nitro, and cyano substituents, 1f afforded the corresponding
quinoline 4f in moderate yields (entries 11 and 12); however,
low yields of the cyclic products 4g and 4h were obtained
(entries 13s16). Furthermore, isocyanide 1i bearing a
1-cyclohexenyl group underwent the desired cyclization to
form the corresponding quinoline 4i in good yields (entries
17 and 18). These reaction systems can be applied to
isocyanides bearing aliphatic group on the ethynyl groups.
When the reactions of isocyanide 1j were performed under
both conditions, the corresponding quinoline 4j was obtained
in 82% (condition A) and 88% (condition B) yields,
respectively (entries 19 and 20). Isocyanides 1k having
propargylic protons also afforded 4k in good yields (entries
21 and 22).
The cyclization products have two kinds of telluro groups,
which are formally imidoyltelluro and aryltelluro groups, and
are potentially useful synthetic intermediates.13 Thus, we next
examined the reductive elimination of telluro groups via Te/
Li exchange reactions.14 Upon treatment of 4a and 4j with
t-BuLi, the reductive elimination of telluro groups took place
successfully, leading to the corresponding quinolines 5a and
5b in good yields, respectively (Scheme 2).
Scheme 2
In the case of 1l, oligomerization of 1l took place
predominantly. Unfortunately, isocyanides 1m and 1n did
not react under these reaction conditions (most subatrates
were recovered unchanged). These results suggest that the
presence of bulky substituents such as t-Bu and TMS groups
at ethynyl groups inhibited the desired reactions.
In summary, we have developed a novel visible-light-
induced intramolecular radical cyclization of o-ethynylaryl
isocyanides, affording the corresponding bistellurated quino-
lines, selectively. We also showed that the generated C-Te
bonds can be reduced by an organolithium reagent.
Acknowledgment. This work is supported by a Grant-
in-Aid for Scientific Research on Priority Areas (Area 444,
No. 19020061) and Scientific Research (B, 19350095), from
the Ministry of Education, Culture, Sports, Science and
Technology, Japan.
The possible reaction pathways considered for this pho-
toinduced radical cyclization are shown in Scheme 1. Path
Scheme 1
Supporting Information Available: General experimental
1
procedures, characterization data, and H and 13C NMR
spectra for bistellurated quinolines and 3-substituted quino-
lines. This material is available free of charge via the Internet
OL901267H
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(a): radical addition of PhTe• to the isocyano group, forming
an imidoyl radical; intramolecular cyclization; abstraction
of the telluro group to afford 4. Path (b): radical addition of
PhTe• to the ethynyl group, forming a vinyl radical; intramo-
lecular cyclization; abstraction of the telluro group to give
4.12
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(12) Another possible reaction pathway is the Bergman-like cyclization
under photoirradiation to generate a biradical species and sequential
abstraction of telluro groups. However, the determination of the precise
reaction pathways should wait for further detailed mechanistic study.
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