2,6-Di-tert-butyl-4-(3,3-diarylpropadienylidene)-2,5-cyclohexadien-1-ones, the first stable p-quinopropadienes

Article abstract of DOI:10.1002/ejoc.200400021

Treatment of 2,6-di-tert-butyl-4-ethynylphenol with 2 equivalents of nBuLi, followed by addition of diaryl ketones, afforded the corresponding p-quinopropadienes 2a-i upon appropriate dehydrative treatments. These compounds are fairly stable, orange to pu

Full text of DOI:10.1002/ejoc.200400021

FULL PAPER
2,6-Di-tert-butyl-4-(3,3-diarylpropadienylidene)-2,5-cyclohexadien-1-ones, the
First Stable p-Quinopropadienes
Takeshi Kawase,*[a] Naoki Nishigaki,[a] Hiroyuki Kurata,[a] and Masaji Oda*[a]
Keywords: Chromophores / Cumulenes / Quinones / Redox chemistry
Treatment of 2,6-di-tert-butyl-4-ethynylphenol with
equivalents of nBuLi, followed by addition of diaryl ketones,
2
2a also indicates the highly amphoteric redox properties of
2a; however, both the anion and cation radicals of 2 are
afforded the corresponding p-quinopropadienes 2a−f upon highly reactive. The molecular structures of 2a and 2e exhibit
appropriate dehydrative treatments. These compounds are
fairly stable, orange to purple, crystalline substances, exhib-
iting intense absorptions at longer wavelengths. In particular,
the bis(dimethylamino) derivative 2a absorbs across the double bond (2a for 1.228 A and 2e for 1.235 A) indicates
whole of the visible spectrum and into the near infrared. Un- the importance of the resonance contribution of the dipolar
like the quinone methides 1, compounds 2 exhibited irrevers- structure with an acetylenic bond.
relatively small dihedral angles between two aromatic ring
planes (2a for 47° and 2e for 52°), and each has a short central
double bond and long side double bonds. The short central
˚
˚
ible oxidation waves together with irreversible reduction
waves on cyclic voltammetry. The very small E1sum value of
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2004)
Introduction
for 2. Here we report the syntheses, structures, and proper-
ties of 2aϪf (Figure 1).
Intensely colored organic compounds have attracted con-
siderable attention in relation to development of new mate-
rials.[1] The extension of conjugation by schematic insertion
of π units into a simple π system has been regarded as the
most effective methods for designing new dyes, and in this
context a number of conjugated systems possessing inserted
π units such as 1,4-phenylene, 2,5-thienylene, and 1,2-ethy-
nyl groups have been prepared.[2] Although 7,7-diaryl-p-
quinone methides 1, which are appreciably dipolar and col-
ored compounds, have been fairly extensively studied,[3,4]
the novel extended p-quinone methides (quinopropadienes)
2, in which a p-quinone methide is united with 1,1-diaryl-
butatriene, are little known. The quinopropadienes 2 would
be intriguing molecules because the extended conjugation
and the cumulene structure should decrease their
HOMOϪLUMO energy gaps and enhance their dipolari-
ties.[5] Although the quinopropadiene derivative 3 was
studied as a reactive intermediate by G. Cevasco and his
co-workers,[6] no stable derivatives have been prepared so
far. Recently we reported the generation and reaction be-
havior of lithium 2,6-di-tert-butyl-4-lithiophenoxide as a
key synthon for p-quinone methides 1.[7] As an extension
of this finding, we expected that lithium 2,6-di-tert-butyl-4-
lithioethynylphenoxide (4) should be a promising synthon
Figure 1. Chemical structures of 1Ϫ4
Results and Discussion
[a]
Synthesis of Quinopropadienes 2a؊f
Department of Chemistry, Graduate School of Science, Osaka
University,
Di-tert-butyl-4-ethynylphenol (5), a precursor of 4, had
previously been prepared from 2,6-di-tert-butylphenol in
Toyonaka, Osaka 560-0043, Japan
E-mail: tkawase@chem.sci.osaka-u.ac.jp
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2,6-Di-tert-butyl-4-(3,3-diarylpropadienylidene)-2,5-cyclohexadien-1-ones
FULL PAPER
36% total yield in four steps including a Vilsmeier reac- spectrum and into the near infrared could have useful tech-
tion.[8a] To increase the availability of 5, we modified the nical implications (Figure 2). Moreover, the intensely col-
synthesis by using the Sonogashira reaction as a key step; ored 2a shows appreciably large positive solvatochromism:
treatment of 2,6-di-tert-butyl-4-bromo(trimethylsiloxy)ben- λmax. ϭ 579 nm in cyclohexane, 631 nm in chloroform, 654
zene, which was obtained from bromination and silylation and 720 (shoulder) nm in acetonitrile, and 668 and 731 nm
of di-tert-butylphenol,[8b] with (trimethylsilyl)acetylene and in methanol. The new band at long wavelength in the polar
subsequent desilylation with nBu4NF afforded 5 in 64% to- solvents may be attributable to twisted intramolecular
tal yield. Treatment of a THF solution of 5 with 2 equiva- charge transfer (TICT), because the band appears even in
lents of n-butyllithium at Ϫ78 °C, followed by addition of the polar aprotic solvent acetonitrile.[10]
diaryl ketones and conventional workup, afforded the cor-
responding alkynol 6aϪf (Scheme 1). The colorless nature
of the products of these reactions indicated the formation
of 6. The alcohols 6e and 6f were obtained in good yields
(6e: 70%; 6f: 71%) by chromatography on silica gel as color-
less crystals. On the other hand, 6a and 6b were dehydrated
on the column even at 0 °C, to afford the quinopropadienes
2a (34%) and 2b (35%), respectively, as the sole isolated
products. Compounds 2a and 2b are also sensitive to silica
gel, and chromatography at ambient temperature drastically
decreased the yields of products. On the other hand, similar
chromatographic treatment of 6c and 6d afforded mixtures
of the corresponding quinopropadiene and unchanged 6a.
Upon loading of the alcohols onto silica gel at room temp.
for appropriate periods (3 h for 6c; 12 h for 6d), pure 2c and
2d were eluted from the column (2c: 67%, 2d: 67%). How-
ever, similar dehydration of 6e and 6f to 2e and 2f on silica
gel ended in failure. Dehydrative treatments with anhydrous
Figure 2. UV/Vis spectra of 2aϪ2f in CH2Cl2 solution
The selective IR stretching frequencies and 13C NMR
CuSO4 were then examined; we have reported that the re- chemical shifts of 2aϪf are summarized in Table 1, together
agent is effective for dehydration of acid-sensitive al- with those of 1a and 1d. The extended conjugation would
cohols.[9] However, treatment of 6e and 6f with anhydrous be expected to enhance the dipolarity of 2aϪf; actually, the
CuSO4 (10 equiv.) in THF at reflux for 16 h gave 2e and 2f carbonyl stretching absorptions of 2aϪf in the IR spectra
only in poor yields (28% for 2e, and 19% for 2f). The most (ν˜ ϭ 1551Ϫ1598 cmϪ1) are at frequencies 15 to 50 cmϪ1
successful results were achieved by heating with anhydrous lower than those of the corresponding quinone methides.[7]
CuSO4 in THF in the presence of ZnCl2, giving good yields Moreover, 2aϪc, 2f, and 1a each exhibit two CO vibrations,
(2e: 70%; 2f: 71%). The Lewis-acidic properties of ZnCl2 whereas 2dϪe and 1e each have one. The splits become
appears to play an important role in the synthesis.
larger with stronger electron-donating properties of the sub-
stituents, probably due to the large contribution of the
highly polarized zwitterionic forms in the solid state. The
13C NMR chemical shifts also indicate the dipolar charac-
ter of 2, through large difference in the chemical shifts be-
tween C4 and C9. Those of C4 and C7 of 1a and 1e shift
in opposite directions (∆δ of C4 ϭ Ϫ0.9 ppm and ∆δ of
C7 ϭ 3.3 ppm), suggesting increasing dipolar properties.
On the other hand, the chemical shifts of all the butatriene
carbon atoms (C4, C7ϪC9) of 2 monotonically change with
the electronic properties of the substituents on aromatic
rings. The electron-donating substituents of 2 should in-
crease the electron density of all the butatriene carbon
atoms but not the dipolar character of the molecule.
Scheme 1. Reagents and conditions: i) 2.2 equiv. nBuLi, THF, Ϫ78
°C, ii) diaryl ketone, Ϫ78 °C then to room temp., iii) silica gel for
2aϪd, iv) 6 equiv. ZnCl2, 5 equiv. CuSO4, THF, reflux for 2eϪf
Variable temperature 1H NMR spectra of unsymmetrical
2b in [D6]DMSO show broadening of the tert-butyl protons
Spectral Properties
The thus obtained quinopropadienes 2aϪf are fairly (δ ϭ 1.33 and 1.36 ppm at 30 °C) at 60 °C, and the signals
stable, orange to purple, crystalline substances, exhibiting coalesce at about 85 °C, indicating fairly easy rotation of
intense absorptions at longer wavelengths than the corre- the butatriene bond, probably at the C4ϪC7 double bond
sponding p-quinone methides. For example, the longest-ab- (∆G‡ ϭ 18.5 Ϯ 0.5 kcal·molϪ1). The energy barrier is con-
sorption band of 2a (λmax. ϭ 641 nm/CH2Cl2) is ca. 150 nm siderably lower than that in the p-quinone methide 1b (no
longer than that of 1a (λmax. ϭ 495 nm/CH2Cl2). In particu- broadening of the tert-butyl signals at 120 °C), but higher
lar, the fact that 2a absorbs across the whole of the visible than that of the quinodimethane 7[11] (Tc ϭ Ϫ10 °C; ∆G‡ ϭ
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T. Kawase, N. Nishigaki, H. Kurata, M. Oda
FULL PAPER
Table 1. Selected spectroscopic data of 2aϪf, and quinone methide 1a and 1e
Compound
IR stretching (cmϪ1 [a]
)
13C NMR chemical shifts (δ ppm)[b]
CϭO
CϭCϭCϭC
C1
C4
C7
C8
C9
2a
2b
2c
2d
2e
2f
1594 s, 1551 s
1598 m, 1571 s
1595 m, 1579 s
1585 s
2043 m
2037 m
2040 m
2033 m
2027 m
2027 m
184.72
185.21
185.39
185.52
185.64
185.62
185.9
109.09
111.95
113.04
114.38
115.54
116.42
128.8
153.73
155.68
156.73
157.76
158.27
157.09
137.27
138.70
137.36
139.77
141.60
141.63
130.40
131.23
133.39
135.65
138.27
136.40
159.2[c]
155.9[c]
1588 s
1590 s, 1585 s
1601 s, 1587 s
1604 s
1a
1e
186.1
129.7
[a]
[b]
[c]
KBr disk. δ in CDCl3. Based on CϪH COSY (HMQC and HMBC) spectra. Diarylmethylene carbon (C7).
11.5 Ϯ 0.5 kcal·molϪ1 in [D7]DMF). Thus, 2b has a sub-
stantial dipolar property, intermediate between 1b and 7.
Electrochemical Properties
Figure 3. Cyclic voltammogram of 2e in DMF
The quinopropadienes 2 have higher electron affinity
than the p-quinone methides 1, as exemplified by the lower
first reduction potential of 2e (E1red ϭ Ϫ0.85 V) in relation
to 1e (E1red ϭ Ϫ1.14 V) (Table 2, Figure 3). However, while
the first reduction wave of 1e is reversible, that of 2e is al-
most irreversible. The results indicate the transient nature
of the anion radical 2e·Ϫ. The second weak reduction wave
Notably, a common re-oxidation wave at about Ϫ0.40 V
is observed for each of the compounds 2aϪf. These obser-
vations are best explained in terms of easy coupling of the
anion radical of 2aϪf at the C-9 position to form the dimer
dianion 9 (Scheme 2). The substituents on the aryl group in
this dimer should have little effect on the oxidation poten-
tial of the 4-ethynylphenoxide parts.
probably corresponds to the formation of the dianion 2e2Ϫ
.
On the other hand, 2aϪf also each exhibited an irreversible
oxidation wave in the measurable range (Ͻ ϩ1.5 V), unlike
the corresponding quinone methides. In particular, the elec-
tron-releasing properties of 2a are significantly high, so 2a
can be regarded as a highly amphoteric redox system
(E1sum ϭ 1.37 V). This ability of 2a is quite similar to that
of 8, the best amphoteric redox system containing a butatri-
ene moiety.[12]
Table 2. Electrochemical data of 2aϪf, 1a, and 1e
Compound
Redox potentials (V)[a]
E1
E1red
E2
red
ox
2a
2b
2c
2d
2e
2f
0.36
0.51
0.85
1.01
1.08
1.13
Ϫ1.07
Ϫ0.96
Ϫ0.95
Ϫ0.88
Ϫ0.85
Ϫ0.80
Ϫ1.42
Ϫ1.14
Ϫ1.76
Ϫ1.61
Scheme 2. Coupling of radical anions of 2 to generate the dimer 9
1a
1e
Ϫ1.98
Ϫ1.73
[a]
V vs. Ag/Agϩ (ferrocene/ferrocenium cation ϭ ϩ0.24 V) in 0.1
mol·dmϪ3 nBu4NClO4, 25 °C, sweep rate 100 mV·secϪ1
.
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2,6-Di-tert-butyl-4-(3,3-diarylpropadienylidene)-2,5-cyclohexadien-1-ones
FULL PAPER
Molecular Structures of 2a and 2e
Good single crystals of 2a and 2e suitable for X-ray
analysis were obtained from hexane and benzene-hexane
solutions, respectively. Figure 4 shows the molecular struc-
tures. Both molecules have almost planar butatriene moiet-
ies, and the aryl rings are inclined from the butatriene plane
propeller fashion. However, the dihedral angles between
two aromatic ring planes (2a for 47° and 2e for 52°) are
appreciably smaller than those of the known p-quinone me-
thides (ca. 95°),[13] probably due to the low steric hindrance
around the central carbon of diarylmethylidenes. The struc-
tural properties account for the higher reactivity of radical
anions 2Ϫ· relative to 1Ϫ·. The characteristic points of each
of these structures are the short central double bond
(C7ϪC8) and the long side double bonds (C4ϪC7 and
Figure 5. Dimeric structures of: a) 2a, and b) 2e in the crystals
˚
C8ϪC9); the central double bond of 2a (1.228 A) is the
second shortest among the known butatrienes, the shortest
one being the highly polarized 1,1-dicyano-4,4-bis(dimethy-
[14]
˚
lamino)butatriene (10) (1.201 A).
In those structures of
low symmetry, the lengths of the side double bonds are dif-
ferent; the quinone methide double bonds (C4ϪC7) are
Conclusion
˚
˚
0.24A for 2a and 0.27 A for 2e longer than the diarylmethy-
lene double bonds (C8ϪC9). These structural character-
istics should indicate a large resonance contribution by the
dipolar structure possessing an acetylenic bond 11. The
other interesting feature in each molecular structures is that
the butatriene part is strongly bent, the bond angles around
the sp carbon atoms being 171.9 and 170.5° for 2a and
175.2 and 175.7° for 2e. The electron-rich 2a is thus more
bent than 2e and the other butatrienes reported so far.[14]
Although spectroscopic data such as variable-temperature
NMR and theoretical calculations on 2a tell little about its
bent structure, the larger bending of 2a in the crystal might
be associated with the higher electron density at the butatri-
ene carbon atoms, as indicated by the 13C chemical shifts.
Both molecules form head-to-tail dimeric structure in the
crystals, as shown in Figure 5. The molecules are stacked in
a parallel-displaced manner, probably due to the presence
of bulky tert-butyl groups.
We have provided a synthetic route to p-quinopropadi-
enes 2, using lithium 2,6-di-tert-butyl-4-lithioethynyl-
phenoxide (4) as an effective synthon, and have been able
to establish the structural and some of the electronic
properties of these interesting π systems. The extension of
conjugation causes bathochromic shifts in absorption spec-
tra and increases the dipolar character of molecules. The
rotational barriers of the diarylmethylidene bond of 2b indi-
cate that the order of the dipolar character are dicyanoqui-
nodimethanes Ͼ 2 Ͼ quinone methides. From cyclic vol-
tammetric analyses of 2, both the electron-releasing and
Ϫaccepting properties are enhanced; the amphoteric
character of 2a is almost similar to that of 8. However, the
corresponding radical anions and cations of 2 are highly
reactive. The crystallographic analyses reveal that the di-
hedral angles between the two aromatic rings (47° for 2a
and 52° for 2e) are significantly smaller than those of the
known p-quinone methides. The structural properties ac-
count for the high reactivity of radical anions 2Ϫ·. The mo-
lecular structures are also characterized by the short central
double bond and the long side double bonds, probably indi-
cating large resonance contributions of the dipolar struc-
tures possessing an acetylenic bond. Thus, the extension to
conjugation by insertion of two sp carbon atoms has been
shown to be an effective way to construct highly colored
organic compounds. Work along these lines is under way
and the results will be communicated in due course.
Experimental Section
Figure 4. Molecular structures of: a) 2a, and b) 2e in the crystal;
˚
selected bond lengths (A) and angles (°): 2a; O1ϪC1 1.252(4),
General Remarks: Melting points were recorded with a Yanaco MP
500D apparatus and are uncorrected. FAB and EI mass spectra
were measured with a JEOL JMS-SX 102 instrument. 1H NMR
spectra (tetramethylsilane; δ ϭ 0 ppm as an internal standard) and
13C NMR spectra (CDCl3; 77.0 ppm as an internal standard) were
C4ϪC7 1.380(5), C7ϪC8 1.228(5), C8ϪC9 1.356(5); C4ϪC7ϪC8
171.9(5), C7ϪC8ϪC9 170.5(5), dihedral angle of least-squares
planes A and B 52°; 2e; O1ϪC1 1.232(4), C4ϪC7 1.375(4), C7ϪC8
1.235(4), C8ϪC9 1.348(4); C4ϪC7ϪC8 175.2(4), C7ϪC8ϪC9
175.7(5), dihedral angle of least-squares planes A and B 47°
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T. Kawase, N. Nishigaki, H. Kurata, M. Oda
FULL PAPER
recorded with JEOL EX-270 and JEOL GSX-400 instruments. The
chemical shifts are given in ppm. IR spectra were obtained with a
PerkinϪElmer 1650 spectrometer. The microanalyses were per-
formed at the Elemental Analysis Center, Faculty of Science, Osaka
University. Electronic spectra (UV/Vis) were obtained with a Jasco
V-570 spectrophotometer. Column chromatography was performed
with Merck Kieselgel 60. Cyclic voltammograms were recorded
with a BAS Voltammetric Analyzer BAS100B/W(CV-50 W). All
electrochemical measurements were carried out in DMF solutions
containing 0.1 mol·dm3 tetra(n-butyl)ammonium perchlorate
(Nakarai Tesque) at 25 °C under argon. All reagents were of com-
mercial quality and were used as supplied unless otherwise stated;
tetrahydrofuran was dried by standard procedures where necessary.
Compounds 1 were prepared as described previously.
C33H4N2O (444.4): calcd. C 82.45, H 8.39, N 5.83, found C 82.46,
H 8.39, N 5.78.
Quinopropadiene 2b: This compound was prepared from
5
(1 mmol) and 4-(dimethylamino)benzophenone (149 mg,
0.66 mmol); elution with benzene/hexane (1:1, v/v) at 0 °C afforded
the product 2b (102 mg, 35%) as green prisms; m.p. 147Ϫ149 °C.
IR (KBr): ν˜ ϭ 2952 (m), 2037 (s, CϭCϭCϭC), 1598 (s), 1571 (s,
CϭO), 1482 (w), 1442 (w), 1371 (m), 1298 (m), 1166 (s), 1099 (w),
906 (w), 817 (w), 691 (w), 524 (w) cmϪ1 1H NMR (270 MHz,
.
CDCl3): δ ϭ 1.33 (s, 9 H), 1.36 (s, 9 H), 3.09 (s, 6 H), 6.73 (d, J ϭ
9.2 Hz, 2 H), 7.07 (d, J ϭ 2.3 Hz, 1 H), 7.14(d, J ϭ 2.3 Hz, 1 H),
7.44Ϫ7.46 (m, 3 H), 7.59 (d, J ϭ 9.2 Hz, 2 H), 7.62Ϫ7.65 (m, 2 H)
ppm. 13C NMR (67.8 MHz, CDCl3): δ ϭ 29.7 [ϪC(CH3)], 35.4
[ϪC(CH3)], 40.2 [ϪN(CH3) 2), 111.9 (CЈ-3), 112.0 (C-4), 126.4 (CЈ-
1), 128.4 (CЈЈ-1), 128.6 (CЈЈ-3), 129.5 (C-3 or 5), 130.2 (CЈЈ-2), 131.1
(C-5 or 3), 131.2 (C-9), 131.8 (CЈ-2), 135.2 (CЈЈ-1), 138.7 (C-8),
147.3 (C-2 or 5), 147.4 (C-5 or 2), 151.6 (CЈ-4), 155.7 (C-7), 185.2
(C-1) ppm. UV/Vis (CH2Cl2): λmax. (log ε) ϭ 284 (4.19), 332 (4.13),
362 (4.06), 455 (4.01), 595 nm (4.65). MS (EI): m/z (%) ϭ 438 (34)
2,6-Di-tert-butyl-4-ethynylphenol (5): (Dichloro)bis(triphenylphos-
phane)palladium (240 mg, 0.4 mmol) and CuI (40 mg, 0.2 mmol)
were added to a solution of 4-bromo-2,6-di-tert-butyl(trimethylsi-
loxy)benzene (7.15 g, 0.02 mol) and (trimethylsilyl)acetylene
(5.6 mL, 0.02 mol) in anhydrous triethylamine (90 mL). The reac-
tion mixture was stirred at reflux under N2. After 4 h, the mixture
was cooled to 0 °C, diluted with hydrochloric acid (2 , 100 mL),
and extracted with hexane (100 mL ϫ 2). The extracts were com-
bined, washed with brine (100 mL), dried with anhydrous MgSO4,
concentrated, and chromatographed on silica gel with hexane elu-
tion to give 4-(2-trimethylsilylethynyl)-2,6-di-tert-butyl(trimethylsi-
loxy)benzene as a colorless oil (6.14 g). The oil was diluted with
THF (80 mL) under N2. nBu4NF (1  solution in THF, 60 mL,
60 mmol) was added to the degassed solution, and the mixture was
stirred at 0 °C under N2. After 2 h, the mixture was diluted with
aqueous NH4Cl (100 mL) and extracted with hexane (2 ϫ 100 mL).
The extracts were combined, washed with brine (100 mL), dried
with anhydrous MgSO4, concentrated, and chromatographed on
silica gel with hexane elution to give 3.91 g (85%, two steps) of
colorless prisms. M.p. 107Ϫ108 °C (ref. 106Ϫ107 °C).[15]
[Mϩ ϩ H], 437 (95) [Mϩ], 422 (96) [Mϩ Ϫ Me], 380 (100) [Mϩ
Ϫ
tBu]. C31H35NO (437.6): calcd. C 85.08, H 8.06, N 3.20; found C
84.86, H 7.94, N 3.01.
Quinopropadiene 2c: This compound was prepared from 5 (2 mmol)
and 4,4Ј-dimethoxybenzophenone (484 mg, 2 mmol); the residue
was loaded onto chromatography silica gel at room temp. for 3 h,
and then eluted with benzene/hexane (1:2, v/v) to afford the prod-
uct 2c (609 mg, 67%) as reddish purple needles; m.p. 175Ϫ176 °C.
IR (KBr): ν˜ ϭ 2955 (m), 2040 (m, CϭCϭCϭC), 1595 (m), 1579
(s, CϭO), 1507 (m), 1458 (w), 1387 (w), 1361 (m), 1302 (m), 1259
(s), 1202 (w), 1171 (s), 1098 (w), 1036 (m), 913 (w), 834 (m), 579
1
(w), 508 (w) cmϪ1. H NMR (270 MHz, CDCl3): δ ϭ 1.34 (s, 18
H), 3.89 (s, 6 H), 6.98 (d, J ϭ 8.9 Hz, 4 H), 7.09 (s, 2 H), 7.60 (d,
J ϭ 8.9 Hz, 4 H) ppm. 13C NMR (67.8 MHz, CDCl3): δ ϭ 29.7
[ϪC(CH3) 3), 35.4 (ϪC(CH3) 3), 55.5 (ϪOCH3), 113.0 (C-4), 114.3
(CЈ-3), 131.0 (CЈ-1), 131.6 (CЈ-2), 133.4 (C-9), 137.4 (C-8), 147.8
(C-2), 156.7 (C-7), 161.3 (CЈ-4), 185.4 (C-1) ppm. UV/Vis
(CH2Cl2): λmax. (log ε) ϭ 290 (4.17), 378 (3.99), 399 (3.98), 520 nm
(4.64). MS (EI): m/z (%) ϭ 455 (17) [Mϩ ϩ H], 454 (61) [Mϩ], 439
(60) [Mϩ Ϫ Me], 397 (100) [Mϩ Ϫ tBu]. C31H34O3 (454.6): calcd.
C 81.90, H 7.54; found C 81.81, H 7.52.
General Procedure for the Preparation of Compounds 2a؊d, and
6e؊f: nBuLi (1.3  solution in hexane, 1.3 mL, 2.1 mmol) was ad-
ded at Ϫ78 °C under N2 to a solution of 5 (230 mg, 1 mmol) in
dry THF (20 mL), and the mixture was stirred at Ϫ78 °C for 1 h
to generate anion 4. A solution of the appropriate diaryl ketone
(1 mmol) in THF (10 mL) was added dropwise by syringe at Ϫ78
°C to the reaction mixture. The mixture was warmed to room
temp., stirred for 1 h, diluted with aqueous NH4Cl (100 mL), and
extracted with benzene (2 ϫ 100 mL). The extracts were combined,
washed with brine (100 mL), dried with anhydrous MgSO4, and
concentrated. Silica gel column chromatography of the residue as
indicated afforded the relevant product 6 and/or 2.
Quinopropadiene 2d: This compound was prepared from
5
(2 mmol) and 4,4Ј-dimethylbenzophenone (452 mg, 2 mmol); the
residue was loaded onto chromatography silica gel at room temp.
for 12 h, and then eluted with benzene/hexane (1:2, v/v) to afford
the product 2d (570 mg, 67%) as reddish purple plates; m.p.
201Ϫ203 °C. IR (KBr): ν˜ ϭ 2954 (m), 2033 (m, CϭCϭCϭC), 1585
(s, CϭO), 1458 (w), 1359 (w), 1312 (w), 1294 (m), 1252 (w), 1202
Quinopropadiene 2a: This compound was prepared from
5
(w), 1180 (m), 1096 (w), 908 (w), 823 (w), 613 (w), 576 (w) cmϪ1
.
(1 mmol) and Michler’s ketone (268 mg, 1 mmol); elution at 0 °C
with benzene/hexane (1:1, v/v) afforded the product 2a (158 mg,
32%) as green prisms; m.p. 195Ϫ197 °C. IR (KBr): ν˜ ϭ 2949 (m),
2043 (s, CϭCϭCϭC), 1594 (s), 1551 (s, CϭO), 1481 (m), 1446 (m),
1371 (m), 1320 (m), 1228 (m), 1164 (s), 1097 (m), 947 (w), 910 (w),
820 (w), 572 (w), 478 (w) cmϪ1. 1H NMR (270 MHz, CDCl3): δ ϭ
1.35 (s, 18 H), 3.09 (s, 12 H), 6.75 (d, J ϭ 9.1 Hz, 4 H), 7.14 (s, 2
H), 7.61 (d, J ϭ 9.1 Hz, 4 H). 13C NMR (67.8 MHz, CDCl3): δ ϭ
1H NMR (270 MHz, CDCl3): δ ϭ 1.33 (s, 18 H), 2.42 (s, 6 H),
7.08 (s, 2 H), 7.26 (d, J ϭ 8.2 Hz, 4 H), 7.54 (d, J ϭ 8.2 Hz, 4
H) ppm. 13C NMR (67.8 MHz, CDCl3): δ ϭ 21.5 (ϪCH3), 29.6
[ϪC(CH3) 3], 35.4 [ϪC(CH3) 3], 114.4 (C-4), 129.5 (C-2), 129.9 (C-
3), 131.0 (C-3), 133.6 (CЈ-1), 135.7 (C-9), 139.8 (C-8), 140.3 (CЈ-4),
148.1 (C-2), 157.8 (C-7), 185.5 (C-1) ppm. UV/Vis (CH2Cl2): λmax.
(log ε) ϭ 282 (4.23), 350 (3.83), 491 nm (4.67). MS (EI): m/z (%) ϭ
423 (7) [Mϩ ϩ H], 422 (23) [Mϩ], 407 (33) [Mϩ Ϫ Me], 365 (100)
[Mϩ Ϫ tBu]. C31H34O (422.6): calcd. C 88.11, H 8.11: found C
88.11, H 8.14.
29.7 [ϪC(CH3)], 35.3 [ϪC(CH3)], 40.2 [ϪN(CH3) ), 109.1 (C-4),
2
111.7 (CЈ-3), 126.5 (CЈ-1), 130.4 (C-9), 131.4 (C-3), 132.1 (CЈ-2),
137.3 (C-8), 146.3 (C-2), 151.6 (CЈ-4), 153.7 (C-7), 184.7 (C-1) ppm.
UV/Vis (cyclohexane): λmax. (log ε) ϭ 283 (4.12), 332 (4.25), 424
Alcohol 6e: This compound was prepared from 5 (1 mmol) and
(3.59), 505 (4.49), 641 nm (4.65). MS (EI): m/z (%) ϭ 481 (39) [Mϩ benzophenone (180 mg, 1 mmol); elution with benzene/hexane (1:1,
ϩ H], 480 (100) [Mϩ], 465 (76) [Mϩ Ϫ Me], 396 (76) [Mϩ Ϫ tBu]. v/v) afforded the alcohol 6e (370 mg, 90%) as a colorless powder;
3094
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
Eur. J. Org. Chem. 2004, 3090Ϫ3096

2,6-Di-tert-butyl-4-(3,3-diarylpropadienylidene)-2,5-cyclohexadien-1-ones
m.p. 148Ϫ149 °C. IR (KBr): ν˜ ϭ 3588 (m, OH), 3367 (br. s, OH),
FULL PAPER
refined by full-matrix, least-squares against F2 of all data, by use of
2962 (s), 2225 (w, CϵC), 1490 (m), 1448 (s), 1432 (s), 1390 (m), SHELXS-86. All non-hydrogen atoms were refined anisotropically.
1361 (m), 1201 (m), 1225 (m), 1181 (m), 1155 (m), 1056 (m), 767
Hydrogen atoms were placed geometrically and refined by use of a
(s), 697 (s) cmϪ1. 1H NMR (270 MHz, CDCl3): δ ϭ 1.43 (s, 18 H), rigid model.
2.81 (s, 1 H), 5.37 (s, 1 H), 7.40Ϫ7.53 (m, 6 H), 7.65Ϫ7.75 (m, 4
H) ppm. 13C NMR (67.8 MHz, CDCl3): δ ϭ 30.3, 34.4, 74.9, 88.4,
Crystal Data for 2a: C33H40N2O, M ϭ 480.69, triclinic, space group
˚
˚
˚
3
¯
P1 (#2), a ϭ 12.924(3) A, b ϭ 13.377(2) A, c ϭ 8.735(1) A, α ϭ
89.3, 113.2, 126.0, 127.5, 128.2, 128.7, 136.0, 145.3, 154.5 ppm. MS
(EI): m/z ϭ 412 (30) [Mϩ], 397 (4) [Mϩ Ϫ Me], 354 (28) [Mϩ
Ϫ
˚
100.76(1)°, β ϭ 102.49(1)°, γ ϭ 81.99(2)°, V ϭ 1440.8(5) A , Z ϭ
2, Dcalcd. ϭ 1.108 g·cm3, µ ϭ 0.66 cmϪ1, R(Rw) ϭ 0.158 (0.159),
R1 ϭ 0.052 for 1573 reflections [I Ͼ 2σ(I)]. CCDC-207099.
tBuH], 279 (22), 149 (50), 87 (100). HRMS calcd. 412.2404;
found 412.2465.
Alcohol 6f: This compound was prepared from 5 (2 mmol) and 4,4Ј-
dichlorobenzophenone (502 mg, 2 mmol); elution with benzene/
hexane (1:1, v/v) afforded the alcohol 6f (590 mg, 61%) as a color-
less powder; m.p. 137Ϫ138 °C. IR (KBr): ν˜ ϭ 3632 (s, OH), 3406
(br. s, OH), 2959 (s), 2872 (m), 2215 (w, CϵC), 1490 (s), 1434 (s),
1362 (m), 1236 (m), 1070 (m), 1093 (s), 1016 (m), 901 (m), 830 (s)
Crystal Data for 2e: C29H30O, M ϭ 394.56, monoclinic, space
˚
˚
group P21/a (#14), a ϭ 8.351(7) A, b ϭ 23.185(5) A, c ϭ 12.557(4)
3
A, β ϭ 99.98(4)°, V ϭ 2394(2) A , Z ϭ 4, Dcalcd. ϭ 1.094 g cm3,
µ ϭ 0.64 cmϪ1, R(Rw) ϭ 0.111 (0.121), R1 ϭ 0.054 for 1439 reflec-
tions [I Ͼ 2σ(I)]. CCDC-207100.
˚
˚
1
cmϪ1. H NMR (270 MHz, CDCl3): δ ϭ 1.43 (s, 18 H), 2.83 (s, 1
CCDC-207099 (for 2a) and -207100 (for 2e) contain the sup-
plementary crystallographic data for this paper. These data can be
obtained free of charge at www.ccdc.cam.ac.uk/conts/retriev-
ing.html [or from the Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; Fax: ϩ44-1223/336-033;
E-mail: deposit@ccdc.cam.ac.uk].
H), 5.42 (s, 1 H), 7.31 (m, J ϭ 8.6 Hz, 4 H), 7.58 (m, J ϭ 8.6 Hz,
4 H) ppm. 13C NMR (67.8 MHz, CDCl3): δ ϭ 30.2, 43.4, 74.1,
88.3, 89.1, 112.6, 127.4, 128.4, 128.7, 133.6, 136.2, 143.5, 154.8
ppm. MS (EI): m/z (%) ϭ 482 (18) [Mϩ, 2 ϫ 37Cl], 481 (11) [Mϩ,
37Cl ϩ 35Cl], 480 (29) [Mϩ, 2 ϫ 35Cl], 465 (7) [Mϩ Ϫ Me]. HRMS
calcd. 480.1625; found 480.1598.
Preparation of Compounds 2e؊f: Degassed suspensions of the pre-
cursors 6 (0.5 mmol), anhydrous CuSO4 (400 mg, 2.5 mmol), and
anhydrous ZnCl2 (340 mg, 2.5 mmol) in THF (20 mL) were heated
at reflux with stirring for 2 h. After cooling, the mixtures were fil-
tered through celite columns and eluted with benzene/hexane (1:1,
v/v). The eluents were concentrated and chromatographed on silica
gel with benzene/hexane (1:2, v/v) elution to give 138 mg of 2e
(70%) and 165 mg of 2f (71%), respectively:
Acknowledgments
This work was supported by Grant-in-Aid for Scientific Research
(No. 11440189 and 14340197) from the Ministry of Education,
Science, Sports and Culture, Japan.
Compound 2e: Reddish orange prisms; m.p. 185Ϫ187 °C. IR (KBr):
ν˜ ϭ 2956 (m), 2027 (m, CϭCϭCϭC), 1588 (s, CϭO), 1481 (w),
1455 (m), 1381 (w), 1360 (m), 1250 (w), 1198 (w), 1181 (m), 1099
(w), 906 (m), 883 (w), 817 (w), 776 (m), 691 (m), 626 (w), 519 (w)
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1197Ϫ1226.
1
cmϪ1. H NMR (270 MHz, CDCl3): δ ϭ 1.34 (s, 18 H), 7.08 (s, 2
[2]
[2a] R. West, D. C. Zecher, J. Am. Chem. Soc. 1967, 92, 155. [2b]
H), 7.43Ϫ7.48 (m, 6 H), 7.62Ϫ7.66 (m, 4 H). 13C NMR (67.8 MHz,
CDCl3): δ ϭ 29.6 [ϪC(CH3)3], 35.5 [ϪC(CH3) 3], 115.5 (C-4), 128.7
(CЈ-2), 129.7 (CЈ-4), 129.8 (CЈ-3), 130.8 (C-3), 132.9 (CЈ-1), 138.3
(C-9), 141.6 (C-8), 148.6 (C-2), 158.3 (C-7), 185.6 (C-1) ppm. UV/
Vis (CH2Cl2): λmax. (log ε) ϭ 276 (4.19), 349 (3.56), 472 nm (4.67).
MS (EI): m/z (%) ϭ 395 (8) [Mϩ ϩ H], 394 (37) [Mϩ], 379 (41)
[Mϩ Ϫ Me], 337 (100) [Mϩ Ϫ tBu]. C29H30O (394.6): calcd. C
88.28, H 7.66; found C 88.25, H 7.66.
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ν˜ ϭ 2959 (m), 2027 (m, CϭCϭCϭC), 1590 (s, CϭO), 1585 (s),
1487 (m), 1397 (m), 1361 (m), 1198 (w), 1177 (w), 1099 (s), 1012
(m), 904 (m), 834 (m), 816 (w), 724 (w), 612 (w), 531 (w), 472 (w)
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[2j]
R. Faust, B.
[2k]
1
cmϪ1. H NMR (270 MHz, CDCl3): δ ϭ 1.33 (s, 18 H), 7.04 (s, 2
H. Meier, S.
[2l]
H), 7.43 (d, J ϭ 8.6 Hz, 4 H), 7.52 (d, J ϭ 8.6 Hz, 4 H) ppm. 13C
NMR (67.8 MHz, CDCl3): δ ϭ 29.6 [ϪC(CH3)3], 35.5 [ϪC(CH3)3],
116.4 (C-4), 129.1 (CЈ-2), 129.4 (CЈ-4), 130.6 (C-3), 130.8 (CЈ-3),
136.0 (CЈ-1 or C9), 136.4 (C-9 or CЈ-1), 141.6 (C-8), 149.0 (C-2),
157.1 (C-7), 185.6 (C-1) ppm. UV/Vis (CH2Cl2): λmax. (log ε) ϭ
286 (4.27), 300 (4.29), 349 (3.76), 473 nm (4.73). MS (EI): m/z
(%) ϭ 466 (9) [Mϩ, 2 ϫ 37Cl], 464 (17) [Mϩ, 37Cl ϩ 35Cl], 462 (2)
[Mϩ, 2 ϫ 35Cl], 447 (32) [Mϩ, Ϫ Me], 405 (76) [Mϩ Ϫ tBu].
C29H28Cl2O (463.4): calcd. C 75.16, H 6.09; found C 75.29, H 6.07.
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J. Qin, J. Cheng, Y. Shen, Z. Lu, P. Wang, C. Ye, Chem. Com-
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Eur. J. Org. Chem. 2004, 3090Ϫ3096
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Received January 14, 2004
3096
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
Eur. J. Org. Chem. 2004, 3090Ϫ3096