Photon Factory Activity Report 2016 #34 (2017) B

AR-NE3A/2015G097

An obtuse-angled corner unit for fluctuating carbon nanohoops
1

Zhe Sun1,4, Naoya Miyamoto2, Sota Sato1,3 Hidetoshi Tokuyama2 and Hiroyuki Isobe1,3,4 *JST, ERATO, Isobe Degenerate π-integration Project and Advanced Institute for Material Research
2
Graduate School of Pharmaceutical Sciences, Tohoku University
3
Advanced Institute for Material Research and Department of Chemistry, Tohoku University
4
Department of Chemistry, The University of Tokyo

1 Introduction
The chemistry of carbon nanohoop is heavily relied onthe devise of the corner unit to construct the macrocyclicstructure. In preceding reports, the corner units commonly
possessed directing angles of ≤90°, which enabled themacrocyclization of multiple units up to six. In this report,
an obtuse-angled corner unit with oxanorbornadienepossessed a directing angle of 126° and thus allowed forthe macrocyclization of larger structures with up to sevenunits. Structural studies with experimental and theoreticalmethods revealed a fluctuating structure with an intrinsic
non-belt shape.[1]2 Experiment
The synthesis of the [n]CPP congeners 4 is shown inscheme1.
Benzynegeneratedfromphenyltrifluoromethanesulfonate
andmagnesiumamide[Mg(TMP)2•2LiCl] was adopted for the Diels-Alderreaction with bromophenylated isobenzofuran 1 to afford
the corner unit 2 in a good yield.[2] The corner unit 2 wasthen subjected to the Ni-mediated, Yamamoto-type
macrocyclization reaction. The aromatization reaction
proceeded under reductive conditions using Zn/AcOH,
and [n]CPP congeners containing anthracenylene panels
were obtained.
Single crystals of 3 (m = 5, 7) and 4 (m = 5) wereobtained by diffusion of poor solvents (methanol orisopropanol) to the solution of the compounds in good
solvents (dichloromethane or chloroform). A single
crystal was mounted on a thin polymer tip withcryoprotectant oil and frozen at measurement temperature
via flash-cooling. The diffraction analysis of a single
crystal with a synchrotron X-ray source was conducted at–178 °C at the beamline PF-AR NE3A at the KEK
Photon Factory using a diffractometer equipped with anDectris Pilatus 2M-F PAD detector.
3 Results and Discussion
The crystal structures of macrocycles revealed
important structural features of 3 and 4. As shown in Fig.
1, The directing angles embedded in the macrocyclic
structures did not deviate from the original angle in themonomer (126°) and were, on average, 122° and 125° for
5-mer and 7-mer, respectively. Although naive
considerations of the geometries may suggest that thedirecting angle of 126° should match better with internalangles of an equilateral heptagon (129°) than those of anequilateral pentagon (108°), the pentagonal 5-mer wasobtained as the major product. To tolerate the mismatch,the macrocycles possessed contorted structures in which
ipso carbons and linking carbons were not on a flat plane:from a mean plane of ipso and linking carbons, theaverage distances of the carbon atoms from the plane
were measured 1.13 and 1.45 Å for 5-mer and 7-mer 3,
respectively. Upon aromatization from 3 to 4, thedirecting angles were widened by 40° to 162° on average,
and the aromatized structure was found to be an ovalshaped ring.
BrBr
OTf
Mg(TMP)2•2LiClO

Ni(cod)22,2'-bipyridyl
1,4-cycloctadieneO

toluene/DMF
80 °C

THF-78 °C to 0 °C
90%BrTMP = N

Br213Ph
2PhZn, AcOH
O2An

8An 7An

1Ano-DCB
100 °Cmm

4
isolated (yield based on 2)
m = 5: 13%m = 6: 7%m = 7: <6%single crystal
m=53
detected by MS
m = 5, 6, 7, 8
single crystal
m = 5, 7

Scheme 1: Synthetic route to [n]CPP congeners 4.

3 (m = 5)

3 (m = 7)

4 (m = 5)

Fig. 1: Crystal structures of 3 (m = 5, 7) and 4 (m = 5).
References[1] Z. Sun, N. Miyamoto, S. Sato, H. Tokuyama, H. Isobe,Chem Asian J 2017, 12, 271–275.
[2] K. Okano, H. Fujiwara, T. Noji, T. Fukuyama, H.
Tokuyama, Angew. Chem. Int. Ed. 2010, 49, 5925–5929.
* isobe@chem.s.u-tokyo.ac.jp