Angewandte
Chemie
DOI: 10.1002/anie.200903779
Polycyclic Hydrocarbons
9-Stannafluorenes: 1,4-Dimetal Equivalents for Aromatic Annulation
by Double Cross-Coupling**
Ikuhiro Nagao, Masaki Shimizu,* and Tamejiro Hiyama
In the field of organic materials science, the design and
characterization of polycyclic aromatic hydrocarbons
(PAHs), which exhibit superior electronic, optical, and/or
self-assembling properties, has been studied intensely.[1]
Hence, efficient synthetic methods leading to functionalized
PAHs are expected to assist the rapid developments of PAH-
based functional materials.[2] The transition-metal-catalyzed
cross-coupling reactions of organometals with organic halides
are an efficient method for regio- and stereospecific forma-
Our research group has recently demonstrated that the
palladium-catalyzed double cross-coupling reaction of vic-
bis(pinacolatoboryl)alkenes and -phenanthrenes is a versatile
synthetic method for the preparation of functionalized
phenanthrenes and dibenzo[g,p]chrycenes.[4i] As illustrated
in Scheme 1, the annulation reaction can be categorized as the
2
2
[3]
À
tion of C(sp ) C(sp ) bond. As a result, double cross-
coupling reactions of organodimetallic reagents and dihalides
would provide a straightforward and promising method for
designing PAHs if the annulation reaction takes place
efficiently in preference to the possible oligomerization and/
or polymerization. However, the examples of such annula-
tions are limited.[4]
Herein, we report that the palladium-catalyzed double
cross-coupling reaction of 9-stannafluorenes 1 with 1,2-
dihaloarenes 2 serves as a new entry to aromatic annulation
and provides a variety of triply annulated benzene derivatives
3 in good to excellent yields [Eq. (1)]. Moreover, the
approach is applicable to the synthesis of twisted PAHs[5]
such as phenanthro[9,10-b]triphenylenes and diphenan-
thro[9,10-b:9’,10’-d]thiophene through double annulation
with tetrabromoarenes, and the reaction can be extended to
annulation with 1,1-dibromoalkenes leading to the produc-
tion of dibenzofulvenes.
Scheme 1. Modes of [4+2]-type aromatic annulation using dimetal
reagents and dihalogenated compounds.
coupling of 1,2-dimetal reagents 1,2-M2 and 1,4-dihalogen-
ated compounds 1,4-X2 (mode A). To expand the synthetic
utility of palladium-catalyzed aromatic annulation using
dimetal reagents, we were interested in the combination of
1,2-dihalogenated compounds 1,2-X2 and 1,4-dimetal
reagents 1,4-M2 (umpolung of mode A) as an alternative
approach (mode B). Considering that 1,4-M2 can be readily
prepared from the corresponding 1,4-X2 and, in particular, the
structural variation of available 1,2-X2 is much broader than
that of 1,2-M2: thus mode B-type annulation could greatly
expand the repertoire of accessible PAHs. However, the
precedents of mode B-type annulation were limited to only
the reactions of 2,2’-diborylbiphenyls,[4a] zirconacyclopenta-
dienes,[4b–d] [Zr(2,2’-biphenyldilyl)3][Li·(THF)4]2,[4e–g] 2,2’-dis-
tannylbinaphthyl,[4h] and 1,4-dilithiobutadienes[4j] with 1,2-
dihalobenzenes, and there is still much room for improvement
in the scope of the substrates and reagents, yields, and
reaction conditions.
We focused our attention on 9-stannafluorene derivatives
as equivalents of 1,4-dimetal reagents, which are available
from the corresponding 2,2’-dihalobiphenyls and are often
used as precursors of 9-borafluorenes[6] but never employed
for the synthesis of PAHs.[7] We anticipated that the cyclic
form would have a beneficial effect on the reactivity toward
the first coupling of the annulation owing to the strain.[8] In
addition, the use of 9-stannafluorenes is favorable for low-
ering metal waste as compared with the corresponding 2,2’-
distannylbiphenyls.
[*] I. Nagao, Prof. Dr. M. Shimizu, Prof. Dr. T. Hiyama
Department of Material Chemistry, Graduate School of Engineering
Kyoto University, Kyoto University Katsura
Nishikyo-ku, Kyoto 615-8510 (Japan)
Fax: (+81)75-383-2445
E-mail: m.shimizu@hs2.ecs.kyoto-u.ac.jp
[**] This work was supported by Grants-in-Aid for Creative Scientific
Research (grant no. 16GS0209) from the Ministry of Education,
Culture, Sports, Science, and Technology (Japan) and The Asahi
Glass Foundation.
Supporting information for this article is available on the WWW
Angew. Chem. Int. Ed. 2009, 48, 7573 –7576
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
7573