucleophilic nature of the
WCA allows these unstabilized vinyl cations to
engage in C–C bond–forming reactions with
alkanes and a variety of arenes, modes of re-
activity that have been largely unreported despite
extensive previous work. We find that the C–H
insertion reactions of vinyl cations proceed through
mechanisms that feature post–transition state
bifurcation and nonclassical ions, mechanistic
features that are common in terpene biosynthesis
(32) but rarely found in synthetic methodology.
These findings lay the conceptual and experimen-
tal groundwork for further discoveries in the field
of alkane C–H bond functionalization using ke-
tone derivatives and WCA catalysis.
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SUPPLEMENTARY MATERIALS
Materials and Methods
Supplementary Text
Figs. S1 to S44
Tables S1 and S2
References (42–66)
Movies S1 to S5
9 March 2018; accepted 5 June 2018
10.1126/science.aat5440
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