A Facile Cascade Synthesis of 5,6-Diaryldibenzo[a,e]cyclooctenes from (Z,Z)-1-Aryl-3,5-octadiene-1,7-diynes

Article abstract of DOI:10.1021/jo9802473

Sequential treatment of (Z)-3-methyl-2-penten-4-ynal (10) with the allenylborane 2 and 2-amino- ethanol furnished 11. The use of 11 for cross-coupling with aryl iodides followed by the KH-induced syn elimination of the coupled adducts 13 provided easy access to a variety of dienediynes 14 for subsequent conversions to dibenzo[a,e]cyclooctenes (sym-dibenzocyclooctatetraenes) 17. By cross- coupling with 1,2- and 1,4-diiodobenzene, it was possible to obtain 19 and 25 having two dienediynyl moieties. It was anticipated that the oligomers 21 and 26 containing multiple dibenzo[a,e]cyclooctenyl units could thus be synthesized. The ¹H NMR spectrum of 32 having three dibenzo[a,e]- cyclooctenyl units indicates the presence of three diastereomers 32a-c in a random statistical distribution of 2:1:1. Similarly, the ¹H NMR spectrum of 33 having two dibenzo[a,e]cyclooctenyl units exhibits signals that support the presence of two diastereomers 33a and 33b in a 1:1 ratio.

Full text of DOI:10.1021/jo9802473

J . Org. Chem. 1998, 63, 4413-4419
4413
A F a cile Ca sca d e Syn th esis of 5,6-Dia r yld iben zo[a ,e]cycloocten es
fr om (Z,Z)-1-Ar yl-3,5-octa d ien e-1,7-d iyn es†
Kung K. Wang,* Chongsheng Shi, and J effrey L. Petersen‡
Department of Chemistry, West Virginia University, Morgantown, West Virginia 26506-6045
Received February 10, 1998
Sequential treatment of (Z)-3-methyl-2-penten-4-ynal (10) with the allenylborane 2 and 2-amino-
ethanol furnished 11. The use of 11 for cross-coupling with aryl iodides followed by the KH-induced
syn elimination of the coupled adducts 13 provided easy access to a variety of dienediynes 14 for
subsequent conversions to dibenzo[a,e]cyclooctenes (sym-dibenzocyclooctatetraenes) 17. By cross-
coupling with 1,2- and 1,4-diiodobenzene, it was possible to obtain 19 and 25 having two dienediynyl
moieties. It was anticipated that the oligomers 21 and 26 containing multiple dibenzo[a,e]cy-
1
clooctenyl units could thus be synthesized. The H NMR spectrum of 32 having three dibenzo[a,e]-
cyclooctenyl units indicates the presence of three diastereomers 32a -c in a random statistical
1
distribution of 2:1:1. Similarly, the H NMR spectrum of 33 having two dibenzo[a,e]cyclooctenyl
units exhibits signals that support the presence of two diastereomers 33a and 33b in a 1:1 ratio.
Sch em e 1
In tr od u ction
We recently reported a new synthetic pathway to (Z,Z)-
3,5-octadiene-1,7-diynes 4 (dienediynes) as precursors of
the highly reactive benzocyclobutadienes leading to
dimers with unusual polycyclic structures (Scheme 1).1
Treatment of enynyl aldehydes 1 with γ-(tert-butyldi-
methylsilyl)allenylborane 22 followed by 2-aminoethanol
afforded the condensation adducts 3. Subsequent KH-
induced syn elimination3 of 3 furnished dienediynes 4
with high geometric purity (Z:E g 92:8). When diene-
diyne 4a having a 1-phenyl substituent was treated with
tetrabutylammonium fluoride (TBAF) at room temper-
ature, the desilylated adduct 5 underwent two consecu-
tive electrocyclic reactions to produce the benzocyclobu-
tadiene 7, which then dimerized to form 8 (Scheme 2).
The dimer 8 was thermally unstable at room temperature
and slowly transformed to the dibenzo[a,e]cyclooctene 9.
Fortunately, it was possible to separate a portion of 8
(19%) cleanly by column chromatography for structural
elucidation along with a second portion containing a
mixture of 8 and 9 (40:60) in 36% yield. On heating at
60 °C, 8 was converted to 9 within 3 h in 89% yield.
methyl-2-penten-4-ynal (10)5 for condensation with the
allenylborane 2. The presence of a terminal alkynyl
group in 10 and consequently in the condensation adduct
11 made it possible to promote a Pd(PPh3)4-catalyzed
cross-coupling reaction between 11 and a variety of aryl
iodides,6 enhancing versatility and flexibility of this
synthetic strategy for preparation of (Z,Z)-1-aryl-3,5-
octadiene-1,7-diynes with diverse structures as precur-
sors of 5,6-diaryldibenzo[a,e]cyclooctenes.
The reaction sequence outlined in Schemes 1 and 2
provides a simple and facile route to 5,6-diaryldibenzo-
[a,e]cyclooctenes.4 We now have further extended this
pathway to the synthesis of several other 5,6-diaryldiben-
zo[a,e]cyclooctenes by using the readily available (Z)-3-
Resu lts a n d Discu ssion
† Dedicated to Professor William R. Moore on the occasion of his
70th birthday.
‡ Author to whom correspondence concerning the X-ray structures
should be addressed.
Enynyl aldehyde 10 was synthesized by oxidation of
the commercially available (Z)-3-methyl-2-penten-4-yn-
1-ol.5 Treatment of 10 with the allenylborane 2, prepared
in situ by the procedure reported previously,1,2 followed
by 2-aminoethanol furnished the condensation adduct 11
in 69% yield with high diastereoselectivity (de > 99%)
(1) Wang, K. K.; Liu, B.; Petersen, J . L. J . Am. Chem. Soc. 1996,
118, 6860-6867.
(2) (a) Wang, K. K.; Wang, Z.; Sattsangi, P. D. J . Org. Chem. 1996,
61, 1516-1518. (b) Wang, K. K.; Wang, Z.; Gu, Y. G. Tetrahedron Lett.
1993, 34, 8391-8394.
(3) Hudrlik, P. F.; Peterson, D. J . Am. Chem. Soc. 1975, 97, 1464-
1468.
(4) (a) Stiles, M.; Burckhardt, U.; Haag, A. J . Org. Chem. 1962, 27,
4715-4716. (b) Blomquist, A. T.; Bottomley, C. G. J . Am. Chem. Soc.
1965, 87, 86-93. (c) Straub, H. Liebigs Ann. Chem. 1978, 1675-1701.
(d) Straub, H. Angew. Chem., Int. Ed. Engl. 1974, 13, 405-406. (e)
Filip, P.; Stefan, N.; Chiraleu, F.; Dinulescu, I. G.; Avram, M. Rev.
Roum. Chim. 1984, 29, 549-555.
(5) Derguini, F.; Balogh-Nair, V.; Nakanishi, K. Tetrahedron Lett.
1979, 4899-4902.
(6) Farina, V. In Comprehensive Organometallic Chemistry II;
Hegedus, L. S., Ed.; Elsevier Science: New York, 1995; Vol. 12, pp
222-225.
S0022-3263(98)00247-3 CCC: $15.00 © 1998 American Chemical Society
Published on Web 06/05/1998

4414 J . Org. Chem., Vol. 63, No. 13, 1998
Wang et al.
Ta ble 1. Syn th esis of En yn yl Alcoh ols 13, Dien ed iyn es
14, a n d Diben zo[a ,e]cycloocten es 17
isolated
yield, %
isolated
yield, %
isolated
yield, %
R
13a
14
17
H
13a
13b
13c
13d
13e
78
66
69
42
50
14a
14b
14c
14d
14e
98
98
95
72
84
17a
17b
17c
17d
17e
74
54
47
40
43
4-Me3Si
2-iodo
3-iodo
4-iodo
a
The preferential formation of the Z,Z isomer (>98%) of 14 by
treatment of 13 with KH to induce syn elimination indicates that
the RS/SR pair was produced predominantly.
Sch em e 2
F igu r e 1. ORTEP drawing of the crystal structure of diben-
zo[a,e]cyclooctene 17e.
Sch em e 4
Sch em e 3
The use of 2 equiv of 11 for cross-coupling with 1,2-
diiodobenzene was very efficient in producing 18 in 83%
yield. Because 11 is a racemic mixture, 18 was obtained
most likely as a 1:1 mixture of two diastereomers, but
without any chemical consequences for the formation of
the Z geometry in the next step (Scheme 5). The KH-
induced syn elimination of 18 furnished 19 having two
dienediynyl moieties. Treatment of 19 with TBAF pro-
duced a shining black solid, which exhibited broad 1H
NMR signals (DMSO-d6) around δ 7.3 and 2.1. We
suspect that this black solid with the appearance resem-
bling that of graphite is a mixture of the oligomers
depicted in 21, which could be produced from consecutive
intermolecular dimerizations as outlined in Scheme 5.
A more definitive structural elucidation and character-
ization of 21 awaits further study. The reaction did not
appear to produce the dimer 23, which would allow
structural elucidation by conventional spectroscopic meth-
ods. Presumably because of high reactivity of the ben-
zocyclobutadienyl moiety, 20 or its precursors are more
likely to undergo intermolecular dimerization rather than
to form the second benzocyclobutadienyl unit in 22 for
(Scheme 3). The Pd(PPh3)4-catalyzed cross-coupling be-
tween 11 and aryl iodides 12 gave 13 in 42-78% yield
(Table 1). The adducts 13c-e were obtained from mono-
coupling with 1,2-, 1,3-, and 1,4-diiodobenzene. Conver-
sions of 13 to dienediynes 14 were carried out with
potassium hydride in diethyl ether at 0 °C to induce syn
elimination (Table 1).3 Dienediynes 14 having predomi-
nantly the Z,Z geometry (>98%) were thermally stable
at room temperature.
Treatment of 14 with TBAF triggered a cascade
sequence, starting from the desilylated dienediynes 15
through benzocyclobutadienes 16 and giving rise to
dibenzo[a,e]cyclooctenes 17 (Scheme 4) in 40-74% iso-
lated yields (Table 1). The X-ray crystal structure of 17e7
showed that it has a tublike shape (Figure 1) resembling
the parent dibenzo[a,e]cyclooctene.8
(7) The authors have deposited atomic coordinates for this structure
with the Cambridge Crystallographic Data Centre. The coordinates
can be obtained, on request, from the Director, Cambridge Crystal-
lographic Data Centre, 12 Union Road, Cambridge, CB2 1EZ, U.K.
(8) Irngartinger, H.; Reibel, W. R. K. Acta Crystallogr., Sect. B 1981,
37, 1724-1728.

Cascade Synthesis of Diaryldibenzo[a,e]cyclooctenes
J . Org. Chem., Vol. 63, No. 13, 1998 4415
Sch em e 5
F igu r e 2. ORTEP drawing of the crystal structure of 27.
Sch em e 7
Sch em e 6
the homo-coupling reaction to occur preferentially.9 The
homo-coupling adduct 27 was also obtained by treatment
of 17c with 8 mol % of Pd(PPh3)4 in the absence of 11.
intramolecular cycloaddition to furnish the dimer 23
(Scheme 6).
Similarly, cross-coupling of 1,4-diiodobenzene with 2
equiv of 11 afforded 24 most likely as a 1:1 mixture of
two diastereomers which were readily converted to 25
having two dienediynyl functionalities (Scheme 7). Treat-
ment of 25 with TBAF produced a yellow solid exhibiting
1
two broad H NMR signals (C6D6) around the regions of
δ 6.8 and δ 2.2 with an approximately 2:1 ratio in
integration. Again, it is assumed that a mixture of the
oligomers depicted in 26 was produced.
Interestingly, when diiodide 17c was treated with 2
equiv of 11 for the Pd(PPh3)4-catalyzed cross-coupling
reaction, the homo-coupling adduct 27 was isolated in
94% yield without formation of the expected cross-
coupling product (eq 1). The structure of 27 was estab-
lished by an X-ray structural analysis (Figure 2).7
Apparently, the proximity of the two iodo groups enabled
The cross-coupling reaction between diiodide 17e and
2 equiv of 11 was successful in producing 28 most likely
as a 1:1 mixture of two diastereomers in 64% isolated
yield (Scheme 8). Conversion of 28 to 29 was again
(9) (a) Clark, F. R. S.; Norman, R. O. C.; Thomas, C. B. J . Chem.
Soc., Perkin Trans. 1 1975, 121-125. (b) Semmelhack, M. F.; Ryono,
L. S. J . Am. Chem. Soc. 1975, 97, 3873-3875.

4416 J . Org. Chem., Vol. 63, No. 13, 1998
Wang et al.
Sch em e 8
F igu r e 3. 1H NMR signals of the methyl groups of 32 in
CDCl3 at 22 °C.
Sch em e 9
inversion of 5-phenyl-6-(p-methoxycarbonylphenyl)diben-
zo[a,e]cyclooctene was reported to be relatively slow even
at 156 °C.10 The presence of the methyl groups on the
fused benzene rings in 32 could further increase the
nonbonded steric interactions in the transition states,
reducing the rate of ring inversion.11 Since 32a has no
symmetry, all six methyl groups of 32a are different,
while 32b and 32c each have a plane of symmetry and
consequently each possesses three different types of
methyl groups with each signal having twice the intensity
of a single methyl group. Because 32a has twice the
1
population in the 2:1:1 mixture, the H NMR spectrum
achieved with KH. Treatment of 29 with TBAF appeared
to produce a mixture of the oligomers 26 as well.
Because of difficulties in characterizing the mixtures
of the oligomers of 21 and 26, the polycyclic 32 having
only three dibenzo[a,e]cyclooctenyl units was synthesized
by the sequence outlined in Scheme 9 for structural
elucidation by conventional spectroscopic methods. Treat-
ment of 17e with 1 equiv of 11 for cross-coupling
produced the mono-coupling adduct 30 in 25% yield,
which was then transformed to 31 (57%) having only one
dienediynyl moiety. The cascade sequence triggered by
TBAF then led to 32 in 21% isolated yield.
of the mixture could therefore exhibit a maximum of 12
singlets of equal intensity arising from the methyl groups.
The actual spectrum shown in Figure 3 suggests that two
of the signals overlap at δ 2.34 with 10 other signals
1
clearly discernible. The aromatic region of the H NMR
spectrum has too many overlapping signals to be of use
for structural elucidation.
The 13C NMR spectrum of 32 exhibits sets of signals
with up to four peaks in each set. For example, a set of
four distinct peaks was observed at δ 141.38, 141.32,
141.31, and 141.28 as well as at δ 140.97, 140.79, 140.72,
and 140.69. This pattern of signals is consistent with
the presence of the three diastereomers 32a -c with two
peaks from 32a and one peak each from 32b and 32c for
each set of signals.
The structure assignment of 32 is based on high-
resolution mass spectra and the 1H and 13C NMR spectra.
The molecular ion was detected on a high-resolution mass
1
spectrometer (m/z ) 1248.2604). The H NMR spectrum
The possibility of interconversions among 32a , 32b ,
and 32c by ring inversion of the tublike dibenzo[a,e]cy-
(CDCl3) exhibits 11 singlets between δ 2.36 and 2.12 with
10 of the peaks having approximately the same intensity
and the one at δ 2.34 with twice the intensity (Figure 3).
This observation could be accounted for on the basis of
the presence of the three diastereomers 32a , 32b, and
32c in a random statistical distribution of 2:1:1. Pre-
sumably because the rates of ring inversion of the three
tublike dibenzo[a,e]cyclooctenyl units in 32 are relatively
1
clooctenyl units was studied by recording their H NMR
signals at elevated temperatures using 1,1,2,2-tetrachlo-
roethane-d2 as the solvent. At 22 °C, nine distinct signals
were observed for the methyl groups with the peak at δ
(10) Salisbury, L. E. J . Org. Chem. 1978, 43, 4991-4995.
(11) (a) Mislow, K.; Perlmutter, H. D. J . Am. Chem. Soc. 1962, 84,
3591-3592. (b) Senkler, G. H., J r.; Gust, D.; Riccobono, P. X.; Mislow,
K. J . Am. Chem. Soc. 1972, 94, 8626-8627.
1
slow, distinct H NMR signals due to the three diaster-
eomers 32a -c could thus be observed. The rate of ring

Cascade Synthesis of Diaryldibenzo[a,e]cyclooctenes
J . Org. Chem., Vol. 63, No. 13, 1998 4417
Sch em e 10
two singlets at δ 0.18 and 0.17 from the trimethylsilyl
groups. At 115 °C in 1,1,2,2-tetrachloroethane-d2, the
two trimethylsilyl signals collapsed into a singlet and the
two aromatic signals originally at δ 6.67 and 6.65 at 22
°C also coalesced into a singlet. However, the four methyl
signals remained well separated at 135 °C and exhibited
no significant line broadening. Again, these observations
suggest a relatively slow rate of ring inversion.
Con clu sion s
A new and versatile pathway to (Z,Z)-1-aryl-3,5-
octadiene-1,7-diynes as precursors of 5,6-diaryldiben-
zo[a,e]cyclooctenes has been established. Specifically, 11
serves as a latent dienediyne moiety to allow cross-
coupling with aryl iodides, providing easy access to a
variety of dienediynes for subsequent conversions to 5,6-
diaryldibenzo[a,e]cyclooctenes. By placing two dienedi-
ynyl moieties in the same molecule, it was possible to
produce oligomers having multiple dibenzo[a,e]cyclo-
octenyl units.
F igu r e 4. 1H NMR signals of the methyl groups of 32 in
1,1,2,2-tetrachloroethane-d2.
2.22 having twice the intensity and the peak at δ 2.16
having three times the intensity (Figure 4). At 65 °C,
the two most downfield signals and the next two most
downfield signals collapsed into two singlets. At 115 °C,
they further coalesced into a singlet. In addition, the
second and the third most upfield signals also collapsed
into a singlet. However, the three other signals remained
clearly separated at 135 °C and exhibited no significant
line broadening. These variable-temperature studies
appear to suggest that ring inversion is relatively slow
on the NMR time scale even at 135 °C. The overlapping
of some signals beginning at 65 °C is due to accidental
isochrony arising from dependence of chemical shift on
temperature and cannot be attributed to lower coales-
cence temperatures due to smaller differences of chemical
shifts. The 1H NMR spectrum of the same sample
retaken at 22 °C is identical to the one recorded before
heating, indicating no decomposition of the sample and
no rearrangement to the isomer having the aryl groups
on the opposite sides of the eight-membered ring.10,12
A small amount of 33 (4% yield) having two diben-
zo[a,e]cyclooctenyl units was isolated from treatment of
a mixture of 25 and an excess of 14b with K2CO3 (Scheme
10). The molecular ion of 33 (m/z ) 834.4064) was
detected as the base peak on a high resolution mass
spectrometer. Because there are only two dibenzo[a,e]-
cyclooctenyl units in 33, the two diastereomers 33a and
33b could exist in a random statistical distribution of 1:1.
With the presence of a plane of symmetry in 33a and C2
Exp er im en ta l Section
All reactions were conducted in oven-dried (120 °C) glass-
ware under a nitrogen atmosphere. Tetrahydrofuran (THF)
and diethyl ether (Et2O) were distilled from benzophenone
ketyl prior to use. (Z)-3-Methyl-2-penten-4-yn-1-ol, KH (35 wt
% dispersion in mineral oil), a 1.0 M solution of tetrabutyl-
ammonium fluoride (TBAF) in THF, a 1.0 M solution of
B-methoxy-9-borabicyclo[3.3.1]nonane (B-methoxy-9-BBN) in
hexanes, and Pd(PPh3)4 were purchased from Aldrich Chemical
Co. and were used as received. Diiodobenzenes were obtained
from Oakwood Products, Inc., and were used without further
purification. (Z)-3-Methyl-2-penten-4-ynal (10) was synthe-
sized by oxidation of (Z)-3-methyl-2-penten-4-yn-1-ol as de-
scribed previously.5 Allenylborane 2 was prepared from 3-(tert-
butyldimethylsilyl)-1-(trimethylsilyl)-1-propyne according to
the reported procedure.1,2 1-Iodo-4-(trimethylsilyl)benzene
(97% yield) was prepared by treatment of 1,4-diiodobenzene
in THF at -78 °C with n-butyllithium followed by trimethyl-
silyl chloride. 1H (270 MHz) and 13C (67.9 MHz) NMR spectra
were recorded in CDCl3 using CHCl3 (1H δ 7.25) and CDCl3
(13C δ 77.10) as internal standards.
(()-(3R,4S,5Z)-3-(ter t-Bu tyld im eth ylsilyl)-6-m eth yl-1-
(tr im eth ylsilyl)-5-octen e-1,7-d iyn -4-ol (11). To a solution
of 1.67 g (7.38 mmol) of 3-(tert-butyldimethylsilyl)-1-(trimeth-
ylsilyl)-1-propyne in 20 mL of THF at -10 °C was added 2.95
mL of a 2.5 M solution of n-butyllithium (7.38 mmol) in
hexanes. After 30 min of stirring at -10 °C, 7.38 mL (7.38
mmol) of a 1.0 M solution of B-methoxy-9-BBN in hexanes was
introduced with a syringe. After an additional 45 min at 0
°C, 1.25 mL of BF3‚OEt2 (1.40 g, 9.84 mmol) was added, and
the mixture was stirred at 0 °C for 20 min to allow for the
formation of the allenylborane 2 before 0.694 g of 10 (7.38
mmol) in 10 mL of THF was introduced. The mixture was
allowed to warm to room temperature and stirred for 5 h. THF
and hexanes were evaporated at reduced pressure, and the
1
symmetry in 33b, one can expect to observe four H NMR
signals as singlets of equal intensity arising from the
methyl groups as well as two signals from the trimeth-
1
ylsilyl groups. Indeed, the H NMR spectrum (CDCl3)
exhibits four singlets of essentially equal intensity at δ
2.42, 2.39, 2.16, and 2.12 from the methyl groups and
(12) Stiles, M.; Burckhardt, U. J . Am. Chem. Soc. 1964, 86, 3396-
3397.

4418 J . Org. Chem., Vol. 63, No. 13, 1998
Wang et al.
pressure was then restored with nitrogen. Hexanes (40 mL)
was added followed by 1.0 mL of 2-aminoethanol, and a
precipitate appeared almost immediately. After 20 min of
stirring, the precipitate was removed by filtration, and the
filtrate was washed with water, dried over MgSO4, and
concentrated. The residue was purified by flash column
chromatography (silica gel/5-10% diethyl ether in hexanes)
to afford 1.63 g (5.09 mmol, 69%) of 11 (de > 99%) as a light
126.17, 124.96, 20.76; MS m/z 307 (M+ - C6H5), 293, 206. Anal.
Calcd for C30H24: C, 93.71; H, 6.29. Found: C, 93.55; H, 6.36.
1,10-Dim eth yl-11,12-bis[4-(tr im eth ylsilyl)ph en yl]diben -
zo[a ,e]cycloocten e (17b). To a suspension of 0.370 g of
K2CO3 (2.68 mmol) in 5 mL of ethanol was added a solution of
0.450 g of 14b (1.34 mmol) in 5 mL of Et2O at room
temperature under a nitrogen atmosphere. After 5 min of
stirring, the reaction mixture was heated to 60 °C for 14 h.
Ethanol was then evaporated in vacuo, and a mixture of Et2O
and water was introduced. After filtration, the organic layer
was separated, washed with water, and concentrated. The
residue was purified by column chromatography (silica gel/
5-10% diethyl ether in hexanes) to afford 0.190 g of 17b (0.36
mmol, 54%) as colorless crystals: IR 1248, 839 cm-1; 1H δ 7.21
(4 H, d, J ) 8.3 Hz), 7.03-6.86 (12 H, m), 2.32 (6 H, s), 0.19
(18 H, s); 13C δ 142.91, 140.95, 140.53, 138.34, 137.28, 135.38,
133.56, 132.66, 129.63, 128.92, 126.11, 124.89, 20.76, -1.06;
MS m/z 528 (M+), 513, 455, 440, 249, 206, 73; HRMS calcd for
C36H40Si2 528.2669, found 528.2651.
1
yellow oil: IR (neat) 3538, 3310, 2156, 1249, 841 cm-1; H δ
6.00 (1 H, dm, J ) 8.5 and 1 Hz), 4.65 (1 H, td, J ) 8.5 and
2.9 Hz), 3.12 (1 H, s), 2.13 (1 H, d, J ) 8.9 Hz), 2.10 (1 H, d,
J ) 3.0 Hz), 1.87 (3 H, d, J ) 1.4 Hz), 0.94 (9 H, s), 0.13 (12
H, s), 0.10 (3 H, s); 13C δ 141.55, 117.72, 105.27, 89.79, 82.12,
82.07, 68.82, 27.40, 27.02, 22.88, 17.66, 0.22, -6.41, -6.60;
MS m/z 320 (M+), 305, 263, 205, 190, 73; HRMS calcd for
C18H33OSi2 (MH+) 321.2070, found 321.2077. Anal. Calcd for
C
18H32OSi2: C, 67.43; H, 10.06. Found: C, 67.54; H, 10.04.
(()-(3R,4S,5Z)-3-(ter t-Bu tyld im eth ylsilyl)-6-m eth yl-8-
p h en yl-1-(tr im eth ylsilyl)-5-octen e-1,7-d iyn -4-ol (13a ). The
following procedure for the preparation of 13a is representative
for the cases using 11 for cross-coupling. A suspension of 0.685
g of 11 (2.14 mmol), 0.479 g of iodobenzene (2.35 mmol), 0.033
g of CuI (0.17 mmol), 0.127 g of Pd(PPh3)4 (0.11 mmol), and
1.12 mL of diisopropylethylamine (6.42 mmol) in 8 mL of DMF
was cooled to -78 °C and degassed by three cycles of freeze-
thaw. The resulting mixture was stirred at 42 °C under a
nitrogen atmosphere for 22 h before 30 mL of a saturated
ammonium chloride solution and 100 mL of Et2O were added.
The solid material was removed by filtration, and the aqueous
layer was separated and extracted with Et2O. The combined
organic layers were washed with a saturated NH4Cl solution,
dried over MgSO4, and concentrated. The residue was purified
by column chromatography (silica gel/5-10% diethyl ether in
hexanes) to furnish 0.664 g of 13a (1.68 mmol, 78%) as a pale
Diol 18. The same procedure was repeated as described
for 13a except that 0.704 g of 11 (2.2 mmol) was used to couple
with 0.330 g of 1,2-diiodobenzene (1.0 mmol) to afford 0.593 g
of 18 (0.83 mmol, 83%, most likely a 1:1 mixture of two
diastereomers) as a pale yellow solid: IR 3514, 2156, 1249,
1
840 cm-1; H δ 7.38 (2 H, dd, J ) 5.7 and 3.4 Hz), 7.24 (2 H,
dd, J ) 5.9 and 3.4 Hz), 6.01 (2 H, dm, J ) 8.7 and 1.4 Hz),
4.78 (2 H, tm, J ) 7.9 and 2.2 Hz), 2.23 (2 H, br d, J ) 8.3
Hz), 2.14 (2 H, d, J ) 3.0 Hz), 1.97 (6 H, d, J ) 1.0 Hz), 0.92
(18 H, s), 0.15 (6 H, s), 0.14 (18 H, s), 0.11 (6 H, s); 13C δ 140.24,
131.76, 128.00, 125.49, 118.60, 105.43, 92.91, 91.69, 89.72,
1
69.12, 27.50, 27.04, 23.18, 17.61, 0.25, -6.36, -6.48. The H
NMR spectrum showed the presence of 14% of the homo-
coupling adduct of 11 derived from joining the acetylenic CH
terminus of two molecules of 11.
Dien ed iyn e 19. The same procedure was repeated as
described for 14a except that 0.270 g of 18 (0.38 mmol) and
0.121 g of KH (3.03 mmol) were used to afford 0.115 g (0.256
mmol, 67%) of 19 (geometric purity >98%) as a brown oil: IR
1
yellow oil: IR (neat) 3510, 2155, 1249, 840 cm-1; H δ 7.43-
7.39 (2 H, m), 7.33-7.29 (3 H, m), 5.99 (1 H, dq, J ) 8.7 and
1.4 Hz), 4.78 (1 H, td, J ) 8.3 and 2.8 Hz), 2.20 (1 H, d, J )
8.9 Hz), 2.16 (1 H, d, J ) 3.0 Hz), 1.97 (3 H, d, J ) 1.2 Hz),
0.95 (9 H, s), 0.17 (3 H, s), 0.16 (9 H, s), 0.14 (3 H, s); 13C δ
139.66, 131.50, 128.38, 128.33, 123.17, 118.80, 105.34, 94.18,
89.85, 87.71, 69.10, 27.52, 27.05, 23.18, 17.64, 0.25, -6.37,
-6.47; MS m/z 378 (M+ - H2O), 339, 264, 249, 233, 171.
1
(neat) 2141, 1249, 843 cm-1; H δ 7.47 (2 H, dd, J ) 5.9 and
3.3 Hz), 7.27 (2 H, dd, J ) 5.7 and 3.4 Hz), 6.99 (2 H, t, J )
11.1 Hz), 6.82 (2 H, dm, J ) 11.1 and 1 Hz), 5.46 (2 H, d, J )
10.7 Hz), 2.08 (6 H, s), 0.23 (18 H, s); 13C δ 138.79, 133.57,
132.09, 128.23, 125.40, 123.16, 109.55, 102.44, 102.37, 95.67,
92.59, 23.72, 0.09.
(3Z,5Z)-3-Meth yl-1-p h en yl-8-(tr im eth ylsilyl)-1,7-octa -
d iyn e-3,5-d ien e (14a ). The following procedure for the
preparation of 14a is representative. To a dispersion of 0.514
g (12.8 mmol) of KH in 15 mL of diethyl ether at 0 °C under
a nitrogen atmosphere was added 1.271 g (3.21 mmol) of 13a
in 15 mL of diethyl ether. After 1 h of stirring, the reaction
mixture was filtered through a short Florisil column to remove
excess KH. The filtrate was washed with a saturated aqueous
solution of NH4Cl, dried over MgSO4, and concentrated. The
residue was purified by flash column chromatography (silica
gel/hexanes) to furnish 0.828 g (3.14 mmol, 98%) of 14a
(geometric purity >98%) as a yellow oil: IR (neat) 2141, 1250,
5,14-Dim eth yld iben zo[3,4:7,8]cycloocta [1,2-l]p h en a n -
th r en e (27). A suspension of 0.366 g of 17c (0.58 mmol), 0.422
g of 11 (1.32 mmol), 0.005 g of CuI (0.024 mmol), 0.035 g of
Pd(PPh3)4 (0.03 mmol), and 0.5 mL of diisopropylethylamine
(3.0 mmol) in 7 mL of DMF was cooled to -78 °C and degassed
by three cycles of freeze-thaw. The resulting mixture was
stirred at 42 °C under a nitrogen atmosphere for 46 h before
20 mL of a saturated ammonium chloride solution and 30 mL
of Et2O were introduced. The solid material was removed by
filtration, and the aqueous layer was separated and extracted
with Et2O. The combined organic layers were washed with a
saturated NH4Cl solution, dried over MgSO4, and concen-
trated. The residue was purified by flash column chromatog-
raphy (silica gel/5-10% diethyl ether in hexanes) to furnish
0.212 g (0.55 mmol, 94%) of 27 as colorless crystals: 1H δ 8.77
(2 H, d, J ) 8.3 Hz), 7.61 (2 H, td, J ) 7.6 and 1.4 Hz), 7.43 (2
H, td, J ) 7.6 and 1.2 Hz), 7.20-7.09 (6 H, m), 6.99 (2 H, dd,
J ) 7.2 and 1.5 Hz), 6.68 (2 H, s), 2.00 (6 H, s); 13C δ 138.84,
138.29, 136.64, 135.94, 133.13, 130.49, 130.10, 128.38, 126.89,
126.68 (two signals overlapped), 126.29, 125.03, 122.74, 20.60.
The structure of 27 was unequivocally established by an X-ray
structural analysis.7 Similarly, 27 was obtained by treatment
of 17c with 8 mol % of Pd(PPh3)4, 8 mol % of CuI, and 5 equiv
of diisopropylethylamine in DMF at 52 °C for 66 h without
11.
1
845, 755, 689 cm-1; H δ 7.49-7.45 (2 H, m), 7.35-7.31 (3 H,
m), 6.97 (1 H, t, J ) 11.1 Hz), 6.81 (1 H, d, J ) 11.5 Hz), 5.52
(1 H, d, J ) 10.7 Hz), 2.10 (3 H, s), 0.24 (9 H, s); 13C δ 138.76,
133.01, 131.60, 128.51, 128.43, 123.51, 123.16, 109.18, 102.36,
102.33, 97.01, 88.56, 23.72, 0.08; MS m/z 264 (M+), 249, 247,
205, 73.
1,10-Dim e t h yl-11,12-d ip h e n yld ib e n zo[a ,e]cyclooc-
ten e (17a ). The following procedure for the preparation of
17a is representative. To a solution of 14a (0.828 g, 3.14
mmol) in a mixture of THF (35 mL) and ethanol (5 mL) was
added 9.4 mL of a 1.0 M solution of TBAF (9.4 mmol) in THF
at room temperature under a nitrogen atmosphere. After 5
min of stirring, the reaction mixture was heated under reflux
for 14 h. Diethyl ether was added, and the mixture was
washed with water, dried over MgSO4, and concentrated. The
residue was purified by flash column chromatography (silica
gel/5-10% diethyl ether in hexanes) to give 0.445 g (1.16 mmol,
74%) of 17a as colorless crystals: IR 3053, 3011, 700 cm-1; 1H
δ 7.07-6.88 (18 H, m), 2.35 (6 H, s); 13C δ 142.83, 140.77,
140.61, 137.31, 135.31, 133.61, 130.50, 129.00, 127.69, 126.52,
Alcoh ol 30. The same procedure was repeated as described
for 13a except that 0.240 g of 11 (0.75 mmol) was used to
couple with 0.477 g of 17e (0.75 mmol) to afford 0.152 g of 30
(0.184 mmol, 25%) as a pale yellow solid: IR 3540, 2153, 1250,
842 cm-1; 1H δ 7.38 (2 H, d, J ) 8.3 Hz), 7.12 (2 H, d, J ) 8.3
Hz), 7.04-6.85 (10 H, m), 6.74 (2 H, d, J ) 8.3 Hz), 5.96 (1 H,

Cascade Synthesis of Diaryldibenzo[a,e]cyclooctenes
J . Org. Chem., Vol. 63, No. 13, 1998 4419
dq, J ) 8.6 and 1.5 Hz), 4.72 (1 H, tm, J ) 6.8 and 1 Hz), 2.32
(3 H, s), 2.25 (3 H, s), 2.15 (1 H, br), 2.13 (1 H, d, J ) 3.0 Hz),
1.92 (3 H, d, J ) 1.2 Hz), 0.93 (9 H, s), 0.15 (12 H, s), 0.11 (3
H, s); 13C δ 142.09, 140.74, 140.59, 140.24, 139.88, 139.72,
137.41, 137.34, 137.16, 137.00, 135.30, 134.98, 133.58, 133.56,
132.27, 131.04, 130.35, 129.30, 129.17, 129.11, 126.52, 126.47,
125.07, 121.38, 118.80, 105.36, 94.26, 92.53, 89.84, 88.27,
69.08, 27.53, 27.09, 23.14, 20.71, 20.68, 17.65, 0.26, -6.35,
-6.42.
Diben zo[a ,e]cycloocten e 33. To a suspension of 2.76 g
of K2CO3 (20 mmol) in 50 mL of ethanol were added a solution
of 0.396 g of 25 (0.88 mmol) and 2.496 g of 14b (7.43 mmol) in
20 mL of Et2O via cannula at room temperature under a
nitrogen atmosphere. After 5 min of stirring, the reaction
mixture was heated to 60 °C for 14 h. Ethanol was then
evaporated in vacuo, and a mixture of Et2O and water was
introduced. After filtration, the organic layer was separated,
washed with water, dried over MgSO4, and concentrated. The
residue was purified by column chromatography (silica gel/
5-10% diethyl ether in hexanes) to give 0.554 g of 17b (1.05
mmol, 28%) and, after further purification by HPLC (7%
diethyl ether in hexanes), 0.029 g of 33 (0.035 mmol, 4%) as a
pale yellow solid: 1H δ 7.14 (2 H, m), 7.0-6.9 (18 H, m), 6.87
(4 H, s), 6.74 (2 H, s), 6.72 (2 H, s), 2.40 (3 H, s), 2.37 (3 H, s),
2.14 (3 H, s), 2.10 (3 H, s), 0.18 (9 H, s), 0.17 (9 H, s); MS m/z
834 (M+, base peak), 455, 379, 206; HRMS calcd for C60H58Si2
834.4075, found 834.4064.
Dien ed iyn e 31. The same procedure was repeated as
described for 14a except that 0.063 g of 30 (0.076 mmol) and
0.012 g of KH (0.30 mmol) were used to afford 0.030 g of 31
(0.043 mmol, 57%) as a yellow solid: 1H δ 7.38 (2 H, d, J )
8.5 Hz), 7.17 (2 H, d, J ) 8.5 Hz), 7.03-6.86 (11 H, m), 6.76 (1
H, dm), 6.74 (2 H, d, J ) 8.5 Hz), 5.47 (1 H, d, J ) 10.5 Hz),
2.31 (3 H, s), 2.25 (3 H, s), 2.04 (3 H, s), 0.21 (9 H, s); 13C δ
142.09, 140.75, 140.33, 139.95, 138.75, 137.51, 137.41, 137.31,
137.16, 137.03, 135.25, 135.00, 133.56, 133.03, 132.26, 131.14,
130.39, 129.44, 129.28, 129.16, 126.53, 125.08, 123.46, 121.31,
109.15, 102.35, 97.08, 92.59, 89.15, 23.68, 20.68, 0.07.
Diben zo[a ,e]cyclooct en e 32. The same procedure was
repeated as described for 17a except that 0.123 g of 31 (0.177
mmol) and 1.7 mL of a 1.0 M solution of TBAF (1.7 mmol) in
THF were used, and the product was purified further by HPLC
(5% diethyl ether in hexanes) to afford 0.023 g of 32 (0.0184
mmol, 21%) as a yellow solid: 1H δ 7.31 (2 H, d, J ) 8.5 Hz),
7.26 (2 H, dd, J ) 8.7 and 1.8 Hz), 7.01-6.82 (24 H, m), 6.74-
6.64 (12 H, m), 2.36 (1.5 H, s), 2.35 (1.5 H, s), 2.34 (3 H, s),
2.28 (1.5 H, s), 2.24 (1.5 H, s), 2.23 (1.5 H, s), 2.20 (1.5 H, s),
2.17 (1.5 H, s), 2.16 (1.5 H, s), 2.15 (1.5 H, s), 2.12 (1.5 H, s);
13C δ 142.55, 142.53, 142.51, 142.47, 142.34, 142.29, 142.25,
142.23, 142.19, 141.38, 141.33, 141.31, 141.28, 140.97, 140.79,
140.72, 140.69, 139.99, 139.93, 139.89, 139.88, 139.68, 139.61,
139.54, 139.10, 139.03, 139.02, 139.00, 138.94, 138.92, 138.82,
137.41, 137.40, 137.38, 137.33, 137.31, 137.28, 137.13, 137.07,
137.02, 136.77, 136.74, 136.71, 135.52, 135.49, 135.42, 135.34,
135.30, 135.16, 134.98, 134.89, 134.84, 133.56, 133.50, 133.44,
132.37, 132.34, 132.31, 130.16, 129.55, 129.52, 129.12, 128.99,
126.46, 126.39, 126.34, 126.30, 126.20, 125.06, 125.02, 124.91,
124.87, 92.30, 92.27, 20.82, 20.79, 20.77, 20.66, 20.62; HRMS
calcd for C78H58I2 1248.2620, found 1248.2604.
Ack n ow led gm en t. The financial support of the
National Science Foundation (CHE-9618676) to K.K.W.
is gratefully acknowledged. J .L.P. acknowledges the
support (CHE-9120098) provided by the Chemical In-
strumentation Program of the National Science Foun-
dation for the acquisition of a Siemens P4 X-ray
diffractometer in the Department of Chemistry at West
Virginia University.
Su p p or tin g In for m a tion Ava ila ble: Experimental pro-
cedures and spectroscopic data for 13b-e, 14b-e, 17c-e, 24,
25, 28, and 29 and 1H and 13C NMR spectra of 11, 13a -e,
14a -e, 17a -e, 18, 19, 24, 25, and 27-33 (59 pages). This
material is contained in libraries on microfiche, immediately
follows this article in the microfilm version of the journal, and
can be ordered from the ACS; see any current masthead page
for ordering information.
J O9802473