Synthesis of a C44H26 hydrocarbon having a carbon framework represented on the surface of C60 via benzoenyne-allenes

Article abstract of DOI:10.1021/jo9911903

The C₄₄H₂₆ hydrocarbon 20 was synthesized in 13% overall yield in eight steps from acenaphthenequinone (6) and 2 equiv of 1-(2-ethynylphenyl)- 2-phenylethyne. Condensation of the monoketal 7 with the lithium acetylide 8 afforded the benzoenediynyl propargylic alcohol 9. On exposure to thionyl chloride, 9 underwent a cascade of reactions with the formation of the chloro-substituted benzoenyne-allene 11 in situ followed by a C2-C6 cyclization to produce the biradical 12, leading to the formal Diels-Alder adduct 13 and subsequently, after tautomerization, the chloride 14. Reduction with sodium borohydride then gave 15. Deprotection of the ketal group produced 16 to allow a repeat of condensation with the acetylide 17 followed by the cascade transformation to afford the chloride 19. Subsequent reduction then furnished the C₄₄H₂₆ hydrocarbon 20 having a carbon framework represented on the surface of C₆₀.

Full text of DOI:10.1021/jo9911903

7996
J . Org. Chem. 1999, 64, 7996-7999
Syn th esis of a C44H26 Hyd r oca r bon Ha vin g a Ca r bon F r a m ew or k
Rep r esen ted on th e Su r fa ce of C60 via Ben zoen yn e-Allen es
Hai-Ren Zhang and Kung K. Wang*
Department of Chemistry, West Virginia University, Morgantown, West Virginia 26506
Received J uly 27, 1999
The C44H26 hydrocarbon 20 was synthesized in 13% overall yield in eight steps from acenaph-
thenequinone (6) and 2 equiv of 1-(2-ethynylphenyl)-2-phenylethyne. Condensation of the monoketal
7 with the lithium acetylide 8 afforded the benzoenediynyl propargylic alcohol 9. On exposure to
thionyl chloride, 9 underwent a cascade of reactions with the formation of the chloro-substituted
benzoenyne-allene 11 in situ followed by a C2-C6 cyclization to produce the biradical 12, leading
to the formal Diels-Alder adduct 13 and subsequently, after tautomerization, the chloride 14.
Reduction with sodium borohydride then gave 15. Deprotection of the ketal group produced 16 to
allow a repeat of condensation with the acetylide 17 followed by the cascade transformation to
afford the chloride 19. Subsequent reduction then furnished the C44H26 hydrocarbon 20 having a
carbon framework represented on the surface of C60.
Sch em e 1
In tr od u ction
Thermal cyclization of the benzoenyne-allenes 1 pro-
vides easy access to the naphthalene biradicals 21 and
the benzofulvene biradicals 32 (Scheme 1). The nature
of the substituent at the acetylenic terminus is respon-
sible for directing the reaction toward either the Myers
cyclization reaction to generate the naphthalene biradi-
cals 2 or the C2-C6 cyclization reaction to furnish the
benzofulvene biradicals 3. With an aryl substituent or a
sterically demanding group, such as the tert-butyl group
and the trimethylsilyl group, at the acetylenic terminus,
the C2-C6 cyclization reaction becomes the preferred
pathway. The effect of the aryl substituent is attributed
to its ability to stabilize the alkenyl radical center in 3.2c,i
The sterically demanding group inhibits the Myers
cyclization reaction because of the emergence of severe
nonbonded steric interactions in the biradicals 2.2c,f,j If
R1 is a phenyl group, the biradical 3 undergoes an
intramolecular radical-radical coupling to form 4 and
subsequently, after tautomerization, the benzofluorene
5.1h,2 Although the transformation from 1 to 4 could also
be regarded as a Diels-Alder reaction, mechanistic2e and
DNA-cleaving2h studies suggest a two-step biradical
pathway. Several synthetic methods have been reported
for the preparation of benzoenyne-allenes to allow gen-
eration of biradicals for subsequent synthetic elabora-
tions.1,2 We now report a simple and efficient route to
these highly unsaturated compounds for the C2-C6
cyclization reaction. This synthetic pathway was suc-
cessfully adopted for the preparation of a C44H26 hydro-
carbon having a carbon framework represented on the
surface of C60.
(1) (a) Myers, A. G.; Kuo, E. Y.; Finney, N. S. J . Am. Chem. Soc.
1989, 111, 8057-8059. (b) Myers, A. G.; Dragovich, P. S. J . Am. Chem.
Soc. 1989, 111, 9130-9132. (c) Nagata, R.; Yamanaka, H.; Okazaki,
E.; Saito, I. Tetrahedron Lett. 1989, 30, 4995-4998. (d) Nagata, R.;
Yamanaka, H.; Murahashi, E.; Saito, I. Tetrahedron Lett. 1990, 31,
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Org. Chem. 1997, 62, 603-626. (h) Wang, K. K.; Zhang, H.-R.;
Petersen, J . L. J . Org. Chem. 1999, 64, 1650-1656. For reviews, see:
(i) Wang, K. K. Chem. Rev. 1996, 96, 207-222. (j) Grissom, J . W.;
Gunawardena, G. U.; Klingberg, D.; Huang, D. Tetrahedron 1996, 52,
6453-6518.
Resu lts a n d Discu ssion
(2) (a) Engels, B.; Hanrath, M. J . Am. Chem. Soc. 1998, 120, 6356-
6361. (b) Schmittel, M.; Strittmatter, M. Tetrahedron 1998, 54, 13751-
13760. (c) Engels, B.; Lennartz, C.; Hanrath, M.; Schmittel, M.;
Strittmatter, M. Angew. Chem., Int. Ed. Engl. 1998, 37, 1960-1963.
(d) Schmittel, M.; Steffen, J .-P.; Auer, D.; Maywald, M. Tetrahedron
Lett. 1997, 38, 6177-6180. (e) Schmittel, M.; Strittmatter, M.; Kiau,
S. Angew. Chem., Int. Ed. Engl. 1996, 35, 1843-1845. (f) Schmittel,
M.; Kiau, S.; Siebert, T.; Strittmatter, M. Tetrahedron Lett. 1996, 37,
7691-7694. (g) Schmittel, M.; Strittmatter, M.; Vollmann, K.; Kiau,
S. Tetrahedron Lett. 1996, 37, 999-1002. (h) Schmittel, M.; Maywald,
M.; Strittmatter, M. Synlett 1997, 165-166. (i) Schmittel, M.; Stritt-
matter, M.; Kiau, S. Tetrahedron Lett. 1995, 36, 4975-4978. (j)
Gillmann, T.; Hulsen, T.; Massa, W.; Wocadlo, S. Synlett 1995, 1257-
1259. (k) Garcia, J . G.; Ramos, B.; Pratt, L. M.; Rodriguez, A.
Tetrahedron Lett. 1995, 36, 7391-7394.
Treatment of the commercially available acenaph-
thenequinone (6) with 2,2-dimethyl-1,3-propanediol in
the presence of p-TsOH according to the reported proce-
dure produced the monoketal 7 in 90% yield (Scheme 2).3
Condensation of 7 with the lithium acetylide 8, obtained
by lithiation of 1-(2-ethynylphenyl)-2-phenylethyne2b,4
with n-butyllithium, followed by hydrolytic workup, then
furnished the propargylic alcohol 9. Treatment of 9 with
(3) Ray, J . K.; Harvey, R. G. J . Org. Chem. 1983, 48, 1352-1354.
(4) Grubbs, R. H.; Kratz, D. Chem. Ber. 1993, 126, 149-157.
10.1021/jo9911903 CCC: $18.00 © 1999 American Chemical Society
Published on Web 09/21/1999

Synthesis of a C44H26 Hydrocarbon
J . Org. Chem., Vol. 64, No. 21, 1999 7997
Sch em e 2
Sch em e 3
Because of the presence of a chiral center in 14, the
two methylene carbons of the protective group are
diastereotopic, as are the two methyl carbons. They
exhibit different 13C NMR chemical shifts. Interestingly,
the DEPT experiment gives 13 distinct signals for the
aromatic methine carbons (CH) with the peak at δ 125.93
having twice the intensity. This is one more signal than
expected if the rotation of the phenyl substituent is not
restricted. The observation of 13 signals for the aromatic
methine carbons suggests that 14 prefers the conforma-
tion with the phenyl substituent perpendicular to the
remaining aromatic ring system and the rate of rotation
of the phenyl substituent is slower than the NMR time
scale, making the two ortho carbons diastereotopic and
the two meta carbons also diastereotopic. The perpen-
dicular orientation of the phenyl ring was also observed
previously in other similar structures by X-ray1h and is
most likely responsible for shielding the neighboring
aromatic hydrogen located on the top of the phenyl
1
substituent, causing its H NMR signal to shift upfield
thionyl chloride promoted a sequence of reactions with
an initial formation of the chlorosulfite 10 followed by
an SNi′ reaction5 to produce in situ the chlorinated
benzoenyne-allene 11. A C2-C6 cyclization reaction
generated the biradical 12, which in turn underwent a
radical-radical coupling to afford the formal Diels-Alder
adduct 13 and, subsequently after tautomerization, the
chloride 14. The chloride 14 was prone to hydrolysis, and
attempts to purify it on silica gel resulted in the trans-
formation to the corresponding alcohol. Fortunately,
recrystallization of 14 from benzene afforded a pure
sample (35% yield) to allow structural elucidation.
The use of thionyl chloride to induce the transforma-
tion from 9 to 11 represents a new and convenient way
to prepare in situ the chlorinated benzoenyne-allenes for
subsequent cascade radical cyclizations. In addition, the
transformation from 9 to 14 is very facile and can be
carried out at ambient and subambient temperatures.
This is perhaps of critical importance because 1-chloro-
1,3,3-triphenylallene is known to undergo facile dimer-
ization.6 The simplicity of the procedure and the mildness
of the reaction conditions are especially attractive fea-
tures of this synthetic pathway.
to δ 6.53 (doublet). The appearance of this upfield doublet
signal is indicative of a successful formal intramolecular
Diels-Alder reaction of the benzoenyne-allene moiety in
11.
Because the chloride 14 was prone to hydrolysis, it was
operationally convenient to treat the crude 14 without
7
further purification with NaBH4 to furnish 15 in 51%
overall yield from 9. Hydrolysis of the ketal group in 15
gave 16 having a carbonyl group to allow a repeat of the
condensation and C2-C6 cyclization sequence.
Initial attempts to try to prepare 18 from condensation
of 16 with the lithium acetylide 8 were unsuccessful,
presumably because the hydrogen atoms on the five-
membered ring of 16 are very acidic.8 Fortunately, by first
converting 8 to the corresponding cerium derivative 17,9
the condensation reaction went smoothly to afford 18 in
83% yield (Scheme 3). Further treatment of 18 with
thionyl chloride gave 19 in a manner similar to the
transformation from 9 to 14. The chloride 19 was also
prone to hydrolysis to the corresponding alcohol on silica
(7) Hutchins, R. O.; Hoke, D.; Keogh, J .; Koharski, D. Tetrahedron
Lett. 1969, 3495-3498.
(8) Bors, D. A.; Kaufman, M. J .; Streitwieser, A., J r. J . Am. Chem.
Soc. 1985, 107, 6975-6982.
(5) J acobs, T. L.; Fenton, D. M. J . Org. Chem. 1965, 30, 1808-1812.
(6) (a) Rigaudy, J .; Capdevielle, P. Tetrahedron 1977, 33, 767-773.
(b) Landor, P. D.; Landor, S. R. J . Chem. Soc. 1963, 2707-2711.
(9) Imamoto, T.; Sugiura, Y.; Takiyama, N. Tetrahedron Lett. 1984,
25, 4233-4236.

7998 J . Org. Chem., Vol. 64, No. 21, 1999
Zhang and Wang
gel. It was possible to regenerate 19 for structural
elucidation by treatment of the resulting alcohol with
thionyl chloride. Reduction of the crude 19 with NaBH4
then gave the C44H26 hydrocarbon 20 in 47% yield from
18. The overall yield from 6 to 20 was 13% in eight steps.
way was adopted for the preparation of the C44H26
hydrocarbon 20 having a carbon framework represented
on the surface of C60. Using different combinations of
benzoenediynes and diaryl ketones for condensation, it
is possible that a variety of other polycyclic aromatic
hydrocarbons could also be likewise synthesized.
1
The lack of symmetry in 19 is apparent on its H and
13C NMR spectra. For example, the two hydrogens of the
methylene carbon give two sets of doublets at δ 5.38 and
4.49 with a large geminal coupling constant of 22.4 Hz.
In addition, 40 distinct 13C NMR signals are discernible.
The two upfield aromatic hydrogen signals at δ 6.76
(doublet) and 6.66 (doublet) are again indicative of a
successful second formal intramolecular Diels-Alder
reaction. In contrast, the 1H NMR spectrum of the
hydrocarbon 20 exhibits a singlet for the four methylene
hydrogens at δ 4.69. Moreover, only 20 distinct 13C NMR
signals are discernible (one less than expected presum-
ably as a result of low signal intensity and/or overlap-
ping). The presence of an upfield 1H NMR signal at δ
6.78 (doublet) again suggests that the two pendent phenyl
substituents are perpendicular to the central aromatic
rings.
Exp er im en ta l Section
All reactions were conducted in oven-dried (120 °C) glass-
ware under a nitrogen atmosphere except in the case of 16.
Diethyl ether (Et2O) and tetrahydrofuran (THF) were distilled
from benzophenone ketyl prior to use. n-Butyllithium (2.5 M)
in hexanes, 2,2-dimethyl-1,3-propanediol, cerium(III) chloride
heptahydrate (CeCl3‚7H2O), dichlorobis(triphenylphosphine)-
palladium, CuI, piperidine, pyridine (anhydrous), sulfolane,
thionyl chloride, and triethylamine were purchased from
Aldrich and were used as received. Phenylacetylene and
(trimethylsilyl)acetylene were purchased from GFS Chemicals,
Inc. and were used without further purification. 1-Bromo-2-
iodobenzene and acenaphthenequinone were purchased from
Alfa and Lancaster, respectively. The 2,2-dimethylpropylene
monoketal 7 of acenaphthenequinone was prepared in 90%
yield according to the reported procedure.3 Silica gel for flash
column chromatography was purchased from ICN. Melting
points were uncorrected. 1H (270 MHz) and 13C (67.9 MHz)
NMR spectra were recorded in CDCl3 using CHCl3 (1H δ 7.26)
and CDCl3 (13C δ 77.00) as internal standards.
P r op a r gylic Alcoh ol 9. To a solution of 1.666 g of 1-(2-
ethynylphenyl)-2-phenylethyne2b,4 (8.247 mmol) in 80 mL of
diethyl ether was added 3.3 mL of a 2.5 M solution of
n-butyllithium (8.25 mmol) in hexanes at 0 °C. The reaction
mixture was then allowed to warm to room temperature. After
15 min at room temperature, a solution of 2.01 g of 7 (7.50
mmol) in 100 mL of diethyl ether was added via cannula, and
the mixture was stirred at room temperature for 12 h. Water
(30 mL) was introduced, and the organic layer was separated,
washed with water, dried over MgSO4, and concentrated to
furnish a brown solid. Recrystallization from ethanol/water
afforded 2.735 g (5.819 mmol, 77% yield) of 9 as a white solid:
Rf 0.53 (hexanes/diethyl ether ) 1:1); mp 157-159 °C; IR (KBr)
3494, 778, 756 cm-1; 1H NMR δ 7.84 (1 H, d, J ) 8.3 Hz), 7.78-
7.71 (3 H, m), 7.62-7.41 (6 H, m), 7.34-7.22 (5 H, m), 4.25 (1
H, d, J ) 11.5 Hz), 4.13 (1 H, d, J ) 11.1 Hz), 4.00 (1 H, d, J
) 10.9 Hz), 3.84 (1 H, d, J ) 11.5 Hz), 3.75 (1 H, s), 1.23 (3 H,
s), 1.05 (3 H, s); 13C NMR δ 142.92, 139.42, 134.37, 132.09,
131.82, 131.76, 130.98, 128.57, 128.23, 128.14, 127.89, 127.75,
126.17, 126.02, 125.29, 125.24, 123.17, 120.61, 106.86, 93.32,
92.32, 88.09, 86.10, 79.78, 73.60, 72.18, 30.78, 22.82, 22.56;
MS m/z 470 (M+), 453, 442, 385, 369, 339, 326; HRMS calcd
It is worth noting that 20 has a carbon framework
represented on the surface of C60. Although the molecular
model of 20 shows that its central aromatic system has
essentially a planar geometry,10 20 could serve as a
precursor to the C44H22 hydrocarbon 21 containing a
curved corannulene unit (eq 1).11 Development of new
synthetic pathways to such nonplanar polycyclic aromatic
hydrocarbons is a subject of intense current interest
because they could serve as precursors to C60 and larger
carbon cages and may possess useful physical properties
and chemical reactivities.12
for
C33H26O3 470.1882, found 470.1871. Anal. Calcd for
Con clu sion s
C33H26O3: C, 84.23; H, 5.57. Found: C, 84.18; H, 5.60.
Ch lor id e 14. To 0.352 g of the propargylic alcohol 9 (0.749
mmol) in 8 mL of THF at 0 °C was added via cannula a
solution of 0.095 g of thionyl chloride (0.80 mmol) and 0.119 g
of anhydrous pyridine (1.5 mmol) in 2 mL of THF at 0 °C. The
reaction mixture was then allowed to warm to room temper-
ature. After 4 h, the reaction mixture was concentrated, and
20 mL of water and 100 mL of methylene chloride were added.
The organic layer was separated, washed with water, dried
over MgSO4, and concentrated to furnish a light brown solid.
Recrystallization from benzene afforded 0.127 g (0.260 mmol,
35% yield) of 14 as a light brown solid: IR 3053, 1470, 1025
A new synthetic pathway to generate the chloro-
substituted benzoenyne-allenes in situ for the subsequent
cascade radical cyclizations was established. This path-
(10) For the structure of a related compound, see: Attar, S.; Forkey,
D. M.; Olmstead, M. M.; Balch, A. L. Chem. Commun. 1998, 1255-
1256.
(11) (a) Barth, W. E.; Lawton, R. G. J . Am. Chem. Soc. 1966, 88,
380-381. (b) Barth, W. E.; Lawton, R. G. J . Am. Chem. Soc. 1971, 93,
1730-1745. (c) Scott, L. T.; Hashemi, M. M.; Meyer, D. T.; Warren, H.
B. J . Am. Chem. Soc. 1991, 113, 7082-7084. (d) Scott, L. T.; Cheng,
P.-C.; Hashemi, M. M.; Bratcher, M. S.; Meyer, D. T.; Warren, H. B.
J . Am. Chem. Soc. 1997, 119, 10963-10968. (e) Scott, L. T.; Hashemi,
M. M.; Bratcher, M. S. J . Am. Chem. Soc. 1992, 114, 1920-1921. (f)
Borchardt, A.; Fuchicello, A.; Kilway, K. V.; Baldridge, K.; Siegel, J .
S. J . Am. Chem. Soc. 1992, 114, 1921-1923. (g) Liu, C. Z.; Rabideau,
P. W. Tetrahedron Lett. 1996, 37, 3437-3440. (h) Zimmermann, G.;
Nuechter, U.; Hagen, S.; Nuechter, M. Tetrahedron Lett. 1994, 35,
4747-4750. (i) Mehta, G.; Panda, G. Tetrahedron Lett. 1997, 38, 2145-
2148.
cm-1; H NMR δ 7.94 (1 H, d, J ) 7.1 Hz), 7.82 (1 H, d, J )
1
8.1 Hz), 7.71-7.52 (7 H, m), 7.42-7.36 (2 H, m), 7.27 (1 H, t,
J ) 7.5 Hz), 7.07 (1 H, t, J ) 7.6 Hz), 6.53 (1 H, d, J ) 7.9
Hz), 6.44 (1 H, s), 4.64 (1 H, d, J ) 11.7 Hz), 4.62 (1 H, d, J )
11.7 Hz), 3.95 (1 H, dd, J ) 11.7 and 2.0 Hz), 3.85 (1 H, dd, J
) 11.6 and 2.0 Hz), 1.85 (3 H, s), 1.11 (3 H, s); 13C NMR δ
144.85, 141.22, 139.86, 138.66, 138.22, 137.32, 137.17, 135.62,
135.06, 134.92, 129.85, 129.51, 129.16, 129.00, 128.87, 128.42,
128.33, 128.10, 127.85, 127.35, 125.93, 125.83, 123.92, 123.39,
123.28, 109.14, 72.68, 72.30, 54.65, 30.51, 24.38, 22.87; MS
(12) (a) Rabideau, P. W.; Sygula, A. Acc. Chem. Res. 1996, 29, 235-
242. (b) Scott, L. T. Pure Appl. Chem. 1996, 68, 291-300. (c) Balch, A.
L.; Olmstead, M. M. Chem. Rev. 1998, 98, 2123-2165. (d) Fullerenes
and Related Structures. In Topics in Current Chemistry; Hirsch, A.,
Ed.; Springer: Berlin, 1999; Vol. 199.
m/z 490 and 488 (M+), 453, 369, 367; HRMS calcd for C33H25
ClO2 488.1543, found 488.1525.
-

Synthesis of a C44H26 Hydrocarbon
J . Org. Chem., Vol. 64, No. 21, 1999 7999
Keta l 15. The propargylic alcohol 9 (2.312 g, 4.92 mmol)
was converted to the chloride 14, and the resulting crude
product was concentrated and then used directly for reduction
without further purification by recrystallization from benzene.
To a flask maintained at 45 °C were added 0.673 g (17.8 mmol)
of sodium borohydride, 24 mL of sulfolane, and the crude
product 14. The resulting mixture was heated at 100 °C for 1
h before it was allowed to cool to room temperature. The
mixture was poured into a beaker containing 50 mL of water,
and the resulting solution was extracted with diethyl ether.
The combined organic layers were washed with water, dried
over MgSO4, and concentrated. The residue was purified by
flash column chromatography (silica gel/3% diethyl ether in
hexanes) to afford 1.144 g (2.52 mmol, 51% yield from 9) of 15
as a yellow solid: Rf 0.31 (hexanes/diethyl ether ) 8:1); mp
252-253 °C; IR 3050, 1471 cm-1; 1H NMR δ 7.93 (1 H, d, J )
7.1 Hz), 7.82 (1 H, d, J ) 8.1 Hz), 7.65-7.42 (9 H, m), 7.24 (1
H, t, J ) 7.5 Hz), 7.04 (1 H, t, J ) 7.6 Hz), 6.68 (1 H, d, J )
7.9 Hz), 4.61 (2 H, d, J ) 11.5 Hz), 4.42 (2 H, s), 3.84 (2 H, d,
J ) 11.9 Hz), 1.75 (3 H, s), 1.10 (3 H, s); 13C NMR δ 144.29,
141.80, 141.63, 140.51, 138.20, 137.27, 136.61, 135.63, 134.15,
134.02, 129.88, 128.97, 128.29, 127.81, 126.96, 126.67, 126.23,
125.95, 125.00, 124.56, 124.22, 123.30, 123.08, 108.79, 72.56,
33.97, 30.67, 23.91, 22.60; MS m/z 454 (M+), 368, 339; HRMS
calcd for C33H26O2 454.1933, found 454.1919. Anal. Calcd for
H, m), 7.02 (1 H, t, J ) 7.6 Hz), 6.69 (1 H, d, J ) 7.9 Hz), 4.55
(1 H, d, J ) 22.6 Hz), 4.33 (1 H, d, J ) 22.6 Hz), 2.97 (1 H, s);
13C NMR δ 146.56, 144.04, 141.51, 140.56, 139.11, 137.98,
137.55, 135.19, 134.04, 133.90, 132.36, 131.84, 131.56, 129.88,
129.03, 128.45, 128.42, 128.26, 128.19, 127.99, 127.90, 127.85,
127.00, 126.76, 126.29, 126.10, 125.53, 125.11, 124.66, 124.53,
123.32, 122.78, 120.54, 93.58, 91.32, 87.86, 83.16, 77.64, 33.56;
MS m/z 570 (M+), 554, 368, 339, 202; HRMS calcd for C44H26
O
570.1984, found 570.1959.
Ch lor id e 19. The same procedure was repeated as de-
scribed for 14 except that 0.205 g of 18 (0.360 mmol) was used.
Attempts to purify the crude product of 19 by flash column
chromatography (silica gel/10% diethyl ether in hexanes)
resulted in the conversion of 19 to the corresponding alcohol
(0.083 g, 0.146 mmol, 41% yield from 18). A small sample of
pure 19 was obtained by treatment of the alcohol in methylene
chloride with thionyl chloride (rt, 2 h) followed by removal of
the volatile materials in vacuo (0.2 Torr). Da ta for th e
cor r esp on d in g a lcoh ol: 1H NMR δ 7.81-7.75 (3 H, m), 7.70
(1 H, d, J ) 7.3 Hz), 7.64-7.51 (12 H, m), 7.31 (1 H, d, J ) 6.7
Hz), 7.29 (1 H, t, 7 Hz), 7.12 (1 H, t, J ) 7.8 Hz), 7.09 (1 H, t,
J ) 7.3 Hz), 6.77 (1 H, d, J ) 7.9 Hz), 6.65 (1 H, d, J ) 7.7
Hz), 6.25 (1 H, d, J ) 10.7 Hz), 5.30 (1 H, d, J ) 23.1 Hz), 4.56
(1 H, d, J ) 23.1 Hz), 2.17 (1 H, d, J ) 10.9 Hz); 13C NMR δ
145.68, 144.00, 143.09, 142.29, 141.73, 140.89, 140.55, 138.13,
137.68, 135.31, 134.95, 133.71, 133.10, 132.94, 132.42, 130.73,
130.12, 130.02, 129.84, 129.15, 128.88, 128.85, 128.37, 128.07,
127.93, 127.85, 127.11, 126.87, 126.52, 126.36, 125.78, 125.45,
125.36, 125.12, 124.12, 123.56, 123.51, 73.70, 36.56; MS m/z
570 (M+), 568, 552. Da ta for 19: IR 3056, 1601 cm-1; 1H NMR
δ 7.81-7.75 (3 H, m), 7.69 (1 H, d, J ) 7.5 Hz), 7.64-7.49 (12
H, m), 7.31 (1 H, t, J ) 7.1 Hz), 7.29 (1 H, t, J ) 6.7 Hz), 7.14
(1 H, d, J ) 8.1 Hz), 7.10 (1 H, d, J ) 7.9 Hz), 6.76 (1 H, d, J
) 7.9 Hz), 6.66 (1 H, d, J ) 7.7 Hz), 6.54 (1 H, s), 5.38 (1 H, d,
J ) 22.4 Hz), 4.49 (1 H, d, J ) 22.4 Hz); 13C NMR δ 143.62,
143.46, 142.60, 141.63, 140.74, 140.60, 139.83, 137.98, 137.36,
135.67, 135.44, 133.82, 133.12, 133.09, 132.41, 130.63, 130.08,
129.91, 129.40, 128.99, 128.89, 128.80, 128.54, 128.19, 127.97,
127.91, 127.21, 126.92, 126.65, 126.52, 125.98, 125.84, 125.69,
125.40, 124.99, 124.20, 123.67, 123.57, 57.47, 36.56; MS m/z
590 and 588 (M+), 553; HRMS calcd for C44H25Cl 588.1645,
found 588.1621.
C
33H26O2: C, 87.20: H, 5.77. Found: C, 87.23; H, 5.76.
Keton e 16. To a mixture of 0.538 g of 15 (1.19 mmol), 50
mL of acetone, 5 mL of THF, and 4 mL of water was added
0.047 g of p-toluenesulfonic acid monohydrate (0.25 mmol). The
resulting mixture was heated at 56 °C, and the progress of
the reaction was monitored by TLC. After 23 h, the reaction
mixture was allowed to cool to room temperature and concen-
trated in vacuo. The yellow solid residue was dissolved in 100
mL of methylene chloride, and water (50 mL) was added. The
organic layer was separated, washed with a saturated aqueous
NaHCO3 solution and water, dried over MgSO4, and concen-
trated. The residue was purified by flash column chromatog-
raphy (silica gel/2% diethyl ether in hexanes) to afford 0.407
g (1.11 mmol, 93% yield) of 16 as a yellow solid: Rf 0.26
(hexanes/diethyl ether ) 8:1); mp 277-279 °C; IR 1706, 823,
728 cm-1; 1H NMR δ 7.87 (1 H, d, J ) 8.1 Hz), 7.81 (1 H, d, J
) 6.9 Hz), 7.67-7.46 (8 H, m), 7.41 (1 H, d, J ) 9.1 Hz), 7.26
(1 H, td, J ) 7.5 and 0.9 Hz), 7.05 (1 H, t, J ) 7.5 Hz), 6.65 (1
H, d, J ) 7.9 Hz), 4.34 (2 H, s); 13C NMR δ 193.94, 143.88,
141.57, 141.43, 140.58, 138.72, 138.28, 137.71, 137.27, 133.67,
130.69, 129.29, 129.23, 128.84, 128.33, 127.36, 127.19, 127.12,
126.59, 125.20, 124.54, 124.29, 123.33, 122.32, 34.86; MS m/z
368 (M+), 339; HRMS calcd for C28H16O 368.1201, found
368.1195.
Hyd r oca r bon 20. The propargylic alcohol 18 (0.196 g, 0.344
mmol) was converted to the chloride 19, and the resulting
crude product was concentrated and then used directly for
reduction without further purification. Reduction by sodium
borohydride was carried out by using the procedure described
for the ketal 15 to afford 0.090 g (0.16 mmol, 47% yield) of 20
as a yellow solid: Rf 0.32 (hexanes/diethyl ether ) 8:1); mp
(sealed tube) 318-320 °C; IR (KBr) 1598, 1422, 1363, 773, 735,
P r op a r gylic Alcoh ol 18. Cerium(III) chloride heptahy-
drate (CeCl3‚7H2O, 0.596 g, 1.60 mmol) was heated in a flask
with stirring at 150 °C in vacuo (0.2 Torr) for 2 h. The flask
was then allowed to cool to room temperature, and THF (6
mL) was introduced. After 2 h of stirring, the resulting white
suspension was cooled to -78 °C. In a separate flask, a solution
of the lithium acetylide 8 was prepared by adding 0.63 mL of
a 2.5 M solution of n-butyllithium (1.58 mmol) in hexanes to
a solution of 0.323 g of 1-(2-ethynylphenyl)-2-phenylethyne
(1.60 mmol) in 3 mL of THF at -78 °C. After 0.5 h of stirring,
the resulting lithium acetylide 8 was introduced via cannula
to the cerium(III) chloride suspension at -78 °C. After an
additional 0.5 h of stirring, a solution of 0.295 g of the ketone
16 (0.80 mmol) in 165 mL of THF was added via cannula, and
the mixture was allowed to warm to room temperature. After
16 h, 6 mL of water was introduced, and the reaction mixture
was concentrated in vacuo. Water (100 mL) and diethyl ether
(200 mL) were added, and the organic layer was separated,
washed with water, dried over MgSO4, and concentrated. The
residue was purified by flash column chromatography (silica
gel/10% diethyl ether in hexanes) to afford 0.376 g (0.66 mmol,
83% yield) of 18 as a yellow solid: Rf 0.46 (hexanes/diethyl
1
698 cm-1; H NMR δ 7.79 (2 H, d, J ) 8.7 Hz), 7.68-7.54 (14
H, m), 7.29 (2 H, t, J ) 7.3 Hz), 7.10 (2 H, t, J ) 7.5 Hz), 6.78
(2 H, d, J ) 7.9 Hz), 4.69 (4 H, s); 13C NMR δ 143.13, 142.05,
140.49, 140.05, 138.15, 134.88, 132.64, 131 68, 130.11, 128.79,
127.89, 127.07, 126.80, 126.66, 126.42, 125.52, 125.02, 124.41,
123.58, 36.80; MS m/z 554 (M+), 477; HRMS calcd for C44H26
554.2035, found 554.2035.
Ack n ow led gm en t. The financial support of the
National Science Foundation (CHE-9618676) is grate-
fully acknowledged.
Su p p or tin g In for m a tion Ava ila ble: Experimental pro-
cedures and spectroscopic data for 1-(2-bromophenyl)-2-phen-
ylethyne, 1-phenyl-2-[2-(trimethylsilylethynyl)phenyl]ethyne,
1
and 1-(2-ethynylphenyl)-2-phenylethyne and H and 13C NMR
spectra for 1-(2-bromophenyl)-2-phenylethyne, 1-phenyl-2-[2-
(trimethylsilylethynyl)phenyl]ethyne, 1-(2-ethynylphenyl)-2-
phenylethyne and compounds 9, 14-16, 18-20, and the
corresponding alcohol of 19. This material is available free of
charge via the Internet at http://pubs.acs.org.
ether ) 1:1); mp 130-132 °C; IR 3526, 2215, 1494, 756 cm-1
;
1H NMR δ 7.91 (1 H, d, J ) 7.1 Hz), 7.83 (1 H, d, J ) 7.9 Hz),
7.71 (1 H, d, J ) 9.1 Hz), 7.65-7.43 (10 H, m), 7.38-7.12 (8
J O9911903