Thermal and photochemical isomerization of tetraaryl tetrakis(trifluoromethyl)[4]radialenes

Article abstract of DOI:10.1021/jo990699v

The isomerization of tetraaryl tetrakis(trifluoromethyl)[4]radialenes was studied. When type II (all-Z) isomers of 5,6,7,8-tetraaryl-5,6,7,8- tetrakis(trifluoromethyl)[4]radialenes were heated in tetralin at 170-200 °C, isomerization occurred to give mixtures of four [4]radialenes in a ratio of ca. I:II:III:IV = 1:10:5:1. However, when the isomeric mixtures were heated in the solid state at the same temperature, selective isomerization took place to give type II isomers in good selectivity (>91%). Upon irradiation with light, the type II isomers first isomerized to mixtures of the four [4]radialene isomers (I:II:III:IV = 2:2:48:48) and then rearranged to cyclobuta[b]naphthalenes via a 6π-electrocyclic reaction followed by 1,3- hydrogen migration.

Full text of DOI:10.1021/jo990699v

J . Org. Chem. 2000, 65, 1615-1622
1615
Th er m a l a n d P h otoch em ica l Isom er iza tion of Tetr a a r yl
Tetr a k is(tr iflu or om eth yl)[4]r a d ia len es
Hidemitsu Uno,* Ken-ichi Kasahara, Nobumasa Nibu, Shin-ichi Nagaoka,† and Noboru Ono†
Advanced Instrumentation Center for Chemical Analysis and Department of Chemistry,
Faculty of Science, Ehime University, Matsuyama 790-8577, J apan
Received April 26, 1999
The isomerization of tetraaryl tetrakis(trifluoromethyl)[4]radialenes was studied. When type II
(all-Z) isomers of 5,6,7,8-tetraaryl-5,6,7,8-tetrakis(trifluoromethyl)[4]radialenes were heated in
tetralin at 170-200 °C, isomerization occurred to give mixtures of four [4]radialenes in a ratio of
ca. I:II:III:IV ) 1:10:5:1. However, when the isomeric mixtures were heated in the solid state at
the same temperature, selective isomerization took place to give type II isomers in good selectivity
(>91%). Upon irradiation with light, the type II isomers first isomerized to mixtures of the four
[4]radialene isomers (I:II:III:IV ) 2:2:48:48) and then rearranged to cyclobuta[b]naphthalenes via
a 6π-electrocyclic reaction followed by 1,3-hydrogen migration.
In tr od u ction
The cross-conjugated π-electron system of radialenes
is reported to show interesting properties such as ferro-
magnetism and multiredox potential.1 Although many
synthetic methods for accessing these compounds have
been reported so far, most of the successful examples are
limited to the preparation of highly symmetric radi-
alenes,1,2 where the isomerization and determination of
radialene isomers need not be considered. Even funda-
mental reactions of radialenes such as isomerization have
been hardly investigated, probably because of the dif-
ficulty of monitoring the progress of the reaction and of
determining the structure of the isomers. Generally, the
19F NMR technique is useful for monitoring the course
of reactions, if the molecules have a few fluorine atoms,
because of the wide chemical shifts, high nuclear sensi-
tivity, and transparency toward not only other parts of
molecules but also solvents. Moreover, the spatial prox-
imity between fluorine atoms and other NMR-sensitive
nuclei can be easily determined by through-space cou-
pling3 without using the NOE technique. We previously
succeeded in determining four isomers of 5,6,7,8-tet-
raaryl-5,6,7,8-tetrakis(trifluoromethyl)[4]radialenes us-
ing 19F NMR and revealed selective isomerization to the
type II (all-Z) isomer in the solid state.4 In this study,
we examined isomerization of [4]radialenes involving
photochemical rearrangement. For brevity, we used I, II,
III, and IV as the types of the four isomers analogously
to the porphyrin chemistry instead of 1E,2E,3E,4E,
1Z,2Z,3Z,4Z, 1Z,2Z,3E,4E, and 1Z,2E,3Z,4E (Figure 1).5
F igu r e 1. Four isomers of tertraayl tetrakis(trifluoromethyl)-
[4]radialenes.
Resu lts a n d Discu ssion
P r epar ation ofTetr aar yl Tetr akis(tr iflu or om eth yl)-
[4]r a d ia len es. 5,6,7,8-Tetraaryl-5,6,7,8-tetrakis(trifluor-
omethyl)[4]radialenes (3) were prepared by the coupling
reaction6 of the corresponding dibromostyrenes 1 or the
thermal dimerization of cumulenes 2 (Scheme 1).7 The
coupling reaction of 1 with Zn-CuBr was carried out
below -60 °C to give isomeric [4]radialenes 3 in addition
to cumulenes 2.8 The four isomers could be separated only
in the case of 3a by a combination of repeated silica gel
chromatography, preparative GPC, and fractional recrys-
tallization. In other cases, complete separation of the
isomers was not achieved partially as a result of the
instability of these radialenes, although isomeric mix-
tures of radialenes could be separated from other byprod-
ucts. The homogeneity of these [4]radialenes was unam-
biguously proven by thermal reversible isomerization
(vide post). During isolation, new signals appeared in 19F
† Department of Chemistry, Faculty of Science.
(1) Hopf, H.; Maas, G. Angew. Chem., Int. Ed. Engl. 1992, 31, 931
and references therein.
(2) Kaftory, M.; Botoshansky, M.; Hyoda, M.; Watanabe, T.; Toda,
F. J . Org. Chem. 1999, 64, 2287. Boese, R.; Bra¨unlich, G.; Gotteland,
J .-P.; Hwang, J .-T.; Troll, C.; Vollhardt, K. P. C. Angew. Chem., Int.
Ed. Engl. 1996, 35, 995. Lange, T.; Gramlich, V.; Amrein, W.;
Diederich, F.; Gross, M.; Boudon, C.; Gisselbrecht, J .-P. Angew. Chem.,
Int. Ed. Engl. 1995, 34, 805. van Loon, J .-D.; Seiler, P.; Diederich, F.
Angew. Chem., Int. Ed. Engl. 1993, 32, 1187. Iyoda, M.; Kurata, H.;
Oda, M.; Okubo, C.; Nishimoto, K. Angew. Chem., Int. Ed. Engl. 1993,
32, 89.
(3) Hilton, J .; Sutcfiffe, L. H. Prog. Nucl. Magn. Reson. Spectrosc.
1975, 10, 27.
(4) Uno, H.; Nibu, N.; Yamaoka, Y.; Mizobe, N. Chem. Lett. 1998,
105.
(5) Nader, F. W.; Wacker, C.-D.; Irgartinger, H.; Huber-Patz, U.;
J ahn, R.; Rodewald, H. Angew. Chem., Int. Ed. Engl. 1985, 24, 852.
(6) Uno, H.; Nibu, N.; Mizobe, N. Bull. Chem. Soc. J pn. 1999, 72,
1365.
(7) Koster, S. K.; West, R. J . Org. Chem. 1975, 40, 2300.
(8) Morken, P. A.; Bachand, P. C.; Swenson, D. C.; Burton, D. J . J .
Am. Chem. Soc. 1993, 115, 5430.
10.1021/jo990699v CCC: $19.00 © 2000 American Chemical Society
Published on Web 02/19/2000

1616 J . Org. Chem., Vol. 65, No. 6, 2000
Uno et al.
Sch em e 1
Ta ble 1. Th er m a l Dim er iza tion of Cu m u len es 2
temp
°C
time
h
yield
%
ratioa
I:II:III:IV
a
run
substrate
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
2a
2a
2b
2b
2c
2cb
2d
2d
2e
2ed
2ed
2e
2f
150
200
150
200
150
200
150
200
150
170
200
200
150
170
200
24
2
24
2
24
2
24
2
90
80
90
90
85
40c
70
60
0
3:58:29:10
5:45:42:8
6:68:19:7
3:58:29:10
2:64:31:3
4:62:28:6
3:64:24:9
2:71:22:5
24
48
4
90c
80c
80
0
6:54:24:14
3:61:29:7
1:95:3:1
4
24
48
2
2f
2f
40
45
type II >90e
3:61:29:7
a
The yield and ratio were roughly calculated from 19F NMR
spectra of the reaction mixture. The purity was 70%. c The yield
b
was based on the purity of cumulene. The purity was 56%. e The
d
isomeric ratio could not be estimated.
F igu r e 2. Four isomers of [4]radialenes: (a) 3a -I; (b) 3a -II;
(c) 3a -III; (d) 3a -IV.
NMR spectra in some cases. One of the newly formed
compounds in the reaction of 1d could be isolated and
its structure was determined to be trans-anti-1,3-bis-
(vinylidene)cyclobutane 4d by X-ray analysis (see Sup-
porting Information). This 1,3-bis(vinylidene)cyclobutane
4 would be derived from cumulenes, since the formation
of this skeleton has been reported in the photodimeriza-
tion of tetraaryl cumulenes in the solid state.9 The
coupling reaction of cyclohexyl derivative 1g afforded a
complex mixture, from which [3]radialenes 5g, in addi-
tion to [3]cumulenes 2g and [4]radialenes 3g, were
obtained in an impure form by repeated column chro-
matography and GPC. The cumulenes 2 were also
converted to the [4]radialenes 3 by heating neat at 150-
200 °C for 2-48 h (Table 1). The isomeric ratios and
yields were determined by 19F NMR analysis of the
reaction mixtures. In all cases except for runs 12 and 14,
all of the isomers of [4]radialenes 3 were formed, as well
as unidentified products. In runs 12 and 14, type II
isomers were predominantly formed. In these cases, the
starting materials 2e and 2f did not melt,10 whereas in
other cases the starting cumulenes melted gradually or
immediately. Pure type II isomers of [4]radialenes 3 were
easily obtained in 15-40% yields by recrystallization of
the chromatographed mixtures.
Str u ctu r e Deter m in a tion of [4]Ra d ia len e Iso-
m er s. The stereochemistry of [4]radialene isomers 3a
was unambiguously determined by 19F and 1H NMR
(Figure 2). Type III and IV isomers were easily identified
because of their low symmetricity. Two singlets and a
pair of quartets (ca. J ) 10 Hz) with the same intensity
were observed in the type III isomers and two singlets
were seen in the type IV isomers. On the other hand,
the type I and II isomers could not be distinguished by
19F NMR. Fortunately, the type I and II isomers (3a -I
and 3a -II) were assigned by 1H NMR analysis on the
basis of an upfield shift of the aromatic protons of the
type II isomer 3a -II due to the anisotropic effect of the
stacking aromatic rings. All of the protons of four phenyl
groups in 3a -II and the protons of two phenyl groups in
3a -III and 3a -IV appeared at higher fields than chloro-
form, whereas all of the aromatic protons of 3a -I were
at lower fields. This assignment was confirmed by X-ray
(9) Berkovitch-Yellin, Z.; Lahav, M.; Leiserowitz, L. J . Am. Chem.
Soc. 1974, 96, 918. Buddrus, J .; Bauer, H.; Herzog, H. Chem. Ber. 1988,
121, 295.
(10) In the solid state, the type II [4]radialene was reported to be
predominantly formed in the thermal dimerization of dimethyl 2,5-
diphenylhexa-2,3,4-trienedioate; see ref 5.

Isomerization of [4]Radialenes
J . Org. Chem., Vol. 65, No. 6, 2000 1617
Ta ble 2. Th er m a l Isom er iza tion of [4]Ra d ia len es 3
conditions
sub-
starting
temp
°C
final
I:II:III:IV
run strate I:II:III:IV
solvent
time
1
3a
0:97:3:0
tetralina
170 5 min
3:70:24:3
30 min 6:57:32:5
20 h
170 24 h
150 24 h
150 2 h
70 h
7:56:32:5
2:87:9:2
2:95:3:tr
1:64:2:33
1:97:1:1
2:2:85:11
2:83:12:3
5:61:28:6
1:96:2:1
4:70:22:4
1:96:2:1
1:93:5:1
5:77:9:9
7:91:1:1
3:63:26:8
tr:97:3:tr
2
3
4
3a
3a
3a
7:56:32:5
79:2:14:5
0:0:0:>99
neat
neat
neat
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
3a
3a
3b
3b
3c
3c
3c
3c
3d
3e
3e
3f
2:2:85:11
2:2:85:11
0:>99:0:0
5:61:28:6
0:98:2:0
4:56:33:7
4:56:33:7
4:56:33:7
1:67:23:9
0:>99:0:0
3:63:26:8
0:>99:0:0
5:59:29:7b
neat
150 24 h
200 2 h
170 23 h
170 6 h
100 112 h
150 24 h
170 24 h
200 2 h
170 24 h
200 3 h
200 4 h
neat
F igu r e 3. Ortep drawing of 3e-II.
tetralina
neat
a
C6D5CD3
neat
neat
neat
neat
tetralina
neat
tetralina
neat
170 17.5 h 5:59:29:7b
3f
170 9 h
200 2 h
240 13.5 h
200 2 h
142 h
tr:97:3:trc
6d:1d:75:18
e
3g
3g
3g
6d:1d:75:18 neat
6d:1d:75:18 neat
0d:>99d:0:0 tetralina
trd:88d:12:tr
10d:47d:36:7f
a
b
The concentration was ca. 10%. The purity of [4]radialenes
was ca. 90%. c The purity of [4]radialenes was ca. 72%. The
assignment of 3g-I and 3g-II could not be done. e Considerable
decomposition was observed, and the ratio could not be estimated.
f The purity of [4]radialenes was ca. 63%.
d
quite good, and no formation of byproducts at these
temperatures was observed, except for 3f at 170 °C and
3g at 240 °C. In the case of the c-hexyl derivative 3g,
however, isomerization in the solid state was slow even
at 200 °C, and no distinct preference for the formation
of any isomer was observed at 240 °C.
F igu r e 4. Pluto representation of 3e-IV.
One reason the type II isomers are preferentially
formed both in solution and in the solid state is the effect
of stacking,11 which could overwhelm the unfavorable
steric interaction of large trifluoromethyl groups.12 This
is supported by the fact that no preference for the
formation of any isomer was seen in the c-hexyl deriva-
tive 3g (runs 18-20). Let us consider the mechanism of
this isomerization. Cycloreversion of radialenes to cu-
mulenes followed by recombination does not seem to be
applicable in this case; no formation of cumulenes was
observed and no crossover radialene was detected when
radialenes 3a and 3c were heated at 170 °C in tetralin.
Thus, rotation of the exomethylene double bonds must
occur during isomerization. If only one exomethylene
double bond rotates, type I and IV isomers must isomer-
ize first to type III and then to type II. However, the type
I and IV isomers of 3a easily isomerized to 3a -II at 150
°C for 24 h, whereas the sample containing 3a -III as the
major component did not isomerize under the same
conditions (runs 3-6). Although some diradical processes
that have been proposed for the thermal [4 + 4] dimer-
ization of the parent radialene13 might be applicable in
this isomerization, the reason is not clear.
analyses of 3e-II and 3a -IV (Figures 3 and 4). In these
figures, trifluoromethyl groups are quite close to each
other, and the distances between their center carbons are
3.71 Å in 3a -IV and 3.70 and 3.75 Å in 3e-II. These
trifluoromethyl groups are, of course, equivalent and do
not have coupling constants. Although X-ray analysis of
the type III isomer 3a -III was not done, a similar
proximity between the trifluoromethyl groups would be
expected, and this could explain the large through-space
coupling constant (10 Hz). On the basis of this structure
determination of 3a , the structures of the other radialene
isomers 3b-f were assigned by comparison of their 19F
NMR spectra.
Th er m a l Isom er iza tion of [4]Ra d ia len es. In the
preparation of [4]radialenes, different isomeric ratios
were observed as the conditions varied. The thermal
isomerization of [4]radialenes was examined in solution
or in the solid state, and the results are summarized in
Table 2. A ca. 10% solution of 3a -II (I:II:III:IV ) 0:97:
3:0) in tetralin was heated at 170 °C in an NMR tube,
and the progress was monitored by 19F NMR. The ratio
reached 6:57:32:5 in 30 min and did not change there-
after. This ratio is almost the same as that obtained in
the thermal dimerization of 2a (Table 1, run 1). When
this isomeric mixture was heated at the same tempera-
ture in the solid state after removal of the solvent, the
ratio was 2:87:9:2 after 24 h. During both isomerizations,
no byproduct was detected by 19F NMR. The predominant
formation of 3-II was also realized in the thermal
isomerization of other tetraaryl [4]radialenes in the solid
state (Table 2). The thermal stability of [4]radialenes is
P h otoch em ica l Isom er iza tion of [4]Ra d ia len es. In
preparating single crystals for X-ray analysis, the slow
(11) For recent examples for aromatic π-π interaction, see: Ran-
ganathan, D.; Haridas, V.; Gilardi, R.; Karle, L. I. J . Am. Chem. Soc.
1998, 120, 10793. Shetty, A. S.; Zhang, J .; Moore, J . S. J . Am. Chem.
Soc. 1996, 118, 1019.
(12) Bott, G.; Field, L. D.; Sternhell, S. J . Am. Chem. Soc. 1980,
102, 5618.
(13) Hopf, H.; Trabert, L. Liebigs Ann. Chem. 1980, 1786.

1618 J . Org. Chem., Vol. 65, No. 6, 2000
Uno et al.
F igu r e 6. Ortep drawing of 6C.
F igu r e 5. Assigned structures of cyclobuta[b]naphthalenes
6. Structures 6B and 6D are tentative assignments based on
only 19F NMR spectra.
solvent-evaporation method was used for [4]radialene
isomers. The type II isomer 3a -II was dissolved in toluene
(ca. 0.1 g/mL) and left in a laboratory. Even after 22 days,
no crystallization was observed. From the 19F NMR
spectra of this sample, 3a -II isomerized into a mixture
of [4]radialene isomers (I:II:III:IV ) 1:28:47:24), as well
as two new compounds 6A and 6B (A:B ) 36:64). After
130 d, all four [4]radialenes disappeared and at least nine
other compounds were detected. Four major isomers 6A,
6C, 6E, and 6F were isolated by chromatography on silica
gel and preparative GPC followed by repeated fractional
recrystallization. These compounds showed distinctive
features in 1H and 19F NMR spectra. An aliphatic
methine proton was observed at δ 5.05 (7.3 Hz), 3.85 (7.6
Hz), 5.17 (7.5 Hz), and 5.11 (7.8 Hz) as a quartet in the
F igu r e 7. Ortep drawing of 6F .
other major isomers 6A and 6C were then formed, after
isomerization between the [4]radialenes was complete
(runs 1 and 2).
The type II isomers of [4]radialenes 3 show distinctive
fluorescence on TLC and in the solid state compared to
other isomers. UV and fluorescence spectra of all of the
isomers 3a were measured in n-hexane (Table 4). As
shown in this Table, the absorption maxima of the four
isomers are almost the same, and the absorption coef-
ficients increase as the symmetricity decreases. The
fluorescence quantum yields increase in the order type
IV < I < III < II. The higher yield of 3a -III compared to
3a -IV and 3a -I may be due to the restricted movement
of exomethylene moieties observed in 1H NMR. The
unexpectedly small difference in quantum yields between
3a -II and other isomers may be related to the easy
photoisomerization of 3a -II to other isomers in solution.
In fact, no isomerization of 3a -II was observed in the solid
state after 35 h of irradiation with light.
1
respective H NMR spectra of 6A, 6C, 6E, and 6F . This
indicated that the methine groups were adjacent to a CF3
group. By NMR analyses, these compounds were revealed
to have a cyclobuta[b]naphthalene skeleton. On the basis
of the long-range coupling constants of F-F, the stere-
ochemical structures were determined as illustrated in
Figure 5. These assignments are supported by the
unambiguous structure determination of 6C and 6F by
X-ray analysis (Figures 6 and 7). Other products in the
mixture could not be isolated, and their structures were
not determined, although the two other major products
were supposed to have structures 6B and 6D illustrated
in Figure 5, based on 19F NMR.
This reaction must be driven by light irradiation.
Photochemical investigations of [4]radialenes are very
rare.1 Thus, the photochemical behavior of the [4]radi-
alenes was examined, and the results are summarized
in Table 3. The cyclobuta[b]naphthalenes 6A-F were all
shown to be photostable (run 6). In the isomerization of
3a -II, 6B was preferentially formed first and the two
The formation of cyclobuta[b]naphthalene isomers
6A-F can be adequately explained by the Woodward-
Hoffmann rule. The possible isomerization routes start-
ing from the type II isomer 3a -II is illustrated in Scheme
2. First, the antarafacial 6π-electrocyclic reaction would

Isomerization of [4]Radialenes
J . Org. Chem., Vol. 65, No. 6, 2000 1619
Ta ble 3. P h otoch em ica l Isom er iza tion of [4]Ra d ia len es 3
ratioa
conditions
time
22 d
radialenes 3
I:II:III:IV
cyclobuta[b]naphthalenes 6
run
1
substrate
hνb
%
%
A:B:C:D:E:Fc
3a -II
A
78
32
0
87
73
59
7
24
3
0
1:28:47:24
-d:9:41:50
-
4:18:44:34
6:9:41:44
4:8:44:44
-d:10:39:51
8:17:46:29
e
22
64
90
12
25
31
35
38
84
94
81
100
36:64:-d:-d:-d:-d
31:30:15:3:7:6
44:27:17:2:6:4
67 d
130 d
30 min
1 h
2
3a -II
B
33:29:11:4:18:5
29:24:14:3:18:12
32:13:16:-d:23:16
30:16:11:-d:20:23
39:16:21:5:13:5
43:6:38:2:5:6
41:11:19:4:18:7
43:10:21:4:16:6
45:28:13:3:7:4
2 h
10 h
90 d
180 d
1 h
2 h
42 d
3
4
5
3a -I
3a -IV
3a f
A
A
B
0
6
6g
A
a
b
The ratio was calculated on the basis of an analysis of the 19F NMR spectra. A: The substrate was dissolved in toluene (ca. 0.1
g/mL) and left in a room without protection from light. B: The substrate was dissolved in benzene (0.005 mol/L) and irradiated by a 40-W
d
UV lamp. c Structures B and D are tentative. The ratio could not be determined because of signal overlapping. e Only type IV 3a -IV
g
could be detected. f A mixture of isomers (I:II:III:IV ) 4:25:52:19) containing 6E (17%) was used. A mixture of 6 (A:B:C:D:E:F ) 45:28:
13:3:7:4) was used.
Ta ble 4. F lu or escen ce Qu a n tu m Yield s a n d Absor p tion
Coefficien ts of 3a
Sch em e 2. P h otoisom er iza tion of 3a -II
UV
fluorescence
λmax
nm
ꢀ × 105
λmax
nm
Φfa
×
compound
M-1 cm-1
10-3
3a -I
334
337
348
334
1.26
1.66
2.24
1.74
450
460
464
471
2.4
4.1
2.9
1.6
3a -II
3a -III
3a -IV
a
The quantum yield was calculated by using a 0.5 N solution
of quinine sulfate as a standard (Φf ) 0.546).
give the intermediate 7-II, and this reaction should be
photoreversible. Thus, there would be three possible fates
for this intermediate 7-II: going back to 3a -II, leading
to the cyclobuta[b]naphthalene 6B via 1,3-hydrogen shift
by absorbing another photon, and giving the type III
radialene 3a -III through a thermal 6π-elecrocyclic ring
opening process. The type III radialene 3a -III would be,
in turn, photoisomerized through four inermediates 7-III,
one of which leading to 6A and 3a -IV is illustrated in
Scheme 2. The isomerization of 3a -IV would give only
the type III radialene 3a -III and two cyclobuta[b]naph-
thalenes 6C and 6F . The other cyclobuta[b]naphthalenes
6D and 6E would be formed from 3a -III.
Because an intermediate such as 7 was not detected
in any experiment and the photon density was low (room
light), the thermal process resulting in the isomerization
between the radialenes would be the main pathway. In
fact, the isomerization between the radialene isomers
reached an equilibrium within 30 min under the irradia-
tion of a 40 W fluorescent lamp (Table 3, run 2). As the
absorption maxima of the radialene isomers are ca. 340
nm, the intermediates 7 are expected to absorb visible
light as a result of low symmetry. Therefore, there would
be a fair chance for 7 to absorb anothor photon, causing
a 1,3-hydrogen shift.
Con clu sion
In the solid state, 5,6,7,8-tetraaryl-5,6,7,8-tetrakis-
(trifluoromethyl)[4]radialenes isomerized to type II iso-
mers in more than 90% selectivity at appropriate tem-
peratures (>150 °C), whereas in solution, equilibrium
mixtures of ca. I:II:III:IV ) 1:10:5:1 were obtained. On
the other hand, upon irradiation with light, the type II

1620 J . Org. Chem., Vol. 65, No. 6, 2000
Uno et al.
1
isom er ): pale yellow crystals, mp 220-221 °C (decomp); H
isomers easily first isomerized to ca. 1:1:5:5 mixtures of
[4]radialene isomers and then underwent a 6πa-electro-
cyclic reaction followed by a 1,3-hydrogen shift to afford
cyclobuta[b]naphthalenes.
NMR δ 2.28 (12H, s), 6.72 (8H, m), and 6.84 (8H, m); 13C NMR
δ 21.2 (Me), 122.1 (m), 122.7 (q, J ) 275 Hz), 127.9, 128.8,
128.9, 137.5 (br), and 138.6; 19F NMR δ -62.87 (s); IR (KBr)
1322s, 1224s, 1172vs, 1164vs, 1130vs, and 1070s cm-1. 3b-III
(typ e III isom er ): 19F NMR δ -62.34 (3F, s), -62.51 (3F, q,
J ) 10 Hz), -62.85 (3F, s), and -63.27 (3F, q, J ) 10 Hz).
3b-IV (typ e IV isom er ): 19F NMR δ -62.49 (6F, s) and -63.10
(6F, s).
Exp er im en ta l Section
Dim er iza tion of Cu m u len es 2. Typ ica l P r oced u r e
(Ta ble 1, r u n 1). The cumulene 2a (340 mg, 1 mmol) was
placed in a flask, and then the flask was purged with argon.
The flask was put in a preheated glass-tube oven at 150 °C.
After 24 h, the gummy solid was subject to NMR analysis and
then chromatographed on silica gel (3-5% EtOAc/hexane) to
give 251 mg (74%) of radialene isomers 3a (I:II:III:IV ) 1:20:
10:3), as well as the recovered 2a (19 mg, 6%). Purity of the
radialene isomers was ca. 90% estimated by 19F NMR. Separa-
tion of the isomers was carried out by the combination of
preparative GPC and fractional recrystallization from CH2-
Cl2/hexane.
Th er m a l Isom er iza tion of Ra d ia len es (3) in Tetr a lin .
Typ ica l P r oced u r e (Ta ble 2, r u n 1). The radialene 3a -II
(40 mg) was dissolved in tetralin (0.4 mL), and the solution
was introduced in a 5-mm NMR tube. After the solution was
bubbled with argon for 15 min, an inner tube containing
DMSO-d6 was inserted, and the tube was capped. The sample
tube was placed in a NMR probe and then heated to 170 °C.
The 19F NMR spectra were taken after the indicated time in
Table 2.
5,6,7,8-Te t r a -p -m e t h oxyp h e n yl-5,6,7,8-t e t r a k is(t r i-
flu or om eth yl)[4]r a d ia len e (3c). MS m/z 800 (M+), 739, and
400. Anal. Calcd for C40H28F12O4: C, 60.01; H, 3.52. Found:
C, 60.07; H, 3.67. 3c-I (typ e I isom er ): 19F NMR δ -62.22
(s). 3c-II (typ e II isom er ): yellow crystals, mp 195-210 °C
(decomp); 1H NMR δ 3.78 (12H, s), 6.59 (8H, m), and 6.81 (8H,
m); 13C NMR δ 55.2 (Me), 113.7, 121.4 (m), 121.5 (q, J ) 276
Hz), 124.2, 129.4, 137.4 (br), and 160.0; 19F NMR δ -62.61
(s); IR (KBr) 1320s, 1292s, 1256s, 1224s, 1170vs, and 1128vs
cm-1. 3c-III (typ e III isom er ): 19F NMR δ -61.98 (3F, s),
-62.39 (3F, q, J ) 10 Hz), -62.71 (3F, s), and -63.00 (3F, q,
J ) 10 Hz). 3c-IV (typ e IV isom er ): 19F NMR δ -62.01 (6F,
s) and -63.12 (6F, s).
5,6,7,8-T e t r a -p -c h lo r o p h e n y l-5,6,7,8-t e t r a k is (t r i-
flu or om eth yl)[4]r a d ia len e (3d ). MS m/z 820 [M+(37Cl2)], 818
[M+(37Cl35Cl)], and 816 [M+(35Cl2)]. Anal. Calcd for C36H16
-
Cl4F12: C, 52.84; H, 1.97. Found: C, 52.62; H, 1.94. 3d -I (typ e
I isom er ): 19F NMR δ -62.47 (s). 3d -II (typ e II isom er ): pale
yellow crystals, mp 255-257 °C (decomp); 1H NMR δ 6.78 (8H,
m) and 7.12 (8H, m); 13C NMR δ 122.1 (q, J ) 276 Hz), 122.4
(m), 128.8, 129.3, 129.8, 135.7, and 137.3 (br); 19F NMR δ
-63.05 (s); IR (KBr) 1320vs, 1220s, 1172vs, 1134vs, and 1096s
cm-1. 3d -III (typ e III isom er ): 19F NMR δ -62.31 (3F, s),
-62.72 (3F, q, J ) 10 Hz), -62.88 (3F, s), and -63.47 (3F, q,
J ) 10 Hz). 3d -IV (typ e IV isom er ): 19F NMR δ -62.46 (6F,
s), and -63.35 (6F, s).
Th er m a l Isom er iza tion of Ra d ia len es (3) in Solid .
Typ ica l P r oced u r e (Ta ble 2, r u n 4). Isomerization of 3a -
IV (40 mg) was performed similarly as the dimerization
described above. After 2 h, 4 mg of the sample was taken out
for 19F NMR analysis. After 70 h, the remaining solid was
subject to the NMR analysis and then recrystallized from
hexane (1 mL) to give 25 mg (63%) of pure type II isomer 3a -
II.
1,3-Di-p-ch lor op h en yl-2,4-bis[2-(p-ch lor op h en yl)eth e-
n yliden e]-1,3-bis(tr iflu or om eth yl)cyclobu tan e (4d). tr a n s-
1
5,6,7,8-Tet r a p h en yl-5,6,7,8-t et r a k is(t r iflu or om et h yl)-
[4]r a d ia len e (3a ). MS m/z 680 (M+), 611, and 340. Anal. Calcd
for C36H20F12: C, 63.54; H, 2.96. Found: C, 63.44; H, 3.14. 3a -I
(typ e I isom er ): Rf ) 0.45 (5% EtOAc/hexane); pale yellow
crystals, mp 196-198 °C (decomp); 1H NMR δ 7.28 (8H, m)
and 7.38-7.48 (12H, m); 13C NMR δ 122.2 (q, J ) 275 Hz),
122.8 (q, J ) 33 Hz), 128.1, 128.7, 129.6, 132.3, and 137.1 (br);
19F NMR δ -62.56 (s); IR (KBr) 1322s, 1224vs, 1176vs, 1130vs,
and 1058s cm-1. 3a -II (typ e II isom er ): Rf ) 0.45 (5% EtOAc/
hexane); pale yellow crystals, mp 180-224 °C (decomp); 1H
NMR δ 6.82 (8H, m), 7.06 (8H, m), and 7.16 (4H, m); 13C NMR
δ 122.6 (q, J ) 275 Hz), 122.6 (q, J ) 37 Hz), 127.8, 128.5,
128.7, 131.7, and 137.5 (br); 19F NMR δ -63.01 (s); IR (KBr)
1318s, 1222s, 1208s, 1174vs, 1128vs, and 1060s cm-1. 3a -III
(typ e III isom er ): Rf ) 0.4 (5% EtOAc/hexane); pale yellow
crystals, mp 180-181 °C (decomp); 1H NMR δ 6.70 (2H, br
m), 6.87 (2H, m), 6.95-7.2 (6H, m), 7.34 (2H, m), and 7.4-
7.55 (8H, m); 13C NMR δ 121.7 (q, J ) 275 Hz), 122.0 (q, J )
275 Hz), 122.2 (q, J ) 33 Hz), 122.6 (q, J ) 274 Hz), 122.6 (q,
J ) 33 Hz), 122.9 (q, J ) 274 Hz), 123.2 (q, J ) 33 Hz), 124.5
(q, J ) 34 Hz), 127.7, 127.8, 128.1, 128.4, 128.4, 128.5, 128.6,
128.6, 128.8, 128.8, 129.5, 129.6, 131.7, 131.8, 132.5, 132.7,
136.8 (br), 137.6 (br, 2 carbons), and 137.9 (br); 19F NMR δ
-63.40 (3F, q, J ) 10 Hz), -62.89 (3F, s), -62.54 (3F, q, J )
10 Hz), and -62.48 (3F, s); IR (KBr) 1322vs, 1222s, 1208s,
1174vs, 1126vs, and 1060s cm-1. 3a -IV (typ e IV isom er ): Rf
) 0.35 (5% EtOAc/hexane); pale yellow crystals, mp 194-196
a n ti Isom er : pale yellow crystals, mp 235-237 °C; H NMR
δ 7.32 (4H, m), 7.35 (4H, m), and 7.46 (8H, m); 19F NMR δ
-60.42 (6F, s) and -73.70 (6F, s); IR (KBr) 1978w, 1902w,
1496s, 1298s, 1166vs, 1138vs, and 1098vs cm-1. Anal. Calcd
for C36H16Cl4F12: C, 52.84; H, 1.97. Found: C, 52.48; H, 1.79.
1
An oth er isom er : H NMR δ 7.20 (8H, m) and 7.50 (8H, m);
19F NMR δ -60.97 (6F, s), and -73.10 (6F, s).
5,6,7,8-Te t r a -4-b ip h e n ylyl-5,6,7,8-t e t r a k is(t r iflu or -
om eth yl)[4]r a d ia len e (3e). MS m/z 984 (M+), 915, and 492.
Anal. Calcd for C60H36F12: C, 73.17; H, 3.68. Found: C, 73.09;
H, 3.95. 3e-I (typ e I isom er ): 19F NMR δ -62.22 (s). 3e-II
(t yp e II isom er ): Rf ) 0.4 (5% EtOAc/hexane); yellow
prismatic crystals (toluene), mp > 300 °C; 1H NMR δ 6.98 (4H,
m, H2′ and H6′), 7.25 (4H, m, H3′ and H5′), and 7.35-7.45 (10H,
m, Ph); 13C NMR δ 122.3 (q, J ) 38 Hz), 122.7 (q, J ) 276
Hz), 126.9, 127.8, 128.5, 128.9, 130.7, 137.6 (m), 140.1, and
141.6; 19F NMR δ -62.54 (s). IR (KBr) 1322s, 1224s, 1174vs,
and 1128vs cm-1. 3e-III (typ e III isom er ): 19F NMR δ -60.14
(3F, s), -62.28 (3F, q, J ) 10 Hz), -62.65 (3F, s), and -62.96
(3F, q, J ) 10 Hz). 3e-IV (typ e IV isom er ): 19F NMR δ -62.20
(6F, s) and -62.94 (6F, s).
5,6,7,8-Tetr a-p-m eth oxycar bon ylpn en yl-5,6,7,8-tetr akis-
(tr iflu or om eth yl)[4]r a d ia len e (3f). MS m/z 912 (M+), 881,
880, and 811. Anal. Calcd for C44H28F12O8: C, 57.90; H, 3.09.
Found: C, 57.74; H, 3.21. 3f-I (typ e I isom er ): 19F NMR δ
-62.43 (s). 3f-II (typ e II isom er ): pale yellow needles, mp
1
220-255 °C (decomp); H NMR δ 3.97 (12H, s), 6.92 (8H, m),
1
and 7.72 (8H, m); 13C NMR δ 52.4 (Me), 122.0 (q, J ) 276 Hz),
°C (decomp); H NMR δ 6.72 (4H, m), 6.99 (4H, m), 7.09 (2H,
m), and 7.49 (10H, m); 13C NMR δ 121.6 (q, J ) 275 Hz), 122.3
(q, J ) 33 Hz), 122.8 (q, J ) 276 Hz, CF3), 124.6 (q, J ) 34
Hz), 127.7, 128.4, 128.5, 128.7, 128.7, 129.6, 131.9, 132.7, 137.2
(br), and 137.9 (br); 19F NMR δ -62.68 (6F, s) and -63.09 (6F,
s); IR (KBr) 1320vs, 1222s, 1208s, 1174vs, 1128vs, and 1058s
123.0 (m), 128.0, 129.8, 130.8, 135.6, 137.3 (br), and 165.9; 19
F
NMR δ -62.82 (s); IR (KBr) 1726vs, 1284vs, 1176vs, and
1130vs cm-1. 3f-III (typ e III isom er ): 19F NMR δ -62.24 (3F,
s), -62.47 (3F, q, J ) 10 Hz), -62.72 (3F, s), and -63.18 (3F,
q, J ) 10 Hz). 3f-IV (typ e IV isom er ): 19F NMR δ -62.34
(6F, s) and -63.05 (6F, s).
cm-1
.
5,6,7,8-Tetr a -p-tolyl-5,6,7,8-tetr a k is(tr iflu or om eth yl)-
[4]r a d ia len e (3b). MS m/z 736 (M+), 667, and 368. Anal. Calcd
for C40H28F12: C, 65.22; H, 3.83. Found: C, 65.40; H, 4.12. 3b-I
(t yp e I isom er ): 19F NMR δ -62.44 (s). 3b -II (t yp e II
5,6,7,8-Tetr acycloh exyl-5,6,7,8-tetr akis(tr iflu or om eth yl)-
[4]r a d ia len e (3g). MS m/z 704 (M+), 622, 540, and 458. 3g-I
(t yp e I isom er ): 19F NMR δ -59.84 (s). 3g-II (t yp e II
isom er ): colorless crystals, mp 230-232 °C; 1H NMR δ 1.10-

Isomerization of [4]Radialenes
J . Org. Chem., Vol. 65, No. 6, 2000 1621
1.35 (12H, m), 1.35-1.60 (12H, m), 1.60-1.85 (16H, m), and
2.53 (4H, br-t, J ) 11.7 Hz); 19F NMR δ -59.14 (s); 13C NMR
δ 25.7, 25.8, 27.1, 28.5, 30.8, 41.8 (CH), 124.1 (q, J ) 30 Hz),
124.3 (q, J ) 277 Hz), 124.2 (q, J ) 29 Hz), 124.3 (q, J ) 277
Hz), and 136.7 (m). 3g-III (typ e III isom er ): 1H NMR δ 1.1-
2.0 (40H, m) and 2.3-2.6 (4H, m); 19F NMR δ -58.66 (3F, s),
-59.13 (3F, s), -59.77 (3F, q, J ) 10 Hz), and -59.96 (3F, q,
J ) 10 Hz). 3g-IV (typ e IV isom er ): 19F NMR δ -58.56 (6F,
s) and -59.94 (6F, s).
4,5,6-T r ic y c lo h e x y l-4,5,6-t r is (t r iflu o r o m e t h y l)[3]-
r a d ia len e (5g). MS m/z 528 (M+), 445, 363, and 321. a sym -
5g: waxy solid; 1H NMR δ 1.10-1.45 (10H, m), 1.50-2.10 (21H,
m), and 2.26-3.00 (2H, m); 19F NMR δ -56.20 (3F, s) and
-58.93 (6F, m); 13C NMR δ 25.5, 25.5, 25.7, 26.5, 26.6 (2C),
30.2, 30.4 (2C), 43.0, 45.6, 45.7, 116.5 (q, J ) 6 Hz), 117.8 (q,
J ) 6 Hz), 118.7 (q, J ) 6 Hz), 124.1 (q, J ) 277 Hz), 124.2 (q,
J ) 29 Hz), 124.3 (q, J ) 277 Hz), 125.1 (q, J ) 30 Hz), 126.1
(q, J ) 278 Hz), and 127.4 (q, J ) 29 Hz). sym -5g: 19F NMR
δ -56.38 (s).
116.1 (q, J ) 33 Hz, C1′), 118.1 (q, J ) 32 Hz, C1′), 122.7 (q,
J ) 272 Hz, CF3), 122.7 (q, J ) 274 Hz, CF3), 123.7 (q, J )
283 Hz, CF3), 124.4 (q, J ) 287 Hz, CF3), 125.8, 127.2 (br),
127.3, 127.4 (br), 127.6, 128.3, 128.3, 128.9, 129.1 (br), 129.2,
129.3, 130.2, 130.4 (br), 130.9, 131.9 (q, J ) 2 Hz) 132.1, 135.1,
136.7, 141.4 (q, J ) 4 Hz, C1 or C2), 142.2 (q, J ) 4 Hz, C1 or
C2), 152.8 (br, C2a or C8a), and 153.5 (br, C2a or C8a). 6D
(ten ta tive a ssign m en t): 1H NMR (typical signal) δ 4.57 (1H,
br q, J ) 7.8 Hz); 19F NMR δ -60.10 (3F, s), -60.72 (3F, q, J
) 11 Hz), -65.14 (3F, q, J ) 11 Hz), and -66.34 (3F, d, J )
8 Hz). 6E: colorless crystals, mp 237-239 °C; 1H NMR δ 5.17
(1H, q, J ) 7.5 Hz) and 6.2-7.6 (19H, br m); 19F NMR δ -58.76
(3F, q, J ) 7 Hz), -61.55 (3F, q, J ) 14 Hz), -63.35 (3F, m),
and -63.70 (3F, septet, J ) 14 Hz). 6F : colorless crystals, mp
197-199 °C; 1H NMR δ 5.11 (1H, q, J ) 7.8 Hz), 6.3-7.0 (5H,
br m), and 7.0-7.6 (15H, m); 19F NMR δ -58.36 (3F, q, J ) 8
Hz), -62.09 (3F, s), -63.34 (3F, q, J ) 13 Hz), and -63.77
(3F, q-quint, J ) 13 and 8 Hz).
X-r a y An a lysis. All measurements were made on a Rigaku
AFC5R diffractometer with graphite monochromator and a 12
kW rotating anode generator. The data were collected at a
temperature of 25 ( 1 °C using the ω scan technique. Omega
scans of several intense reflections, made prior to data
collection, had an average width at half-height of 0.18° with a
taking-off angle of 6.0°/min (in ω). The weak reflections [I <
10.0σ(I)] were rescanned (maximum of 2 rescans). An empirical
correction for the absorption was made on the basis of
azimuthal (Ψ) scans of three reflections.14 The structure was
solved by the direct method (Mithril, SIR, or Multan). The
coordinates of the H-atoms were calculated. Calculations were
carried out on a VAX station 3200 computer with TEXSAN
programs15 or NEC VM45J /6 with PC-teXsan which used the
atomic scattering factors taken from “International Tables for
P h otoch em ica l Isom er iza tion of 3. Typ ica l P r oced u r e
for Con d ition s B (Ta ble 3, r u n 2). The type II isomer 3a -II
(68 mg) and benzene (20 mL) were put in a Pyrex flask, and
the vessel was cooled by a flow of water, surrounded by
aluminum foil, and irradiated by a 40 W fluorescent lamp.
After the indicated time passed, 4 mL of the solution was taken
by a syringe and subject to the NMR analysis.
P h otoch em ica l Isom er iza tion of 3. Typ ica l P r oced u r e
for Con d ition s A (Ta ble 3, r u n 1). The type II isomer 3a -II
(125 mg) was put in a vial and dissolved by 10 mL of toluene.
The vial was left on a bench. After the indicated time passed,
2 mL of the mixture was taken up, and the solvent was
evaporated in vacuo. The residue was dissolved in CDCl3, and
the NMR analysis was carried out. After removal of CDCl3 in
vacuo, the residue was dissolved in 2 mL of toluene, and the
solution was added back to the reaction mixture. After 130 d,
toluene was removed to give a nonfluorescent colorless oil,
which was chromatographed on silica gel to afford 93 mg (74%)
of cyclobuta[b]naphthalenes 6A-F in the ratio of 44:27:17:2:
6:4. Repeated chromatograpy and fractional recrystallization
afforded pure isomers of 6A and 6C, structures of which were
fully assigned by NMR including H-H, F-F, and C-H COSY
spectra. Isomers 6E and 6F were isolated by gathering the
mother liquors of several experiments followed by repeated
chromatography, preparative GPC, and fractional recrystal-
lization.
X-Ray Crystallography.”16 Cr ysta l d a ta for 3e-II: C60H36F12
,
triclinic, space group P-1 (#2), Z ) 2, a ) 12.912(3) Å, b )
17.290(6) Å, c ) 12.927(4) Å, R ) 104.50(2)°, â ) 119.96(1)°, γ
) 89.99(2)°, V ) 2394(2) Å3, Dc ) 1.366 g‚cm-1, dimensions
0.80 × 0.35 × 0.25 mm, Cu KR, µ ) 9.28 cm-1, F(000) ) 1008,
7814 reflections measured, 7436 of which were unique (Rint
)
0.037). Phenyl groups were treated as restricted groups. All
other non-hydrogen atoms were refined anisotropically; R )
0.065 and Rw ) 0.076 for 4255 reflections with I >1σ(I),
reflection/parameter ) 6.56, GOF ) 1.87, ∆Fmin ) -0.19 e‚Å3,
∆Fmax ) 0.20 e‚Å3. Cr ysta l d a ta for 3a -IV: C36H20F12‚0.5C7H8,
monoclinic, space group C2/c (#15), Z ) 8, a ) 30.42(1) Å, b )
11.577(3) Å, c ) 21.589(2) Å, â ) 113.33(2)°, V ) 6982(4) Å3,
Dc ) 1.382 g‚cm-1, dimensions 0.30 × 0.28 × 0.22 mm, Mo
KR, µ ) 1.19 cm-1, F(000) ) 2952, 8559 reflections measured,
8396 of which were unique (Rint ) 0.166). The intensity
decreased to 77% during the measurement. Fluorine and
toluene-carbon atoms were refined anisotropically. The phenyl
groups were treated as restricted groups, and toluene was
disordered; R ) 0.084 and Rw ) 0.073 for 1456 reflections with
3-P h en yl-1,2-b is(1-p h en yl-2,2,2-t r iflu or oet h ylid en e)-
3,8-b ist r iflu or om et h yl-1,2,3,8-t et r a h yd r ocyclob u t a [b]-
n a p h th a len e (6). MS m/z 680 (M+), 611, 602, and 533. Anal.
Calcd for C36H20F12: C, 63.54; H, 2.96. Found: C, 63.53; H,
1
2.99. 6A: colorless crystals, mp 201-203 °C; H NMR (50 °C)
δ 5.05 (1H, q, J ) 7.3 Hz, H8), 6.51 (2H, br), 6.83 (2H, br),
6.84 (2H, m), 6.86 (1H, d-quint, J ) 7.6 and 1.5 Hz, H4), 7.05
(3H, br m), 7.15 (2H, m), 7.18 (1H, ddd, J ) 7.8, 7.6, and 1.5
Hz, H5), 7.31 (1H, td, J ) 7.8 and 1.5 Hz, H6), 7.37 (5H, m),
and 7.51 (1H, br d, J ) 7.8 Hz, H7); 19F NMR (50 °C) δ -58.35
(3F, q, J ) 7.5 Hz, 1-CCF3), -61.81 (3F, s, 2-CCF3), -64.58
(3F, br s, 3-CF3), and -66.04 (3F, quint-d, J ) 7.5 and 1.5 Hz,
8-CF3); 13C NMR (50 °C) δ 43.3 (qq, J ) 29 and 6 Hz, C8),
55.6 (q, J ) 26 Hz, C3), 117.2 (q, J ) 32 Hz, C1′), 117.5 (q, J
) 33 Hz, C1′), 121.7 (q, J ) 274 Hz, CF3), 123.9 (q, J ) 274
Hz, CF3), 124.6 (q, J ) 286 Hz, 2 × CF3), 126.2, 127.3, 127.5,
128.0, 128.5, 128.5, 128.9, 129.1, 129.3, 129.4 (br), 130.3, 130.6,
130.8 (m), 130.8 (m), 131.9, 133.0, 134.7, 137.1, 141.6 (q, J )
4 Hz, C1 or C2), 142.4 (q, J ) 4 Hz, C1 or C2), 153.0 (br, C2a
or C8a), and 154.0 (br, C2a or C8a); IR (KBr) 1312vs, 1232vs,
1192vs, 1166vs, 1112vs, and 1022vs cm-1. 6B (t en t a t ive
a ssign m en t): 1H NMR (typical signal) δ 5.07 (1H, q, J ) 7.3
Hz); 19F NMR δ -58.69 (3F, q, J ) 7 Hz), -60.71 (3F, q, J )
11 Hz), -65.01 (3F, q, J ) 11 Hz), and -66.34 (3F, quint, J )
7 Hz). 6C: colorless crystals, mp 175-176 °C; 1H NMR (50 °C)
δ 3.85 (1H, q, J ) 7.6 Hz, H8), 6.4-7.0 (6H, m), 7.0-7.3 (8H,
m), and 7.3-7.6 (5H, m); 19F NMR δ -61.05 (3F, q, J ) 14
Hz, 1- or 2-CCF3), -62.53 (3F, q, J ) 14 Hz, 1- or 2-CCF3),
-64.72 (3F, s, 3-CF3), and -66.03 (3F, d, J ) 7 Hz, 8-CF3);
13C NMR δ 41.7 (q, J ) 29 Hz, C8), 55.2 (q, J ) 26 Hz, C3),
I > 2.5σ(I), reflection/parameter ) 6.02, GOF ) 1.92, ∆Fmin
)
-0.37 e‚Å3, ∆Fmax ) 0.64 e‚Å3. Cr ysta l d a ta for 4d : C36H16
-
Cl4F12, triclinic, space group P-1 (#2), Z ) 4, a ) 17.077(2) Å,
b ) 19.122(3) Å, c ) 12.248(1) Å, R ) 95.68(1)°, â ) 100.01-
(1)°, γ ) 114.506(9)°, V ) 3517.9(8) Å3, Dc ) 1.545 g‚cm-1
dimensions 0.40 × 0.25 × 0.20 mm, Mo KR, µ ) 4.25 cm-1
,
,
F(000) ) 1632, 16671 reflections measured, 16133 of which
were unique (Rint ) 0.041). The phenyl carbons were treated
as restricted groups, and other non-hydrogen atoms were
refined anisotropically; R ) 0.072 and Rw ) 0.074 for 4475
reflections with I > 3σ(I), reflection/parameter ) 7.98, GOF
) 2.00, ∆Fmin ) -0.44 e‚Å3, ∆Fmax ) 0.61 e‚Å3. Cr ysta l d a ta
for 6C: C36H20F12, monoclinic, space group P21/ c (#14), Z )
4, a ) 9.433(1) Å, b ) 25.193(2) Å, c ) 13.154(1) Å, â ) 98.340-
(8)°, V ) 3093.1(5) Å3, Dc ) 1.461 g‚cm-1, dimensions 0.50 ×
0.31 × 0.30 mm, Mo KR, µ ) 1.29 cm-1, F(000) ) 1376, 7693
(14) G. J . Gilmore, J . Appl. Crystallogr. 1984, 17, 42.
(15) TEXSAN-Texray Structure Analysis Package, Version 5.0;
Molecular Structure Corporation: The Woodlands, TX, 1989.
(16) International Tables for X-Ray Crystallography; Kynoch
Press: Birmingham, 1974; Vol. IV, Table 2.2 A and 2.3.1

1622 J . Org. Chem., Vol. 65, No. 6, 2000
Uno et al.
reflections measured, 7272 of which were unique (Rint ) 0.023).
All non-hydrogen atoms were refined anisotropically; R )
0.063 and Rw ) 0.060 for 3182 reflections with I > 2σ(I),
reflection/parameter ) 7.35, GOF ) 1.68, ∆Fmin ) -0.30 e‚Å3,
∆Fmax ) 0.23 e‚Å3. Cr ysta l d a ta for 6F : C36H20F12, triclinic,
space group P-1 (#2), Z ) 2, a ) 10.4365(8) Å, b ) 16.295(2)
Å, c ) 9.886(1) Å, R ) 105.086(8)°, â ) 104.097(7)°, γ ) 97.057-
(7)°, V ) 1542.9(3) Å3, Dc ) 1.465 g‚cm-1, dimensions 0.55 ×
0.35 × 0.25 mm, Cu KR, µ ) 11.97 cm-1, F(000) ) 688.00, 5097
reflections measured, 4792 of which were unique (Rint ) 0.040).
All non-hydrogen atoms were refined anisotropically, and one
0.054 for 3797 reflections with I > 2.5σ(I), reflection/parameter
) 8.24, GOF ) 2.00, ∆Fmin ) -0.21 e‚Å3, ∆Fmax ) 0.23 e‚Å3.
Ack n ow led gm en t. We thank Prof. Nagao Azuma
for a helpful discussion of X-ray analysis.
Su p p or tin g In for m a tion Ava ila ble: Experimental crys-
tallographic details, positional and thermal parameters for 3a -
IV, 3e-II, 4d , 6C, and 6F . This material is available free of
charge via the Internet at http://pubs.acs.org.
trifluoromethyl group was disordered; R ) 0.042 and Rw
)
J O990699V