Angewandte
Communications
Chemie
Synthetic Methods
Regioselective One-Pot Synthesis of Triptycenes via Triple-
Cycloadditions of Arynes to Ynolates
Satoshi Umezu, Gabriel dos Passos Gomes, Tatsuro Yoshinaga, Mikei Sakae, Kenji Matsumoto,
Takayuki Iwata, Igor Alabugin, and Mitsuru Shindo*
Abstract: We developed the novel one-pot synthetic method of
substituted triptycenes by the reaction of ynolates and arynes.
This four-step process involves three cycloadditions and
electrocyclic ring opening of the strained Dewar anthracene.
Each of the three related but structurally distinct classes of
nucleophiles (ynolate, enolate, and anthracenolate) reacts with
o-benzyne in the same predictable manner controlled by
chelation and negative hyperconjugation. The resulting func-
tionalized C3-symmetrical triptycenes hold promise in the
design of functional materials.
Y
nolates 1 are compact energy-rich nucleophiles with great
potential in synthetic organic chemistry.[1] As dianion equiv-
alents, ynolates are useful as nucleophilic initiators of one-pot
sequences leading to rapid preparation of useful products.[2]
Scheme 1. Cycloadditions of ynolates to polar and non-polar multiple
bonds.
=
Formal cycloaddition reactions of ynolates with polar C X
(X = O, N) double bonds have been reported by us and others
to yield unsaturated four-membered heterocycles 2 such as b-
lactone or b-lactam enolates leading to various reactions and
products (Scheme 1, Equation (1)).[2b,3] In comparison with
cycloadditions to the polar bonds, examples of synthetic
will show that their electronic properties lead to new rich
reactivity features.
We adopted 2-bromophenol triflate 7 as a precursor of
benzyne.[8] Treatment of the precursor 7, added to an in situ
prepared ynolate solution in THF (Scheme 2),[9] with n-BuLi
at ꢀ788C, led to the generation of the anticipated o-benzyne.
As expected, the latter was trapped by the ynolate. Surpris-
ingly, however, the reaction involved three moles of o-
benzyne, leading to 9-hydroxy-10-methyltriptycene (5a) as
the major product in 30% yield.
ꢀ
reactions with nonpolar multiple C C bonds remain, to the
best of our knowledge, relatively scarce.[4] Based on the high
[5]
ꢀ
electrophilicity of the non-polar C C triple bond of arynes,
these strained alkynes can be expected to readily participate
in cycloadditions with nucleophilic ynolates. Herein, we
report a one-pot sequence of three efficient and regioselective
cycloadditions, initiated by the reaction between ynolates and
arynes (Scheme 1, Equation (3)). This sequence provides
substituted triptycenes 5 in a highly regioselective head-to-
head-to-head manner.
In analogy with the known reactions of enolates and
arynes (Scheme 1, Equation (2)),[6] one could expect that
reaction of ynolates 1 and arynes 3 will lead to the formation
of benzocyclobutenone enolates 4. Although these synthetic
intermediates[7] would be destabilized by antiaromaticity, we
Scheme 2. Reaction of ynolate with benzyne to provide 9-hydroxy-10-
methyltriptycene 5a.
[*] S. Umezu, T. Yoshinaga, M. Sakae
Interdisciplinary Graduate School of Engineering Sciences
Kyushu University
The suggested mechanism for the formation of this
unexpected product is shown in Scheme 3. Ynolate 1a adds
to benzyne to give a benzocyclobutenone enolate 4a, which is
sufficiently nucleophilic to add to another benzyne to form
the Dewar anthracene 8a.[10] Relief of antiaromaticity is likely
to contribute to the efficiency of this process. The fused [2.2.0]
core of the product is highly strained and can undergo
spontaneous ring-opening with the formation of electron-rich
anthracene alkoxide 9a.[11] This penultimate intermediate
engages the third benzyne molecule in the final [4+2]
cycloaddition step that furnishes the isolated triptycene
6-1 Kasuga-koen, Kasuga, 816-8580 (Japan)
Dr. K. Matsumoto, Dr. T. Iwata, Prof. Dr. M. Shindo
Institute for Materials Chemistry and Engineering, Kyushu University
6-1 Kasuga-koen, Kasuga, 816-8580 (Japan)
E-mail: shindo@cm.kyushu-u.ac.jp
G. dos Passos Gomes, Prof. Dr. I. Alabugin
Department of Chemistry and Biochemistry, Florida State University
Tallahassee, FL 32310 (USA)
Supporting information for this article can be found under:
Angew. Chem. Int. Ed. 2016, 55, 1 – 6
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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