Synthesis of extended bifunctional triptycenes

Article abstract of DOI:10.1055/s-0028-1083209

Extended triptycenes 5a, b and 7a-c have been designed to serve as convenient building blocks for a stepwise ramification of the parent triptycene structure by Diels-Alder oligomerization. Georg Thieme Verlag Stuttgart · New York.

Full text of DOI:10.1055/s-0028-1083209

PAPER
3615
Synthesis of Extended Bifunctional Triptycenes
Synthesis
i
of
E
xte
ř
nded
B
i
í
functiona
l
Tri
R
ptycenes ybáček, Jiří Závada, Petr Holý*
Institute of Organic Chemistry and Biochemistry, v.v.i., Academy of Sciences of the Czech Republic, Flemingovo n. 2., 166 10 Prague 6,
Czech Republic
Fax +420(2)20183560; E-mail: petrholy@uochb.cas.cz
Received 25 June 2008; revised 4 August 2008
7a–c allow a simple unmasking into reactive dienophilic
Abstract: Extended triptycenes 5a,b and 7a–c have been designed
aryne or p-quinone functionalities, respectively, by well-
to serve as convenient building blocks for a stepwise ramification of
established methodologies7,8 prior to oligomerization.
the parent triptycene structure by Diels–Alder oligomerization.
Synthesis of the synthons 5a,b is outlined in Scheme 1. In
the first approach, a thermal treatment of the easily
accessible9 dibromoanthracene 1a,b with the dienophilic
counterpart 2a,b followed by aromatization of the primary
adduct via acid hydrolysis afforded the target products
5a,b in a one-pot reaction. In another approach, starting
again from the dibromoanthracene 1a, the reactive aryne
generated in situ from the amino acid 310 was employed as
the dienophilic partner in the Diels–Alder reaction with 1a
and the resulting quinoid adduct 4 was subjected to a one-
pot rearomatization, providing the desired synthon 5a.
Key words: anthracenes, arynes, Diels–Alder reaction, quinones,
triptycenes
With their unique three-bladed geometry, mechanical ri-
gidity, and chemical stability, triptycene molecules have
been amply incorporated into molecular machines,1–3 in
particular as parts of molecular motors, and also proposed
to serve as molecular scaffolds4a or as tectons in supramo-
lecular self-assembly of porous structures.4b Since the
branched triptycene structure provides well-defined cavi-
ties tunable in size and shape by design, strategies aimed
at a further elaboration of the key triptych motif are of a
considerable interest.
Triptycenes are conveniently prepared5 by the Diels–
Alder reaction between an anthracene (with its central
ring serving as the diene component), and an appropriate
dienophile. Accordingly, extended triptycenes, bearing
both the requisite anthracene ring and the dienophilic
grouping properly anchored at two separate blades of the
central triptycene, may serve as convenient building
blocks for a stepwise structure ramification by Diels–
Alder oligomerization.5,6
The synthesis of the alternative synthons 7a–c outlined in
Scheme 2 starts from the heptacyclic Diels–Alder adduct
6, which we have made easily accessible by a modifica-
tion of the reported procedure.11 Zinc-mediated reduction
of the quinone functionality in 6 provided the respective
air-unstable hydroquinone, which could be converted in
situ into stable acetoxy or tert-butyldiphenylsilyl deriva-
tives 7a and 7b, respectively. In a more convenient trans-
formation of 6, the quinone reduction was replaced by an
organometallic addition. Reaction of 6 with methyllithi-
um afforded cleanly the diastereomeric mixture of diols 8,
which upon aromatization12 provided the target synthon
7c. The viability of the stepwise Diels–Alder oligomeriza-
tion can thus be addressed.
Accordingly, we have focused attention on the design of
appropriate monomeric units for the oligomerization and
have chosen the extended triptycenes 5a,b and 7a–c, rep-
resenting masked oligomerization synthons as the subject
of the present study (Figure 1). Both the o-dibromoarene
moiety in 5a,b as well as the p-dimethoxyarene unit in
Melting points were determined on a Kofler apparatus and are un-
corrected. NMR spectra were measured on Bruker Avance 400 (1H
at 400 MHz and 13C at 100.6 MHz), Bruker Avance 500 (1H at 500
MHz and 13C at 125.8 MHz), and Varian 300 (1H at 300 MHz and
MeO
R
R
R
Br
Br
MeO
R
R
R
5a R = H
5b R = Me
7a R = OC(O)Me
7b R = OSi-t-BuPh2
7c R = Me
Figure 1 Extended bifunctional triptycenes 5 and 7
SYNTHESIS 2008, No. 22, pp 3615–3618
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x
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Advanced online publication: 23.10.2008
DOI: 10.1055/s-0028-1083209; Art ID: T10708SS
© Georg Thieme Verlag Stuttgart · New York

3616
J. Rybáček et al.
PAPER
lizations and chromatography. 2,3-Dibromo-1,4-dimethylan-
thracene (1b) was prepared analogously to dibromoanthracene 1a9
by a multistep procedure.
R
R
Br
Br
R
2,3-Dibromo-1,4-dimethylanthracene (1b)
6,7-Dibromo-9,10-epoxy-5,8-dimethyl-1,4,4a,9,9a,10-hexahy-
droanthracene
1a R = H
1b R = Me
O
O
A
mixture of 6,7-dibromo-1,4-epoxy-5,8-dimethyl-1,4-dihy-
2a R = H
R
dronaphthalene, prepared7 from easily accessible 1,2,4,5-tetrabro-
mo-3,6-dimethylbenzene, (1.10 g, 3.33 mmol) and butadiene
sulfone (0.470 g, 3.98 mmol) in xylene (5 mL) was heated in a pres-
sure tube at 145 °C for 7 h. Evaporation of the solvent in vacuo was
followed by chromatography on a silica gel column using CH2Cl2–
hexanes (2:3) as eluent. The product was obtained as white crystals;
yield: 650 mg (51%); mp 115–118 °C (CH2Cl2–hexanes).
2b R = Me
NH2
1. xylene, 160 °C
2. TsOH (cat.), 120 °C
COOH
O
26% of 5a, 52% of 5b
3
i-AmONO, DCE
diglyme, reflux
5a,b
1H NMR (400 MHz, CDCl3): d = 1.86–1.92 (m, 2 H), 1.99–2.08 (m,
2 H), 2.40 (s, 6 H), 2.45–2.53 (m, 2 H), 5.04 (s, 2 H), 5.90–5.97 (m,
2 H).
13C NMR (100.6 MHz, CDCl3): d = 21.0 (CH3), 27.4 (CH2), 41.7
(CH), 84.7 (CH), 125.9 (C), 128.8 (C), 129.0 (CH), 144.2 (C).
31%
Zn, aq NH3,
CuSO4 (cat.),
n-BuNH2, reflux
O
Br
Br
43% of 5a
MS (EI): m/z (%) = 384 (1, [M+]), 304 (100), 223 (8), 115 (24).
HRMS-EI: m/z calcd for C16H16Br2O: 381.9568; found: 381.9573.
4
O
1b
Scheme 1 Synthesis of the synthons 5a,b
Rearomatization9 of the aforementioned epoxide yielded 150 mg
(32%) of 1b; mp 156–158 °C (CH2Cl2–hexanes).
1H NMR (400 MHz, CDCl3): d = 3.02 (s, 6 H), 7.49–7.54 (m, 2 H),
7.98–8.03 (m, 2 H), 8.55 (s, 2 H).
13C NMR (100.6 MHz, CDCl3): d = 21.8 (CH3), 124.2 (CH), 124.7
Zn, NaOAc (cat.), Ac2O,
r.t. to 40 °C
MeO
O
(C), 126.2 (CH), 128.2 (CH), 130.1 (C), 131.6 (C), 134.0 (C).
7a
7b
66%
MS (EI): m/z (%) = 364 (100, [M+]), 285 (48), 202 (81).
Zn, t-BuPh2SiCl, THF, DMF,
0 °C to r.t.
HRMS-EI: m/z calcd for C16H12Br2: 361.9306; found: 361.9300.
MeO
O
6
40%
Anal. Calcd for C16H12Br2: C, 52.58; H, 3.32. Found: C, 52.77; H,
3.29.
MeLi, toluene, r.t.
1,4-Epoxy-1,4-dimethyl-1,4-dihydroanthracene (2b)
Prepared analogously to 2a13 starting from 2,3-dibromo-
naphthalene5 and 2,5-dimethylfuran; yield: 57%; mp 108–110 °C
(CH2Cl2) [Lit.14 mp 104–106 °C (hexane)].
2,3-Dibromo-5,14-dihydro-5,14-(o-benzeno)pentacene (5a)
A suspension of anthracene 1a9 (1.50 g, 4.47 mmol) and epoxide
2a13 (1.00 g, 5.15 mmol) in anhyd xylene (10 mL) was heated in a
pressure tube at 160 °C for 50 h. After cooling, a catalytic amount
of PTSA was added and the mixture was heated at 120 °C for 1 h
and cooled to r.t. The precipitated product was chromatographed on
a silica gel column using CH2Cl2–hexanes (1:2) as eluent; yield: 600
mg (26%); mp >320 °C (CH2Cl2–hexanes).
OH
Me
MeO
1. NaI, TMSCl, MeCN, r.t.
2. Bu3SnH, AIBN, toluene, 100 °C
Me
7c
MeO
64% from 6
OH
8
Scheme 2 Synthesis of the synthons 7a–c
1H NMR (400 MHz, CDCl3): d = 5.49 (s, 2 H), 7.06–7.11 (m, 2 H),
7.39–7.46 (m, 4 H), 7.71 (s, 2 H), 7.90 (s, 2 H), 7.92–7.96 (m, 2 H),
8.26 (s, 2 H).
13C NMR (100.6 MHz, CDCl3): d = 52.6 (CH), 121.2 (C), 121.9
(CH), 124.0 (CH), 125.2 (CH), 125.8 (CH), 126.2 (CH), 128.0
(CH), 128.9 (CH), 130.3 (C), 131.8 (C), 139.5 (C), 143.1 (C), 145.2
(C).
13C at 75 MHz) spectrometers. Chemical shifts (in ppm, d scale)
were referenced to TMS as an internal standard. Coupling constants
(J) are given in Hz. Mass spectra were recorded on a ZAB-EQ (VG-
Analytical) spectrometer using EI ionization (ionizing voltage 70
eV, relative intensities in %). ESI MS analyses were performed on
a LCQ Classic (Thermo Finnigan) quadrupole ion trap mass spec-
trometer. The reaction progress was monitored by TLC on alumi-
num sheets pre-coated with silica gel 60 F254 (Merck) and column
chromatography was carried out using silica gel 60 (Merck). Com-
mercially available reagent grade chemicals were used as received.
THF was freshly distilled from sodium/benzophenone under N2.
Anhyd toluene was distilled from sodium. A hexane fraction with
bp range of 66–70 °C (hexanes) was used as the solvent for crystal-
MS (EI): m/z (%) = 512 (24, [M+]), 432 (6), 352 (17).
HRMS-EI: m/z calcd for C28H16Br2: 509.9619; found: 509.9612.
Anal. Calcd for C28H16Br2: C, 65.65; H, 3.15. Found: C, 65.19; H,
3.16.
Synthesis 2008, No. 22, 3615–3618 © Thieme Stuttgart · New York

PAPER
Synthesis of Extended Bifunctional Triptycenes
3617
9,10-Dibromo-7,12-dihydro-7,12-(o-benzeno)pentacene-5,14-
dione (4)
5,14-Dihydro-1,4-dimethoxy-5,14-(o-benzeno)pentacene-6,13-
dione (6)
To a refluxing suspension of anthracene 1a9 (200 mg, 0.595 mmol)
and amino acid 310 (636 mg, 2.38 mmol) in 1,2-dichloroethane (50
mL) and diglyme (50 mL) was added a solution of isoamyl nitrite
(0.320 mL, 2.38 mmol) in 1,2-dichloroethane (10 mL) over 2.5 h.
The mixture was evaporated to dryness, the residue was dissolved
in CHCl3 and passed through a short pad of silica gel. The pure
product was isolated by chromatography on a silica gel column us-
ing EtOAc–hexanes (1:9) as eluent to give a white solid; yield: 100
mg (31%); mp >320 °C (EtOAc–hexanes).
Prepared by a modification of the known procedure11 employing
FeCl3 as an additional oxidant.15
A suspension of 1,4-
dimethoxyanthracene16 (300 mg, 1.26 mmol), 1,4-anthraquinone17
(260 mg, 1.26 mmol) and FeCl3 (410 mg, 2.52 mmol) in AcOH (20
mL) was heated at 60 °C for 6.5 h. After cooling to r.t., the precipi-
tate was collected by filtration and chromatographed on a silica gel
column using CH2Cl2–hexanes (1:1) as eluent. The orange solid was
then triturated with boiling AcOH (150 mL) and cooled. Filtration
gave the pure product as orange crystals; yield: 265 mg (47%); mp
310 °C (AcOH, dec.) [Lit.11 mp 310 °C (dec.)].
1H NMR (400 MHz, CDCl3): d = 5.59 (s, 2 H), 7.06–7.11 (m, 2 H),
7.42–7.47 (m, 2 H), 7.70 (s, 2 H), 7.74–7.79 (m, 2 H), 8.23–8.28 (m,
4 H).
13C NMR (100.6 MHz, CDCl3): d = 53.1 (CH), 121.5 (C), 122.2
(CH), 124.3 (CH), 126.4 (CH), 127.2 (CH), 129.1 (CH), 131.9 (C),
133.4 (C), 134.0 (CH), 142.4 (C), 144.5 (C), 150.3 (C), 182.8 (C).
1H NMR (400 MHz, CDCl3): d = 3.84 (s, 6 H), 6.52 (s, 2 H), 6.56
(s, 2 H), 7.03–7.05 (m, 2 H), 7.51–7.53 (m, 2 H), 7.62–7.64 (m, 2
H), 8.00–8.02 (m, 2 H), 8.58 (s, 2 H).
13C NMR (100.6 MHz, CDCl3): d = 41.9 (CH3), 56.5 (CH), 109.5
(CH), 124.6 (CH), 125.3 (CH), 128.6 (CH), 128.9 (C), 129.2 (CH),
130.1 (CH), 133.6 (C), 134.8 (C), 144.2 (C), 149.6 (C), 156.4 (C),
180.9 (C).
MS (EI): m/z (%) = 542 (88, [M+]), 463 (15), 382 (78), 324 (33),
250 (14), 163 (29), 97 (29), 83 (37), 69 (60), 57 (86), 43 (100).
HRMS-EI: m/z calcd for C28H14Br2O2: 539.9361; found: 539.9374.
6,13-Bis(acetoxy)-5,14-dihydro-1,4-dimethoxy-5,14-(o-ben-
zeno)pentacene (7a)
Anal. Calcd for C28H14Br2O2: C, 62.02; H, 2.60. Found: C, 62.31;
H, 2.89.
A suspension of quinone 6 (50.0 mg, 0.110 mmol), Zn dust (200
mg, 3.10 mmol) and a catalytic amount of NaOAc in Ac2O (1.5 mL)
was stirred at r.t. for 16 h and then agitated at 40 °C for 1 h in an
ultrasonic bath. H2O (20 mL) was added and the stirring was con-
tinued for 1 h at r.t. The mixture was then extracted with CH2Cl2
(3 × 20 mL), the combined organic layers were dried (Na2SO4), and
the solvents were evaporated. The residue was crystallized from
CH2Cl2–MeOH to give an off-white solid; yield: 35 mg (60%); mp
>320 °C (CH2Cl2–MeOH).
1H NMR (400 MHz, CDCl3): d = 2.68 (s, 6 H), 3.83 (s, 6 H), 6.02
(s, 2 H), 6.57 (s, 2 H), 7.05–7.07 (m, 2 H), 7.41–7.44 (m, 2 H), 7.45–
7.47 (m, 2 H), 7.91–7.94 (m, 2 H), 8.23 (s, 2 H).
13C NMR (100.6 MHz, CDCl3): d = 20.8 (CH3), 41.4 (CH3), 56.6
(CH), 109.8 (CH), 120.4 (CH), 124.5 (CH), 125.2 (C), 125.8 (CH),
125.9 (CH), 128.2 (CH), 131.7 (C), 131.9 (C), 133.2 (C), 138.1 (C),
143.2 (C), 149.2 (C), 169.0 (C).
2,3-Dibromo-5,14-dihydro-5,14-(o-benzeno)pentacene (5a)
To a suspension of dione 4 (50 mg, 0.092 mmol) in n-butylamine
(2.5 mL) was added 25% aq ammonia (1 mL), Zn dust (130 mg, 1.9
mmol) and a catalytic amount of CuSO4. The mixture was refluxed
for 5 h and cooled to r.t. The deposit was filtered off and washed
with CHCl3 (25 mL) and H2O (25 mL). The layers were separated,
the organic layer was washed with aq 10% HCl (15 mL), brine (15
mL), and dried (MgSO4). The pure product was isolated by chroma-
tography on a silica gel column using EtOAc–hexanes (1:9) as elu-
ent to give a white solid; yield: 20 mg (43%), mp >320 °C (EtOAc–
hexanes).
1H NMR: Identical to that of the sample prepared from 2a (vide
supra).
2,3-Dibromo-5,14-dihydro-1,4,6,13-tetramethyl-5,14-(o-ben-
zeno)pentacene (5b)
MS (ESI): m/z = 553 (28 %, [M + Na]+).
A suspension of anthracene 1b (300 mg, 0.820 mmol) and epoxide
2b (210 mg, 0.950 mmol) in anhyd xylene (5 mL) was heated in a
pressure tube at 160 °C for 48 h. After cooling, a catalytic amount
of PTSA was added and the mixture was heated at 100 °C for 3 h.
Toluene (50 mL) and H2O (50 mL) were added and the phases were
separated. The organic phase was washed with sat. aq NaHCO3 (25
mL) and brine (25 mL), and dried (MgSO4). After evaporation of
solvents, the residue was chromatographed on a silica gel column
using CH2Cl2–hexanes (3:7) as eluent to give a white solid; yield:
240 mg (52%); mp >320 °C (CH2Cl2–hexanes).
1H NMR (400 MHz, CDCl3): d = 2.78 (s, 6 H), 2.94 (s, 6 H), 6.23
(s, 2 H), 7.07–7.11 (m, 2 H), 7.40–7.49 (m, 4 H), 7.95–7.99 (m, 2
H), 8.43 (s, 2 H).
13C NMR: Solubility in commonly used solvents was not sufficient
to obtain a spectrum.
HRMS-ESI: m/z calcd for C34H26O6 + Na: 553.1622; found:
553.1612.
Anal. Calcd for C34H26O6: C, 76.97; H, 4.94. Found: C, 76.59; H,
4.89.
6,13-Bis(tert-butyldiphenylsilyloxy)-5,14-dihydro-1,4-
dimethoxy-5,14-(o-benzeno)pentacene (7b)
To a suspension of quinone 6 (200 mg, 0.450 mmol) and Zn dust
(300 mg, 4.50 mmol) in a mixture of THF (5 mL) and DMF (5 mL)
was added tert-butyldiphenylsilyl chloride (495 mg, 1.80 mmol) at
0 °C under argon and the mixture was stirred at r.t. for 20 h. H2O
(50 mL) was then added, the mixture was extracted with CH2Cl2
(3 × 30 mL), the combined organic layers were dried (Na2SO4), and
the solvents were evaporated to dryness. The residue was chromato-
graphed on a silica gel column using toluene–hexanes (1:1) as elu-
ent to give a white solid; yield: 165 mg (40%); mp 270–272 °C
(toluene–hexanes).
1H NMR (400 MHz, CDCl3): d = 1.37 (s, 18 H), 3.65 (s, 6 H), 6.42
(s, 2 H), 6.56 (s, 2 H), 6.78 (s, 4 H), 7.08–7.14 (m, 4 H), 7.21–7.31
(m, 8 H), 7.35–7.42 (m, 4 H), 7.73 (dd, J = 8.1, 1.3 Hz, 4 H), 7.81
(dd, J = 8.1, 1.3 Hz, 4 H), 8.25 (s, 2 H).
MS (EI): m/z (%) = 568 (44, [M+]), 256 (6), 189 (6), 149 (13), 97
(27), 83 (98), 69 (73), 55 (86), 43(100).
HRMS-EI: m/z calcd for C32H24Br2: 566.0245; found: 566.0234.
Anal. Calcd for C32H24Br2: C, 67.63; H, 4.26. Found: C, 67.31; H,
4.29.
13C NMR (100.6 MHz, CDCl3): d = 20.5 (C), 27.9 (CH3), 41.2
(CH3), 55.7 (CH), 108.4 (CH), 122.4 (CH), 123.8 (CH), 124.5 (CH),
124.6 (CH), 126.3 (C), 127.6 (CH), 127.6 (CH), 127.7 (C), 127.8
Synthesis 2008, No. 22, 3615–3618 © Thieme Stuttgart · New York

3618
J. Rybáček et al.
PAPER
(CH), 129.7 (CH), 129.7 (CH), 130.3 (C), 134.4 (C), 134.6 (C),
134.9 (C), 135.7 (CH), 135.7 (CH), 140.5 (C), 144.6 (C), 148.8 (C).
Anal. Calcd for C32H26O2: C, 86.85; H, 5.92. Found: C, 86.83; H,
6.13.
MS (ESI): m/z (%) = 923 (89, [M + H]+), 845 (100), 752 (46), 585
(41), 288(34).
Acknowledgment
HRMS-ESI: m/z calcd for C62H58O4Si2: 922.3874; found: 922.3885.
This work was carried out as a part of the research project Z4 055
0506. The financial support provided by the Grant Agency of the
Czech Republic to the authors (Grant No. 203/03/0087) is gratefully
acknowledged.
Anal. Calcd for C62H58O4Si2: C, 80.65; H, 6.33. Found: C, 80.41; H,
6.29.
5,14-Dihydro-1,4-dimethoxy-6,13-dimethyl-5,14-(o-ben-
zeno)pentacene (7c)
To a suspension of quinone 6 (300 mg, 0.670 mmol) in anhyd tolu-
ene (30 mL) was added a solution of MeLi (1.60 M in Et2O, 1.50
mL, 2.40 mmol) and the mixture was stirred at r.t. overnight. Anoth-
er portion of MeLi (1.60 M in Et2O, 0.50 mL, 0.80 mmol) was then
added and the stirring was continued for 2 h. The reaction was
quenched by sat. aq NH4Cl (10 mL) and after 20 min of stirring, the
mixture was extracted with toluene (3 × 25 mL). The combined ex-
tracts were dried (Na2SO4) and evaporated to dryness. The residue
consisting of the diol 8 (320 mg) was dissolved in anhyd MeCN (20
mL), NaI (404 mg, 2.69 mmol) was added followed, after 10 min of
stirring at r.t., by trimethylsilyl chloride (0.34 mL, 2.69 mmol). The
mixture was stirred for 1 h and quenched with sat. aq NaHSO3 (5
mL). The resulting mixture was stirred for 10 min, diluted with H2O
(50 mL) and extracted with CH2Cl2 (3 × 20 mL). The combined ex-
tracts were dried (Na2SO4) and evaporated to dryness. The residue
was then redissolved in CH2Cl2 (5 mL) and the crude product was
precipitated by the addition of MeOH (20 mL) and dried in vacuo.
Since the 1H NMR spectrum of the crude product revealed a roughly
equimolar mixture of iodomethyl derivative with its characteristic
signal of the methylene group at d = 5.27 (dd, J = 41.2, 10.0 Hz), a
unifying reduction protocol18 was applied. The product (320 mg)
was suspended in anhyd toluene (20 mL) together with a catalytic
amount of AIBN and then Bu3SnH (0.150 ml, 0.563 mmol) was
added while stirring at r.t. The mixture was heated to 100 °C for 3 h
and after cooling it was evaporated to dryness. The residue was
crystallized from CH2Cl2–hexanes to give yellowish crystals; yield:
190 mg (64%); mp >320 °C (CH2Cl2–hexanes).
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1H NMR (400 MHz, CDCl3): d = 2.93 (s, 6 H), 3.84 (s, 6 H), 6.40
(s, 2 H), 6.55 (s, 2 H), 7.03–7.05 (m, 2 H), 7.39–7.41 (m, 2 H), 7.47–
7.49 (m, 2 H), 7.94–7.97 (m, 2 H), 8.41 (s, 2 H).
13C NMR (100.6 MHz, CDCl3): d = 14.6 (CH3), 43.8 (CH3), 56.5
(CH), 109.0 (CH), 123.0 (CH), 124.0 (CH), 124.7 (C), 124.8 (CH),
125.5 (CH), 128.1 (CH), 130.4 (C), 131.1 (C), 134.5 (C), 138.1 (C),
144.7 (C), 149.0 (C).
(14) Kitamura, T.; Fukatsu, N.; Fujiwara, Y. J. Org. Chem. 1998,
63, 8579.
(15) Zhu, X.-Z.; Chen, C.-F. J. Org. Chem. 2005, 70, 917.
(16) Quast, H.; Fuchsbauer, H.-L. Chem. Ber. 1986, 119, 1016.
(17) Hua, D. H.; Tamura, M.; Huang, X.; Stephany, H. A.;
Helfrich, B. A.; Perchellet, E. M.; Sperfslage, B. J.;
Perchellet, J.-P.; Jiang, S.; Kyle, D. E.; Chiang, P. K. J. Org.
Chem. 2002, 67, 2907.
MS (ESI): m/z (%) = 443 (36, [M + H]+), 316 (49), 288 (100).
HRMS-ESI: m/z calcd for C32H27O2: 443.2011; found: 443.2013.
(18) Raw, A. S.; Jang, E. B. Tetrahedron 2000, 56, 3285.
Synthesis 2008, No. 22, 3615–3618 © Thieme Stuttgart · New York