Generation of synthetic equivalents of benzdiynes from benzobisoxadisiloles

Article abstract of DOI:10.1021/jo049091z

Linear and angular benzobisoxadisiloles 14 and 16 can serve as the precursors for stepwise generations of the syntetic equivalents of 1,4- and 1,3-benzdiynes. Benzynes generated were trapped as [4+2] cycloaddition products. Two identical or different ring

Full text of DOI:10.1021/jo049091z

Gen er a tion of Syn th etic Equ iva len ts of Ben zd iyn es fr om
Ben zobisoxa d isiloles
Ya-Li Chen, J iang-Qin Sun, Xin Wei, Wai-Yeung Wong, and Albert W. M. Lee*
Department of Chemistry, Centre for Advanced Luminescence Materials and Central Laboratory of the
Institute of Molecular Technology for Drug Discovery and Synthesis, Hong Kong Baptist University,
Kowlooon Tong, Hong Kong, China
alee@hkbu.edu.hk
Received May 31, 2004
Linear and angular benzobisoxadisiloles 14 and 16 can serve as the precursors for stepwise
generations of the syntetic equivalents of 1,4- and 1,3-benzdiynes. Benzynes generated were trapped
as [4+2] cycloaddition products. Two identical or different rings can be fused to the benzdiyne
equivalents. Highly substituted arenes were obtained by removing the oxygen bridges from the
furan adducts. The synthesis of naphthoxadisilole 28, which can serve as the precursor of 2,3-
naphthyne, is also described.
SCHEME 1
In tr od u ction
Benzyne 1 is one of the most important reactive
intermediates and synthons in organic chemistry. Since
its discovery,1 benzyne has been subjected to theoretical
studies as well as many practical applications.2 For
example, it has been widely used as the building block
of many aromatic based molecular architectures. Benzyne
is also a versatile intermediate in natural product
synthesis.3
There are many known methods for benzyne genera-
tion.4 Basically, these methods can be divided into two
main categories. The first set of methods involves â-e-
limination of â-carbanion 2 or its equivalent generated
from various precursors (3) (Scheme 1). The second set
of approaches relies on retro-cycloaddition processes of
benzo-fused heterocycles such as 4 and 5. A recent
addition to the first category reported by Kitamura
involves the use of (phenyl)[o-(trimethylsilyl)phenyl]-
iodonium triflate (7).4a,5 The iodonium compound 7 is
synthesized through phenyliodination of bis(trimethyl-
silyl)benzene 6, which is prepared from 1,2-dichloroben-
zene via Grignard type reaction in HMPA (Scheme 2).
Upon treatment with fluoride ion, benzyne can be gener-
ated in good yield under very mild conditions. Since its
publication, this highly attractive and efficient hyperva-
lent iodine approach to benzyne generation has caught
the attention of many research groups. Various applica-
tions, particularly in the syntheses of theoretically in-
teresting molecules and functional materials, were re-
ported.6 To avoid the uses of carcinogenic HMPA, the
same research team also introduced (phenyl)[2-(hydroxy-
dimethylsilyl)phenyliodonium triflate (9) as an alternate
benzyne procursor.7 Iodonium triflate 9 is prepared from
1,3-dihydro-1,1,3,3-tetramethyl-2,1,3-benzoxadisilole (8)
which can be synthesized from 1,2-bromobenzene without
the use of HMPA (Scheme 2).
(1) (a) Wittig, G. Naturwissenschaften 1942, 30, 696. (b) Wittig, G.;
Harborth, G. Ber. Dtsch. Chem. Ges. 1944, 77, 306, 316. (c) Roberts, J .
D.; Simmons, H. E.; Carlsmith, L. A.; Vaughan, C. W. J . Am. Chem.
Soc. 1953, 75, 3290. (d) Panar, M.; Roberts. J . D. J . Am. Chem. Soc,
1960, 82, 3629. (e) Huisgen R.; Rist, H. Naturwissenschaften 1954,
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(2) (a) Hoffmann, R. W. Dehydrobenzene and Cycloalkynes; Academic
Press: New York, 1967. (b) Hart, H. In The Chemistry of Triple-Bonded
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in Organic Synthesis; Scolastico, C., Nicotra, F., Eds.; Plenum Publish-
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(4) Recent examples for the preparation and chemistry of benzynes.
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Meng, Z.; Fujiwara, Y. J . Am. Chem. Soc. 1999, 121, 11674-11679.
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Lett. 1991, 32, 6735-6736. (c) Kawabata, H.; Nishino, T.; Nishiyama,
Y.; Sonoda, N. Tetrahedron Lett. 2002, 43, 4911-4913. (d) Uchiyama,
M.; Miyoshi, T.; Kajihara, Y.; Sakamoto, T.; Otani, Y.; Ohwada, T.;
Kondo, Y. J . Am. Chem. Soc. 2002, 124, 8514-8515. (e) Duong, H. M.;
Bendikov, M.; Steiger, D.; Zhang, Q.; Sonmez, G.; Yamada, J .; Wudl,
F. Org. Lett. 2003, 5, 4433-4436.
(5) (a) Kitamura, T.; Yamane, M. J . Chem. Soc., Chem. Commun.
1995, 983-984. (b) Kitamura, T.; Todaka, M.; Fujiwara, Y. In Organic
Syntheses; Roush, W. R., Ed.; Wiley: New York, 2000; Vol. 78, pp 104-
112.
10.1021/jo049091z CCC: $27.50 © 2004 American Chemical Society
Published on Web 09/14/2004
7190
J . Org. Chem. 2004, 69, 7190-7197

Generation of Benzdiynes from Benzobisoxadisiloles
SCHEME 2a
a
Reagents and conditions: (i) X ) Cl, Mg/HMPA, Me3SiCl; (ii) X ) Br, Mg/THF, Me2HSiCl; (iii) PhI(OAc)2, TfOH, CH2Cl2, 0 °C to
room temperature; (iv) (a) NaOMe/MeOH, rt, (b) H2O, 50 °C;(v) n-Bu4NF/THF.
SCHEME 3a
a
Reagents and conditions: (i) Mg/Me2HSiCl, THF, reflux; (ii) (a) NaOMe/MeOH, rt, (b) H2O, 50 °C.
1,3- and 1,4-benzdiynes (tetradehydrobenzenes, 10 and
11) are extraordinary labile owing to the high ring strain
that arises from the two triple bonds in a benzene ring.
They have been subjected to theoretical calculations8 and
have been detected in gas phase or by means of matrix
isolation techniques.9 However, they have not been
established as intermediates in solution chemistry. Syn-
thetic equivalents leading to the stepwise generation of
these benzdiynes as well as the metal complexes of 11
have been reported in the literature.2b,10 Herein, we
describe our results of the generation of benzynes from
linear and angular benzobisoxadisiloles (14 and 16) via
the corresponding iodonium triflate intermediates, which
can be viewed as the synthetic equivalents of benzdiynes
10 and 11.
(13 and 15) cyclized into the corresponding linear and
angular benzobisoxadisiloles 14 and 16 as crystalline
solids in 87% and 84% yields, respectively. The structure
of 1414 is also confirmed by X-ray analyses.
St ep w ise Gen er a t ion of Ben zyn e fr om Lin ea r
Ben zobisoxa d isilole 14 a n d th e Tr a p p in g Exp er i-
m en ts. With the linear benzobisoxadisilole 14 in hand,
we were ready to explore its benzyne generation chem-
istry. In situ phenyliodination of 14 with a 1.5:3 mixture
of phenyliodium diacetate (PhI(OAc)2) and trifluoro-
methanesulfonic acid (TfOH) took place readily at room
temperature in CH2Cl2 (Scheme 4). Without isolation of
the ring-opened iodination intermediate 17, benzyne 18
could be generated in situ upon treatment with a 1.0 M
(6) (a) Ye, S. S.; Li, W. K.; Wong, H. N. C. J . Am. Chem. Soc. 1996,
118, 2511-2512. (b) Ye, S. S.; Wong, H. N. C. J . Org. Chem. 1997, 62,
1940-1954. (c) Kitamura, T.; Todaka, M.; Shin-machi, I.; Fujowara,
Y. Heterocycl. Commun. 1998, 4, 205-208. (d) Okuma, K.; Shiki, K.;
Shioji, K. Chem. Lett. 1998, 79-80. (e) Winling, A.; Russell, R. A. J .
Chem. Soc., Perkin Trans. 1 1998, 3921-3923. (f) Kitamura, T.;
Fukatsu, N.; Fijiwara, Y. J . Org. Chem. 1998, 63, 7579-8581. (g) Liu,
J . H.; Chan, H. W.; Xue, F.; Wang, G. G.; Mak, T. C. W.; Wong, H. N.
C. J . Org. Chem. 1999, 64, 1630-1634. (h) Yick, C. Y.; Chan, S. H.;
Woy, H. N. Tetrahedron Lett. 2000, 4, 5957-5961.
Resu lts a n d Discu ssion
P r ep a r a tion of Lin ea r a n d An gu la r Ben zobisox-
a d isiloles, 1,3,5,7-Tetr a d ih yd r o-1,1,3,3,5,5,7,7-octa -
m eth ylben zo[1,2-c:4,5-c′]bis[1,2,5]oxadisilole (14) an d
1,3,6,8-Tetr adih ydr o-1,1,3,3,6,6,8,8-octam eth yl-ben zo-
[1,2-c:3,4-c′]bis[1,2,5]oxa d isilole (16). The preparation
of linear and angular benzobisoxadisiloles 14 and 16
based on modified literature procedures is outlined in
Scheme 3.11,12 The tetrasilylated compounds 13 and 15
can be readily prepared from the tetrabromobenzenes
12a and 12b, respectively, via Grignard-type reactions
with chlorodimethylsilane. 1,2,4,5-Tetrabromobenzene
(12a ) is commercially available. The isomeric 1,2,3,4-
tetrabromobenzene (12b) was prepared by regioselective
debromination of hexabromobenzene with excess hydra-
zine hydrate.13 Upon treatment with sodium methoxide
and warming in water, the tetra(dimethylsilyl)benzenes
(7) Kitamura, T.; Meng, Z.; Fujiwara, T. Tetrahedron Lett. 2000, 41,
6611-6614.
(8) (a) Sattelmeyer, K. W.; Stanton, J . F. J . Am. Chem. Soc. 2000,
122, 8220-8227. (b) Bettinger, H. F.; Schleyer, P. R.; Schaefer, H. F.
J . Am. Chem. Soc. 1999, 121, 2829-2835. (c) Zahradnik, R.; Hoba, P.;
Burcl, R.; Andes, H. B. J .; Radziszewski, J . G. THEOCHEM 1994, 3,
335-349. (d) Radom, L.; Nobes, R. H.; Underwood, D. J . Pure Appl.
Chem. 1986, 1, 75-88.
(9) (a) Sato, T.; Nino, H.; Yabe, A. J . Am. Chem. Soc. 2003, 125,
11936-11941. (b) Sato, T.; Arulmozhiraja, S.; Nino, H.; Sasaki, S.;
Yabe, A. J . Am. Chem. Soc. 2002, 124, 4512-4521.
(10) (a) Hart, H.; Lai, C.; NwoRogu, G. C.; Shamonilian, S. Tetra-
hedron 1987, 43 5203-5224. (b) Stephen, L.; Lucas, E. A.; Dewan, J .
C. J . Am. Chem. Soc. 1987, 109, 4396-4397. (c) Hsu, D. P.; Lucas, E.
A.; Buchwald, L. Tetrahedron Lett. 1990, 31, 5563-5566.
(11) Fink, W. Helv. Chim. Acta 1974, 57, 1010-1015.
(12) A preliminary communication: Chen, Y. L.; Zhang, H.; Wong,
W. Y.; Lee, A. W. M. Tetrahedron Lett. 2002, 43, 2259-2262.
(13) Collins, I.; Suschitzk, H. J . Chem. Soc. (C) 1969, 2337-2341.
(14) Daly, J . J .; Sanz, F. J . Chem. Soc., Dalton. Trans. 1973, 2474-
2475.
J . Org. Chem, Vol. 69, No. 21, 2004 7191

Chen et al.
SCHEME 4a
a
Reagents and conditions: (i) PhI(OAc)2, TfOH, CH2Cl2, 0 °C to room temperature; (ii) n-Bu4NF/THF, i-Pr2NH, rt; (iii) H2, Pd/C, rt.
SCHEME 5a
a
Reagents and conditions: (i) PhI(OAc)2, TfOH, CH2Cl2, 0 °C to room temperature; (ii) n-Bu4NF/THF, i-Pr2NH, rt.
THF solution of tetrabutylammonium fluoride (n-Bu4NF).
It is worth mentioning that despite the use of excess
phenyliodination reagents (PhI(OAc)2/TfOH), only one of
the oxadisilole rings of 14 could be opened. There was
no sign for the formation of the bis-hypervalent iodine
intermediate from 14. Trapping experiments were carried
out with various carbocyclic and heterocyclic dienes
(furan, cyclopentadiene, 1,3-cyclohexadiene, N-tert-butoxy-
carbonylpyrrole, and N-benzoylpyrrole) as well as aryl
azide with good isolated yields of the cycloadducts from
14. The cycloadducts could be easily hydrogenated to
20a -e in 85% to 95% yields. We also observed that addi-
tion of 2 equiv of diisopropylamine to the reaction mixture
improved the overall transformation yields. In the furan
trapping experiment, a trace amount of dimer 22 was
detected. Therefore, we ran a control experiment without
the trapping agents. In the absence of the trapping
agents, dimer 22 was isolated in 80% yield. In addition
to the spectroscopic evidence, structures of selected
compounds (19a , 19d , 20b, 20c, and 22) were also con-
firmed by X-ray analyses.
perature (Scheme 5). Without isolation of the intermedi-
ate, the homogeneous reaction mixture was treated with
n-Bu4NF to generate benzyne 24. In the presence of
excess trapping diene (furan or cyclopentadiene), cycload-
ducts 25a /26a and 25b/26b were obtained as mixtures
of syn and anti isomers in 65% and 58% yields (three
1
steps from 20b), respectively. From the H NMR spec-
trum, the ratio of 25a and 26a was estimated to be 1:1.
The syn isomer of the furan cycloadduct 25a could be
purified by recrystallization. Its structure is confirmed
by X-ray analyses. Benzyne 24 could also be trapped with
p-methoxylphenyl azide as adduct 27 in 59% yield. The
overall transformation of 14 to 25/26 and 27 demon-
strated that the linear benzobisoxadisilole 14 can be
viewed as a synthetic equivalent for the stepwise genera-
tion of 1,4-benzdiyne (11). Two different rings can be
selectively fused to the benzene ring in a stepwise
manner.
F u r th er Ma n ip u la tion of 19a a n d Syn th esis of a
2,3-Na p h th yn e P r ecu r sor . A previously unknown 2,3-
naphthoxadisilole 28 can be prepared by deoxygenation
Hydrogenated product 20b was further treated with
excess PhI(OAc)2/TfOH (1.5:3) in CH2Cl2 at room tem-
7192 J . Org. Chem., Vol. 69, No. 21, 2004

Generation of Benzdiynes from Benzobisoxadisiloles
SCHEME 6a
a
Reagents and conditions: (i) TiCl4, LiAlH4, Et3N-THF, reflux; (ii) PhI(OAc)2, TfOH, CH2Cl2, 0 °C to room temperature; (iii) n-Bu4NF/
THF, i-Pr2NH, rt; (iv) furan.
SCHEME 7a
a
Reagents and conditions: (i) (a) PhI(OAc)2, TfOH, CH2Cl2, 0 °C to room temperature, (b) n-Bu4NF/THF, i-Pr2NH, rt; (iii) furan.
of 19a with TiCl4-LiAlH4-Et3N in THF15 in almost
quantitative yield. Obviously, naphthoxadisilole 28 can
be used as a 2,3-naphthyne (30) precursor. Compound
28 reacted readily under the phenyliodination conditions
and opened up to 29 at room temperature. Without
isolation of 29, treatment of 29 with n-Bu4NF in the
presence of excess furan afforded the cycloadduct 31 in
22% yield.
The hydrogenated compound 20a (obtained from 19a
in 90% yield) was also subjected to the phenyliodination
followed by fluoride-induced benzyne generation and
furan trapping. A complicated mixture resulted with only
a trace amount (7%) of 31. It is possible that under these
conditions 20a was first transformed to 28, which then
served as the naphthyne precursor leading to 31. To
support this speculation, phenyliodination of 20a was
worked up after 1 h, and a good yield (71%) of naph-
thoxadisilole 28 was obtained.
Step w ise Gen er a tion of Ben zyn e fr om An gu la r
Ben zobisoxa d isilole 16 a n d th e Tr a p p in g Exp er i-
m en ts. The ring-opening phenyliodination of the angular
benzobisoxadisilole 16 was found to be slower than its
linear counterpart 14. Without isolation of the intermedi-
ate, the homogeneous reaction mixture was treated with
n-Bu4NF and i-Pr2NH to afford benzyne 32, which was
trapped with furan, cyclopentadiene, and N-t-BOC-pyr-
role (Scheme 7) to afford the racemic cycloadducts (33a -
c). The yields of the racemic cycloadducts were relatively
lower as compared with similar reactions of the linear
series. In addition to 33, a trace amount of a less polar
byproduct was also detected from the reaction mixtures
of the trapping experiments. However, no dimeric product
similar to 22 was detected. This less polar byproduct 34b
was isolated by column chromatography. Compound 34b
whose structure is confirmed by X-ray analysis contains
a macrocyclic siloxy ring. Cycloadducts 33b and 33c were
saturated via hydrogenation reactions. To further dem-
onstrate that 16 can serve as a 1,3-benzdiyne equivalent,
the saturated cyclopentadiene adduct 35b was subjected
to another cycle of phenyliodination (PhI(OAc)2/TfOH,
1.5:3) and n-Bu4NF treatment followed by furan trapping.
Benzyne 36 generated was successfully trapped with
furan as an inseparable mixture of syn and anti adducts
(37b/38b). It is worth nothing that without any plane of
symmetry, benzyne 36 can exist in two chiral forms. Of
course, under the present reaction conditions, the angular
bis-annulated benzo-fused cycloadducts obtained are in
racemic forms.
In summary, we have demonstrated that benzynes 18,
24, 32, and 36 could be generated from the linear benzo-
[1,2-c:4,5-c′]bis[1,2,5]oxadisilole (14) and angular benzo-
[1,2-c:3,4-c′]bis[1,2,5]oxadisilole (16), respectively. They
were trapped as the [4+2] cycloadducts. In the case of
18, cyclodimerization was also observed. These linear and
angular benzobisoxadisiloles (14 and 16) can also be
viewed as the synthetic equivalents for the stepwise
generations of 1,3- and 1,4-benzdiynes. The synthesis of
naphthoxadisilole 28, which can serve as the precursor
of 2,3-naphthyne 30, is also reported.
Exp er im en ta l Section
1,2,3,4-Tetr a br om oben zen e (12b). Hexabromobenzene
(5.00 g, 9.07 mmol), hydrazine hydrate (100 mL), and ethanol
(100 mL) were heated under reflux for 24 h. The cooled
reaction mixture was poured into water. Filtered crude product
was dissolved in n-hexane. The n-hexane solution was washed
with water, then dried over anhydrous MgSO4 and concen-
trated under reduced pressure. The residue was purified by
column chromatography on silica gel with n-hexane as eluent.
Compound 12b (2.00 g, 5.08 mmol) was obtained in 56% yield
(15) (a) Mueller, P.; Schaller, J . P. Chimia 1986, 40, 430-431. (b)
Wang, X. M.; Hou, X. L.; Zhou, Z. Y.; Mak, T. C. W.; Wong, H. N. C. J .
Org. Chem. 1993, 58, 7498-7506.
J . Org. Chem, Vol. 69, No. 21, 2004 7193

Chen et al.
as white powder. Mp 62-63 °C (lit.13 mp 62-63 °C); 1H NMR
(400 MHz) δ 7.45 (s, 2H); 13C NMR (101 MHz) δ 124.8, 129.1,
132.7.
and for 2 h at room temperature. The clear yellow solution
was cooled again to 0 °C followed by dropwise addition of a
cold (0 °C) solution of the benzobisoxadisilole 14 (338 mg, 1.0
mmol in 5 mL of CH2Cl2). The mixture was stirred for 0.5 h
at 0 °C and warmed to room temperature. After the benzo-
bisoxadisilole 14 disappeared (monitored by TLC), diisopro-
pylamine (0.35 mL, 2.5 mmol) and the diene (furan, cyclopen-
tadiene, 1,3-cyclohexadiene, N-tert-butoxycarbonylpyrrole, or
N-benzoylpyrrole, 10 mmol) were added followed by a solution
of tetrabutylammonium fluoride (2.5 mL, 2.5 mmol, 1.0 M
solution in THF). After a further 10 min, water was added
and the resulting mixture was extracted with CH2Cl2. The
organic extracts were dried over anhydrous MgSO4, filtered,
and concentrated under reduced pressure. The crude product
was purified by column chromatography on silica gel with a
gradient of 2-5% EtOAc in petroleum ether (60-80 °C) as
eluent.
1,2,4,5-Tetr a k is(d im eth ylsilyl)ben zen e (13). 1,2,4,5-Tet-
rabromobenzene (3.93 g, 10.00 mol) and chlorodimethylsilane
(8.90 mL, 0.08 mol) were added to magnesium (1.94 g, 0.08
mol) in 20 mL of THF. The mixture was refluxed at 85-90 °C
for 5 h. After the tetrabromobenzene disappeared (monitored
by TLC), the solvent was evaporated. The mixture was
extracted with Soxhlet extractor by n-hexane at 95-100 °C.
The extract was concentrated under reduced pressure, then
purified by column chromatography on silica gel with n-hexane
as eluent. Compound 13 (2.18 g, 7.01 mmol) was obtained in
70% yield as white powder. Mp 64 °C (lit.11 mp 66 °C); 1H NMR
(400 MHz) δ 0.37 (d, J ) 3.6 Hz, 24H), 4.63-4.67 (m, 4H),
7.75 (s, 2H); 13C NMR (101 MHz) δ -2.7, 139.5, 144.0; IR (KBr,
cm-1) 2958, 2146, 2105, 1251, 1093; MS m/z 311 (M+).
1,3,5,8-Tetr ah ydr o-1,1,3,3-tetr am eth yl-5,8-epoxyn aph th -
[2,3-c][1,2,5]oxa d isilole (19a ): 79% yield (216 mg, 0.79
mmol), mp 121-123 °C; 1H NMR (400 MHz) δ 0.32 (s, 6H),
0.33 (s, 6H), 5.70 (s, 2H), 7.03 (s, 2H), 7.42 (s, 2H); 13C NMR
(101 MHz) δ 1.0, 1.1, 82.2, 122.2, 142.7, 145.9, 150.1; IR (KBr,
cm-1) 3038, 2957, 1277, 1252, 1098; MS m/z 274 (M+); HRMS
for C14H18O2Si2:[M]+ calcd 274.0835, found 274.0845. Anal.
Calcd for C14H18O2Si2: C, 61.25; H, 6.62. Found: C, 61.17; H,
6.75. Recrystallization from CH2Cl2/n-hexane mixture afforded
the crystal sample for X-ray structure determination.
1,3,5,8-Tet r a h yd r o-1,1,3,3-t et r a m et h yl-5,8-m et h a n o-
n a p h th [2,3-c][1,2,5]oxa d isilole (19b): 83% yield (226 mg,
0.83 mmol), mp 64-65 °C; 1H NMR (400 MHz) δ 0.31 (s, 6H),
0.33 (s, 6H), 2.25-2.27 (m, 1H), 2.33-2.35 (m, 1H), 3.88-3.89
(m, 2H), 6.80 (t, J ) 2.0 Hz, 2H), 7.40 (s, 2H); 13C NMR (101
MHz) δ 1.1, 1.2, 50.2, 69.7, 123.7, 142.9, 144.6, 153.2; IR (KBr,
cm-1) 3065, 2962, 1565, 1250, 1100; MS m/z 272 (M+); HRMS
for C15H20OSi2 [M + H]+ calcd 273.113, found 273.1144. Anal.
Calcd for C15H20OSi2: C, 66.10; H, 7.41. Found: C, 65.94; H,
7.31.
1,3,5,7-Tet r a d ih yd r o-1,1,3,3,5,5,7,7-oct a m et h ylb en zo-
[1,2-c:4,5-c′]bis[1,2,5]oxa d isilole (14). A solution of sodium
methoxide in methanol (1.84 g of sodium, 0.08 mol; 30 mL of
methanol) was added to 1,2,4,5-tetrakis(dimethylsilyl)benzene
13 (3.11 g, 10.00 mol). The mixture was stirred under N2 for
1 h at room temperature. The reaction mixture was added to
1 mL of H2O and the sooution was warmed to 45-50 °C. After
13 disappeared (monitored by TLC), the crude product was
filtered and redissolved in EtOAc. After being washed with
H2O and dried over MgSO4, the EtOAc solution was concen-
trated under reduced pressure. Recrystallization from CH2-
Cl2/n-hexane mixture afforded 14 (2.94 g, 8.70 mmol) in 87%
1
yield. Mp 243-245 °C (lit.11 mp 244 °C); H NMR (400 MHz)
δ 0.38 (s, 12H), 7.80 (s, 2H); 13C NMR (101 MHz) δ 1.1, 133.5,
148.5; IR (KBr, cm-1) 2959, 1248, 1105; MS m/z 338 (M+);
HRMS for C14H26O2Si4 [M + Na]+ calcd 361.0907, found
361.0896. Recrystallization from CH2Cl2/n-hexane mixture
afforded the crystal sample for X-ray structure determination.
1,2,3,4-Tetr a k is(d im eth ylsilyl)ben zen e (15). 1,2,3,4-Tet-
rabromobenzene (3.93 g, 10.0 mol) and chlorodimethylsilane
(8.90 mL, 0.08 mol) were added to magnesium (1.94 g, 0.08
mol) in 20 mL of THF. The mixture was refluxed at 85-90 °C
for 5 h. After tetrabromobenzene disappeared (monitored by
TLC), the solvent was evaporated. The mixture was extracted
with Soxhlet extractor by n-hexane at 95-100 °C. The extract
was concentrated under reduced pressure and then purified
by column chromatography on silica gel with n-hexane as
eluent. Compound 15 (1.96 g, 6.30 mmol) was obtained in 63%
1,3,5,8-Te t r a h yd r o-1,1,3,3-t e t r a m e t h yl-5,8-e t h a n o-
n a p h th [2,3-c][1,2,5]oxa d isilole (19c): 51% yield (146 mg,
0.51 mmol), mp 122-124 °C; 1H NMR (400 MHz) δ 0.31 (s,
6H), 0.36 (s, 6H), 1.48-1.50 (m, 2H), 1.57-1.60 (m, 2H), 3.96-
3.97 (m, 2H), 6.51-6.53 (m, 2H), 7.36 (s, 2H); 13C NMR (101
MHz) δ 1.1, 1.2, 25.6, 40.5, 125.0, 135.1, 144.6, 145.5; IR (KBr,
cm-1) 2962, 1653, 1249, 1112; MS m/z 286 (M+); HRMS for
C
16H22OSi2 [M + H]+ calcd 287.1287, found 287.1292.
1
yield as a colorless oil. H NMR (400 MHz) δ 0.37 (d, J ) 4.0
N-ter t-Bu t oxyca r b on yl-1,3,5,8-t et r a h yd r o-1,1,3,3-t et -
Hz, 12H), 0.48 (d, J ) 4.0 Hz, 12H), 4.68-4.72 (m, 2H), 4.80-
4.84 (m, 2H), 7.58 (s, 2H); 13C NMR (101 MHz) δ -1.9, -0.6,
134.2, 146.3, 152.1.
r a m eth yl-5,8-im in en a p h th [2,3-c][1,2,5]oxa d isilole (19d ):
70% yield (261 mg, 0.70 mmol), mp 156-157 °C; 1H NMR (400
MHz) δ 0.30 (s, 6H), 0.32 (s, 6H), 1.38 (s, 9H), 5.47-5.53 (m,
2H), 6.95-7.02 (m, 2H), 7.42 (s, 2H); 13C NMR (101 MHz) δ
0.96, 1.04, 28.1, 66.7, 80.7, 122.4, 123.0, 142.1, 143.5, 145.7,
149.2, 155.0; IR (KBr, cm-1) 3000, 2978, 1713, 1367, 1254,
1163, 1102; HRMS for C19H27NO3Si2 [M + Na]+ calcd 396.1427,
found 396.1445. Anal. Calcd for C19H27NO3Si2: C, 61.08; H,
7.28. Found: C, 61.14; H, 7.23. Recrystallization from CH2-
Cl2/n-hexane mixture afforded the crystal sample for X-ray
structure determination.
1,3,6,8-Tet r a d ih yd r o-1,1,3,3,6,6,8,8-oct a m et h ylb en zo-
[1,2-c:3,4-c′]bis[1,2,5]oxa d isilole (16). A solution of sodium
methoxide in methanol (1.84 g of sodium, 0.08 mol; 30 mL of
methanol) was added to 1,2,3,4-tetrakis(dimethylsilyl)benzene
(15) (3.11 g, 10.00 mol). The mixture was stirred under N2 for
1 h at room temperature. The reaction mixture was added to
1 mL of H2O and the solution was warmed to 45-50 °C. After
15 disappeared (monitored by TLC), the crude product was
filtered and redissolved in EtOAc. After being washed with
H2O and dried over MgSO4, the EtOAc solution was concen-
trated under reduced pressure. The crude product was purified
by column chromatography on silica gel with 2% EtOAc in
petroleum ether (60-80 °C) as eluent. Compound 16 (2.84 g,
8.40 mmol) was obtained in 84% yield. Mp 90-92 °C (lit.11 mp
89-91 °C); 1H NMR (400 MHz) δ 0.38 (s, 12H), 0.43 (s, 12H),
7.62 (s, 2H); 13C NMR (101 MHz) δ 1.0, 2.2, 131.1, 149.3, 151.9;
MS m/z 338 (M+); HRMS for C14H26O2Si4 [M + H]+ calcd
339.1088, found 339.1104.
N-Ben zoyl-1,3,5,8-t et r a h yd r o-1,1,3,3-t et r a m et h yl-5,8-
im in en a p h th [2,3-c][1,2,5]oxa d isilole (19e): 78% yield (294
mg, 0.78 mmol), mp 160-162 °C; 1H NMR (400 MHz) δ 0.31-
0.36 (m, 12H), 5.56 (s 1H), 6.02 (s, 1H), 6.89-6.91 (m, 1H),
7.18-7.20 (m, 1H), 7.36 (s, 1H), 7.41-7.56 (m, 6H); 13C NMR
(101 MHz) δ 1.0, 63.7, 68.1, 122.2, 123.4, 128.0, 128.5, 131.0,
134.4, 142.1, 144.8, 146.0, 146.3, 148.9, 149.0, 167.5; IR (KBr,
cm-1) 2957, 1646, 1365, 1252, 1184, 1104; HRMS for C21H23
-
NO2Si2 [M + Na]+ calcd 400.1165, found 400.1155. Anal. Calcd
for C21H23NO2Si2: C, 66.80; H, 6.14. Found: C, 66.62; H, 6.21.
Ad d u cts 19a -c fr om Ben zyn e Gen er a ted fr om Ben -
zobisoxa d isilole 14. Trifluoromethanesulfonic acid (0.27 mL,
3.0 mmol) was added with a syringe to a stirred solution of
phenyliodium diacetate (493 mg, 1.5 mmol in 10 mL of CH2-
Cl2) at 0 °C. The mixture was stirred under N2 for 1 h at 0 °C
Hyd r ogen a ted P r od u cts (20a -e). Palladium on activated
carbon (Pd/C, 10%) was added to a stirred solution of 19a -e
(1.0 mmol) in 10 mL of ethanol. The mixture was stirred under
H2 at room temperature for 2 h. After filtering off the
palladium catalyst, the organic solvent was concentrated under
7194 J . Org. Chem., Vol. 69, No. 21, 2004

Generation of Benzdiynes from Benzobisoxadisiloles
reduced pressure. The residue was purified by column chro-
matography on silica gel by using a gradient of 2-5% EtOAc
in petroleum ether (60-80 °C) as eluent.
cm-1) 2955, 1256, 1075; MS m/z 412 (M+); HRMS for C20H28O2-
Si4 [M]+ calcd 412.1166, found 412.1164. Recrystallization from
a CH2Cl2/n-hexane mixture afforded the crystal sample for
X-ray structure determination.
Ad d u cts 25a ,b/26a ,b (Syn a n d An ti) fr om Com p ou n d
20b. The trapping experiment of arene 20b described above
was repeated with the diene (furan or cyclopentadiene) as the
trapping agents. The crude product was purified by column
chromatography on silica gel by using a gradient of 2-5%
EtOAc in petroleum ether (60-80 °C) as eluent to afford the
mixture 25a ,b and 26a ,b.
1,3,5,6,7,8-H exa h yd r o-1,1,3,3-t et r a m et h yl-5,8-ep oxy-
n a p h th [2,3-c][1,2,5]oxa d isilole (20a ): 90% yield (248 mg,
0.9 mmol), mp 122-124 °C; 1H NMR (400 MHz) δ 0.32 (s, 6H),
0.36 (s, 6H), 1.43-1.44 (m, 2H), 2.07-2.10 (m, 2H), 5.39-5.40
(m, 2H), 7.41 (s, 2H); 13C NMR (101 MHz) δ 1.0, 1.2, 26.4, 78.8,
120.9, 146.7, 146.9; IR (KBr, cm-1) 3011, 2952, 1275, 1249,
1097; MS m/z 276 (M+). Anal. Calcd for C14H20O2Si2: C, 60.82;
H, 7.29. Found: C, 60.84; H, 7.34; HRMS for C14H20O2Si2 [M
+ Na]+ calcd 299.0899, found 299.0889.
1,4,5,6,7,8-H exa h yd r o-1,4-ep oxy-5,8-m et h a n oa n t h r a -
1,3,5,6,7,8-H exa h yd r o-1,1,3,3-t et r a m et h yl-5,8-m et h a -
n on a p h th [2,3-c][1,2,5]oxa d isilole (20b): 90% yield (247 mg,
0.90 mmol), mp 71-72 °C; 1H NMR (400 MHz) δ 0.33 (s, 6H),
0.34 (s, 6H), 1.20-1.22 (m, 2H), 1.52-1.54 (m, 1H), 1.75-1.77
(m, 1H), 1.91-1.93 (m, 2H), 3.34 (s, 2H), 7.34 (s, 2H); 13C NMR
(101 MHz) δ 1.1, 1.3, 26.9, 43.6, 49.1, 122.8, 145.2, 149.5; IR
(KBr, cm-1) 3053, 2965, 1253, 1099; MS m/z 274 (M+); HRMS
for C15H22OSi2 [M + H]+ calcd 275.1287, found 275.1293. Anal.
Calcd for C15H22OSi2: C, 65.63; H, 8.08. Found: C, 65.43; H,
8.08. Recrystallization from a CH2Cl2/n-hexane mixture af-
forded the crystal sample for X-ray structure determination.
1,3,5,6,7,8-Hexa h yd r o-1,1,3,3-tetr a m eth yl-5,8-eth a n on -
a p h th [2,3-c][1,2,5]oxa d isilole (20c): 96% yield (276 mg, 0.96
cen e (25a /26a ) (syn a n d a n ti): 65% yield (137 mg, 0.65
mmol); H NMR (400 MHz) δ 1.05-1.12 (m, 2H), 1.45-1.48
1
(m, 1H), 1.69-1.73 (m, 1H), 1.83-1.86 (m, 2H), 3.24-3.25 (m,
2H), 5.62 (s, 1H), 5.65 (s, 1H), 7.0 (s, 2H), 7.07 (s, 1H), 7.09 (s,
1H); 13C NMR (101 MHz) δ 26.8 (26.9), 43.5 (43.6), 49.5 (50.0),
82.4 (82.6), 113.9 (114.1), 143.3 (145.1), 145.2, 146.7 (146.8);
IR (KBr, cm-1) 3005, 2974, 2961, 1562, 1278; MS m/z 210 (M+);
HRMS for C15H14O [M + Na]+ calcd 233.0942, found 233.0942.
Anal. Calcd for C15H14O: C, 85.68; H, 6.71. Found: C, 85.56;
H, 6.70. The syn isomer was recrystallized from n-hexane. Mp
125-127 °C. The X-ray structure was determined.
1,4,5,6,7,8-H exa h yd r o-1,4,5,8-d im et h a n oa n t h r a cen e
(25b/26b) (syn a n d a n ti): 58% yield (121 mg, 0.58 mmol);
1H NMR (400 MHz) δ 1.09-1.14 (m, 2H), 1.43-1.48 (m, 1H),
1.69-1.74 (m, 1H), 1.81-1.86 (m, 2H), 2.20-2.31 (m, 2H),
3.22-3.23 (m, 2H), 3.80-3.82 (m, 2H), 6.78-6.79 (m, 2H), 7.04
(s, 1H), 7.05 (s, 1H); 13C NMR (101 MHz) δ 27.1 (27.2), 43.6,
49.5, 50.0 (50.3), 70.4 (70.9), 114.9 (115.0), 143.2 (143.4), 144.1,
149.1; IR (KBr, cm-1) 2961, 1559; MS m/z 208 (M+); HRMS
for C16H16 [M + Na]+ calcd 231.1149, found 231.1155.
1
mmol), mp 148-150 °C; H NMR (400 MHz) δ 0.36 (s, 12H),
1.42 (d, J ) 8.0 Hz, 4H), 1.80 (d, J ) 8.0 Hz, 4H), 2.99 (S, 2H),
7.33 (s, 2H); 13C NMR (101 MHz) δ 1.2, 26.2, 34.3, 126.1, 145.1,
145.4; IR (KBr, cm-1) 2942, 1248, 1110; MS m/z 288 (M+);
HRMS for C16H24OSi2 [M + H]+ calcd 289.1443, found 289.1448.
Recrystallization from a CH2Cl2/n-hexane mixture afforded the
crystal sample for X-ray structure determination.
N-ter t-Bu t oxyca r b on yl-1,3,5,6,7,8-h exa h yd r o-1,1,3,3-
tetr am eth yl-5,8-im in en aph th [2,3-c][1,2,5]-oxadisilole (20d):
98% yield (368 mg, 0.98 mmol), mp 180-182 °C; 1H NMR (400
MHz) δ 0.31 (s, 6H), 0.35 (s, 6H), 1.34-1.36 (m, 2H), 1.41 (s,
9H), 2.11 (b, 2H), 5.11 (s, 2H), 7.41 (s, 2H); 13C NMR (101 MHz)
δ 1.0, 1.2, 26.6, 28.2, 60.9, 80.0, 121.5, 145.9, 146.4, 154.9; IR
(KBr, cm-1) 2958, 1695, 1366, 1250, 1161, 1100; HRMS for
Ad d u cts 27 fr om Com p ou n d 20b. The trapping experi-
ment of 20b described above was repeated with p-methox-
yphenyl azide as the trapping agent. The crude product was
purified by column chromatography on silica gel with a
gradient of 2-5% EtOAc in petroleum ether (60-80 °C) as
eluent to afford 27 (172 mg, 0.59 mmol) in 59% yield as
1
colorless oil. H NMR (400 MHz) δ 1.21-1.27 (m, 2H), 1.62-
C
19H29NO3Si2 [M + Na]+ calcd 398.1583, found 398.1578.
N-Ben zoyl-1,3,5,6,7,8-h exa h yd r o-1,1,3,3-t et r a m et h yl-
1.65 (m, 1H), 1.80-1.83 (m, 1H), 1.96-1.98 (m, 2H), 3.42 (s,
1H), 3.49 (s, 1H), 3.88 (s 3H), 7.06-7.09 (m, 2H), 7.37 (s, 1H),
7.61-7.63 (m, 2H), 7.76 (s, 1H); 13C NMR (101 MHz) δ 27.3,
27.4, 43.2, 43.8, 48.6, 55.6, 101.6, 110.6, 114.7, 124.6, 130.2,
131.9, 145.4, 146.0, 150.4, 159.5; IR (KBr, cm-1) 2964, 1518,
1456, 1253; HRMS for C18H17N3O [M + H]+ calcd 292.1449,
found 292.1452. Anal. Calcd for C18H17N3O: C, 74.20; H, 5.88.
Found: C, 74.30; H, 5.86.
5,8-im in en a p h th [2,3-c][1,2,5]oxa d isilole (20e): 85% yield
1
(322 mg, 0.85 mmol), mp 173-175 °C; H NMR (400 MHz) δ
0.34 (s, 6H), 0.35 (s, 6H), 1.41-1.43 (m, 2H), 2.11 (s, 1H), 2.30
(s, 1H), 5.11 (s 1H), 5.66 (s, 1H), 7.34 (s, 1H), 7.40-7.56 (m,
6H); 13C NMR (101 MHz) δ 1.0, 1.1, 25.6, 28.1, 58.6, 63.2, 121.1,
122.0, 128.0, 128.4, 130.8, 135.1, 145.2, 145.8, 146.8, 147.1,
168.1; IR (KBr, cm-1) 2954, 1635, 1387, 1251, 1111, 1097;
HRMS for C21H25NO2Si2 [M + Na]+ calcd 402.1321, found
402.1303.
1,3-Dih yd r o-1,1,3,3-t et r a m et h yln a p h t h [2,3-c][1,2,5]-
oxa d isilole (28). To a suspension of LiAlH4 (0.38 g, 10 mmol)
in 10 mL of anhydrous THF was carefully added TiCl4 (3.1
mL, 28 mmol) followed by Et3N (5.0 mL, 36 mmol) at 0 °C
under N2. The mixture was stirred and refluxed for 30 min
and then allowed to warm to room temperature. A solution of
19a (0.22 g, 0.8 mmol) in 10 mL of anhydrous THF was added.
The mixture was refluxed for 24 h and then was poured into
crushed ice (20 g) containing 20 mL of 1 N HCl. The resulting
mixture was extracted with CH2Cl2. The organic extract was
dried over anhydrous MgSO4, filtered, and concentrated under
reduced pressure. The crude product was purified by column
chromatography on silica gel with a gradient of 2-5% EtOAc
in petroleum ether (60-80 °C) as the eluent to afford product
28 (202 mg, 0.78 mmol) in 98% yield. Mp 110-112 °C; 1H NMR
(400 MHz) δ 0.43 (s, 6H), 7.50-7.52 (AA′BB′, m, 2H), 7.85-
7.87 (AA′BB′, m, 2H), 8.07 (s, 2H); 13C NMR (101 MHz) δ 1.0,
1.2, 126.5, 128.2, 131.2, 133.6, 143.7; IR (KBr, cm-1) 3024,
2955, 1251, 1093; MS m/z 258 (M+); HRMS for C14H18OSi2 [M]+
calcd 258.0896, found 258.0897. Anal. Calcd for C14H18OSi2:
C, 65.04; H, 7.03. Found: C, 64.69; H, 6.88.
Ad d u cts 21 w ith Ben zyn e Gen er a ted fr om Ben zo-
bisoxa d isilole 14. The trapping experiment of benzobisoxa-
disilole 14 described above was repeated with p-methoxyphe-
nyl azide as the trapping agent. The crude product was
purified by column chromatography on silica gel with 2%
EtOAc in petroleum ether (60-80 °C) as eluent to afford
adduct 21 (149 mg, 0.42 mmol) in 42% yield. Mp 113-115 °C;
1H NMR (270 MHz) δ 0.41 (s, 6H), 0.44 (s, 6H), 3.90 (s, 3H),
7.11-7.14 (m, 2H), 7.64-7.68 (m, 2H), 7.82 (d, J ) 1.1 Hz,
1H), 8.30 (d, J ) 1.1 Hz, 1H); 13C NMR (68 MHz) δ 1.27, 1.30,
55.6, 112.6, 114.9, 123.0, 124.7, 129.7, 133.7, 142.5, 147.37,
147.42, 159.7; IR (KBr, cm-1) 2953, 1515, 1462, 1254, 1083;
HRMS for C17H21N3O2Si2 [M + H]+ calcd 356.1250, found
356.1241. Anal. Calcd for C17H21N3O2Si2: C, 57.43; H, 5.95.
Found: C, 57.28; H, 5.99.
Dim er 22. The trapping experiment of benzobisoxadisilole
14 described above was repeated without the trapping agent.
The crude product was purified by column chromatography
on silica gel with 2% EtOAc in petroleum ether (60-80 °C) as
eluent to afford adduct 22 (165 mg 0.40 mmol) in 80% yield.
1,4-Dih ydr o-1,4-epoxyan th r acen e (31). Trifluoromethane-
sulfonic acid (0.05 mL, 0.6 mmol) was added with a syringe to
a stirred solution of phenyliodium diacetate (98.6 mg, 0.3 mmol
in 3 mL of CH2Cl2) at 0 °C. The mixture was stirred under N2
1
Mp 255-257 °C; H NMR (400 MHz) δ 0.32 (s, 24H), 6.83 (s,
4H); 13C NMR (101 MHz) δ 0.8, 118.8, 149.7, 152.6; IR (KBr,
J . Org. Chem, Vol. 69, No. 21, 2004 7195

Chen et al.
for 1 h at 0 °C and for 2 h at room temperature. The clear
yellow solution was cooled again to 0 °C followed by dropwise
addition of a cold (0 °C) solution of the naphthoxadisilole 28
(51.6 mg, 0.2 mmol in 3 mL of CH2Cl2). The mixture was
stirred for 0.5 h at 0 °C and warmed to room temperature.
After the naphthoxadisilole 28 disappeared (monitored by
TLC), diisopropylamine (0.07 mL, 0.5 mmol) and furan (0.15
mL, 2.0 mmol) were added followed by a solution of tetrabu-
tylammonium fluoride (0.5 mL, 0.5 mmol, 1.0 M solution in
THF). After a further 10 min, water was added and the
resulting mixture was extracted with CH2Cl2. The organic
extract was dried over anhydrous MgSO4, filtered, and con-
centrated under reduced pressure. The residue was purified
by column chromatography on silica gel with a gradient of
2-5% EtOAc in petroleum ether (60-80 °C) as eluent to afford
product 31 (8.54 mg, 0.044 mmol) in 22% yield. Mp 152-154
°C (lit.16 mp 163-164 °C); 1H NMR (400 MHz) δ 5.82 (m, 2H),
6.98 (m, 2H), 7.45-7.46 (m, 2H), 7.60 (m, 2H), 7.72-7.74 (m,
2H); 13C NMR (101 MHz) δ 81.7, 118.6, 126.1, 128.1, 131.9,
141.6, 144.1; IR (KBr, cm-1) 3032, 2957, 1605, 1284; MS m/z
194 (M+); HRMS for C14H10O [M + Na]+ calcd 217.0629, found
217.0628.
Ad d u ct s 33a -c (R a cem ic) fr om Ben zyn e Gen er a t ed
fr om Ben zobisoxa d isilole 16. Trifluoromethanesulfonic acid
(0.27 mL, 3.0 mmol) was added with a syringe to a stirred
solution of (diacetoxyiodo)benzene (493 mg, 1.5 mmol in 10
mL of CH2Cl2) at 0 °C. The mixture was stirred under N2 for
1 h at 0 °C and for 2 h at room temperature. The clear yellow
solution was cooled again to 0 °C and then treated dropwise
with a cold (0 °C) solution of arene 16 (338 mg, 1.0 mmol in 5
mL of CH2Cl2). The mixture was stirred for 0.5 h at 0 °C and
warmed to room temperature. After benzobisoxadisilole 16
disappeared (monitored by TLC), the mixture was cooled to
-50 °C. Diisopropylamine (0.35 mL, 2.5 mmol) and the diene
(furan, cyclopentadiene, or N-tert-butoxycarbonylpyrrole, 10
mmol) were added followed by a solution of tetrabutylammo-
nium fluoride (2.5 mL, 2.5 mmol, 1.0 M solution in THF). The
reaction mixture was kept at -50 °C for 1 h, then gradually
warmed to room temperature and stirred for 2 h. Water was
added and the resulting mixture was extracted with CH2Cl2.
The organic extract was dried over anhydrous MgSO4, filtered,
and concentrated under reduced pressure. The crude product
was purified by column chromatography on silica gel with a
gradient of 2-5% EtOAc in petroleum ether (60-80 °C) as
eluent to afford the adducts 33a -c.
1H), 7.30-7.35 (m, 1H); 13C NMR (101 MHz) δ 1.1, 1.2, 1.5,
28.1, 66.7, 80.7, 122.4, 124.9, 128.0, 142.1, 142.7, 143.4, 144.1,
148.3; IR (neat, cm-1) 2965, 1711, 1368, 1253, 1167, 1085;
HRMS for C19H27NO3Si2 [M + Na]+ calcd 396.1427, found
396.1441.
1
Com p ou n d 34b: mp 70-72 °C, H NMR (400 MHz) δ 0.09
(s, 3H), 0.12 (s, 3H), 0.19 (s, 3H), 0.22 (s, 3H), 0.42 (s, 3H),
0.45 (s, 3H), 0.47 (s, 3H), 0.50 (s, 3H), 2.15-2.17 (m, 1H), 2.28-
2.31 (m, 1H), 3.86-3.87 (m, 1H), 4.09-4.10 (m, 1H), 6.76-
6.77 (m, 1H), 6.79-6.81 (m, 1H), 7.24 (d, J ) 7.2 Hz, 1H), 7.31
(d, J ) 7.2 Hz, 1H); 13C NMR (101 MHz) δ 1.5, 1.6, 3.4, 3.5,
4.0, 4.1, 49.8, 51.4, 68.1, 121.6, 131.6, 137.9, 139.6, 142.4, 143.2,
151.8, 157.2; IR (KBr, cm-1) 2959, 1571, 1259, 1092; MS m/z
420 (M+); HRMS for C19H32O3Si4 [M + Na]+ calcd 443.1326,
found 443.1323. Recrystallization from CH2Cl2/n-hexane mix-
ture afforded the crystal sample for X-ray structure determi-
nation.
Hyd r ogen a ted P r od u cts 35b,c. Palladium on activated
carbon (Pd/C, 10%) was added to a stirred solution of 33b,c
(1.0 mmol) in 10 mL of ethanol. The mixture was stirred under
H2 at room temperature for 2 h. The palladium catalyst was
filtered and the organic solvent was concentrated under
reduced pressure. The residue was purified by column chro-
matography on silica gel with a gradient of 2-5% EtOAc in
petroleum ether (60-80 °C) as eluent to afford the adducts
35b,c.
1,3,6,7,8,9-H exa h yd r o-1,1,3,3-t et r a m et h yl-6,9-m et h a -
n on a p h th [2,3-c][1,2,5]oxa d isilole (35b): 73% yield (200 mg,
0.73 mmol), oil; 1H NMR (400 MHz) δ 0.33 (s, 3H), 0.34 (s,
3H), 0.36 (s, 3H), 0.43 (s, 3H), 1.13-1.18 (m, 2H), 1.52-1.55
(m, 1H), 1.77-1.80 (m, 1H), 1.91-1.95 (m, 2H), 3.29-3.38 (m,
2H), 7.22-7.24 (m, 1H), 7.29-7.30 (m, 1H); 13C NMR (101
MHz) δ 1.2, 1.32, 1.34, 26.67, 26.68, 43.4, 43.9, 49.2, 121.7,
128.5, 138.8, 144.7, 148.3, 151.4; IR (neat, cm-1) 2960, 1258,
1094; MS m/z 274 (M+); HRMS for C15H22OSi2 [M + Na]+ calcd
297.1106, found 297.1099.
N-ter t-Bu t oxyca r b on yl-1,3,6,7,8,9-h exa h yd r o-1,1,3,3-
tetr am eth yl-6,9-im in en aph th [2,3-c][1,2,5]oxadisilole (35c):
98% yield (368 mg, 0.98 mmol), oil; 1H NMR (270 MHz) δ 0.33
(s, 3H), 0.35 (s, 3H), 0.37 (s, 3H), 0.47 (s, 3H), 1.24-1.30 (m,
2H), 1.40 (s, 9H), 2.12-2.15 (m, 2H), 5.02 (s, 1H), 5.14 (s, 1H),
7.28-7.36 (m, 2H); 13C NMR (68 MHz) δ 1.2, 1.3, 1.4, 1.5, 26.6,
28.3, 60.8, 80.0, 120.5, 129.2, 145.0, 145.9, 147.7, 155.1; IR
(neat, cm-1) 2981, 2951, 1703, 1366, 1248, 1158, 1103; HRMS
for C19H29NO3Si2 [M + Na]+ calcd 398.1583, found 398.1586.
1,3,6,9-Tetr ah ydr o-1,1,3,3-tetr am eth yl-6,9-epoxyn aph th -
[2,3-c][1,2,5]oxa d isilole (33a ): 14% yield (38.4 mg, 0.14
mmol), mp 88-90 °C; 1H NMR (270 MHz) δ 0.33-0.34 (m, 9H),
0.46 (s, 3H), 5.63-5.64 (m, 1H), 5.74-5.75 (m, 1H), 6.98-7.01
(m, 1H), 7.04-7.06 (m, 1H), 7.19 (d, J ) 7.0 Hz, 1H), 7.33 (d,
J ) 7.0 Hz, 1H); 13C NMR (101 MHz) δ 1.2, 1.3, 1.8, 82.2, 82.4,
121.3, 124.9, 128.0, 142.6, 143.2, 144.1, 149.1, 152.5; IR (KBr,
cm-1) 2958, 1274, 1254, 1099; MS m/z 274 (M+); HRMS for
1,4,7,8,9,10-Hexah ydr o-1,4-epoxy-7,10-m eth an oph en an -
th r en e (37b/38b) (Syn a n d An ti). Trifluoromethanesulfonic
acid (0.05 mL, 0.6 mmol) was added with a syringe to a stirred
solution of phenyliodium diacetate (98.6 mg, 0.3 mmol in 2
mL of CH2Cl2) at 0 °C. The mixture was stirred under N2 for
1 h at 0 °C and for 2 h at room temperature. The clear yellow
solution was cooled again to 0 °C and followed by dropwise
addition of a cold (0 °C) solution of 35b (54.8 mg, 0.2 mmol in
2 mL of CH2Cl2). The mixture was stirred for 0.5 h at 0 °C
and warmed to room temperature. After 35b disappeared
(monitored by TLC), diisopropylamine (0.07 mL, 0.5 mmol) and
furan (0.15 mL, 2.0 mmol) were added followed by a solution
of tetrabutylammonium fluoride (0.50 mL, 0.5 mmol, 1.0 M
solution in THF). After a further 2 h, water was added and
the resulting mixture was extracted with CH2Cl2. The organic
extract was dried over anhydrous MgSO4, filtered and con-
centrated under reduced pressure. The residue was purified
by column chromatography on silica gel with a gradient of
2-5% EtOAc in petroleum ether (60-80 °C) as eluent to afford
the mixture 37b/38b (syn and anti) (10.9 mg, 0.052 mmol) in
C
14H18O2Si2 [M + Na]+ calcd 297.0743, found 297.0732.
1,3,6,9-Tet r a h yd r o-1,1,3,3-t et r a m et h yl-6,9-m et h a n o-
n a p h th [2,3-c][1,2,5]oxa d isilole (33b): 43% yield (117 mg,
0.43 mmol), mp 68-70 °C; 1H NMR (400 MHz) δ 0.33 (s, 3H),
0.36 (s, 3H), 0.37 (s, 3H), 0.45 (s, 3H), 2.29-2.31 (m, 1H), 2.36-
2.39 (m, 1H), 3.84-3.93 (m, 2H), 6.77-6.84 (m, 2H), 7.18 (d,
J ) 7.2 Hz, 1H), 7.32 (d, J ) 7.2 Hz, 1H); 13C NMR (101 MHz)
δ 1.2, 1.3, 1.40, 1.43, 50.1, 50.6, 70.2, 122.9, 127.3, 139.5, 142.7,
143.1, 143.3, 152.2, 155.5; IR (KBr, cm-1) 2959, 1563, 1258,
1092; MS m/z 272 (M+); HRMS for C15H20OSi2 [M + Na]+ calcd
295.095, found 295.0946.
N-ter t-Bu t oxyca r b on yl-1,3,6,9-t et r a h yd r o-1,1,3,3-t et -
r a m eth yl-6,9-im in en a p h th [2,3-c][1,2,5]oxa d isilole (33c):
22% yield (82.1 mg, 0.22 mmol), oil; 1H NMR (400 MHz) δ 0.31
(s, 3H), 0.32 (m, 3H), 0.35 (m, 3H), 0.48 (s, 3H), 1.37 (s, 9H),
5.35-5.52 (m, 2H), 6.91-7.00 (m, 2H), 7.17 (d, J ) 7.2 Hz,
1
26% yield as a colorless oil. H NMR (400 MHz) δ 1.07-1.18
(m, 2H), 1.50-1.54 (m, 1H), 1.66-1.77 (m, 1H), 1.86-1.90 (m,
2H), 3.30 (s, 1H), 3.41(d, J ) 13.2 Hz, 1H), 5.65-5.67 (m, 1H),
5.75-5.79 (m, 1H), 6.71-6.74 (m, 1H), 6.94-7.02 (m, 3H); 13
C
NMR (101 MHz) δ 26.9 (27.0), 29.7 41.2 (41.4), 43.2, 48.3 (48.9),
80.7, 82.2 (82.5), 115.6 (115.8), 117.0 (117.3), 139.4, 140.1
(142.1), 142.1 (142.3), 142.9 (143.2), 145.5 (145.7), 145.97
(16) Kitamura, T.; Fukatsu, N.; Fujiwara, Y. J . Org. Chem. 1998,
63, 8579-8581.
7196 J . Org. Chem., Vol. 69, No. 21, 2004

Generation of Benzdiynes from Benzobisoxadisiloles
(146.00); IR (neat, cm-1) 2963, 1559, 1280; MS m/z 210 (M+);
HRMS for C15H14O [M + H]+ calcd 211.1122, found 211.1123.
Su p p or tin g In for m a tion Ava ila ble: Carbon and proton
spectra for reaction products, and X-ray crystallographic
structures and data for 14, 19a , 19d , 20b, 20c, 22, 25a , and
34b. This material is available free of charge via the Internet
at http://pubs.acs.org.
Ack n ow led gm en t. Financial support from the Fac-
ulty Research Grants (FRG/02-03/II-35, 03-04/I-11) is
gratefully acknowledged.
J O049091Z
J . Org. Chem, Vol. 69, No. 21, 2004 7197