Synthesis and structures of helical polycyclic aromatic hydrocarbons bearing aryl substituents at the most sterically hindered positions

Article abstract of DOI:10.1016/j.tet.2007.11.073

A three-step synthetic sequence starting from condensation between a benzannulated enediyne and an aryl tert-butyl ketone was established to provide easy access to angularly fused polycyclic aromatic hydrocarbons bearing one or two aryl substituents at th

Full text of DOI:10.1016/j.tet.2007.11.073

Available online at www.sciencedirect.com
Tetrahedron 64 (2008) 1285e1293
www.elsevier.com/locate/tet
Synthesis and structures of helical polycyclic aromatic hydrocarbons
bearing aryl substituents at the most sterically hindered positions
*
Yanzhong Zhang, Jeffrey L. Petersen , Kung K. Wang
*
C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, WV 26506-6045, USA
Received 24 September 2007; received in revised form 19 November 2007; accepted 21 November 2007
Available online 24 November 2007
Abstract
A three-step synthetic sequence starting from condensation between a benzannulated enediyne and an aryl tert-butyl ketone was established
to provide easy access to angularly fused polycyclic aromatic hydrocarbons bearing one or two aryl substituents at the most sterically hindered
positions to cause helical twists. The dynamic behaviors involving the helix inversion and the restricted rotation of the aryl substituents were
investigated by temperature-dependent NMR studies. The X-ray structure of an indeno-fused 1-phenylpentahelicene derivative showed severe
distortion of the [5]helicene system from planarity.
Ó 2007 Elsevier Ltd. All rights reserved.
Keywords: Helical polycyclic aromatic hydrocarbons; Benzannulated enyneeallenes; Cascade biradical cyclization
1. Introduction
Ph
Ph
We recently reported an efficient synthetic pathway outlined
in Scheme 1 to produce 8 as an indeno-fused 11H-benzo[b]-
fluorene derivative.1 Condensation between pivalophenone (1)
and lithium acetylide 2 furnished the benzannulated enediynyl
alcohol 3, which was then reduced with triethylsilane in the
presence of trifluoroacetic acid to give the benzannulated ene-
diyne 4. Treatment of 4 with potassium tert-butoxide in reflux-
ing toluene then produced 8 via a sequence of cascade
reactions. Presumably, an initial 1,3-prototropic rearrangement
of 4 furnished the benzannulated enyneeallene 5, which then
underwent a Schmittel cyclization reaction to generate benzo-
fulvene biradical 6.2e7 A subsequent intramolecular radicale
radical coupling then gave the formal DielseAlder adduct 7
1.
O
Li
2
HO t-Bu
3, 94%
t-Bu
1
2. H2O
Ph
KO-t-Bu
Et3SiH
CF3CO2H
refluxing
toluene
t-Bu
H
4, 96%
Ph
Ph
t-Bu
C
t-Bu
Ph
5
6
Ph
H
* Corresponding authors. Tel.: þ1 304 293 3068x6441; fax: þ1 304 293
4904 (K.K.W.); Tel.: þ1 304 293 3435x6423; fax: þ1 304 293 4904 (to
whom correspondence concerning the X-ray structures should be addressed)
(J.L.P).
t-Bu
t-Bu
7
8, 90%
E-mail addresses: jeffrey.petersen@mail.wvu.edu (J.L. Petersen), kung.
wang@mail.wvu.edu (K.K. Wang).
Scheme 1.
0040-4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.11.073

1286
Y. Zhang et al. / Tetrahedron 64 (2008) 1285e1293
and, after a prototropic rearrangement, the indeno-fused 11H-
benzo[b]fluorene 8 in excellent yield. Similarly, by using ke-
tones 9 and 11 for condensation with 2 and a related binaphthyl
derivative, the synthetic sequence led to polycyclic aromatic
compounds 10 and 12, respectively (Scheme 2).8,9 In addition,
this synthetic pathway was also adopted for the preparation of
helical 4,5-diarylphenanthrenes and related derivatives.10e12
Furthermore, by using tetraacetylene 13 for condensation with
2 equiv of 1, the reaction sequence led to 1,2-bis[5-(11H-benzo-
[b]fluorenyl)]benzenes 16a and 16b as atropisomers (Scheme
3).13 We envisioned that by replacing the 3-phenanthryl group
of 11 with a 2-benzo[c]phenanthryl group, the synthetic se-
quence could lead to a dibenzo[c,g]phenanthrene ([5]helicene)
derivative bearing a phenyl substituent at the most sterically
hindered position to cause a helical twist. Helicenes and related
compounds have continued to attract considerable attention due
in part to their unusual structures and interesting optical and
electronic properties.14e25 The highly efficient assembly of
two benzo[b]fluorenyl units by employing tetraacetylene 13 to
initiate the reaction sequence also prompted us to explore the
use of other tetraacetylenes for the construction of helical poly-
cyclic aromatic hydrocarbons.
2. Results and discussion
The requisite 2-benzo[c]phenanthryl tert-butyl ketone (22)
was prepared as outlined in Scheme 4. Treatment of benzo[c]-
phenanthrene-2-carboxylic acid (21) with thionyl chloride to
produce the corresponding acid chloride followed by tert-
butylcopper, prepared from tert-butyllithium and CuBr$SMe2,
produced 22 in 64% yield. A synthetic procedure for carbox-
ylic acid 21 involving oxidation of 2-methylbenzo[c]phenan-
threne was reported previously.26 We used an alternative
synthetic sequence to prepare 21. The Wittig reaction between
2-(bromomethyl)naphthalene (17) and methyl 4-formylbenz-
oate (18), using lithium ethoxide as the base, produced ethyl
4-[2-(2-naphthalenyl)ethenyl]benzoate (19) as a mixture of
the cis and trans isomers (cis/trans¼4.5:5.5). A subsequent
photocyclization reaction27,28 furnished ethyl benzo[c]phenan-
threne-2-carboxylate (20), which then was hydrolyzed to give
21.
Ph
3 steps
84% overall yield
O
O
t-Bu
t-Bu
9
10
1. PPh3
2. LiOEt/EtOH
Ar
3 steps
60% overall yield
Ar = a binaphthyl
derivative
O
CH2Br
O
17
H
t-Bu
t-Bu
3.
11
12
O
OEt
19, 80%
cis:trans = 4.5:5.5
Scheme 2.
18
OMe
R
t-Bu
1. SOCl2
hν, I2
2. t-BuLi
O
O
.
1. 2 BuLi
O
CuBr SMe2
2. 2 equiv of 1
3. H2O
OR
t-Bu
20, R = Et, 74%
21, R = H, 96%
NaOH
Scheme 4.
22, 64%
13
R
t-Bu
Et3SiH
CF3CO2H
The use of 11 and 22 for condensation with 2 furnished the
benzannulated enediynyl alcohols 23and 25, respectively, which
werereducedwithtriethylsilaneinthepresenceof trifluoroacetic
acid to afford the benzannulated enediynes 24 and 26 (Table 1).
Treatment of 24 and 26 with potassium tert-butoxide in refluxing
toluene converted them to the indeno-fused benzo[c]phenan-
threne 27 and dibenzo[c,g]phenanthrene ([5]helicene]) 28,
respectively, with a phenyl substituent at the most sterically
hindered position in a single operation. The parent 1-phenylben-
zo[c]phenanthrene29,30 and10-phenyldibenzo[c,g]phenanthrene
(1-phenylpentahelicene)31 and related compounds29e33 were
prepared previously by photocyclization reactions. Minor
amounts of 29 (ca. 2%) and 30 (ca. 12%), derived from the intra-
molecular [2þ2] cycloaddition reactions of the corresponding
14, R = OH, 91%
15, R = H, 89%
t-Bu
t-Bu
KO-t-Bu
+
refluxing
toluene
5 h
t-Bu
t-Bu
16a
16b
16a + 16b = 72% (16a : 16b = 8 : 1)
Scheme 3.

Y. Zhang et al. / Tetrahedron 64 (2008) 1285e1293
1287
Table 1
Synthesis of benzo[c]phenanthrene 27 and dibenzo[c,g]phenanthrene 28
R
R
R
32a, R = H
32b, R = t-octyl
Benzannulated enediynyl
alcohols and enediynes
Phenanthrenes
I
I
Pd(PPh3)2Cl2
CuI, Et3N
Br
Br
Br
31
Br
Ph
33a, 83%; 33b, 70%
Ph
4
R
R
1
3
2
1. 2 n-BuLi
R
t-Bu
t-Bu
2. 2 I2
23, R = OH, 94%
24, R = H, 98%
27, 83%
I
I
34a, R = H; 34b, R = t-octyl
Ph
R
R
R
R
Ph
1
SiMe3
Pd(PPh3)2Cl2
CuI, Et3N
4
2
3
R
t-Bu
Me3Si
SiMe3
t-Bu
35a, 57%; 35b, 50%
25, R = OH, 87%
26, R = H, 89%
28, 78%
NaOH/MeOH
benzannulated enyneeallene precursors, were also produced as
observed previously.1,10,11
H
H
36a, R = H, 97%; 36b, R = t-octyl, 98%
Scheme 5.
Ph
Ph
Condensation between 36a and 2 equiv of pivalophenone
(1) produced the benzannulated enediynyl diol 37a, which
was readily reduced with triethylsilane in the presence of
trifluoroacetic acid to give 38a bearing two benzannulated
enediynyl units (Scheme 6). Treatment of 38a with potassium
tert-butoxide in refluxing toluene promoted two rounds of the
cascade cyclization reactions leading to polycyclic aromatic
hydrocarbon 39a having a 7-fused-ring system. Similarly,
39b was produced from 36b in three steps. Polycyclic
aromatic hydrocarbons 44a/b and 45a containing a 9-fused-
ring system and an 11-fused-ring system, respectively, were
likewise synthesized by employing 2 equiv of ketones 9 and
11 for condensation (Table 2).
Recorded on a 600 MHz NMR spectrometer, the proton
signal of the two hydrogens on the five-membered ring of
10 in CDCl3 appeared as a singlet at d 4.45.8 This observation
is consistent with the planar geometry of the indeno[2,1-b]-
phenanthrene ring system of 10 with the phenyl substituent
oriented roughly perpendicular to the phenanthrene ring as
observed in the X-ray structure (Fig. 1).40
t-Bu
t-Bu
29
30
It is worth noting that the intramolecular radicaleradical
coupling reaction of the biradicals derived from 24 and 26
involved preferentially the 4-position of the phenanthryl
ring9 and the 1-position of the benzo[c]phenanthryl ring to
produce the angularly fused 27 and 28, respectively. Such
a preference is reminiscent of what was observed in 10 in
which only the a-position of the naphthyl ring was attacked.
Attaching the b-position to form an indeno-fused anthracene
derivative did not appear to occur. The regioselectivity was
attributed to the higher reactivity of the a-position than the
b-position of naphthalene in radical addition.34,35 A similar
preference could also account for the formation of the angu-
larly fused 27 and 28.
Tetraacetylene 36a was prepared from 1,5-dibromo-2,4-
diiodobenzene (31)36,37 to test the feasibility of assembling
two benzannulated enediynyl alcohol units for the synthesis
of helical polycyclic aromatic hydrocarbons (Scheme 5).
The Sonogashira reactions between 31 and 2 equiv of phenyl-
acetylene (32a) produced 33a as reported previously.38 Trans-
formation of 33a to diiodide 34a followed by Sonogashira
reactions with 2 equiv of (trimethylsilyl)acetylene furnished,
after desilylation, 36a. Similarly, tetraacetylene 36b bearing
two sterically demanding 1,1,3,3-tetramethylbutyl (tert-octyl)
groups was prepared by using 32b39 for the initial Sonogashira
reactions with 31.
Interestingly, the proton signals of the methylene hydrogens
of 27 in CDCl3, also recorded on a 600 MHz NMR spectrometer
at 25 ꢀC, appeared as an AB quartet at d 4.55 and 4.34 with a cou-
pling constant of 20.7 Hz, indicating that the indeno-fused ben-
zo[c]phenanthrene ring system with the phenyl substituent at
the most sterically hindered position is nonplanar, and the rate
of racemization is relatively slow on the NMR time scale. As
a result, the methylene hydrogens are diastereotopic, exhibiting

1288
Y. Zhang et al. / Tetrahedron 64 (2008) 1285e1293
R
R
R
R
1. 2 n-BuLi
2. 2 1
3. H2O
Et3SiH
36a or 36b
CF3CO2H
HO t-Bu
OH
H
t-Bu
H
t-Bu
t-Bu
37a, R = H, 87%; 37b, R = t-octyl, 47%
38a, R = H, 85%; 38b R = t-octyl, 85%
H
H
KO-t-Bu
refluxing
toluene
or
t-Bu
t-Bu
t-Bu
t-Bu
39a, 78%
39b, 71%
Scheme 6.
a large geminal coupling constant. The helical nature of the
structures of several 1-phenylbenzo[c]phenanthrene derivatives
was established by temperature-dependent NMR studies
earlier.30 The rate of racemization with the phenyl group
moving from one side of the helical twist to the other side was
determined to be ca. 16 kcal/mol. The well resolved AB quartet
of the proton signals of the methylene hydrogens of 27 also pro-
vided an opportunity to determine the activation barrier of race-
mization by temperature-dependent NMR studies. However, the
AB signals of 27 in 1,1,2,2-tetrachloroethane-d2, recorded on
a 270 MHz NMR spectrometer, remained well separated and
exhibited essentially no line broadening at 125 ꢀC, indicating
that the rate of the hezlix inversion is relatively slow on the
NMR time scale. DGrac of 27 is estimated to be at least
19.4 kcal/mol on the basis of the AB signals at d 4.60 and
4.39 (dAꢁdB¼56.6 Hz) with a coupling constant of 20.7 Hz at
125 ꢀC. The higher energy barrier for racemization than those
of the earlier cases may be attributed to the buttressing effect
of the fused indeno group and the tert-butyl substituent in 27
as observed previously in related systems.10
The 1H NMR spectrum of 27 in CDCl3 recorded on
a 600 MHz NMR spectrometer at 25 ꢀC also showed four broad
humps at d 8.01, 7.33, 6.72, and 6.07. At ꢁ20 ꢀC, the signals at
d 8.01 and 6.07 became doublets and the signals at d 7.33 and
6.72 became triplets, attributable to the ortho and meta hydro-
gens on the phenyl substituent, respectively. The fact that four
separate signals were observed suggests that rotation around
the carbonecarbon single bond attaching the phenyl substituent
to the benzo[c]phenanthrene ring system is restricted on the
NMR time scale. The signals of the ortho hydrogens coalesced
at ca. 60 ꢀC and the signals of the meta hydrogens coalesced at
ca. 50 ꢀC, corresponding to a rotational barrier of ca. 14.5 kcal/
Table 2
Synthesis of helical polycyclic aromatic hydrocarbons 44a, 44b, and 45a
Benzannulated enediynyl diols and enediynes
Polycyclic aromatic hydrocarbons
R
R
R
R
R1
t-Bu
t-Bu
R1
t-Bu
t-Bu
40a, R = H, R1 = OH, 74%; 41a, R = R1 = H, 85%
44a, R = H, 72%
44b, R = t-octyl, 71%
40b, R = t-octyl, R1 = OH, 46%; 41b, R = t-octyl, R1 = H, 78%
H
H
R1
t-Bu
t-Bu
t-Bu
42a, R1 = OH, 73%; 43a, R1 = H, 84%
R1
t-Bu
45a, 70%

Y. Zhang et al. / Tetrahedron 64 (2008) 1285e1293
1289
Figure 1. Perspective view of the molecular structures of 10 and 28 with the thermal ellipsoids scaled to enclose 30% probability.
mol, which is slightly higher than the rotational barriers of ca.
13 kcal/mol of several other 1-phenylbenzo[c]phenanthrene
derivatives reported earlier.30
hydrogens appeared as a triplet at d 7.35 (J¼7.2 Hz), indicating
relatively free rotation around the carbonecarbon single bonds
attaching the phenyl substituents to the 7-fused-ring system.
However, in the case of 39b having two tert-octyl groups at
the para positions of the phenyl substituents, the proton signals
of the methylene hydrogens on the five-membered rings
appeared as an AB quartet at d 4.58 (J¼21.6 Hz) and 4.44
(J¼21.6 Hz), indicating that the rate of racemization is slow
on the NMR time scale. Apparently, the sterically demanding
tert-octyl groups impede the helix inversion. In addition, rota-
tion around the carbonecarbon single bonds attaching the
two 4-tert-octylphenyl substituents to the 7-fused-ring system
is also restricted on the NMR time scale, and the proton signals
from the ortho and meta hydrogens became too broad to be
detected at 25 ꢀC. However, at ꢁ25 ꢀC, four additional signals
appearing at d 6.70, 7.08, 7.20, and 7.55, attributable to the two
ortho hydrogens and the two meta hydrogens on each of the
4-tert-octylphenyl substituent, were clearly discernible.
Compared to 27, the structural distortion of 28 with an
additional fused benzene ring could be expected to be even
more profound. The X-ray structure of 28 (Fig. 1)40 shows
that the indeno-fused dibenzo[c,g]phenanthrene ([5]helicene)
skeleton is severely twisted to minimize unfavorable van der
Waals contact with the p electrons of the phenyl substituent
at the most sterically hindered position. The acute dihedral
angle between the mean planes of the benzene ring bearing
the phenyl substituent and the benzene ring at the other end
of the [5]helicene system is a pronounced 58.4ꢀ from planar-
ity. The phenyl substituent is oriented at an angle of 60.6ꢀ
from the mean plane of the benzene ring where it is attached.
As observed in 27 the AB quartet signals of the methylene
hydrogens of 28 in 1,1,2,2-tetrachloroethane-d2 at d 4.63 and
4.35 (dAꢁdB¼77.8 Hz, J¼21.1 Hz), recorded on a 270 MHz
NMR spectrometer, remained well separated and exhibited
essentially no line broadening at 125 ꢀC, corresponding to
a DGzrac of at least 19.3 kcal/mol. The proton signals of the
ortho hydrogens on the phenyl substituent appeared as dou-
blets at d 6.43 and 5.75, whereas those of the meta hydrogens
appeared as overlapping triplets at d 6.56 and 6.54. The coa-
lescence temperature of the ortho hydrogens was determined
to be at 100 ꢀC, corresponding to a higher rotational barrier
of 17.5 kcal/mol than the rotational barrier of 14.5 kcal/mol
of 27.
Recorded on a 600 MHz NMR spectrometer, the proton
signal of the methylene hydrogens on the five-membered rings
of 39a in CDCl3 appeared as a singlet at d 4.52, indicating that
the rate of racemization is relatively fast on the NMR time
scale. Apparently, the two phenyl substituents in 39a are rela-
tively far apart, allowing them to move pass each other easily
from one side of the helical twist to the other side. As a result,
the proton signal of the methylene hydrogens appeared as a
singlet. In addition, only one proton signal from the four ortho
hydrogens on the phenyl substituents was observed as a doublet
at d 7.06 (J¼7.8 Hz) and one proton signal from the four meta
As in the case of 39a, the methylene hydrogens on the five-
membered rings of 44a in CDCl3 appeared as a singlet at d 4.47,
indicating that the rate of racemization is also relatively fast on
the NMR time scale. Again, only one proton signal from the
ortho hydrogens and one proton signal from the meta hydro-
gens on the phenyl substituents were observed at d 6.99 (d,
J¼8.4 Hz) and 7.17 (t, J¼7.5 Hz), respectively. As expected,
the methylene hydrogens on the five-membered rings of 44b
in CDCl3 appeared as an AB quartet at d 4.45 (J¼21.6 Hz)
and 4.43 (J¼21.6 Hz) at 25 ꢀC. Two broad humps at d 6.95
and 7.28 attributable to the ortho and meta hydrogens on the
4-tert-octylphenyl substituents were also observed.
In the case of 45a, one set of an AB quartet signals of the
methylene hydrogens on the five-membered rings at d 4.53
(J¼21.0 Hz) and 4.44 (J¼21.0 Hz) was observed. This is remi-
niscent of what was observed in 27, which possesses a relatively
stable helical configuration of 1-phenylbenzo[c]phenanthryl
group on the NMR time scale. On the other hand, the helical
configuration due to the steric interactions between the two
phenyl substituents is less likely to be stable, and the helix inver-
sion could occur rapidly as observed in the cases of 39a and 44a.

1290
Y. Zhang et al. / Tetrahedron 64 (2008) 1285e1293
The presence of two helical subunits of 1-phenylbenzo[c]phe-
nanthryl group in 45a makes it possible for 45a to exist as
a P,M-(meso) compound with the two phenyl substituents on
the same side of the 11-fused-ring system or as a P,P- and
M,M-racemic mixture with the two phenyl substituents on the
opposite sides. The fact that only one set of AB quartet signals
was observed indicates that either the meso compound or the
racemic mixture was produced preferentially. At 25 ꢀC, very
broad humps of the ortho and meta hydrogens of the phenyl
substituents were observed. At ꢁ20 ꢀC, two signals at d 5.71
(d, J¼7.2 Hz,) and 7.72 (overlapping signal) attributable to
the ortho hydrogens and two signals at d 6.13 (t, J¼7.2 Hz)
and 6.60 (t, J¼7.2 Hz) attributable to the meta hydrogens could
be clearly discerned.
excess thionyl chloride was removed in vacuo to furnish the
crude 3-phenanthrenecarbonyl chloride. To a suspension of
0.562 g of CuBr$SMe2 (2.71 mmol) in 17 mL of THF was
added 1.6 mL of a 1.7 M solution of tert-butyllithium
(2.71 mmol) in pentane at ꢁ50 ꢀC. After 30 min of stirring,
a solution of the crude 3-phenanthrenecarbonyl chloride in
15 mL of THF was introduced dropwise via cannula. After
an additional 4 h at ꢁ50 ꢀC, the reaction mixture was allowed
to warm to room temperature and treated with 20 mL of a
saturated aqueous ammonium chloride solution. The organic
layer was separated, and the aqueous layer was back extracted
with diethyl ether. The combined organic layers were washed
with brine and water, dried over sodium sulfate, and concen-
trated. Purification by flash column chromatography (silica
gel/20% diethyl ether in hexanes) afforded 0.558 g of 11
(2.13 mmol, 95%) as an orange solid. Mp 57e59 ꢀC; IR 1667,
3. Conclusion
1
842 cmꢁ1; H NMR d 9.13 (1H, s), 8.64 (1H, d, J¼7.9 Hz),
Several helical polycyclic aromatic hydrocarbons bearing
aryl substituents at the most sterically hindered positions
were synthesized. The efficiency of the three-step synthetic
sequence coupled with the ready availability of the starting
benzannulated enediynes and aryl tert-butyl ketones make
the process especially attractive for the construction of helical
molecules. The convergent approach could also allow the
synthetic sequence to be easily adopted for the preparation
of other helical molecules bearing diverse structural features.
7.93 (1H, dd, J¼8.2, 1.4 Hz), 7.76 (2H, t, J¼8.7 Hz), 7.67e7.51
(4H, m), 1.50 (9H, s); 13C NMR d 209.0, 136.2, 133.4, 132.2,
130.5, 129.6, 128.85, 128.78, 128.1, 127.09, 127.03, 126.2, 125.6,
123.2, 122.6, 44.4, 28.3; MS m/z 262 (Mþ), 205, 177.
4.3. 2-Benzo[c]phenanthryl tert-butyl ketone (22)
The same procedure was repeated as described for 11
except that 0.264 g (0.97 mmol) of benzo[c]phenanthrene-
2-carboxylic acid (21) was heated with 17 mL of thionyl
chloride under reflux for 12 h to furnish the crude benzo[c]-
phenanthrene-2-carbonyl chloride. The acid chloride was treated
with tert-butylcopper, prepared from 0.241 g of CuBr$SMe2
(1.16 mmol) and 0.68 mL of a 1.7 M solution of tert-butyllithium
(1.16 mmol) in pentane, to afford 0.193 g of 22 (0.62 mmol,
64%) as an orange solid. Mp 68e70 ꢀC; IR 1668,
4. Experimental
4.1. General
All reactions were conducted in oven-dried (120 ꢀC) glass-
ware under a nitrogen atmosphere. Diethyl ether and tetrahy-
drofuran (THF) were distilled from benzophenone ketyl prior
to use. n-Butyllithium (2.5 M) in hexanes, tert-butyllithium
(1.7 M) in pentane, CuBr$SMe2, triethylsilane, trifluoroacetic
acid, potassium tert-butoxide, 2-naphthoyl chloride, 3-acetyl-
phenanthrene, 2-(bromomethyl)naphthalene (17), triphenyl-
phosphine, methyl 4-formylbenzoate (18), phenylacetylene
(32a), and (trimethylsilyl)acetylene were purchased from
chemical suppliers and were used as received. 1,5-Dibromo-
2,4-diiodobenzene (31),36,37 1-ethynyl-2-(2-phenylethynyl)-
benzene,10 and 1-ethynyl-4-(1,1,3,3-tetramethylbutyl)benzene
(32b)39 were prepared according to the reported procedures.
3-Phenanthrenecarboxylic acid was prepared from 3-acetylphe-
nanthrene as reported previously.41 Melting points were
uncorrected. Recrystallization of 10 from CH2Cl2/hexanes pro-
duced a single crystal suitable for X-ray structure analysis. 1H
(270 MHz) and 13C (67.9 MHz) NMR spectra were recorded
in CDCl3 using CHCl3 (1H d 7.26) and CDCl3 (13C d 77.0) as
internal standards unless otherwise indicated.
1
848 cmꢁ1; H NMR d 9.57 (1H, s), 9.03 (1H, d, J¼8.4 Hz),
8.07e7.97 (3H, m), 7.94 (1H, d, J¼8.4 Hz), 7.90 (2H, s), 7.84
(1H, d, J¼8.6 Hz), 7.77e7.63 (2H, m), 1.49 (9H, s); 13C NMR
d 208.8, 135.4, 134.6, 133.6, 131.2, 129.9, 129.2, 128.73,
128.66, 128.5, 128.2, 127.9, 127.7, 126.8, 126.7, 126.5, 126.2,
125.1, 44.2, 28.2; MS m/z 255 (Mþꢁ57), 226.
4.4. Benzannulated enediynyl alcohol 23
To a solution of 0.516 g of 1-ethynyl-2-(2-phenylethynyl)-
benzene (2.56 mmol) in 15 mL of THF at 0 ꢀC was added
1.0 mL of a 2.5 M solution of n-butyllithium (2.5 mmol) in
hexanes. After 30 min of stirring, a solution of 0.558 g of 11
(2.13 mmol) in 20 mL of THF was introduced via cannula,
and the reaction mixture was allowed to warm to room temper-
ature. After an additional 2 h, 20 mL of water was introduced,
and the reaction mixture was extracted with diethyl ether. The
combined organic extracts were washed with brine and water,
dried over sodium sulfate, and concentrated. Purification by
flash column chromatography (silica gel/20% diethyl ether
in hexanes) afforded 0.931 g of 23 (2.01 mmol, 94%) as
4.2. tert-Butyl 3-phenanthryl ketone (11)
To a flask containing 0.500 g (2.25 mmol) of 3-phenanthre-
necarboxylic acid41 was introduced 39 mL of thionyl chloride.
The reaction mixture was heated under reflux for 12 h. The
a white solid. IR 3546, 2213, 753 cmꢁ1 1H NMR d 9.32
;
(1H, s), 8.96 (1H, d, J¼7.7 Hz), 8.25 (1H, d, J¼8.2 Hz),
7.99 (1H, d, J¼6.9 Hz), 7.90e7.70 (7H, m), 7.60 (2H, d,

Y. Zhang et al. / Tetrahedron 64 (2008) 1285e1293
1291
J¼7.4 Hz), 7.44e7.28 (5H, m), 3.17 (1H, s), 1.44 (9H, s); 13
C
126.1, 125.7, 123.1, 95.8, 93.0, 88.6, 82.9, 51.2, 36.0, 27.9;
MS m/z 498 (Mþ), 441.
NMR d 140.3, 132.14, 132.10, 131.9, 131.5, 131.1, 130.4,
129.1, 128.4, 128.2, 128.03, 127.98, 127.86, 127.0, 126.9, 126.7,
126.4, 126.3, 125.8, 124.9, 122.75, 122.68, 121.4, 96.4, 93.4,
88.3, 84.8, 79.8, 39.9, 25.6.
4.8. 9-(1,1-Dimethylethyl)-15-phenyl-10H-
benz[c]indeno[1,2-h]phenanthrene (27)
4.5. Benzannulated enediyne 24
To 0.280 g of 24 (0.63 mmol) in 10 mL of anhydrous toluene
under a nitrogen atmosphere were added 0.077 g of potassium
tert-butoxide (0.69 mmol) and 0.48 mL of 2-methyl-2-propanol
(5.0 mmol). The reaction mixture was then heated under reflux
for 3 h. After the reaction mixture was allowed to cool to room
temperature, 10 mL of water and 20 mL of methylene chloride
were introduced. The organic layer was separated, dried over
sodium sulfate, and concentrated. Purification by flash column
chromatography (silica gel/5% diethyl ether in hexanes)
afforded 0.232 g of 27 (0.52 mmol, 83%) as a yellow solid.
To a solution of 0.114 g of 23 (0.25 mmol) and 0.043 g of
triethylsilane (0.37 mmol) in 10 mL of methylene chloride
was added 0.08 mL of trifluoroacetic acid (1 mmol). After
10 min of stirring at room temperature, a solution of 0.068 g
of sodium carbonate (0.64 mmol) in 10 mL of water was intro-
duced, and the reaction mixture was extracted with diethyl
ether. The combined organic extracts were washed with brine
and water, dried over sodium sulfate, and concentrated. Purifi-
cation by flash column chromatography (silica gel/5% diethyl
ether in hexanes) afforded 0.107 g of 24 (0.24 mmol, 98%) as
a yellow solid. IR 2214, 1493, 842, 756 cmꢁ1; 1H NMR d 8.90
(2H, m), 8.04e7.97 (1H, m), 7.94e7.81 (4H, m), 7.77e7.69
(4H, m), 7.55 (2H, d, J¼6.9 Hz), 7.44e7.22 (5H, m), 4.18
(1H, s), 1.35 (9H, s); 13C NMR d 137.6, 132.1, 132.0, 131.6,
130.8, 130.2, 129.7, 128.5, 128.4, 128.1, 128.0, 127.9, 127.8,
127.4, 126.53, 126.50, 126.4, 126.2, 125.7, 123.5, 123.1,
122.6, 95.7, 93.0, 88.6, 82.8, 51.1, 35.7, 27.9; MS m/z 448
(Mþ), 391, 207.
1
Mp 169e171 ꢀC; IR 1366, 831 cmꢁ1; H NMR d (600 MHz,
CDCl3, ꢁ20 ꢀC) 8.34 (1H, d, J¼8.4 Hz), 8.01 (1H, d, J¼
7.8 Hz), 7.84 (1H, d, J¼7.8 Hz), 7.76 (1H, t, J¼8.4 Hz), 7.75
(1H, t, J¼8.4 Hz), 7.62 (1H, d, J¼7.8 Hz), 7.55 (1H, d, J¼
8.4 Hz), 7.52 (1H, d, J¼7.8 Hz), 7.33 (1H, t, J¼7.5 Hz), 7.18
(1H, t, J¼7.2 Hz), 7.16 (1H, t, J¼7.2 Hz), 7.02 (1H, t,
J¼7.5 Hz), 6.97 (1H, t, J¼7.2 Hz), 6.88 (1H, t, J¼7.2 Hz),
6.72 (1H, t, J¼7.8 Hz), 6.27 (1H, d, J¼8.4 Hz), 6.07 (1H, d,
J¼7.8 Hz), 4.545 (1H, d, J¼21.6 Hz), 4.331 (1H, d, J¼
13
21.0 Hz), 1.84 (9H, s); C NMR d (150 MHz, CDCl3, 25 ꢀC)
144.4, 140.9, 140.7, 140.6, 139.0, 138.6, 134.6, 133.2, 131.5,
130.9, 130.6, 130.4, 130.1, 128.0, 127.7, 127.1, 126.8, 126.5,
126.0, 125.9, 125.5, 124.8, 124.4, 124.3, 124.2, 123.9, 122.3,
40.0, 38.2, 33.5; MS m/z 448 (Mþ), 433, 391; HRMS calcd
for C35H28 448.2191, found 448.2193.
In addition to 27, the formation of a minor amount (ca. 2%)
of the intramolecular [2þ2] cycloaddition adduct 29 was also
detected with characteristic 1H NMR signals (600 MHz,
CDCl3) at d 8.84 (1H, s), 8.40 (1H, d, J¼9.0 Hz), 8.12 (2H,
d, J¼8.4 Hz), 7.84 (1H, d, J¼7.8 Hz), 6.49 (1H, s, vinylic),
and 1.29 (9H, s) and a 13C NMR signal (150 MHz, CDCl3) at
d 76.1 attributable to the sp3 carbon on the four-membered
ring as observed previously in similar systems.10,11
4.6. Benzannulated enediynyl alcohol 25
The same procedure was repeated as described for 23 except
that 0.102 g of 22 (0.33 mmol) was treated with 2, prepared
from 0.079 g of 1-ethynyl-2-(2-phenylethynyl)benzene
(0.39 mmol) and 0.16 mL of a 2.5 M solution of n-butyllithium
in hexanes, to afford 0.146 g of 25 (0.28 mmol, 87%) as a white
solid. IR 3556, 2217, 730 cmꢁ1; 1H NMR d 9.58 (1H, s), 9.23
(1H, d, J¼8.4 Hz), 8.09 (1H, dd, J¼8.4, 1.7 Hz), 8.01 (1H, d,
J¼7.9 Hz), 7.95e7.82 (5H, m), 7.67e7.61 (2H, m), 7.57 (1H,
t, J¼7.4 Hz), 7.44e7.32 (5H, m), 7.28e7.12 (3H, m), 2.74
(1H, s), 1.24 (9H, s); 13C NMR d 140.1, 133.4, 132.7, 132.3,
132.1, 131.5, 131.1, 130.2, 129.1, 128.4, 128.3, 128.1, 128.0,
127.9, 127.6, 127.4, 127.07, 126.96, 126.91, 126.7, 126.2,
126.1, 125.9, 125.8, 125.1, 122.7, 96.5, 93.4, 88.3, 84.9, 80.0,
40.2, 25.7.
4.9. Indeno-fused dibenzo[c,g]phenanthrene 28
The same procedure was repeated as described for 27 except
that 0.120 g of 26 (0.24 mmol) was treated with a mixture of
0.030 g of potassium tert-butoxide (0.26 mmol) and 0.18 mL
of 2-methyl-2-propanol (1.92 mmol) in 10 mL of anhydrous tol-
uene under reflux for 3 h to afford 0.094 g of 28 (0.19 mmol,
4.7. Benzannulated enediyne 26
The same procedure was repeated as described for 24 except
that 0.140 g of 25 (0.27 mmol) was treated with 0.048 g of trie-
thylsilane (0.41 mmol) and 0.90 mL of trifluoroacetic acid
(1.08 mmol) in 10 mL methylene chloride to afford 0.121 g of
1
78%) as a yellow solid. Mp>250 ꢀC; IR 1366, 839 cmꢁ1; H
NMR d (600 MHz, CDCl3) 8.42 (1H, d, J¼8.4 Hz), 7.85 (1H,
d, J¼8.4 Hz), 7.81 (1H, d, J¼7.8 Hz), 7.76 (1H, d, J¼8.4 Hz),
7.618 (1H, d, J¼6.0 Hz), 7.605 (1H, d, J¼9 Hz), 7.52 (1H, d,
J¼8.4 Hz), 7.45 (1H, d, J¼7.8 Hz), 7.40 (1H, d, J¼8.4 Hz),
7.32 (1H, td, J¼7.5, 1.2 Hz), 7.12 (1H, ddd, J¼7.8, 6.6,
1.2 Hz), 7.08 (1H, td, J¼7.8, 0.8 Hz), 6.73 (2H, t, J¼7.5 Hz),
6.558 (1H, t, J¼8.4 Hz), 6.546 (1H, t, J¼7.8 Hz), 6.42 (1H, d,
J¼7.8 Hz), 6.04 (1H, d, J¼8.4 Hz), 5.76 (1H, d, J¼7.8 Hz),
4.58 (1H, d, J¼21.0 Hz), 4.28 (1H, d, J¼21.0 Hz), 1.97 (9H,
26 (0.24 mmol, 89%) as a yellow solid. IR 2217, 844 cmꢁ1
;
1H NMR d 9.23e9.17 (2H, m), 8.01 (1H, J¼7.9 Hz), 7.93e
7.75 (6H, m), 7.63e7.54 (3H, m), 7.45 (1H, tm, J¼7.8,
1.2 Hz), 7.36e7.27 (4H, m), 7.21 (1H, m), 7.16e7.08 (2H, m),
4.06 (1H, s), 1.17 (9H, s); 13C NMR d 137.4, 133.4, 132.4,
132.2, 132.0, 131.5, 131.0, 130.3, 129.7, 128.4, 128.1, 128.0,
127.9, 127.6, 127.5, 127.4, 127.3, 127.0, 126.7, 126.5, 126.3,

1292
Y. Zhang et al. / Tetrahedron 64 (2008) 1285e1293
s); 13C NMR d (150 MHz, CDCl3) 144.3, 141.0, 140.8, 139.3,
139.2, 138.3, 134.5, 132.7, 132.0, 131.8, 131.5, 131.4, 131.3,
129.5, 129.22, 129.18, 127.7, 127.0, 126.8, 126.6, 126.5,
126.4, 126.0, 125.74, 125.70, 125.67, 125.59, 125.45, 125.3,
125.04, 125.03, 123.82, 123.80, 122.1, 40.1, 38.3, 33.8;
MS m/z 498 (Mþ), 441, 363; HRMS calcd for C39H30
498.2348, found 498.2351. Recrystallization of 28 from
CH2Cl2/hexanes produced a crystal suitable for X-ray structure
analysis.
In addition to 28, the formation of a minor amount (ca. 12%)
of the intramolecular [2þ2] cycloaddition adduct 30 was also
detected with characteristic 1H NMR signals (600 MHz,
CDCl3) at d 9.28 (1H, s), 8.88 (1H, d, J¼8.4 Hz), 8.12 (2H,
d, J¼8.4 Hz), 7.99 (1H, d, J¼7.8 Hz), 6.51 (1H, s, vinylic),
and 1.27 (9H, s) and a 13C NMR signal (150 MHz, CDCl3) at
d 76.3 attributable to the sp3 carbon on the four-membered
ring as observed previously in similar systems.10,11
4.12. Polycyclic aromatic hydrocarbon 44a
The same procedure was repeated as described for 27 except
that a solution of 0.209 g of 41a (0.29 mmol) in 10 mL of anhy-
drous toluene was treated with 0.61 mL of a 1.0 M solution of
potassium tert-butoxide (0.61 mmol) in 2-methyl-2-propanol
and 0.43 mL of 2-methyl-2-propanol (4.64 mmol). The result-
ing mixture was heated under reflux for 3 h to afford 0.150 g
of 44a (0.21 mmol, 72%) as a yellow solid. IR 1459, 822,
699 cmꢁ1 1H NMR (600 MHz, CDCl3) d 8.24 (2H, d,
;
J¼9.6 Hz), 7.69 (2H, d, J¼7.8 Hz), 7.68 (1H, s), 7.47 (2H, d,
J¼9.0 Hz), 7.26 (2H, t, J¼8 Hz) 7.21 (2H, t, J¼7.8 Hz), 7.17
(4H, t, J¼7.5 Hz), 6.99 (4H, d, J¼8.4 Hz), 6.74 (2H, t,
J¼7.8 Hz), 6.58 (2H, d, J¼7.8 Hz), 6.44 (1H, s), 4.47 (4H, s),
1.83 (18H, s); 13C NMR (150 MHz, CDCl3) d 143.6, 140.7,
140.4, 139.2, 139.0, 138.7, 132.9, 132.4, 131.3, 131.0, 130.7,
130.3, 129.2, 127.3, 126.4, 125.7, 125.1, 122.8, 39.9, 38.5,
34.0; MS m/z 718 (Mþ); HRMS calcd for C56H46 718.3594,
found 718.3594.
4.10. Polycyclic aromatic hydrocarbon 39a
4.13. Polycyclic aromatic hydrocarbon 44b
The same procedure was repeated as described for 27 except
that a solution of 0.076 g of 38a (0.12 mmol) in 10 mL of anhy-
drous toluene was treated with 0.25 mL of a 1.0 M solution of
potassium tert-butoxide (0.25 mmol) in 2-methyl-2-propanol
and 0.18 mL of 2-methyl-2-propanol (1.93 mmol). The result-
ing mixture was heated under reflux for 3 h to afford 0.059 g
of 39a (0.09 mmol, 78%) as a yellow solid. IR 1368,
The same procedure was repeated as described for 27 except
that a solution of 0.024 g of 41b (0.025 mmol) in 10 mL of an-
hydrous p-xylene was treated with 0.03 mL of a 1.0 M solution
of potassium tert-butoxide (0.03 mmol) in 2-methyl-2-propanol
and 0.02 mL of 2-methyl-2-propanol (0.16 mmol). The result-
ing mixture was heated under reflux for 5 h to afford 0.017 g
of 44b (0.018 mmol, 71%) as a yellow solid. IR 1464,
761 cmꢁ1 1H NMR (600 MHz, CDCl3) d 8.54 (2H, d,
;
J¼8.4 Hz), 7.63 (1H, s), 7.41 (2H, t, J¼7.2 Hz), 7.35 (6H, t, J¼
1365 cmꢁ1 1H NMR (600 MHz, CDCl3) d 8.25 (2H, d,
;
7.2 Hz), 7.30 (2H, d, J¼8.4 Hz), 7.20 (2H, t, J¼7.5 Hz), 7.06
J¼9.6 Hz), 7.69 (2H, d, J¼7.8 Hz), 7.64 (1H, s), 7.48 (2H, d,
J¼9.6 Hz), 7.29 (2H, d, J¼8.4 Hz), 7.28 (4H, br), 6.95 (4H,
br), 6.92 (2H, d, J¼8.4 Hz), 6.72 (2H, td, J¼7.5, 1.2 Hz),
6.64 (1H, s), 4.45 (2H, d, J¼21.6 Hz), 4.43 (2H, d,
J¼21.6 Hz), 1.84 (2H, d, J¼15 Hz), 1.83 (18H, s), 1.70 (2H,
d, J¼15 Hz), 1.50 (6H, s), 1.28 (6H, s), 0.85 (18H, s); MS
m/z 942 (Mþ); HRMS calcd for C72H78 942.6098, found
942.6150.
(4H, d, J¼7.8 Hz), 6.65 (1H, s), 4.52 (4H, s), 1.89 (18H, s); 13
C
NMR (150 MHz, CDCl3) d 144.1, 140.3, 138.7, 138.5, 138.1,
137.7, 134.7, 132.5, 131.2, 130.3, 129.3, 127.7, 127.2, 127.0,
123.9, 123.1, 120.1, 119.4, 40.0, 38.8, 34.3; MS m/z
618 (Mþ), 561; HRMS calcd for C48H42 618.3281, found
618.3295.
4.11. Polycyclic aromatic hydrocarbon 39b
4.14. Polycyclic aromatic hydrocarbon 45a
The same procedure was repeated as described for 27 except
that a solution of 0.024 g of 38b (0.028 mmol) in 10 mL of an-
hydrous p-xylene was treated with 0.03 mL of a 1.0 M solution
of potassium tert-butoxide (0.03 mmol) in 2-methyl-2-propanol
and 0.02 mL of 2-methyl-2-propanol (0.16 mmol). The result-
ing mixture was heated under reflux for 5 h to afford 0.017 g
of 39b (0.020 mmol, 71%) as a yellow solid. IR 1466,
The same procedure was repeated as described for 27 except
that a solution of 0.155 g of 43a (0.19 mmol) in 10 mL of anhy-
drous toluene was treated with 0.40 mL of a 1.0 M solution of
potassium tert-butoxide (0.40 mmol) in 2-methyl-2-propanol
and 0.15 mL of 2-methyl-2-propanol (3.03 mmol). The result-
ing mixture was heated under reflux for 3.5 h to afford
0.109 g of 45a (0.13 mmol, 70%) as a yellow solid. IR 1365,
1365 cmꢁ1
;
1H NMR (600 MHz, CDCl3) d 8.53 (2H, d,
830 cmꢁ1 1H NMR (600 MHz, CDCl3) d 8.26 (2H, d,
;
J¼9.0 Hz), 7.59 (1H, s), 7.55 (2H, d, J¼7.8 Hz, at ꢁ25 ꢀC),
7.40 (2H, dd, J¼8.4, 1.2 Hz), 7.34 (2H, td, J¼7.8, 1.2 Hz), 7.20
(2H, d, J¼7.2 Hz, at ꢁ25 ꢀC), 7.17 (2H, t, J¼7.5 Hz), 7.08 (2H,
d, J¼7.2 Hz, at ꢁ25 ꢀC), 6.85 (1H, s), 6.70 (2H, d, J¼7.2 Hz, at
ꢁ25 ꢀC), 4.58 (2H, d, J¼21.6 Hz), 4.44 (2H, d, J¼21.6 Hz),
1.88 (18H, s), 1.81 (2H, d, J¼15 Hz), 1.79 (2H, d, J¼15 Hz),
1.72 (6H, s), 1.45 (6H, s), 0.77 (18H, s); MS m/z 842 (Mþ),
785; HRMS calcd for C64H74 842.5785, found 842.5751.
J¼9.0 Hz), 7.72 (2H, d, J¼7.2 Hz, at ꢁ20 ꢀC), 7.71 (1H, s),
7.68 (2H, d, J¼9.0 Hz), 7.67 (2H, d, J¼9.0 Hz), 7.48 (2H, d,
J¼7.2 Hz), 7.47 (2H, d, J¼9.0 Hz), 7.18 (2H, d, J¼8.4 Hz),
6.94 (2H, td, J¼7.2, 1.2 Hz), 6.60 (2H, t, J¼7.2 Hz, at
ꢁ20 ꢀC), 6.57 (2H, td, J¼7.5, 1.2 Hz), 6.40 (1H, s), 6.35 (2H,
t, J¼7.2 Hz), 6.13 (2H, t, J¼7.2 Hz, at ꢁ20 ꢀC), 5.71 (2H, d,
J¼7.2 Hz, at ꢁ20 ꢀC), 4.53 (2H, d, J¼21.0 Hz), 4.44 (2H, d,
J¼21.0 Hz), 1.84 (18H, s); 13C NMR (150 MHz, CDCl3)

Y. Zhang et al. / Tetrahedron 64 (2008) 1285e1293
1293
10. Li, H.; Petersen, J. L.; Wang, K. K. J. Org. Chem. 2001, 66, 7804e7810.
11. Dai, W.; Petersen, J. L.; Wang, K. K. Org. Lett. 2004, 6, 4355e4357.
12. Zhang, Y.; Petersen, J. L.; Wang, K. K. Org. Lett. 2007, 9, 1025e1028.
13. Yang, H.; Petersen, J. L.; Wang, K. K. Tetrahedron 2006, 62, 1231e1238.
14. Martin, R. H. Angew. Chem., Int. Ed. Engl. 1974, 13, 649e660.
15. Laarhoven, W. H.; Prinsen, W. J. C. Top. Curr. Chem. 1984, 125, 63e130.
d 143.7, 139.3, 138.98, 138.89, 138.4, 138.1, 133.4, 132.8,
130.5, 130.3, 130.20, 130.17, 130.09, 127.5, 126.9, 125.6,
125.3, 124.6, 124.0, 123.8, 121.8, 120.8, 119.4, 39.6, 38.2,
33.6; MS m/z 818 (Mþ), 761, 650; HRMS calcd for C64H50
818.3907, found 818.3916.
16. Meurer, K. P.; Vogtle, F. Top. Curr. Chem. 1985, 127, 1e76.
¨
17. Lovinger, A. J.; Nuckolls, C.; Katz, T. J. J. Am. Chem. Soc. 1998, 120,
264e268.
Acknowledgements
18. Grimme, S.; Harren, A.; Sobanski, F.; Vogtle, F. Eur. J. Org. Chem. 1998,
1491e1509.
¨
K.K.W. thanks the Petroleum Research Fund (38169-AC1),
administered by the American Chemical Society, and the
National Science Foundation (CHE-0414063) for financial
support. J.L.P. acknowledges the support (CHE-9120098)
provided by the National Science Foundation for the acquisi-
tion of a Siemens P4 X-ray diffractometer. The financial
support of the NSF-EPSCoR (1002165R) for the purchase of
a 600 MHz NMR spectrometer is gratefully acknowledged.
19. Fox, J. M.; Lin, D. J. Org. Chem. 1998, 63, 2031e2038.
20. Katz, T. Angew. Chem., Int. Ed. 2000, 39, 1921e1923.
~
´
21. Carreno, M. C.; Garcıa-Cerrada; Urbano, A. J. Am. Chem. Soc. 2001, 123,
7929e7930.
22. Schmuck, C. Angew. Chem., Int. Ed. 2003, 42, 2448e2452.
23. Urbano, A. Angew. Chem., Int. Ed. 2003, 42, 3986e3989.
´
24. Paruch, K.; Vyklicky, L.; Wang, D. Z.; Katz, T. J.; Incarvito, C.; Zakharov,
L.; Rheingold, A. L. J. Org. Chem. 2003, 68, 8539e8544.
´
´
´
´
ꢀ
ˇ
´
25. Teply, F.; Stara, I. G.; Stary, I.; Kollarovic, A.; Lustinec, D.; Krausova, Z.;
ˇ
Saman, D.; Fiedler, P. Eur. J. Org. Chem. 2007, 4244e4250.
Supplementary data
26. Newman, M. S.; Boden, H. J. Org. Chem. 1961, 26, 1759e1761.
27. Brooks, M. A.; Scott, L. T. J. Am. Chem. Soc. 1999, 121, 5444e5449.
28. Liu, L.; Yang, B.; Katz, T. J.; Poindexter, M. K. J. Org. Chem. 1991, 56,
3769e3775.
Experimental procedures and spectroscopic data for 19e21,
33a/b, 35a/b, 36a/b, 37a/b, 38a/b, 40a/b, 41a/b, 42a, and 43a,
1H and/or 13C NMR spectra of compounds 11, 19e28, 33a/b,
35a/be41a/b, 42a, 43a, 44a/b, and 45a, and the ORTEP draw-
ings of the crystal structures of 10 and 28. Supplementary data
associated with this article can be found in the online version, at
doi:10.1016/j.tet.2007.11.073.
29. Tinnemans, A. H. A.; Laarhoven, W. H. Tetrahedron Lett. 1973, 817e820.
30. Laarhoven, W. H.; Peters, W. H. M.; Tinnemans, A. H. A. Tetrahedron
1978, 34, 769e777.
31. Tinnemans, A. H. A.; Laarhoven, W. H. J. Am. Chem. Soc. 1974, 96,
4611e4616.
32. Laarhoven, W. H.; Boumans, P. G. F. Recul. Trav. Chim. Pays-Bas 1975,
94, 114e118.
33. Kelly, T. R.; Sestelo, J. P.; Tellitu, I. J. Org. Chem. 1998, 63, 3655e3665.
34. Tinnemans, A. H. A.; Laarhoven, W. H. J. Chem. Soc., Perkin Trans. 2
1976, 1115e1120.
References and notes
35. Tinnemans, A. H. A.; Laarhoven, W. H. J. Am. Chem. Soc. 1974, 96,
4617e4622.
1. Li, H.; Zhang, H.-R.; Petersen, J. L.; Wang, K. K. J. Org. Chem. 2001, 66,
6662e6668.
2. Schmittel, M.; Strittmatter, M.; Vollmann, K.; Kiau, S. Tetrahedron Lett.
1996, 37, 999e1002.
36. Hart, H.; Harada, K.; Du, C.-J. F. J. Org. Chem. 1985, 50, 3104e3110.
37. Goldfinger, M. B.; Crawford, K. B.; Swager, T. M. J. Am. Chem. Soc.
1997, 119, 4578e4593.
3. Schmittel, M.; Strittmatter, M.; Kiau, S. Angew. Chem., Int. Ed. 1996, 35,
1843e1845.
4. Schmittel, M.; Keller, M.; Kiau, S.; Strittmatter, M. Chem.dEur. J. 1997,
3, 807e816.
38. Price, D. W., Jr.; Dirk, S. M.; Maya, F.; Tour, J. A. Tetrahedron 2003, 59,
2497e2518.
39. Han, X.; Zhang, Y.; Wang, K. K. J. Org. Chem. 2005, 70, 2406e2408.
40. Crystallographic data of 10 and 28 have been deposited with the Cam-
bridge Crystallographic Data Centre. The CCDC nos. 661596 and
661597 have been assigned for the compounds 10 and 28, respectively.
Copies of the data can be obtained, free of charge, on application to
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [fax: þ44 1223
336033 or e-mail: deposit@ccdc.cam.ac.uk].
5. Schmittel, M.; Maywald, M. Chem. Commun. 2001, 155e156.
6. Schmittel, M.; Vavilala, C. J. Org. Chem. 2005, 70, 4865e4868.
7. Wang, K. K. Modern Allene Chemistry; Krause, N., Hashmi, A. S. K.,
Eds.; Wiley-VCH: Weinheim, Germany, 2004; Vol. 2, pp 1091e1126.
8. Yang, Y.; Dai, W.; Zhang, Y.; Petersen, J. L.; Wang, K. K. Tetrahedron
2006, 62, 4364e4371.
ˇ
ꢀ
41. Zabjek, A.; Petric, A. Tetrahedron Lett. 1999, 40, 6077e6078.
9. Yang, H.; Petersen, J. L.; Wang, K. K. Tetrahedron 2006, 62, 8133e8141.