Fulvadienes derived from fluorenes and their oxidation to spirodiazatetracenes

Article abstract of DOI:10.1055/s-0029-1218773

Based on the acylation reaction of fluorenyl anions with the bis(imidoyl) chlorides of oxalic acid, a short and efficient synthesis for a series of novel bis(arylamino) fulvadienes was developed. The products were isolated as red colored and crystalline compounds in good yields. Their structures were determined by elemental analysis, MS, NMR, and additionally by X-ray crystal structural analysis. Monoimidoyl chlorides showed the same reactivity. Enamines were isolated in good yields as products. The bis(arylamino) fulvadienes can be transformed by an oxidation-ring annulation sequence into diazatetracene derivatives. These to date unknown bis-spiro derivatives of diazatetracene are well soluble in common solvents and display green fluorescence in solution. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-0029-1218773

PAPER
2049
Fulvadienes Derived from Fluorenes and Their Oxidation to Spirodiaza-
tetracenes
O
xidation of Fulva
u
dienes toSp
n
irodiazatetra
c
enes her Buehrdel,a Rainer Beckert,*a Helmar Görlsb
a
Institute of Organic and Macromolecular Chemistry, Friedrich-Schiller-University Jena, Humboldtstr. 10, 07743 Jena, Germany
Fax +49(3641)948212; E-mail: C6bera@uni-jena.de
b
Institute of Inorganic and Analytical Chemistry, Friedrich-Schiller-University Jena, Lessingstr. 8, 07743 Jena, Germany
Received 5 February 2010; revised 18 March 2010
tion, the products are unable to undergo subsequent elec-
trocyclization processes.
Abstract: Based on the acylation reaction of fluorenyl anions with
the bis(imidoyl) chlorides of oxalic acid, a short and efficient syn-
thesis for a series of novel bis(arylamino) fulvadienes was devel-
oped. The products were isolated as red colored and crystalline
compounds in good yields. Their structures were determined by
elemental analysis, MS, NMR, and additionally by X-ray crystal
structural analysis. Monoimidoyl chlorides showed the same reac-
tivity. Enamines were isolated in good yields as products. The
bis(arylamino) fulvadienes can be transformed by an oxidation-ring
annulation sequence into diazatetracene derivatives. These to date
unknown bis-spiro derivatives of diazatetracene are well soluble in
common solvents and display green fluorescence in solution.
Cl
ArHN
ArN
NHAr
NAr
1
Cl
3
2
Key words: amines, oxidation, radical reaction, fulvadienes,
bis(imidoyl) chlorides
Scheme 1 Retrosynthetic approach for diaminofulvadienes
Fluorene 2a reacted readily with bis-electrophile 1a under
quite mild conditions (THF in the presence of t-BuOK at
–78 °C), forming a red crystalline product in good yield.
Elemental analysis and MS data confirmed the presence
of a 2:1 acylation product 3a. Evidence for the symmetry
in this novel diarylaminofulvadiene 3a (Scheme 2) was
provided by single sets of signals in its 1H and 13C NMR
spectra. The NH protons of derivative 3a showed reso-
nance at d = 6.19.
Among fulvalenes, their heteroanaloguos derivatives,
such as tetrathia- and tetraazafulvalenes, are mainly of
considerable interest to material sciences. These cross-
conjugated, p-electron systems display a multi-step redox
activity, which can be used in widespread applications.
Their vinylogous derivatives, which can be regarded as
fulvadienes are not only of theoretical interest, but are also
capable of forming polycylic hydrocarbons via electrocy-
clization processes.1
Employing the same procedure, the bis(imidoyl) chlorides
1b–e, as well as 2-bromofluorene (2b) and 2,7-dibromo-
fluorene (2c) were integrated into this reaction. The prod-
ucts 3b–g were obtained in good yields as crystalline
compounds, which showed similar chemical properties to
3a. It must be noted that derivatives 3e,f were isolated as
inseparable mixtures of E/Z-isomers originating from the
asymmetry of 2-bromofluorene (2b). Therefore, these
mixtures display a complex set of signals in their 1H and
13C NMR spectra.
As a continuation of our studies on cross-conjugated sys-
tems, amino substructures should be integrated into fulva-
dienes. A promising synthetic pathway to compounds of
type 3 based on our previous experience should consist of
the acylation reaction of cyclopentadienyl anions with
bis(arylimidoyl) chlorides 1 (Scheme 1). During the last
decade, we demonstrated that the latter derivatives are ex-
cellent (and selective) bis-electrophiles that can be em-
ployed as C2-building blocks for heterocyclic as well as
for carbocyclic compounds.2 It has been observed in many
cases during the acylation of substrates with 1 that a very
fast prototropic shift takes place, forming enamino sub-
structures. Our aim was, therefore, to develop a short and
efficient route to diarylamino fulvadienes 3 exploiting this
acylation-prototropism cascade. We first studied the reac-
tion of 1 with fluorenyl anions from 2. They are easily
available due to the high acidity of fluorene and, in addi-
Further structural details were obtained from single crys-
tal X-ray analyses of 3a and 3d, hence the derivatives 3
have a 1,2-difluorenylidene-1,2-diarylaminoethane struc-
ture. The result of these analyses showed that 3a and 3d
are monomers in the solid state. Figure 1 displays the sol-
id state structures of 3a and 3d. The bond lengths and an-
gles were within the expected range; only the bonds
between N1–C1/N2–C2 (1.38 Å) were somewhat short-
ened. Because of the bulky fluorene moiety, the C=C
bond is twisted by around 16°, and the torsion angle for 3a
between N2–C2–C3–C15 is –17.3(2)°; N1–C1–C16–C18
for 3d is –16.4(3)°. As a result of the steric demand of the
fluorenyl and arylamino groups, the central C–C bond
SYNTHESIS 2010, No. 12, pp 2049–2056
x
x.
x
x
.
2
0
1
0
Advanced online publication: 05.05.2010
DOI: 10.1055/s-0029-1218773; Art ID: T02810SS
© Georg Thieme Verlag Stuttgart · New York

2050
G. Buehrdel et al.
PAPER
Cl
NAr
As a result of two donor–acceptor chromophores, in com-
bination with torsion of the double bonds in the molecule,
compounds 3 formed dark red solutions; 3a, for example,
absorbed in CHCl3 at lmax = 450 nm, (log e = 4.2).
ArN
Cl
1
1a Ar = 4-Tol
1b Ar = 4-MeOC6H4
X2
X1
CCH2OC6H4
1c Ar = 4-HC
Finally, we tested the synthetic concept on monofunction-
al imidoyl chlorides. The reaction of the imidoyl chlorides
4a,b with fluorene (2a), under the same mild conditions,
resulted in the yellow products 5a,b (Scheme 3). Elemen-
tal analyses and MS data confirmed the presence of 1:1
acylation products 5. The enamine substructure was prov-
en by characteristic signals for the NH protons at d = 6.09
(5a) and d = 6.77 (5b) in the 1H NMR spectra.
1d Ar = 4-BrC6H4
t-BuOK
THF, –78 °C
ArHN
+
NHAr
X2
X1
X2
X1
2
3
2a X1 = X2 = H
2b X1 = H, X2 = Br
2c X1 = X2 = Br
3a X1 = X2 = H, Ar = 4-Tol
3b X1 = X2 = H, Ar = 4-MeOC6H4
3c X1 = X2 = H, Ar = 4-HCCCH2OC6H4
3d X1 = X2 = H, Ar = 4-BrC6H4
3e X1 = H, X2 = Br, Ar = 4-Tol
3f X1 = H, X2 = Br, Ar = 4-MeOC6H4
3g X1 = X2 = Br, Ar = 4-Tol
t-BuOK
THF, –78 °C
NTol
R
NHTol
R
Cl
2a
+
3h X1 = X2 = Br, Ar = 4-MeOC6H4
4
R
R
4a R = CF3
4b R = 4-CF3C6H4
5a R = CF3
5b R = 4-CF3C6H4
NH
NH
(Ph3P)2PdCl2 (10 mol%)
CuI (10 mol%)
Et3N, toluene, 80 °C
Scheme 3 Reaction of fluorene with monoimidoyl chlorides
3d
The formation of yellow by-products 6 was observed by
TLC even during the recrystallization of derivatives 3 un-
der aerobic conditions. Based on electrochemical mea-
surements, we suggest that these new products originated
from oxidative transformation processes of 3. Thus, the
cyclovoltammogram of compound 3a revealed two irre-
versible oxidation peaks. Employing square wave mea-
surements on derivative 3a, two peaks at 1.133 and at
1.709 V can be ascribed to two different electron transfer
steps.
R
3i
R = Si(i-Pr)3
Scheme 2 Synthesis of 1,2-difluorenylidene-1,2-diarylaminoeth-
anes 3 and modification by Sonogashira cross-coupling reaction
(C1–C2) is twisted by around 57°, and the torsion angle
for 3a between C16–C1–C2–C3 is –56.9(2)°. The stag-
gered arrangement of the substituents on the C–C bond
(C1–C2) leads to a propeller-like structure.
We tested several oxidants for the oxidation of 3b. Using
lead(IV) acetate in the presence of potassium carbonate,
the formation of a yellow side product 6b displaying
green fluorescence (lEm = 512 nm) was observed. How-
ever, due to the formation of several by-products, this
product was only isolated in a low yield. Better results
The bromo-substituted derivatives offer the preconditions
for subsequent modifications, as exemplified here for the
Sonogashira cross-coupling method. The red bis-acety-
lene 3i was isolated in a high yield upon treatment of
3d with (triisopropylsilyl)acetylene under standard
Sonogashira conditions (Scheme 2).
Figure 1 ORTEP plot (50% probability ellipsoids) of the solid state molecular structure (X-ray analysis) of derivative 3a (left side) and 3d
(right side, view along the central C1–C2 bond), selected bond lengths in Å for 3a: N1–C1 1.387(2), N2–C2 1.386(2), C1–C2 1.493(3), C2–C3
1.363(3), C1–C16 1.364(3)
Synthesis 2010, No. 12, 2049–2056 © Thieme Stuttgart · New York

PAPER
Oxidation of Fulvadienes to Spirodiazatetracenes
2051
were obtained by using ceric ammonium nitrate (CAN)/
potassium carbonate. We succeeded in isolating this yel-
low colored and green fluorescent product 6b by column
chromatography in a satisfactory yield. The MS data indi-
cated, in this case, the loss of four hydrogen atoms.
Evidence for the structure of bis(spirofluorene)dihydro-
diazanaphthacene derivative 6b (Scheme 4) was mainly
1
provided by the H and 13C NMR spectra. Instead of the
characteristic signals for a 4-methoxy-substituted phenyl
substructure, the typical signals for a AMX spin system of
a 1,2,4-trisubstituted benzene were detected in the
1H NMR spectra, a doublet at d = 7.11 (3J = 8 Hz), a double
doublet d = 6.72 (3J = 8 Hz, 4J = 2.8 Hz), and a doublet at
d = 5.70 (4J = 2.8 Hz) were observed. Only the simple set
of signals for a 1,2-disubstituted benzene were observed
for the fluorenyl moiety. In the 13C NMR spectra, the
characteristic resonance of a spiro carbon at d = 61.3 was
detected. A resonance at 60.8 ppm in the 13C NMR was
measured for the spiro carbon of bis(spirofluorene)dihy-
dronaphthacene.3
Figure 2 ORTEP plot (50% probability ellipsoids) of the solid state
molecular structure (X-ray analysis) of derivative 6b, selected bond
lengths in Å: N1–C21 1.287(3), N2–C20 1.281(3), C7–C20 1.527(3),
C20–C21 1.484(3), C21–C22 1.517(4)
13C NMR spectra. All new synthesized bis(spirofluo-
rene)diazatetracenes 6a–h display a green fluorescence in
solution, whereby the emission maxima and the quantum
yields were influenced by the substituents R [6b:
R
3
2
4
1
X
X
l
max = 402 nm, (log e = 4.1), lEm = 512 nm, F = 0.1).
X
X
N
As a side product of the oxidation of 3d, compound 7 was
isolated, in traces, as yellow crystals after column chro-
matography. The MS data indicated, in this case, the loss
of only two hydrogen atoms. In the 1H NMR, a singlet for
the NH proton at d = 8.00 was observed; in the 13C NMR
spectra of 7, the signal for a spiro carbon was detected at
d = 61.3. A single crystal X-ray analysis of 7 displays the
structure of this side product as a spirofluoranthene deriv-
ative (Scheme 4) (Figure 3).
12
CAN, K2CO3
MeCN, r.t.
5
3
N
6
11
Ox.
7
10
8
9
R
6a X = H, R = Me
6b X = H, R = OMe
6c X = H, R = OCH2C
6d X = H, R = Br
CH
6e X = H or Br, R = Me
6f X = H or Br, R = OMe
ArN
NAr
H
7
7 Ar = 4-BrC6H4 (from 3d)
Scheme 4 Oxidative transformation of 3
A single crystal X-ray analysis of 6b confirmed the mo-
lecular structure of a bis-spiro annulated diazanaph-
thacene (Figure 2). The result of this analysis showed that
6b is a monomer in the solid state in which the bond
lengths and angles lie in the expected range.
The molecule exhibits a ‘twisted-saddle’ conformation,
whereby the fluorenyl moieties are each folded to the
same side of the tetracene framework by about 15°. More-
over, the two spiro connected fluorenyl substructures,
which are orthogonal to their attached six-membered
rings, are bent slightly in the opposite direction from the
dihydronaphthacene framework.
Figure 3 ORTEP plot (50% probability ellipsoids) of the solid state
molecular structure (X-ray analysis) of derivative 7, selected bond
lengths in Å: N1–C1 1.381(4), N2–C2 1.270(4), C1–C2 1.513(4),
C2–C3 1.556(4), C1–C18 1.364(4)
The other fulvadienes of type 3 could successfully be in-
volved into this oxidative reaction cascade (Scheme 4),
whereby the bromofluorenyl substituted derivatives 6e,f
could be isolated in higher yields. Compounds 6e and 6f
were isolated as inseparable mixture of two isomers,
which displayed a complex set of signals in their 1H and
Based on recent results, we postulate the following mech-
anism (Scheme 5) for the formation of the diazanaph-
thacenes of type 6. Firstly, oxidation/deprotonation takes
Synthesis 2010, No. 12, 2049–2056 © Thieme Stuttgart · New York

2052
G. Buehrdel et al.
PAPER
doyl chlorides such as 4a,b showed the same reactivity; as
products the enamines 5a,b were isolated as yellow crys-
tals in good yields.
•
C
– e– – H+
H
7
The fulvadienes 3 can be transformed by an oxidation–
annulation sequence into dibenzonaphthyridine deriva-
tives 6. These to date unknown bis-spiro derivatives of di-
azatetracene are well soluble in common solvents and
display green fluorescence in solution.
Ph
N
NPh
H
E
path b
•
CH
The reagents described in the following section were purchased
from commercial sources and were used directly unless otherwise
stated in the text. All solvents were of reagent grade and dried ac-
cording to common practice and were distilled prior to use. The
bis(aryloxaldiimidoyl) chlorides 1 were synthesized according to
literature.2a Reactions were monitored by TLC, carried out on 0.2
mm Merck silica gel plates (60 F254). The 1H and 13C NMR spectra
were recorded on Bruker Avance 250 and 400 spectrometers, shifts
are relative to the signals of the solvent. Melting points were mea-
sured with a Galen III apparatus (Boëtius system) or with the Kofler
apparatus and are uncorrected. Electrochemical measurements were
carried out in CH2Cl2 with a Metrohm 663 VA Stand using platinum
electrodes (reference electrode SCE) and tetrabutylammonium
hexafluorophosphate as conductive salt.
a
H
N
N
– e– – H+
path a
•
3
C
NH
NH
b
A
B
– e– – H+
– e– – H+
– e– – H+
6
HN
N
C
•
N
N
1,2-Difluorenylidene-1,2-diarylaminoethanes 3 and Fluoren-
ylidene(4-tolylamino)methanes (5); General Procedure
D
C
A solution of the corresponding fluorene 2 (12 mmol) in anhyd THF
(60 mL) was cooled down to –30 °C and t-BuOK (2.7 g, 24 mmol)
was added. To the solution, the corresponding bis(arylimidoyl)
chloride 1 (6 mmol) or the corresponding arylimidoyl chloride 4 (12
mmol) was added. The deep red reaction mixture was stirred at
–30 °C for 15 min. The mixture was acidified by the addition of HCl
to pH 5–6. The mixture was diluted with H2O (500 mL) and the red
(for 5 yellow) precipitate was collected by filtration, washed with
H2O and after drying, it was purified by column chromatography on
silica gel (CHCl3–n-heptane). Recrystallization from CHCl3–n-hep-
tane gave 3 as red crystals and 5 as yellow crystals.
Scheme 5 Proposed mechanism for the formation of 6 and 7
place under the intermediate formation of the radical A
derived from a secondary amine. Radical A is able to in-
tramolecularly attack the adjacent double bond on the C-
9 fluorene carbon to give B (path a). A proton allyl shift,
followed by oxidation, results in the intermediate C. A
second two-electron oxidation reaction is then leading
(via D) to the main product 6. On the other hand, the flu-
oranthene derivative 7 also originates from radical A (path
b), which in this case attacks the adjacent fluorenyl-ring
on C-1 to give E and finally 7.
1,2-Bis(4-tolylamino)-1,2-difluorenylideneethane (3a)
Yield: 82%; red crystals; mp 280–281 °C.
1H NMR (250 MHz, CDCl3): d = 8.21 (m, 2 H, Ar-H), 7.83 (m, 4 H,
Ar-H), 7.70 (m, 2 H, Ar-H), 7.34 (m, 4 H, Ar-H), 7.10 (m, 2 H, Ar-
H), 6.91 (m, 6 H, Ar-H), 6.60 (m, 4 H, Tol-H), 6.19 (s, 2 H, NH),
2.23 (s, 6 H, Tol-H).
13C NMR (63 MHz, CDCl3): d = 139.1, 138.21, 138.18, 137.9,
137.2, 136.5, 131.8, 129.5, 126.9, 126.8, 126.6, 125.6, 123.9, 123.0,
122.9, 119.9, 119.3, 118.8, 20.7.
This mechanism where aminyl radicals/radical cations are
the key intermediates is supported by experimental facts.
Generally, anilines can easily be oxidized and the thus
formed amine radical cations tend to deprotonate quick-
ly.4 The aryl-substituted aminyl radicals are relatively sta-
ble and under suitable conditions they undergo
substitution reactions.5
MS (EI): m/z (%) = 564 (10, [M+]), 282 (100, [M/2+]), 165 (80,
+
[C13H9 ]).
UV/Vis (CHCl3): lmax (log e) = 311 (4.3), 359 (4.4), 450 nm (4.2).
We have recently found that heterocycles, which possess
vicinal arylamino-arylimino substructures gave deriva-
tives of quinoxaline under oxidative conditions; quantum
chemical calculations suggest a mechanism where aminyl
radicals are the key intermediates.6
Anal. Calcd for C42H32N2: C, 89.33; H, 5.71; N, 4.96. Found: C,
89.01; H, 5.90; N, 4.93.
1,2-Bis(4-methoxyphenylamino)-1,2-difluorenylideneethane
(3b)
Yield: 79%; red crystals; mp 305–307 °C.
1H NMR (250 MHz, DMSO-d6): d = 8.91 (s, 2 H, NH), 8.00–6.70
(m, 20 H, CH), 6.62 (d, J = 8 Hz, 4 H, CH), 3.59 (s, 6 H, OCH3).
13C NMR (63 MHz, DMSO-d6): d = 155.0, 139.9, 138.7, 137.3,
137.6, 137.2, 135.8, 135.3, 126.8, 126.2, 125.6, 124.6, 123.9, 122.3,
120.8, 119.8, 119.7, 114.1, 55.5.
In conclusion a short and efficient synthesis for a series of
novel bis(arylamino) fulvadienes 3 was developed based
on the acylation reaction of fluorenyl anions with bis(im-
idoyl) chlorides 1. The products 3 were isolated as red
crystalline compounds in good yields. Their structure was
determined by elemental analysis, MS, NMR and addi-
tionally, by X-ray crystal structural analysis. Monoimi-
MS (EI): m/z (%) = 596 (10, [M+]), 595 (20), 431 (10), 298 (100,
[M/2+]), 165 (60).
Synthesis 2010, No. 12, 2049–2056 © Thieme Stuttgart · New York

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Oxidation of Fulvadienes to Spirodiazatetracenes
2053
Anal. Calcd for C42H32N2O2: C, 84.54; H, 5.41; N, 4.69. Found: C,
84.33; H, 5.53; N, 4.23.
13C NMR (63 MHz, acetone-d6): d = 140.5, 140.0, 138.7, 138.4,
135.6, 135.4, 132.6, 129.2, 128.4, 127.6, 126.1, 125.3, 121.1, 121.0,
120.2, 119.8, 119.4, 19.9.
1,2-Bis[4-(propargyloxy)phenylamino]-1,2-difluorenylidene-
ethane (3c)
MS (ESI negative, MeOH–acetone): m/z (%) = 883/881/879/877/
875 (30/70/100/70/20, [M – H–]).
Yield: 73%; red crystals; mp 320 °C (dec.).
Anal. Calcd for C42H28Br4N2: C, 57.31; H, 3.21; N, 3.18. Found: C,
57.03; H, 3.05; N, 2.92.
1H NMR (250 MHz, acetone-d6): d = 8.20–7.70 (m, 8 H, CH), 7.33–
7.26 (m, 4 H, CH), 7.03–7.01 (m, 2 H, CH), 6.95 (d, J = 8 Hz, 4 H,
CH), 6.90–6.77 (m, 2 H, CH), 6.70 (d, J = 8 Hz, 4 H, CH), 4.63 (d,
J = 2.4 Hz, 4 H, OCH2), 3.02 (t, J = 2.4 Hz, 2 H, CºCH).
1,2-Bis(2,7-dibromofluorenylidene)-1,2-bis(4-methoxyphenyl-
amino)ethane (3h)
13C NMR (63 MHz, acetone-d6): d = 153.4, 138.5, 138.4, 138.1,
137.8, 137.4, 135.5, 126.4, 125.9, 125.7, 124.8, 123.5, 122.5, 121.4,
120.6, 119.3, 119.2, 115.0, 79.1, 75.8, 55.8 (OCH2).
Yield: 82%; red crystals; mp 273–276 °C.
IR (ATR): 3064, 3006, 2921, 2838, 1602, 1574, 1479, 1446, 1430,
1279, 1257, 1223, 1205, 1157, 1121, 1030, 993 cm–1.
+
MS (EI): m/z (%) = 644 (2, [M+]), 606 (1, [M – C3H3 ], 458 (1), 322
1H NMR (250 MHz, acetone-d6): d = 8.10 (s, 2 H, NH), 7.81–7.65
(20, [M/2+]), 181 (100).
(m, 6 H, CH), 7.44 (dd, 3J = 8 Hz, 4J = 1.7 Hz, 2 H, CH), 7.16 (dd,
4
3
Anal. Calcd for C46H32N2O2: C, 85.69; H, 5.00; N, 4.34. Found: C,
85.47; H, 4.84; N, 4.06.
3J = 8 Hz, J = 1.7 Hz, 2 H, CH), 6.91 (d, J = 8 Hz, 4 H, Ar-H),
6.71 (d, 3J = 8 Hz, 4 H, Ar-H), 3.69 (s, 6 H, OCH3).
1,2-Bis(4-bromophenylamino)-1,2-difluorenylidene-ethane (3d)
13C NMR (63 MHz, acetone-d6): d = 156.3, 141.0, 140.0, 138.7,
135.4, 135.1, 133.7, 128.2, 127.3, 125.8, 125.1, 121.3, 121.1, 121.0,
120.2, 119.8, 117.8, 114.0, 54.8.
MS (DEI): m/z (%) = 914/912/910 (25/30/25, [M+]), 589 (25), 338
(60), 300 (60), 149 (60), 123 (100).
Yield: 86%; red crystals; mp 264–266 °C.
1H NMR (250 MHz, CDCl3): d = 8.1–6.8 (m, 20 H, CH), 6.56 (d,
J = 8 Hz, 4 H, CH), 6.10 (s, 2 H, NH).
13C NMR (63 MHz, CDCl3): d = 140.0, 139.4, 138.8, 137.4, 136.8,
134.4, 132.0, 127.4, 127.1, 126.5, 124.4, 123.5, 123.0, 120.1, 119.7,
119.6, 114.7.
UV/Vis (CHCl3): lmax (log e) = 304 (4.5), 364 (4.3), 454 nm (4.2).
Anal. Calcd for C42H28Br4N2O2: C, 55.30; H, 3.09; N, 3.07. Found:
C, 54.90; H, 3.00; N, 2.95.
MS (EI): m/z (%) = 696/694/692 (20/40/20, [M+]), 524/522/520
(20/40/20), 348/346 (90/100, [M/2+]), 267 (60), 165 (60).
Fluorenylidene(4-tolylamino)trifluoromethylmethane (5a)
Anal. Calcd for C40H26Br2N2: C, 69.18; H, 3.77; N, 4.03. Found: C;
68.84, H 3.58; N, 3.86.
Yield: 71%; yellow solid; mp 82–86 °C.
1H NMR (250 MHz, CDCl3): d = 8.00–7.90 (m, 1 H, CH), 7.70–
7.60 (m, 2 H, CH), 7.50–7.20 (m, 4 H, CH), 7.10–7.00 (m, 1 H, CH),
6.98 (d, J = 8 Hz, 2 H, CH), 6.74 (d, J = 8 Hz, 2 H, CH), 6.09 (s, 1
H, NH), 2.24 (s, 3 H, CH3).
13C NMR (63 MHz, CDCl3): d = 140.8, 140.0, 139.9, 136.1, 134.9,
131.2, 130.0, 129.2 (q, J = 2 Hz), 128.6, 128.5, 127.6, 127.4, 126.5,
125.5 (q, J = 14 Hz), 124.9, 122.7 (q, J = 270 Hz), 119.6, 119.4,
115.9, 20.7.
1,2-Bis(2-bromofluorenylidene)-1,2-bis(4-tolylamino)ethane
(3e)
Yield: 81%; red crystals; mp 270 °C (dec.).
1H NMR (250 MHz, CDCl3): d = 8.20–7.90 (m, 2 H, CH), 7.90–
6.10 (m, 22 H, 20 CH + 2 NH), 2.26 (s, 6 H, CH3).
MS (DEI): m/z (%) = 724/722/720 (20/40/20, [M+]), 479/477 (20/
40, [M – C13H8Br+]), 362/360 (15/20, [M/2+]), 260/258 (60/50), 91
(100).
MS (EI): m/z (%) = 351 (60, [M+]), 267 (30), 186 (80), 165 (80), 91
(100).
Anal. Calcd for C42H30Br2N2: C, 69.82; H, 4.19; N, 3.88. Found: C
69.53; H, 4.01; N, 3.77.
Anal. Calcd for C22H16F3N: C, 78.67; H, 4.72; N, 3.28. Found: C,
78.21; H, 4.63; N, 3.19.
1,2-Bis(2-bromofluorenylidene)-1,2-bis(4-methoxyphenylami-
no)ethane (3f)
Fluorenylidene(4-tolylamino)(4-trifluoromethylphenyl)meth-
ane (5b)
Yield: 87%; red crystals; mp 295 °C (dec.).
Yield: 64%; yellow crystals; mp 155–157 °C.
1H NMR (250 MHz, CDCl3): d = 8.20–7.90 (m, 2 H, CH), 7.90–
7.60 (m, 5 H, CH), 7.60–7.30 (m, 4 H, CH), 7.10–6.90 (m, 3 H, CH),
6.66 (m, 8 H, CH), 6.50–6.10 (m, 2 H, NH), 3.73 (s, 6 H, OCH3).
MS (DEI): m/z (%) = 756/754/752 (15/30/15, [M+]), 511/509 (15/
20, [M – C13H8Br+]), 378/376 (40/60, [M/2+]), 260/258 (90/100),
151 (60).
IR (ATR): 3393, 3334, 3062, 2925, 2863, 1713, 1650, 1650, 1601,
1578, 1514, 1447, 1321, 1300, 1162, 1119, 1105, 1064, 1017 cm–1.
1H NMR (250 MHz, CDCl3): d = 7.90–7.70 (m, 7 H, CH), 7.40–
7.20 (m, 3 H, CH), 7.00–6.90 (m, 3 H, CH), 6.77 (s, 1 H, NH), 6.70–
6.50 (m, 3 H, CH), 2.26 (s, 3 H, CH3).
13C NMR (63 MHz, CDCl3): d = 142.0, 139.8, 138.5, 138.4, 138.3,
138.1, 137.8, 132.0 (q, J = 32 Hz, CCF3), 131.7, 129.8, 126.8,
126.1, 125.9, 125.8, 125.7 (q, J = 4 Hz), 125.4, 124.2 (q, J = 270
Hz, CF3), 122.4, 122.2, 119.9, 119.5, 119.1, 118.3, 20.8.
Anal. Calcd for C42H30Br2N2O2: C, 66.86; H, 4.01; N, 3.71. Found:
C, 66.43; H, 3.88; N, 3.51.
1,2-Bis(2,7-dibromofluorenylidene)-1,2-bis(4-tolylami-
no)ethane (3g)
MS (DEI): m/z (%) = 427 (100, [M+]), 411 (20), 262 (20), 91 (20).
Yield: 85%; red crystals; mp ≥ 350 °C (dec.).
UV/Vis (CHCl3): lmax (log e) = 295 (3.9), 416 nm (3.9).
1H NMR (250 MHz, acetone-d6): d = 8.80 (s, 2 H, NH), 8.06 (s, 2
H, CH), 7.80–7.70 (m, 6 H, CH), 7.64 (dd, 3J = 8 Hz, 4J = 1.7 Hz,
2 H, CH), 7.14 (dd, 3J = 8 Hz, 4J = 1.7 Hz, 2 H, CH), 7.0–6.8 (m, 8
H, Tol-H), 2.19 (s, 6 H, Tol-H).
Anal. Calcd for C42H20N2: C, 89.33; H, 5.71; N, 4.96. Found: C,
89.01; H, 5.90; N, 4.93.
Synthesis 2010, No. 12, 2049–2056 © Thieme Stuttgart · New York

2054
G. Buehrdel et al.
PAPER
Sonogashira Cross-Coupling Reaction with 3d; 1,2-Difluoren-
ylidene-1,2-(4-triisopropylsilylethynylphenylamino)ethane (3i)
6.92 (m, 4 H, CH), 6.72 (dd, 3J = 8 Hz, 4J = 2.8 Hz, 2 H, CH), 5.70
(d, 4J = 2.8 Hz, 2 H, CH), 3.47 (s, 6 H, OCH3).
To a suspension of 3d (1.40 g, 2 mmol), (Ph3P)2PdCl2 (73 mg, 0.1
mmol), Ph3P (55 mg, 0.2 mmol), and CuI (20 mg, 0.1 mmol) in de-
gassed toluene (20 mL) were added (triisopropylsilyl)acetylene
(550 mg, 3 mmol) and Et3N (5 mL, 36 mmol). The mixture was
stirred at 80 °C for 4 h under argon. The mixture was filtered and
the solvent was removed in vacuo. The crude product was purified
by column chromatography on silica gel (CHCl3–n-heptane); yield:
1.52 g (85%); red crystals; mp 320 °C (dec.).
1H NMR (250 MHz, CDCl3): d = 8.00–6.80 (m, 20 H, CH), 6.63 (d,
J = 8 Hz, 4 H, CH), 6.11 (s, 2 H, NH), 1.18–1.01 [m, 42 H, 6 ×
CH(CH3)2].
13C NMR (63 MHz, CDCl3): d = 159.4, 156.1, 148.0, 140.7, 136.8,
135.9, 131.3, 127.9, 127.7, 125.9, 120.3, 112.2, 112.0, 61.3 (spiro-
C), 55.1 (OCH3).
MS (EI): m/z (%) = 592 (100, [M+]), 577 (20), 431 (10), 83 (80).
UV/Vis (CHCl3): lmax (log e) = 307 (3.9), 402 nm (4.1).
Emission (CHCl3): lmax = 512 nm.
Anal. Calcd for C42H28N2O2: C, 85.11; H, 4.76; N, 4.73. Found: C,
84.88; H, 4.51; N, 4.49.
6,6,12,12-Bis[spiro(fluorenyl)]-2,8-di(propargyloxy)-5,11-di-
aza-6,12-dihydrotetracene (6c)
13C NMR (63 MHz, CDCl3): d = 141.0, 139.5, 138.9, 137.3, 137.2,
136.9, 134.4, 133.0, 129.1, 127.5, 127.1, 126.6, 124.3, 123.6, 123.1,
119.6, 117.6, 116.9, 107.1, 89.7, 18.6, 11.3.
Yield: 37%; yellow crystals; mp 310 °C (dec.).
1H NMR (250 MHz, acetone-d6): d = 7.94 (d, J = 8 Hz, 4 H, CH),
7.60–7.15 (m, 10 H, CH), 7.00 (m, 4 H, CH), 6.81 (dd, 3J = 8 Hz,
MS (FAB in NBA): m/z (%) = 897 (20, [M + H+]), 896 (20, [M+]),
4
4J = 2.8 Hz, 2 H, CH), 5.99 (d, J = 2.8 Hz, 2 H, CH), 4.51 (d,
732 (40), 448 (100, [M/2+]).
4J = 2.4 Hz, 4 H, OCH2), 2.92 (t, 4J = 2.4 Hz, 2 H, CºCH).
Anal. Calcd for C62H68N2Si2: C, 82.98; H, 7.64; N, 3.12. Found: C,
82.51; H, 7.83; N, 3.01.
13C NMR (63 MHz, acetone-d6): d = 157.7, 155.9, 149.0, 140.9,
137.0, 135.8, 130.9, 128.2, 127.8, 125.5, 120.4, 113.4, 113.0, 78.1,
76.4, 61.1 (spiro-C), 55.4 (OCH2).
6,6,12,12-Bis[spiro(fluorenyl)]-5,11-diaza-6,12-dihydrotetra-
cenes 6; General Procedure
MS (DEI): m/z (%) = 640 (50, [M+]), 601 (80, [M – C3H3 ]), 533
+
A mixture of the corresponding 1,2-difluorenylidene-1,2-diaryl-
aminoethanes 3 (2 mmol), K2CO3 (1.4 g, 10 mmol), and CAN (2.5
g, 4–5 mmol) in MeCN (50 mL) was stirred at r.t. until no starting
material 3 could be detected (TLC, ca. 0.5 h). Most of the solvent
was removed in vacuo and the residue was added to H2O (100 mL).
The crude product was extracted with CHCl3 (2 × 50 mL), the insol-
uble solid was filtered off, and washed with MeOH (10 mL). The
organic layers were combined and dried (Na2SO4). After removing
the solvent in vacuo, the product was purified by column chroma-
tography on silica gel (CHCl3–n-heptane). Recrystallization from
CHCl3–n-heptane gave 6 as yellow crystals.
(40), 180 (100).
Anal. Calcd for C46H28N2O2: C, 86.23; H, 4.40; N, 4.37. Found: C,
85.89; H, 4.25; N, 4.22.
6,6,12,12-Bis[spiro(fluorenyl)]-2,8-dibromo-5,11-diaza-6,12-di-
hydrotetracene (6d)
Yield: 31%; yellow crystals; mp 390 °C (dec.).
1H NMR (400 MHz, CDCl3): d = 7.85 (d, J = 8 Hz, 4 H, CH), 7.45
4
(m, 4 H, CH), 7.25 (d, J = 2.1 Hz, 2 H, CH), 7.19–7.08 (m, 8 H,
CH), 6.95 (d, 3J = 8 Hz, 2 H, CH), 6.58 (d, 4J = 2.1 Hz, 2 H, CH).
13C NMR (400 MHz, CDCl3): d = 158.4, 146.9, 140.8, 135.9, 132.7,
131.6, 131.3, 129.1, 128.4, 127.9, 125.8, 120.6, 61.0 (spiro-C).
6,6,12,12-Bis[spiro(fluorenyl)]-2,8-dimethyl-5,11-diaza-6,12-di-
hydrotetracene (6a)
MS (DEI): m/z (%) = 692/690/688 (50/80/55, [M+]), 611/609 (60/
Yield: 45%; yellow crystals; mp 315 °C (dec.).
80, [M – HBr+]), 528 (10, [M –2 HBr+]), 305 (35), 264 (100).
1H NMR (400 MHz, CDCl3): d = 7.84 (d, J = 8 Hz, 4 H, CH), 7.43
(m, 4 H, CH), 7.21 (d, J = 8 Hz, 2 H, CH), 7.15 (m, 4 H, CH), 7.01
(d, J = 8 Hz, 4 H, CH), 6.92 (dd, 3J = 8.0 Hz, 4J = 1.5 Hz, 2 H, CH),
6.26 (d, 4J = 1.5 Hz, 2 H, CH), 2,04 (s, 6 H, CH3).
Emission (CHCl3): lmax = 482 nm.
Anal. Calcd for C40H22Br2N2: C, 69.59; H, 3.21; N, 4.06. Found: C,
69.24; H, 3.03; N, 3.89.
13C NMR (100 MHz, CDCl3): d = 157.9, 148.1, 140.8, 140.4, 138.8,
133.7, 129.9, 128.7, 127.9, 127.7, 126.6, 126.0, 120.3, 61.3 (spiro-
C), 21.2
MS (DEI): m/z (%) = 560 (100, [M+]), 545 (25), 280 (20, [M/2+]),
83 (30).
6,6,12,12-Bis[spiro(2-bromofluorenyl)]-2,8-dimethyl-5,11-di-
aza-6,12-dihydrotetracene (6e)
Yield: 61%; yellow crystals; mp 325–326 °C.
1H NMR (250 MHz, CDCl3): d = 7.82 (m, 2 H, CH), 7.68 (m, 2 H,
CH), 7.56–7.42 (m, 4 H, CH), 7.24 (m, 4 H, CH), 7.09–6.94 (m, 6
H, CH), 6.24 (m, 2 H, CH), 2.06 (s, 6 H, CH3).
Emission (CHCl3): lmax = 480 nm.
13C NMR (63 MHz, CDCl3): d = 157.1–120.5, 61.3/61.2 (spiro-C),
21.4.
Anal. Calcd for C42H28N2: C, 89.97; H, 5.03; N, 5.00. Found: C,
89.60; H, 4.71; N, 4.73.
MS (DEI): m/z (%) = 720/718/716 (40/60/40, [M+]), 639/637 (20/
20, [M – Br]), 360/358 (45/40, [M/2+]), 319 (30), 311 (40), 264
(100).
6,6,12,12-Bis[spiro(fluorenyl)]-2,8-dimethoxy-5,11-diaza-6,12-
dihydrotetracene (6b)
Yield: 50%; yellow crystals; mp 241–244 °C.
Emission (CHCl3): lmax = 481 nm.
IR (ATR): 3064, 3006, 2921, 2838, 1602, 1574, 1479, 1446, 1430,
1279, 1257, 1223, 1205, 1121, 1030, 736 cm–1.
1H NMR (250 MHz, CDCl3): d = 7.82 (d, J = 8 Hz, 4 H, CH), 7.40
(m, 4 H, CH), 7.24 (d, J = 8 Hz, 2 H, CH), 7.13 (m, 4 H, CH), 7.00
(m, 4 H, CH), 6.60 (dd, 3J = 8 Hz, 4J = 2.8 Hz, 2 H, CH), 5.98 (d,
4J = 2.8 Hz, 2 H, CH), 3.52 (s, 6 H, OCH3).
Anal. Calcd for C42H26Br2N2: C, 70.21; H, 3.65; N, 3.90. Found: C,
69.81; H, 3.42; N, 3.58.
6,6,12,12-Bis[spiro(2-bromofluorenyl)]-2,8-dimethoxy-5,11-di-
aza-6,12-dihydrotetracene (6f)
Yield: 65%; yellow crystals; mp 292–293 °C.
1H NMR (250 MHz, CDCl3): d = 7.80 (m, 2 H, CH), 7.70 (m, 2 H,
CH), 7.53 (m, 2 H, CH), 7.44 (m, 2 H, CH), 7.31–7.17 (m, 4 H, CH),
1H NMR (250 MHz, DMSO-d6): d = 7.99 (d, J = 8 Hz, 4 H, CH),
7.45 (m, 4 H, CH), 7.15 (m, 4 H, CH), 7.11 (d, J = 8 Hz, 2 H, CH),
Synthesis 2010, No. 12, 2049–2056 © Thieme Stuttgart · New York

PAPER
Oxidation of Fulvadienes to Spirodiazatetracenes
2055
7.12–7.00 (m, 4 H, CH), 6.65 (m, 2 H, CH), 5.98 (m, 2 H, CH), 3.56
(s, 6 H, OCH3).
13C NMR (63 MHz, CDCl3): d = 159.7–112.2, 61.3/61.2 (spiro-C),
55.2.
a = 13.5730(4), b = 17.3936(6), c = 16.016(3) Å, b = 106.146(2)°,
V = 3632.0(7) Å3, T = –90 °C, Z = 4, rcalcd = 1.171 gcm–3, m(Mo-
Ka) = 1.57 cm–1, F(000) = 1333, 24011 reflections in h(–16/17), k(–
22/21), l(–20/17), measured in the range 4.14° £ Q £ 27.49°, com-
pleteness
Q
max = 98.5%,
8213 independent reflections,
MS (DEI): m/z (%) = 752/750/748 (60/100/60, [M+]), 376/374 (30/
Rint = 0.0475, 5444 reflections with Fo > 4r(Fo), 447 parameters, 0
restraints, R1obs = 0.0881, wR2obs = 0.2574, R1all = 0.1270,
wR2all = 0.2971, GOOF = 1.037, largest difference peak and hole:
1.340/–0.357 e Å–3.
30, [M/2+]).
Emission (CHCl3): lmax = 516 nm.
Anal. Calcd for C42H26Br2N2O2: C, 67.22; H, 3.49; N, 3.73. Found:
C, 66.92; H, 3.29; N, 3.41.
Crystal Data for 710
Empirical formula:C40H24Br2N2; yellow-orange prism, size
0.05 × 0.04 × 0.04 mm3, monoclinic, space group P21/n,
a = 9.2484(3), b = 25.9276(9), c = 13.2181(4) Å, b = 107.635(2)°,
V = 3020.60(17) Å3, T = –140 °C, Z = 4, rcalcd = 1.523 gcm–3,
m(Mo-Ka) = 27.17 cm–1, F(000) = 1392, 18354 reflections in h(–11/
10), k(–33/31), l(–17/17), measured in the range 2.51° £ Q £ 27.48°,
5-(4-Bromophenylimino)-6-(4-bromophenylamino)-4,4-
spiro(fluorenyl)-4,5-dihydrofluoranthene (7)
The side product 7 was isolated during the purification of 6d by col-
umn chromatography on silica gel (CHCl3–n-heptane) in traces. Re-
crystallization from CHCl3–n-heptane gave 7 as yellow crystals, mp
340 °C (dec.).
1H NMR (200 MHz, CDCl3): d = 8.00 (s, 1 H, NH), 7.80–6.60 (m,
20 H, CH), 6.00–5.30 (m, 3 H, CH).
13C NMR (50 MHz, CDCl3): d = 149.3, 146.8, 142.0, 141.1, 141.0,
136.1, 134.6, 134.4, 134.3, 131.9, 130.9, 130.5, 129.3, 128.5, 128.1,
127.6, 126.8, 126.4, 124.3, 123.4, 123.1, 121.3, 120.8, 120.6, 120.4,
119.9, 118.1, 114.1, 113.8, 61.3 (spiro-C).
completeness
Qmax = 99.3%, 6865 independent reflections,
Rint = 0.0775, 3736 reflections with Fo > 4s(Fo), 397 parameters, 0
restraints, R1obs = 0.0472, wR2obs = 0.0813, R1all = 0.1252,
wR2all = 0.0980, GOOF = 0.943, largest difference peak and hole:
0.472/–0.588 e Å–3.
Acknowledgment
MS (ESI in MeOH–CHCl3): m/z (%) = 695/693/691 (60/90/60, [M
+ H+]), 587 (100), 559 (90), 413 (80).
We are grateful to the Friedrich Schiller University Jena for finan-
cial support to G. Buehrdel by a grant.
Crystal Structure Determination of 3a, 3d, 6b, and 7
The intensity data for the compound was collected on a Nonius
KappaCCD diffractometer, using graphite-monochromated Mo-Ka
radiation. Data were corrected for Lorentz and polarization effects,
but not for absorption effects.7 The structure was solved by direct
methods (SHELXS),8 and refined by full-matrix least squares tech-
niques against Fo2 (SHELXL-97).9 All hydrogen atoms were in-
cluded at calculated positions with fixed thermal parameters. All
non-hydrogen atoms were refined anisotropically.4 XP (SIEMENS
Analytical X-ray Instruments, Inc.) was used for structure represen-
tations.
References
(1) (a) Fabian, W. M. F.; Kauffman, J. M. J. Luminescence
1999, 85, 137. (b) Prinzbach, H.; Bingmann, H.; Beck, A.;
Hunkler, D.; Sauter, H.; Hädicke, E. Chem. Ber. 1981, 114,
1697.
(2) (a) Buehrdel, G.; Beckert, R.; Petrlikova, E.; Herzigova, P.;
Klimsova, V.; Fleischhauer, J.; Goerls, H. Synthesis 2008,
3071. (b) Buehrdel, G.; Beckert, R.; Birckner, E.; Grummt,
U.-W.; Beyer, B.; Kluge, S.; Weston, J.; Goerls, H. Eur. J.
Org. Chem. 2007, 5404. (c) Buehrdel, G.; Beckert, R.;
Friedrich, B.; Goerls, H. J. Heterocycl. Chem. 2008, 45,
845. (d) Buehrdel, G.; Beckert, R.; Raabe, D.; Görls, H.
J. Sulfur Chem. 2006, 5, 401. (e) Atzrodt, J.; Brandenburg,
J.; Käpplinger, C.; Beckert, R.; Günther, W.; Görls, H.;
Fabian, J. J. Prakt. Chem./Chem.-Ztg. 1997, 339, 729.
(f) Wuckelt, J.; Döring, M.; Langer, P.; Görls, H.; Beckert,
R. Tetrahedron Lett. 1998, 39, 5269. (g) Pufky, D.; Beckert,
R.; Döring, M.; Walther, O. Heterocycles 2002, 57, 1257.
(h) Lindauer, D.; Beckert, R.; Görls, H.; Fehling, P.; Döring,
M. J. Prakt. Chem./Chem.-Ztg. 1995, 337, 143.
(3) Banide, E. V.; Molloy, B. C.; Ortin, Y.; Müller-Bunz, H.;
McGlinchey, M. J. Eur. J. Org. Chem. 2007, 2611.
(4) Jonsson, M.; Wayner, D. D. M.; Lusztyk, J. J. Phys. Chem.
1996, 100, 17539.
Crystal Data for 3a10
Empirical formula: C42H32N2; red prism, size 0.05 × 0.05 × 0.05
mm3, monoclinic, space group P21/n, unit cell dimensions
a = 10.1879(5), b = 18.9116(6), c = 16.3908(7) Å, b = 90.076(3)°,
V = 3158.0(2) Å3, T = –90 °C, Z = 4, rcalcd = 1.188 gcm–3, m(Mo-
Ka) = 0.69 cm–1, F(000) = 1192, 21347 reflections in h(–13/11), k(–
24/24), l(–21/18), measured in the range 2.15° £ Q £ 27.49°, com-
pleteness
Q
max = 99.6%,
7208 independent
reflections,
Rint = 0.0679, 4237 reflections with Fo > 4r(Fo), 407 parameters, 0
restraints, R1obs = 0.0581, wR2obs = 0.1190, R1all = 0.1196,
wR2all = 0.1449, GOOF = 1.023, largest difference peak and hole:
0.242/0.232 e Å–3.
Crystal Data for 3d10
Empirical formula: C40H26Br2N2 2(CHCl3); red prism, size
0.07 × 0.07 × 0.05 mm3, monoclinic, space group P21/n,
(5) Berkenkotter, P.; Nelson, R. F. J. Electrochem. Soc. 1973,
120, 346.
a = 15.0246(4),
b = 9.8644(2),
c = 26.7844(6)
Å,
b = 103.9510(10)°, V = 3852.58(16) Å3, T = –90 °C, Z = 4,
(6) (a) Buehrdel, G.; Beckert, R.; Herzigova, P.; Petrlikova, E.;
Schuch, D.; Birckner, E.; Goerls, H. Eur. J. Org. Chem.
2009, 3404. (b) Herzog, S.; Buehrdel, G.; Beckert, R.;
Klimas, S.; Würthwein, E.-U.; Grimme, S.; Goerls, H.
Synthesis 2009, 4049.
r
calcd = 1.609 gcm–3, m(Mo-Ka) = 25.55 cm–1, F(000) = 1864, 26153
reflections in h(–19/18), k(–12/12), l(–32/34), measured in the
range 2.21° £ Q £ 27.45°, completeness Qmax = 99.8%, 8793 inde-
pendent reflections, Rint = 0.0669, 5553 reflections with Fo
>
(7) (a) COLLECT, Data Collection Software; Nonius B.V.:
Delft, Netherlands, 1998. (b) Otwinowski, Z.; Minor, W.
Processing of X-Ray Diffraction Data Collected in
Oscillation Mode, In Methods in Enzymology,
4r(Fo), 469 parameters,
0
restraints, R1obs = 0.0506,
wR2obs = 0.0949, R1all = 0.1024, wR2all = 0.1095, GOOF = 1.012,
largest difference peak and hole: 1.486/–0.985 e Å–3.
Crystal Data for 6b10
Macromolecular Crystallography, Vol. 276; Carter, C. W.;
Sweet, R. M., Eds.; Academic Press: New York, 1997, 307–
326.
Empirical formula: C42H28N2O2 0.4(CHCl3), yellow prism, size
0.06 × 0.06 × 0.05 mm3, monoclinic, space group P21/c,
Synthesis 2010, No. 12, 2049–2056 © Thieme Stuttgart · New York

2056
G. Buehrdel et al.
PAPER
(8) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467.
(9) Sheldrick, G. M. SHELXL-97 (Release 97-2); University of
Göttingen: Germany, 1997.
data can be obtained free of charge via
www.ccdc.cam.ac.uk/conts/retrieving.html [or from the
Cambridge Crystallographic Data Centre, 12, Union Road,
Cambridge CB2 1EZ, UK; fax: +44(1223)336033; or
deposit@ccdc.cam.ac.uk].
(10) (10)CCDC-762471 (3a), CCDC-762472 (3d), CCDC-
762473 (6b), and CCDC-762474 (7) contain the
supplementary crystallographic data for this paper. These
Synthesis 2010, No. 12, 2049–2056 © Thieme Stuttgart · New York