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bond migration of cation 80 affords intermediate 10 through 9. Finally,
the intramolecular Friedel–Crafts reaction of 10 affords product 4.
In conclusion, we have developed a MeOTf-induced annulation
between arylnitriles and aromatic alkynes. A range of functionalized
indenone products are obtained. Under the same reaction condi-
tions, ortho-substituted benzonitriles afforded indeno[1,2-c]isoquino-
lines with the construction of one carbocycle and one heterocycle.
Further investigations are still in progress in this area.
This work was supported by the National Key Basic Research
Program of China (973 program) (2012CB933402) and the National
Natural Science Foundation of China (21032004 and 21272132). We
also thank Mr Yun Song for his kind assistance in this work.
Scheme 5 Reaction of ortho-substituted benzonitrile, MeOTf, and
diphenylacetylene and the X-ray structure of 4a.
para-position afforded the corresponding indenones in trace amounts
and the alkynes remained. Benzonitriles with a meta-substituted methyl
or bromo group afforded the corresponding indenones as two isomers
(3ia and 3ia0, 3ja and 3ja0), respectively. Notably, when m-methoxyl-
benzonitrile was used, indenone 3ka was formed in 31% isolated yield.
In this case, we did not observe the other isomer. 3,5-Dimethyl-
benzonitrile afforded 3la in 68% isolated yield. 2-Naphthonitrile gave
benzo[e]indenone 3ma in 46% isolated yield as a single product.
When o-chlorobenzonitrile was employed under the same reaction
conditions, the reaction did not afford an indenone product but
indeno[1,2-c]isoquinoline 4a was formed in 46% isolated yield. The
structure of 4a was further confirmed by its X-ray diffraction analysis.‡
The structure of 4a contains two molecules of o-chlorobenzonitrile
and one molecule of diphenylacetylene. Methylene and methyl groups
were derived from methyl triflate. The reaction of benzonitriles
with an ortho-bromo or iodo substituent was similar, and the corre-
sponding indeno[1,2-c]isoquinolines 4b and 4c were isolated in 39%
and 43% yields, respectively (Scheme 5). When o-tolunitrile was
employed as the substrate, the reaction yielded a mixture of inde-
nones and indeno[1,2-c]isoquinoline (see ESI†).
Notes and references
‡ CCDC 965411.
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´
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Scheme 6 Plausible mechanism.
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