Synthesis, structure, and properties of a dibenzo-ortho-terphenoquinone. The first o-terphenoquinone derivative

Article abstract of DOI:10.1246/cl.2003.538

A dibenzo-ortho-terphenoquinone derivative, the first o-terquinone derivative, is largely deviated from coplanarity, is in a slight equilibrium with its diradical form, displays an easy rotation of the exocyclic double bonds, and shows photoresponsive swi

Full text of DOI:10.1246/cl.2003.538

538
Chemistry Letters Vol.32, No.6 (2003)
Synthesis, Structure, and Properties of a Dibenzo-ortho-terphenoquinone. The First
o-Terphenoquinone Derivative
Hiroyuki Kurata, Yuko Takehara, Takeshi Kawase, and Masaji Odaꢀ
Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043
(Received April 1, 2003; CL-030278)
t
t
O
Bu Bu
O
A dibenzo-ortho-terphenoquinone derivative, the first o-ter-
quinone derivative, is largely deviated from coplanarity, is in a
slight equilibrium with its diradical form, displays an easy rota-
tion of the exocyclic double bonds, and shows photoresponsive
switching property traceable by ESR spectroscopy.
t
t
t
t
t
t
Bu
Bu
Bu
Bu
Bu
O
O
Bu
2
1
Extended quinones have attracted considerable attention
from the structural and physicochemical, in particular electro-
chemical points of view.1 Extended p-phenoquinones tend to
be in equilibrium between the quinoid forms and diradical
forms depending on the degree of extension and substituent
effect.2 Recently, we have reported the synthesis and a switch-
ing functionality (ESR detection) of dibenzannelated p-
terphenoquinone (1) which shows a cleanly reversible photo-
chemical and thermal interconversion between the quinone
and diradical forms involving restricted conformational
change.3 The nonplanarity of 1 plays an important role in this
interconversion. Thus, in theory, there can be other switching
systems based on nonplanar extended quinones and quino-
methides. In this context, we have been interested in the devel-
opment of novel extended quinones rich in dynamic processes.
Here we report the synthesis, structure, and properties of diben-
zo-o-terphenoquinone (2), the first derivative of this kind as
well as the structural isomer of 1.
The visible absorption of 2 [ꢀmax 423 nm/CH2Cl2 ("
21900)] is very similar to that of 1 [424 nm/CH2Cl2 (42700)]
in the wavelength but nearly half in the absorption coefficient
to suggest deviation of the quinomethide chromophores from
coplanarity more than 1. The 1H NMR spectra revealed the dy-
namic stereochemical process of 2 around room temperature:
while the spectrum at 30 ꢁC shows the t-butyl protons as a sing-
let and the olefinic protons of quinomethide part almost invisi-
ble owing to broadening, that at ꢂ60 ꢁC shows two singlets of
the t-butyl groups at d 1.21 and 1.24 and two doublets of the
quinomethide protons at d 7.22 and 7.55. These observations in-
dicate fairly easy rotation of the exocyclic double bonds (pinch
bonds) of 2 around room temperature.8 From the variable-tem-
perature NMR measurements, the rotational barrier (ÁGz) is es-
timated
to
be
as
low
as
13:6 Æ 0:3 kcal molꢂ1
(Tc ¼ ꢂ15 Æ 3 ꢁC).
Recrystallization of 2 from ethanol gave single crystals
suitable for X-ray analysis.9 Figure 1 shows the ORTEP draw-
ings. The central six-membered ring takes a twisted chair form
probably to reduce the steric crowding around the quinomethide
units. Dihedral angle of the two pinch bonds (C4–C13–C26–
C10) is as large as 68.0ꢁ. The biphenyl part (C18–C19–C20–
C21) is twisted by 22.2ꢁ. On the other hand, the pinch bonds
areꢁ only slightly twisted with the average torsion angles of
Synthesis of 2 was outlined in Scheme 1. Reaction of 4-
lithio-2,6-di-t-butylphenoxide, generated by treatment of 4-bro-
mo-2,6-di-t-butylphenol with three equivalents of t-BuLi,4 with
9,10-phenanthrenequinone in ether afforded bisadduct (3)5 as a
single stereoisomer in 35% yield. Use of THF as solvent did not
yield 3 at all probably because of electron transfer reaction as
judged from deep blue coloration of the reaction mixture. At-
tempted dehydration of 3 to 2 with either POCl3/pyridine or
CuSO4/THF was not successful, producing a complex mixture
or ketone (4) by the pinacol rearrangement. We, therefore,
transformed 3 to bisphenol (5) through the acid-catalyzed pina-
col rearrangement to 4 and its reductive rearrangement
(LiAlH4/THF and then I2/CH3COOH).6 Oxidation of 5 with al-
kaline K3Fe(CN)6 afforded 2 as orange crystals in 99% yield.7
ꢀ
4.1 . The average length of the pinch bonds of 2 (1.38 A) is sim-
ꢀ
ilar to that of dibenzo-p-terquinone 1 (1.37 A) but is shorter than
2a,b
ꢀ
that of a nonbenzannelated p-terquinone derivative (1.42 A).
Electrochemical properties of 2 (cyclic voltammetry) are
also significantly different from 1. First, 2 (Epc ¼ ꢂ0:87 V)
has a higher electron affinity than 1 (Epc ¼ ꢂ1:08 V; 25 ꢁC).10
t
t
OH
t
t
HO
Bu Bu
OH
HO
Bu Bu
OH
t
Bu
t
OH
Br
t
Bu
Bu
t
t
t
t
t
t
Bu
Bu
Bu
Bu
Bu
Bu
a, b
d, e
c
f
OH
O
2
HO
OH
t
Bu
3
5
4
Scheme 1. a; 3 equiv. t-BuLi/ether, 0 ꢁC, 1 h, b; 0.4 equiv. 9,10-phenanthrenequinone, 35%, c; CF3CO2H/CH3CO2H, r.t., 1 h, 75%,
d; LiAlH4/THF, reflux, 1.5 h, 81%, e; 0.3% I2/CH3CO2H, reflux, 1.5 h, 74%, f; K3Fe(CN)6/0.1 M KOH aq./benzene, r.t., 3 d, 99%.
Copyright Ó 2003 The Chemical Society of Japan

Chemistry Letters Vol.32, No.6 (2003)
539
Figure 2. Change of ESR signal intensity of
2 under intermittent photoirradiation.
References and Notes
Figure 1. ORTEP drawings (50% thermal ellipsoids) of 2.
Hydrogen atoms are omitted for clarity. Selected bond
1
For reviews; a) “The Chemistry of Quinonoid Compounds,”
ed. by S. Patai, Wiley, London (1974). b) “The Chemistry of
Quinonoid Compounds Vol. II,” ed. by S. Patai and Z.
Rappoport, Wiley, Chichester (1988).
ꢁ
ꢀ
lengths (A) and angles ( ): O1–C1 1.228(3), C1–C2
1.485(4), C2–C3 1.350(4), C3–C4 1.455(4), C4–C13
1.378(4), C13–C26 1.490(4), O1–C1–C2 121.1(3), C1–
C2–C3 119.2(3), C2–C3–C4 123.0(3), C3–C4–C13
122.0(2), C4–C13–C26 125.1(2), C13–C26–C10 123.3(2).
2
a) R. West, J. A. Jorgenson, K. L. Stearly, and J. C.
Calabrese, J. Chem. Soc., Chem. Commun., 1991, 1234. b)
P. Boldt, D. Bruhnke, F. Gerson, M. Scholz, P. G. Jones,
Second, 2 exhibits two re-oxidation peaks (Epa) at ꢂ0:79 and
ꢂ0:52 V, which we tentatively assign to each one-electron oxi-
dation forming anion radical 2Áꢂ and diradical form of 2 (2B)
rather than involvement of hysteresis behavior, whereas 1
clearly shows temperature dependent hysteresis behavior
involving conformational change (large differences between
Epc and Epa).3
Although p-terquinone 1 is ESR silent, o-terquinone 2 exhi-
bits weak ESR signals in a degassed toluene solution at room
temperature. The observed triplet pattern (aH ¼ 0:18 mT,
g ¼ 2:0045) is similar to that of the diradical form of 1 and
other 4-substituted-2,6-di-t-butylphenoxy radicals, suggesting
a slight equilibrium of 2 with diradical 2B (Scheme 2).11 The
signals become larger upon heating or more effectively upon
photoirradiation: irradiation of 2 with a high pressure Hg lamp
causes gradual increase of the signal intensity which returns to
the original intensity in the dark in about 1.5 h at room tempera-
ture (Figure 2). Thus, like 1, o-terquinone 2 shows switching
function to some extent, although the response is slower.12
Further studies toward the development of an improved
photoresponsive switching system by structural modification
of 2 are in progress.
and F. Bar, Helv. Chim. Acta, 76, 1739 (1993). c) A.
Rebmann, J. Zhou, P. Schuler, H. B. Stegmann, and A.
Rieker, J. Chem. Res., Synop., 1996, 318.
H. Kurata, T. Tanaka, and M. Oda, Chem. Lett., 1999, 749.
H. Kurata, T. Tanaka, T. Sauchi, T. Kawase, and M. Oda,
Chem. Lett., 1997, 947.
We tentatively assign the trans configuration for 3 from the
viewpoint of steric hindrance on the second nucleophilic ad-
dition of the dianion.
For similar way for the synthesis of 9,10-disubstituted phen-
anthrenes, see; Y.-H. Lai, J. Chem. Soc., Perkin Trans. 2,
1986, 1667.
2: reddish-orange prisms (EtOH), mp 213–214 ꢁC; MS (EI)
m=z 586 [(M+2)þ, 27%], 585 [(M+1)þ, 41], 584 (Mþ, 95),
528 [(M+1-tBu)þ, 100]; UV-vis (cyclohexane) ꢀmax/nm
(log ") = 419 (4.34), 346 (4.72), 333sh, 2,44 (4.41); IR
(KBr) ꢁ (CO) = 1612 cmꢂ1; Found: C, 86.05; H, 8.18%.
Calcd. for C42H48O2: C, 86.26, H, 8.27%.
¨
3
4
5
6
7
8
9
The thermal equilibrium with the diradical form may be re-
sponsible for the easy rotation of the pinch bonds.
Crystal data for 2: C42H48O2, Mr ¼ 584:84, monoclinic,
space group P21=n(no. 14), a ¼ 12:41ð2Þ, b ¼ 18:35ð2Þ,
ꢀ
ꢀ 3
c ¼ 15:36ð2Þ A, ꢂ ¼ 95:4ð1Þ, V ¼ 3483ð8Þ A , Z ¼ 4,
Dcalcd ¼ 1:115 g cmꢂ3, 31553 reflections measured, 7835
unique (Rint ¼ 0:094) used in refinement. R1 ¼ 0:059
(7835 data, I > 2sðIÞ), wR ¼ 0:140 (all data), T ¼ 203 K.
CCDC 206981.
This work was supported by a Grant-in-Aid for Scientific
Research (No. 13640534) from the Ministry of Education, Cul-
ture, Sports, Science, and Technology.
10V vs Ag/Ag þ, in 0.1 M n-Bu4NClO4/CH2Cl2, sweep rate
100 mV/s, ferrocene = þ0:32 V, 25 ꢁC.
t
t
O
Bu Bu
O
O
O
1
tBu
tBu
11 The fact that H NMR signals of 2 are observed normally
t
t
t
t
indicates very low concentration of diradical 2B.
12 Photoirradiation of 2 gave rise to weak ESR signals other
than the triplet pattern that also disappear in the dark to sug-
gest occurrence of a reversible side reaction. There seems a
possibility of electro-cyclization of the bisquinomethyl-
enethane moiety with some similarity to the photochemical
cyclization of cis-stilbene, and further studies on this point
are underway.
Bu
Bu
Bu
Bu
hν or ∆
dark
2A
2B
Scheme 2.
Published on the web (Advance View) May 27, 2003; DOI 10.1246/cl.2003.538