Formation of 6,10-diphenyl-substituted heptalene-4,5-dicarboxylates

Article abstract of DOI:10.1002/hlca.200590065

It is shown that 4,8-diphenylazulene (1) can be easily prepared from azulene by two consecutive phenylation reactions with PhLi, followed by dehydrogenation with chloranil. Similarly, a Me group can subsequently be introduced with MeLi at C(6) of 1 (Schem

Full text of DOI:10.1002/hlca.200590065

Helvetica Chimica Acta ± Vol. 88 (2005)
873
Formation of 6,10-Diphenyl-Substituted Heptalene-4,5-dicarboxylates
by XudongJin 1), Anthony Linden, and Hans-Jürgen Hansen*
Organisch-chemisches Institut der Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich
(phone: ‡ 41-1-635 42 30; fax: ‡ 41-1-635 6812; e-mail: H.-J.H@access.unizh.ch)
It is shown that 4,8-diphenylazulene (1) can be easily prepared from azulene by two consecutive
phenylation reactions with PhLi, followed by dehydrogenation with chloranil. Similarly, a Me group can
subsequently be introduced with MeLi at C(6) of 1 (Scheme 2). This methylation led not only to the expected
main product, azulene 2, but also to small amounts of product 3, the structure of which has been determined by
X-ray crystal-structure analysis (cf. Fig. 1). As expected, the latter product reacts with chloranil at 408 in Et2O to
give 2 in quantitative yields. Vilsmeier formylation of 1 and 2 led to the formation of the corresponding azulene-
1-carbaldehydes 4 and 5. Reduction of 4 and 5 with NaBH4/BF3 ´ OEt2 in diglyme/Et2O 1:1 and BF3 ´ OEt2,
gave the 1-methylazulenes 6 and 7, respectively. In the same way was azulene 9 available from 6 via Vilsmeier
formylation, followed by reduction of azulene-1-carbaldehyde 8 (Scheme 3). The thermal reactions of azulenes
1, 6, and 7 with excess dimethyl acetylenedicarboxylate (ADM) in MeCN at 1008 during 72 h afforded the
corresponding heptalene-4,5-dicarboxylates 11, 12, and 13, respectively (Scheme 4). On the other hand, the
highly substituted azulene 9 gave hardly any heptalene-4,5-dicarboxylate.
1. Introduction. ± In the course of our investigations of the chemistry of highly
substituted heptalene-4,5-dicarboxylates as precursors for new chiral ligand systems in
homogeneous transition metal catalysis [1], we were interested in the synthesis of peri-
phenylated azulenes as starting material for the formation of the corresponding
heptalene-4,5-dicarboxylates. Unfortunately, the elegant synthesis of Hafner and
Kaiser of 4,6,8-trimethylazulene [2] and other trisubstituted azulenes of this type (see,
e.g., [3]), cannot be applied to the synthesis of 4,6,8-triphenylazulene, starting with
commercially available 2,4,6-triphenyl pyrylium tetrafluoroborate (AVOCADO Re-
search Chemicals Ltd.) (Scheme 1). On the other hand, azulenes with substituents at 4-,
6-, and 8-position can be prepared according to Hafner etal. [4][5] by addition of RÀLi
reagents to azulenes. The thus formed dihydroazulenes can easily be dehydrogenated
with chloranil (ˆ2,3,5,6-tetrachlorobenzo-1,4-quinone) in EtOH or MeOH.
Scheme 1
1
)
Part of the projected Ph.D. thesis of X. J., University of Zurich, 2004. Present address: School of Chemical
Science & Engineering, Liaoning University, 110036 P.R. China.
ꢀ 2005 Verlag Helvetica Chimica Acta AG, Zürich

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Helvetica Chimica Acta ± Vol. 88 (2005)
In this paper, we report the synthesis of 4,8-diphenylated azulenes with further Me
substituents at C(1) and C(6) and their thermal reaction with dimethyl acetylenedi-
carboxylate (ADM), resulting in the formation of the corresponding heptalene-4,5-
dicarboxylates.
2. Results and Discussion. ± 2.1. Chemistry. We started with 4,8-diphenylazulene
(1), which was obtained from azulene [6] by two consecutive phenylation reactions in
an overall yield of 67% [4]. The introduction of a further Me substituent at C(6) was
realized by treatment of 1 with MeLi, followed by dehydrogenation of the adduct with
chloranil in MeOH [5]. Purification of the deep blue azulene 2 by chromatography on
silica gel gave a second, orange-colored product, which turned out to be the
corresponding dihydroazulene 3 (Scheme 2). The structure of 3 was evident from its
13
1H- and C-NMR spectrum (see Exper. Part)2). Since it could be crystallized from
hexane/Et2O, we also performed an X-ray crystal-structure analysis of 3 (vide infra).
Scheme 2
Scheme 3
Moreover, compound 3 is energetically favored by 2.8kcal ´ mol À1 (according to AM1 calculations) over its
[1,5]-sigmatropic tautomer, the 2,6-dihydro compound, which represents the other possible product of
protonation of the corresponding intermediary 6-hydro-6-methylazulenide.
2
)

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875
The introduction of a further Me group at C(1) of 1 and 2 was performed by the
established Vilsmeier borane reduction sequence (Scheme 3) [7], thus leading via the
azulene-1-carbaldehydes 4 and 5 to the azulenes 6 and 7, respectively. Azulene 6 was
again subjected to the Vilsmeier borane reduction procedure to give aldehyde 8 and the
further product 1,3-dimethylazulene 9 (see also Scheme 3).
The azulenes 1, 6, 7, and 9 were heated with a twofold molar excess of ADM in
MeCN in a closed Schlenk vessel under Ar at 1008 (Scheme 4). Heptalenedicarboxylate
formation was observed in all cases. However, azulene 9 gave only trace amounts of the
expected heptalenedicarboxylate 10, which could be identified, solely on the TLC plate
by its correlated Rf value and its color. In the other three cases, the heptalene-4,5-
dicarboxylates 11, 12, and 13, respectively, were successfully isolated and spectroscopi-
cally characterized. Moreover, the heptalene-4,5-dicarboxylates 11 and 12 crystallized
well and were subjected to an X-ray crystal-structure analysis (vide infra).
Scheme 4
a) Second value corresponds to DMF, 1708, 48 h. b) Not enough to be isolated, but recognizable in TLC by its
typical Rf value and the pale-yellow color of the spot.
1
The H-NMR analysis of heated probes of the heptalenedicarboxylats 11 and 12
showed that the equilibrium mixtures at room temperature consisted mainly of 11 and
12, respectively. Their DBS isomers 11' and 12' were present to an extent of 7 ± 8%, in
the case of 11, and to < 1% in the case of 12 (Scheme 5). Therefore, the irradiation
experiments of 12 in toluene were conducted with a fluorescence lamp (lmax (emiss.)
366 and 433 nm)3) at room temperature, but failed completely. The formation of 12'
was not observed.
3
)
Both heptalene-dicarboxylats 11 and 12, show shoulders in hexane in the long-wavelength region of 385 ±
400 nm (see Exper. Part).

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Helvetica Chimica Acta ± Vol. 88 (2005)
Scheme 5
a) 93 :7% in CDCl3 and 92 :8% in C6D6. b) In (D6)acetone.
2.2. X-Ray Analysis. The X-ray crystal structure of the dihydroazulene 3 is shown in
Fig. 1. The analysis of the structure of 3 showed a disordered molecule, that results
from the superposition of mirror images of the molecule on the same crystallographic
site. The disorder manifests itself only in the alternation of the double-bound position
within the five-membered ring and, thus of the H-atoms associated with this ring. As a
result, only averaged bond lengths of the C(1)ÀC(2)ˆC(3) part could be determined
(for details, see Exper. Part). Nevertheless, the seven-membered ring of 3 shows a clear
boat conformation, in which MeÀC(6) has an equatorial orientation. That the same
conformation of the seven-membered ring is present in solution at room temperature is
3
indicatated by 3J(HÀC(5),HÀC(6)) ꢀ J(HÀC(6),HÀC(7)) ˆ 5.7 Hz, typical for
corresponding H,H torsion angles in the range of 1208 (X-ray: Æ 1328). Moreover,
the AM1-calculated H,H torsion angles at the five-membered ring amount to almost
608 (HaÀC(1)ÀC(2)ÀH and HbÀC(1)ÀC(2)ÀH) in agreement with a nearly perfect
1
planar five-membered ring. Indeed, the H-NMR data are also in agreement with a
planar five-membered ring, since no visible coupling can be observed between the
2
methylene group, which appears as a clear AB system with J(AB) ˆ 14.4 Hz in the
expected range of 3.2 ± 3.6 ppm, and HÀC(2) and HÀC(3). The slightly broadened
Fig. 1. Stereoscopic view of the X-ray crystal structure of 1,6-dihydro-6-methyl-4,8-diphenylazulene (3)

Helvetica Chimica Acta ± Vol. 88 (2005)
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3
doublet for HÀC(2) and HÀC(3) with J(HÀC(2), HÀC(3)) ˆ 5.4 Hz indicates very
small values for the vicinal and allylic coupling, respectively, with CH2(1).
The asymmetric unit of 11 contains two symmetry-independent molecules. The
molecules differ primarily in the relative orientation of the MeOCO substituent at C(4)
with respect to the C(3)ˆC(4) bond. In one molecule, the CˆO group of
MeOCOÀC(4) occupies more or less a s-trans-conformation (see Fig. 2 and Table 1),
Fig. 2. Stereoscopic view of the X-ray crystal structure of dimethyl 6,10-diphenylheptalene-4,5-dicarboxylate (11;
the s-trans conformation of MeOOCÀC(4) in the (P) configuration of the heptalene skeleton is shown)
Table 1. Characteristic Torsion Angles of X-Ray Crystal Structure Analyses of Heptalenedicarboxylates
Compound
R in Heptalenedicarboxylates
Torsion angles [8]a)
V1
V2
V3
161.4(2)
À 15.3(3)
156.0(6)
À 6.6(12)
À 14.1(2)
159.2(1)
V4
V5
11
12
R1 ˆ R3 ˆ H, R2 ˆ Ph
63.1(3)
64.8(3)
67.0(2)
65.2(3)
65.9(3)
68.2(2)
133.7(2)
136.2(2)
135.2(2)
À 40.6(3)
À 41.8(3)
À 39.3(2)
R1 ˆ Me, R2 ˆ Ph, R3 ˆ H
R1 ˆ R2 ˆ Me, R3 ˆ t-Bu
14c)
15d)
63.9(2)
63.0(1)
65.7(2)
66.3(1)
130.8(2)
134.5(1)
À 33.0(2)
À 40.2(1)
a) The torsion angles V are referring to the (P) configuration. V1 ˆ V(C(5)ÀC(5a)ÀC(10a)ÀC(1)); V2 ˆ
V(C(6)ÀC(5a)ÀC(10a)ÀC(10));
V3 ˆ V(OˆCÀC(4)ÀC(3));
V4 ˆ V(OˆCÀC(5)ÀC(5a));
V5 ˆ
V(MeOOCÀC(4)ÀC(5)ÀCOOMe). Values in the second line refer to the corresponding s-cis conformations
of MeOOCÀC(4). c) Data taken from [3]. d) Data taken from [8]; torsion angles correspond to those defined
under b).

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whereas the other molecule represents almost a perfect s-cis-conformation (Table 1). It
is quite interesting to note that the MeOCO group at C(5) occupies a position close to a
s-trans-conformation in both molecules. This is also true for other heptalenedicarbox-
ylates such as 14 and 15 (Table 1) which carry substituents at the peri-positions, but may
crystallize with MeOCOÀC(4) in s-cis (14) or s-trans conformation (15).
The asymmetric unit of the crystals of 12 contains one molecule in which the
MeOCO group at C(4) is disordered over two orientations, which again can be assigned
to a major s-trans (ca. 65%) and a minor s-cis-conformation (see Fig. 3). The torsion
angles at the ester groups are close to those of 11 and of other heptalenedicarboxylates
(Table 1).
Fig. 3. Stereoscopic view of the X-ray crystal structure of dimethyl 1-methyl-6,10-diphenylheptalene-4,5-
dicarboxylate (12; the s-trans conformation of MeOCOÀC(4) in the (P) configuration of the heptalene
skeleton is shown)
One can assume that the conformation at the ester groups will not change very
much in solution, that means that the MeOCO group at C(5) is almost perfectly
shielded against a nucleophilic attack at its CˆO group, so that all primary nucleophilic
attacks occur at the CˆO group at C(4), which has always been observed by us.
We thank Dr. L. Bigler and his group for mass spectra, our NMR department for NMR support and 2 D-
NMR measurements, and our analytical laboratory for elemental analyses. The financial support of this work by
the Swiss National Science Foundation is gratefully acknowledged.
Experimental Part
General. See [4][5].
1. Syntheses of Azulenes. 1.1. Attempted Synthesis of 4,6,8-Triphenylazulene. The reaction was performed in
analogy to [2]. 2,4,6-Triphenyl pyrylium tetrafluoroborate (AVOCADO Research Chemicals Ltd.) (200 mg,
0.50 mmol) was reacted with freshly prepared cyclopentadiene (0.06 ml, 0.75 mmol) and NaH (30 mg,
0.75 mmol) in DMF (20 ml) at 1508 during 24 h. After normal workup, 4,6,8-triphenylazulene was not
detectable.
1.2. 4,8-Diphenylazulene-1-carbaldehyde (4). POCl3 (15 ml, 165 mmol) was dropped to DMF (20 ml) under
stirring at 08 within 10 min. This Vilsmeier reagent was introduced slowly into a soln. of 1 (4.00 g, 14.3 mmol) in
DMF (50 ml) at 08. After addition, the temp. was raised to 258, and stirring was continued for 30 min. Then, the

Helvetica Chimica Acta ± Vol. 88 (2005)
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red mixture was poured into ice-water, and 2m NaOH (100 ml) was added. Extraction with Et2O and CC (silica
gel; hexane/Et2O 1:2) yielded 4 (3.06 g, 70%) as violet crystals. M.p. 161 ± 1628 (hexane/Et2O). Rf (hexane/Et2O
1:2) 0.42. IR (KBr): 3421w, 3050w, 1690w, 1636s, 1566m, 1491m, 1456m, 1440m, 1429m, 1350m, 1329m, 1291w,
1225m, 1209m, 1157w, 1066w, 1055w, 1024w, 934w, 904w, 8 50w, 8 16w, 793m, 759m, 746m, 702s, 646w, 594w, 516w,
477w. 1H-NMR (300 MHz, CDCl3): 8.80 (s, CHO); 8.26 (d, 3J ˆ 4.5, HÀC(2)); 7.35 (t, 2J ˆ 10.3, HÀC(6)); 7.59 ±
7.42 (m, 10 arom. H, HÀC(5), HÀC(7)); 7.13 (d, 3J ˆ 4.5, HÀC(3)). 13C-NMR (75 MHz, CDCl3): 189.17 (d,
CHO); 153.09, 151.57, 145.32 (3s), 137.94, 135.90, 129.85, 129.40 (4d), 129.00, 116.97, 116.48, 116.16 (4 d, each 2
.
‡
‡
arom. C); 120.62 (d). EI-MS: 309 (24, [M ‡ 1] ), 308(100, M ), 307 (32), 294 (11), 294 (8), 291 (8), 169 (9),
160 (21), 279 (26), 278 (15), 277 (14), 276 (18), 232 (29), 231 (31), 215 (12), 203 (18), 202 (40), 201 (9), 200 (9),
157 (11), 116 (12), 105 (13), 86 (9), 77 (8), 58 (18), 43 (22), 41 (8). Anal. calc. for C 23H16O (308.37): C 89.58, H
5.23; found: C 89.54, H 5.30.
1.3. 1-Methyl-4,8-diphenylazulene (6). Aldehyde 4 (1.74 g, 5.6 mmol) in 100 ml diglyme/Et2O 1 :1 and BF3
´
OEt2 (3 ml, 22.4 mmol) in Et2O (20 ml) were added drop by drop to a soln. of NaBH4 (0.635 g, 16.8mmol) in
diglyme (100 ml) at 08 within 2 h. After addition, the stirring was continued for 1 h, and, then, this mixture was
poured into ice-water. Extraction by hexane and CC (alumina; hexane) gave pure 6 (0.92 g, 55%) as blue
crystals. M.p. 144 ± 1458 (hexane). UV (hexane, c ˆ 0.493  10À4 m)4): lmax 243 (4.31), 264 (4.54), 354 (3.55); lmin
224 (4.16), 250 (4.16), 331 (3.38). IR (KBr): 3424w, 3051w, 3024w, 2922w, 1659w, 1954w, 1551m, 1515m, 1491m,
1457s, 1439m, 1416m, 1267w, 1218w, 1200w, 1167w, 1074m, 1025w, 1005m, 956w, 925w, 901w, 8 43w, 8 15w, 798m,
783m, 755s, 735m, 701s, 623w, 530w. 1H-NMR (300 MHz, CDCl3): 7.51 ± 7.46 (m, 2 arom. H, HÀC(2)); 7.44 ±7.31
(m, 8arom. H, H ÀC(6)); 6.98( d, 3J ˆ 4.0, HÀC(3)); 7.02 (d, 3J ˆ 10.2, HÀC(7)); 6.95 (d, 3J ˆ 10.3, HÀC(5));
1.75 (s, MeÀC(1)). 13C-NMR (75 MHz, CDCl3): 150.88, 149.95, 145.12, 144.34, 140.06 (5d), 139.82, 134.33,
129.01, 116.88 (4d), 116.33, 127.93, 127.62, 127.52, 127.26, 125.29, 124.06, 118.67 (7d); 17.13 (q). EI-MS: 295 (25,
.
‡
‡
[M ‡ 1] ), 294 (100, M ), 293 (24), 169 (7), 279 (12), 278(14), 277 (8), 276 (10), 230 (9), 218(10), 217 (16),
215 (19), 202 (12), 154 (16), 139 (7), 138(7), 91 (10), 44 (8), 43 (14), 32 (30). Anal. calc. for C 23H18 (294.14): C
93.84, H 6.16; found: C 93.78, H 6.16.
1.4. 6-Methyl-4,8-diphenylazulene (2) and 1,6-Dihydro-6-methyl-4,8-diphenylazulene (3). Azulene 2 was
prepared according to [5]. When the mixture was purified by CC (silica gel; hexane), in addition to main
product 2, a small fraction of 3 was collected, which slowly crystallized from hexane/Et2O as orange crystals.
Pure 3, on the treatment with chloranil (ˆ2,3,5,6-tetrachlorobenzo-1,4-quinone) at 408 in Et2O for 5 h, gave 2 in
quantitative yield.
Data of 2: M.p. 156 ± 1578 (hexane; [5]: blue oil). Rf (hexane) 0.48. UV (hexane, c ˆ 0.648  10À4 m)4): lmax
238(4.31), 267 (4.60), 351 (3.52); lmin 219 (4.18), 247 (4.26), 327 (3.38). IR (KBr): 3423w, 3052w, 3022w, 2923m,
1653w, 1953w, 1637w, 1565m, 1550m, 1479m, 1456m, 1443m, 1434s, 1322w, 1270w, 1218m, 1071m, 1024m, 999m,
851w, 8 35w, 769s, 751s, 716m, 68 s9, 654w, 516w. 1H-NMR (300 MHz, CDCl3): 7.63 ± 7.59 (m, 4 arom. H,
HÀC(2)); 7.53 ± 7.45 (m, 6 arom. H); 7.01 (s, HÀC(5), HÀC(7)); 7.06 (d, 3J ˆ 3.9, HÀC(1), HÀC(3)); 2.67 (s,
.
‡
‡
MeÀC(6)). EI-MS: 295 (21, [M ‡ 1] ), 294 (82, M ), 293 (16), 161 (24), 160 (100), 279 (66), 278(35), 277
(26), 276 (16), 252 (12), 218(11), 217 (9), 215 (12), 203 (13), 202 (32), 201 (9), 200 (9), 140 (8), 139 (18), 138
(21), 133 (9), 132 (8), 126 (14).
Data of 3: M.p. 96 ± 978 (hexane/Et2O). Rf (hexane) 0.62. UV (hexane, c ˆ 0.679  10À4 m): lmax 251 (4.42);
lmin 216 (4.24). IR (KBr): 3424w, 3072w, 3032m, 3020m, 2958m, 2924m, 1670w, 1616w, 2738w, 1948w, 1880w,
1807w, 1671w, 1599w, 1573w, 1489m, 1455m, 1443m, 1401w, 1377w, 1340m, 1306w, 1257w, 1235w, 1179w, 1163w,
1141w, 1108w, 1075m, 1041w, 1024w, 1000w, 98 7w, 961m, 936w, 917w, 8 94m, 8 72w, 8 56m, 8 45m, 8 33w, 8 27w, 765s,
738m, 702s, 679s, 659m, 640m, 626w, 541w, 513m. 1H-NMR (300 MHz, CDCl3): 7.35 ± 7.25 (m, 10 arom. H); 6.59
(d, with f.s., 3J ˆ 5.3, HÀC(2)); 6.34 (d, with f.s., 3J ˆ 5.4, HÀC(3)); 5.42 (d, 3J ˆ 5.8, HÀC(5)); 5.21 (d. with f.s.,
3J ˆ 5.7, HÀC(7)); 3.61 (d, A of AB, 2J ˆ 14.4, HAÀC(1)); 3.18( d, B of AB, 2J ˆ 14.4, HBÀC(1)); 1.76 (m,
HÀC(6)); 1.47 (d, 3J ˆ 7.0, MeÀC(6)). 13C-NMR (75 MHz, CDCl3): 145.88, 145.01, 142.47, 140.42, 137.13, 135.32
(6s); 134.48, 130.54, 116.90, 116.70, 116.00, 126.90, 126.81, 126.45, 126.01 (9d); 43.34 (t); 33.22 (d); 19.58( q,
.
‡
‡
MeÀC(6)). EI-MS: 297 (25, [M ‡ 1] ), 296 (100, M ), 295 (7), 162 (18), 161 (73), 160 (9), 279 (11), 268 (10),
267 (38), 266 (22), 265 (16), 253 (10), 252 (15), 204 (10), 203 (22), 202 (18), 126 (7), 32 (11). Anal. calc. for
C23H20 (296.40): C 93.20, H 6.80; found: C 93.21, H 7.01. The structure of 3 was confirmed by X-ray crystal-
structure analysis (cf. Table 2).
1.5. 6-Methyl-4,8-diphenylazulene-1-carbaldehyde (5). The reaction was performed in analogy to 1.2. POCl3
(1.5 ml, 165 mmol) was dropped into DMF (10 ml) under stirring at 08 within 10 min. This Vilsmeier reagent was
4
)
Absorption bands above 400 nm have not been registered.

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Helvetica Chimica Acta ± Vol. 88 (2005)
Table 2. Crystallographic Data of 3, 11, and 12
3
11
12
Empirical formula
C23H20
296.41
orange, prism
0.15 Â 0.20 Â 0.25
160(1)
orthorhombic
Pca21
C16H22O4
C29H24O4
Formula weight [g molÀ1
Crystal color, habit
]
422.48436.50
orange, prism
0.10 Â 0.15 Â 0.180.08
160(1)
yellow, plate
Crystal dimensions [mm]
Temperature [K]
Crystal system
 0.20  0.20
250(1)
triclinic
triclinic
Å
Å
Space group
P1
P1
Z
4
4
2
Reflections for cell determination
2q range for cell determination [8]
2790
4 ± 60
7576
4 ± 50
5183
4 ± 55
Unit-cell parameters:
a [Š]
9.3998(2)
10.2111(2)
17.4501(3)
90
90
90
1674.90(6)
632
1.175
0.0661
f and w
60
9.8774(1)
12.7852(2)
19.0973(3)
92.5045(5)
102.4708(6)
111.825(1)
2165.47(6)
888
10.0117(2)
10.7690(2)
12.6350(2)
110.4560(9)
111.8989(9)
96.1826(9)
1138.99(4)
460
b [Š]
c [Š]
a [8]
b [8]
g [8]
V [Š3]
F(000)
Dx [g cmÀ3
]
1.296
1.273
m(MoKa) [mmÀ1
Scan type
]
0.0859
f and w
50
0.0839
f and w
55
2q(max) [8]
Total reflections measured
32160
35881
41764
Symmetry independent reflections
Rint
4633
0.064
7645
0.072
5188
0.048
Reflections with I > 2s (I)
Reflections used in refinement
3507
3507
5286
7645
3746
3746
Parameters refined
3
20858 326
0.0444
0.0411
±
0.015
1.481
R [on F; I > 2s (I) reflections]
wR [on F; I > 2s (I) reflections]
wR [on F2; all indept. reflections]
Weights: p in w ˆ [s2(Fo) ‡ (pFo)2]À1
Goodness-of-fit
0.0480
±
0.0519
0.0584
0.1369
)
±
a
0.005
1.074
0.011(1)
0.001
0.24; À 0.22
2.976
Secondary extinction coefficient
3.4(5) Â 10À6
0.0004
0.18; À 0.16
7.1(9) Â 10À6
Final Dmax/s
D1 (max; min) [e Š
0.0003
0.18; À 0.19
À3
]
a) wÀ1 ˆ s2 (Fo)2 ‡ (0.0535P)2 ‡ 0.5479P, where P ˆ (Fo2 ‡ 2F2c )/3.
introduced slowly into a soln. of 2 (630 mg, 2.14 mmol) in DMF (10 ml) at 08. After addition, the temp. was
raised to 258, and stirring was continued for 30 min. Then, the red mixture was poured into ice water, and 2m
NaOH (100 ml) was added. Extraction with Et2O and CC (silica gel; hexane/Et2O 1:2) yielded 5 (110 mg, 16%).
Violet crystals. M.p. 132 ± 1338 (Et2O/hexane). Rf (Et2O/hexane 4 :6) 0.62. IR (KBr): 3423w, 3051w, 3022w,
2923m, 1653w, 1953w, 1637w, 1565m, 1550m, 1479m, 1456m, 1443m, 1434s, 1322w, 1270w, 1218m, 1071m, 1024m,
1024m, 999m, 8 50w, 8 35w, 769s, 751s, 716m, 68 9s, 654w, 516w. 1H-NMR (300 MHz, CDCl3): 8.73 (s, CHO); 8.21
(d, 3J ˆ 4.5, HÀC(2)); 7.58± 7.48( m, 10 arom. H); 7.38( s, HÀC(5), HÀC(7)); 7.02 (d, 3J ˆ 4.4, HÀC(3)); 2.72 (s,
.
‡
‡
MeÀC(6)). EI-MS (GC-MS): 323 (25, [M ‡ 1] ), 322 (100, M ), 321 (71), 308(21), 307 (72), 306 (8), 305 (14),
294 (11), 293 (35), 291 (7), 290 (7), 169 (19), 161 (7), 279 (19), 278(25), 277 (26), 276 (35), 252 (7), 245 (10),
244 (24), 216 (12), 215 (41), 214 (11), 207 (33), 201 (10), 189 (11), 153 (10), 145 (22), 144 (12), 139 (35), 138
(40), 132 (10), 131 (18), 126 (15), 125 (10), 91 (13), 77 (8), 57 (8).

Helvetica Chimica Acta ± Vol. 88 (2005)
881
1.6. 1,6-Dimethyl-4,8-diphenylazulene (7). The reaction was performed in analogy to 1.3. Aldehyde 5
(100 mg, 0.31 mmol) in 20 ml diglyme/Et2O 1 :1 and BF3 ´ OEt2 (0.2 ml, 1.50 mmol) in Et2O (20 ml) were added
dropwise to a soln. of NaBH4 (43 mg, 1.14 mmol) in diglyme (20 ml) at 08 within 2 h. After workup, CC
1
(alumina; hexane) gave pure 7 (64 mg, 67%). Blue crystals. 7: M.p. 1128 (hexane). Rf (hexane) 0.5. H-NMR
(300 MHz, CDCl3): 7.51 ± 7.46 (m, 2 arom. H); 7.44 ± 7.16 (m, 8arom. H, H ÀC(2)); 6.87 (s, HÀC(7)); 6.86 (d,
3J ˆ 4.4, HÀC(3)); 6.80 (s, HÀC(5)); 2.50 (s, MeÀC(6)); 1.76 (s, MeÀC(1)). 13C-NMR (75 MHz, CDCl3):
149.89, 149.03, 145.55, 145.41, 144.76, 138.54 (6s); 138.37, 131.97, 116.97, 116.84, 116.44, 127.88, 127.61, 127.17,
‡
126.90, 125.54, 118.81 (11d); 16.29 (q, MeÀC(6)); 17.06 (q, MeÀC(1)). EI-MS: 309 (26, [M ‡ 1] ), 308(100,
.
‡
M
), 307 (19), 294 (16), 293 (14), 292 (10), 291 (10), 169 (9), 278(9), 276 (7), 232 (14), 231 (13), 216 (7), 215
(17), 205 (7), 202 (11), 139 (7), 138(7), 91 (8), 57 (17), 56 (7), 43 (11), 41 (11), 32 (8).
1.7. 3-Methyl-4,8-diphenylazulene-1-carbaldehyde (8). The reaction was performed in analogy to 1.2. POCl3
(0.2 ml, 2.2 mmol) was dropped into DMF (2 ml) under stirring at 08 within 10 min. This Vilsmeier reagent was
introduced slowly into a soln. of 6 (100 mg, 0.34 mmol) in DMF (10 ml) at 08. After addition, the temperature
was raised to 258, and stirring was continued for 30 min. Then, the red mixture was poured into ice water, and 2m
NaOH (20 ml) was added. Extraction with Et2O and CC (silica gel; hexane/Et2O 1 :2) yielded 8 (50 mg, 45%).
Violet crystals. M.p. 150 ± 1518 (Et2O/hexane). IR (KBr): 3393w, 2923m, 1653w, 1722w, 1632s, 1560m, 1520m,
1501m, 1455m, 1424m, 1397m, 1364m, 1353m, 1263w, 1191m, 1071m, 1027w, 1010m, 936w, 907w, 8 11w, 769m,
754s, 701s, 647w, 610w, 598w, 524w. 1H-NMR (300 MHz, CDCl3): 8.64 (s, CHO); 8.09 (s, HÀC(2)); 7.49 (t, partly
overlapped, 3J ˆ 10.4, HÀC(6)); 7.43 ± 7.37 (m, 8arom. H); 7.34 ± 7.28( m, 2 arom. H); 7.25 (d, 3J ˆ 10.1,
HÀC(7)); 7.19 (d, 3J ˆ 9.7, HÀC(5)); 1.67 (s, MeÀC(3)). 13C-NMR (75 MHz, CDCl3): 186.84 (d, CHO); 153.00,
150.57, 145.74, 144.27 (4s); 142.31, 141.08, 139.88 (2s); 134.91, 130.12, 129.17 (3d); 129.03 (s); 116.93, 116.83,
.
‡
‡
116.73, 116.58(4 d); 116.23 (s); 127.89 (d). EI-MS: 323 (24, [M ‡ 1] ), 322 (100, M ), 321 (46), 308(7), 307
(29), 305 (7), 294 (9), 293 (23), 291 (8), 169 (15), 279 (19), 278 (23), 277 (13), 276 (18), 245 (23), 215 (21), 202
(6), 149 (17), 145 (7), 139 (8), 138 (12), 123 (8), 106 (7), 105 (8), 97 (11), 91 (10), 85 (7), 83 (18), 81 (7), 77 (7),
71 (12), 70 (7), 69 (15), 58(9), 57 (22), 56 (8), 55 (17), 43 (41), 41 (15), 32 (16). Anal. calc. for C 24H18O
(322.14): C 89.41, H 5.63; found: C 88.77, H 5.93.
1.8. 1,3-Dimethyl-4,8-diphenylazulene (9). The reaction was performed in analogy to 1.3. Aldehyde 8
(380 mg, 1.13 mmol) in 30 ml diglyme/Et2O 1:1 and BF3 ´ OEt2 (129 mg, 3.4 mmol) in Et2O (20 ml) were added
dropwise to a soln. of NaBH4 (129 mg, 3.40 mmol) in diglyme (20 ml) at 08 within 2 h. After workup, CC
(alumina/hexane) gave pure 9 (50 mg, 14%). Blue crystals. M.p. 100 ± 1018(hexane). Rf (hexane) 0.67. UV
(hexane, c ˆ 0.429  10À4 m)4): lmax 246 (4.32), 262 (4.57), 358(3.60), 374 (3.45); lmin 216 (4.19), 253 (4.29), 335
(3.39), 370 (3.40). IR (KBr): 3443w, 3025w, 3024w, 2924w, 1659w, 1947w, 1646w, 1598w, 1563m, 1550s, 1534m,
1489m, 1463m, 1444s, 1266w, 1201w, 1153w, 1071w, 1029w, 1004m, 996w, 8 95w, 8 58w, 773m, 760s, 701s, 606w,
532m. 1H-NMR (300 MHz, CDCl3): 7.39 ± 7.16 (m, 10 arom. H, HÀC(2)); 7.20 (t, 3J(6,7) ˆ 3J(5,6) ˆ 10.2,
HÀC(6)); 6.73 (d, 3J(7,6) ˆ 3J(5,6) ˆ 10.2, HÀC(5), HÀC(7)); 1.68( s, MeÀC(1)); 1.63 (s, MeÀC(3)).
13C-NMR (75 MHz, CDCl3): 150.02, 145.61 (2s); 144.86 (d); 134.60 (s); 134.43, 116.92, 127.62, 127.10 (4d);
.
‡
‡
126.84, 127.26 (2d); 124.64 (d); 17.08( q). EI-MS: 309 (27, [M ‡ 1] ), 308(100, M ), 307 (8), 296 (8), 294 (10),
293 (17), 292 (8), 291 (11), 169 (8), 278 (8), 276 (6), 230 (9), 215 (13), 202 (6), 139 (7), 138 (8), 57 (13), 55 (5),
43 (8), 41 (6).
2. Synthesis of Dimethyl Heptalene-4,5-dicarboxylates. 2.1. Dimethyl 1-Methyl-6,10-diphenylheptalene-4,5-
dicarboxylate (12) and Dimethyl 3-Methyl-4,8-diphenylazulene-1,2-dicarboxylate (16). Azulene 6 (0.92 g,
3.13 mmol) was dissolved in MeCN (18ml) in a Schlenk vessel and dimethyl acetylenedicarboxylate (ADM;
1.2 ml, 9.84 mmol) was added. The vessel was flushed with Ar and then closed. The blue soln. was stirred during
72 h at 1008 while the color of the soln. changed to brownish yellow. The solvent was removed under reduced
pressure, and the residue was purified by CC (silica gel; hexane/Et2O 1:3) to give 12 (0.55 g, 40%) as yellow
foam, followed by a blue fraction, which contained 16 in small amounts (<1%). Heptalene 12 could be
crystallized from acetone. When the reaction of azulene 6 with ADM was performed in DMF as solvent at 1708
during 48h, the yield of 12 amounted to 22%.
Data of 12: M.p. 200 ± 2018 (hexane/Et2O 1 : 1). Rf (hexane/Et2O 1:3) 0.45. UV (hexane, c ˆ 0.333 Â
10À4 m)4): lmax 198(4.70), 291 (4.37), 385 (sh, 3.24); lmin 272 (4.32). IR (KBr): 3419w, 3019w, 2994w, 2949w,
1736s, 1718s, 1595w, 1573w, 1552w, 1493w, 1432m, 1368w, 1342w, 1257s, 1216m, 1191m, 1171m, 1137m, 1093w,
1067w, 1052m, 1031m, 98 4w, 935w, 8 91w, 8 50w, 796m, 772m, 758s, 734m, 702m, 667w, 576w, 504w. 1H-NMR
(300 MHz, CDCl3): 7.83 (d, J ˆ 6.0, HÀC(3)); 7.47 ± 7.44 (m, 2 arom. H); 7.30 ± 7.15 (m, 8arom. H); 6.90 ( d, 3J ˆ
6.3, HÀC(7)); 6.83 (dd, 3J(8,7) ˆ 6.4, 3J(8,9) ˆ 11.2, HÀC(8)); 6.59 (d, 3J ˆ 11.2, HÀC(9)); 6.44 (dd, J ˆ 1.3/6.4,
HÀC(2)); 3.73 (s, MeOC(O)ÀC(4)); 3.23 (s, MeOC(O)ÀC(5)); 1.61 (s, MeÀC(1)). 1H-NMR (600 MHz,
(D6)acetone): 7.79 (dd, J ˆ 0.8, 6.1, HÀC(3)); 7.51 ± 7.49 (m, 2 arom. H); 7.36 ± 7.34 (m, 3 arom. H); 7.16 (t-like, 2

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Helvetica Chimica Acta ± Vol. 88 (2005)
arom. H); 7.23 (d, 3J ˆ 7.3, 1 arom. H); 7.21 ± 7.19 (m, 2 arom. H); 7.01 (d, 3J ˆ 6.5, HÀC(7)); 6.88 (dd, 3J(8,7) ˆ
6.5, 3J(8,9) ˆ 11.4, HÀC(8)); 6.59 (d, 3J ˆ 11.4, HÀC(9)); 6.56 (dd, J ˆ 0.8
,
6.1, HÀC(2)); 3.67 (s,
MeOC(O)ÀC(4)); 3.17 (s, MeOC(O)ÀC(5)); 1.60 (s, MeÀC(1)). 13C-NMR (150 MHz, (D6)acetone): 168.10
(s, MeOC(O)ÀC(4)); 167.73 (s, MeOC(O)ÀC(5)); 144.85 (s, C(5)); 141.62 (d, C(3)); 140.67 (s, 1 arom. C);
140.48( s, C(5a)); 140.02 (s, 1 arom. C); 137.71 (s, C(10)); 137.06 (s, C(6)); 134.55 (d, C(9)); 134.25 (d, C(8));
134.07 (s, C(4)); 130.77 (d, 2 Â enhanced intensity, 2 arom. C); 130.48( s, C(10a)); 130.00 (d, C(2)); 129.95 (d, 2 Â
enhanced intensity, 2 arom. C); 129.77 (d, 2 Â enhanced intensity, 2 arom. C); 129.50 (d, 1 arom. C); 116.94 (d, 1
arom. C); 116.58( s, C(1)); 127.95 (d, 2 Â enhanced intensity, 2 arom. C); 126.67 (d, C(7)); 52.82 (q,
‡
MeOC(O)ÀC(4)); 52.21 (q, MeOC(O)ÀC(5)); 23.98( q, MeÀC(1)). CI-MS: 455 (9, [M ‡ NH4] ), 454 (29),
.
‡
‡
439 (5), 438(9), 437 (29), 436 (6, M ), 422 (6), 415 (6), 414 (20), 407 (7), 406 (30), 405 (100, [M À OMe] ),
343 (13). Anal. calc. for C29H24O4 (436.50): C 79.80, H 5.54; found: C 79.89, H 5.81. The structure of 12 was
confirmed by X-ray crystal-structure analysis (cf. Tables 1 and 2).
Data of 16: Rf (hexane/Et2O 1 :3) 0.36. 1H-NMR (300 MHz, CDCl3): 7.70 (t, 3J ˆ 10.3, HÀC(6)); 7.57 ± 7.44
(m, 10 arom. H); 7.27 (d, 3J ˆ 11.5, HÀC(7)); 7.23 (d, 3J ˆ 10.5, HÀC(5)); 3.81(s, MeOC(O)ÀC(1)); 3.16(s,
MeOC(O)ÀC(2)); 1.53 (s, MeÀC(3)).
2.1.1. Irradiation of 12. The soln. of 12 in toluene (c ˆ 2.3  10À2 m) was irradiated with the lamp of a
1
fluorescent tube (lmax (emiss.): 366/433 nm) overnight. H-NMR analysis showed that its DBS isomer 12' was
not observed (limit of detection ca. 1%).
2.2. Dimethyl 1,8-Dimethyl-6,10-diphenylheptalene-4,5-dicarboxylate (13). The reaction was performed in
analogy to 2.1. Azulene 7 (50 mg, 0.16 mmol) was reacted with ADM (0.06 ml, 0.49 mmol) in 5 ml of MeCN
yielding 13 (5 mg, 7%) as yellow foam. Rf (hexane/Et2O 1:1) 0.22. 1H-NMR (300 MHz, CDCl3): 7.72 (d, 3J ˆ 5.2,
HÀC(3)); 7.38± 7.31 ( m, 2 arom. H); 7.21 ± 7.04 (m, 8arom. H); 6.65 ( s, HÀC(7)); 6.33 (d, 3J ˆ 6.0, HÀC(2));
6.29 (s, HÀC(9)); 3.66 (s, MeOC(O)ÀC(4)); 3.14 (s, MeOC(O)ÀC(5)); 1.97 (s, MeÀC(8)); 1.52 (s, MeÀC(1)).
.
‡
‡
EI-MS (GC): 450 (56, M ), 391 (100, [M À COOMe] ), 359 (67), 331 (61), 316 (56), 315 (44), 161 (95), 253
(67).
2.3. Attempted Synthesis of Dimethyl 1,3-Dimethyl-6,10-diphenylheptalene-4,5-dicarboxylate (10). The
reaction was performed in analogy to 2.1. Azulene 9 (42 mg, 0.14 mmol) was reacted with ADM (0.05 ml,
0.41 mmol) in 10 ml of MeCN. TLC indicated that a number of products were formed. Trace amounts of 10
could be identified on TLC by its correlated Rf value and its pale yellow color.
2.4. Dimethyl 6,10-Diphenylheptalene-4,5-dicarboxylate (11). The reaction was performed in analogy to 2.1.
Azulene 1 (250 mg, 0.89 mmol) was reacted with ADM (0.33 ml, 2.70 mmol) in 15 ml of MeCN yielding 11
(160 mg, 42%). Red crystals. M.p. 1658 (hexane/Et2O 1 :1). Rf (hexane/Et2O 1 :1) 0.20. UV/VIS (hexane, c ˆ
0.349 Â 10À4 m): lmax 294 (4.32); lmin 276 (4.29); 400 (sh, 3.22). IR (KBr): 3409w, 3057w, 3022w, 2948w, 1730s,
1717s, 1595w, 1574w, 1491w, 1437m, 1404w, 1355w, 1302m, 1268s, 1218m, 1184m, 1116m, 1097m, 1067m, 1027m,
976w, 915w, 8 92w, 8 53w, 8 23w, 799w, 78 4m, 766m, 742s, 699s, 685m, 676m, 566w, 515w. 1H-NMR (300 MHz,
(D6)benzene): 7.77 (d, 3J(3,2) ˆ 6.1, HÀC(3)); 7.59 (d, 3J ˆ 7.1, 2 arom. H); 7.16 ± 6.97 (m, 8arom. H); 6.63 ( d,
3
3
3
3J(7,8) ˆ 5.8, HÀC(7)); 6.51 (dd, J(8,7) ˆ 6.0, J(8,9) ˆ 11.4, HÀC(8)); 6.44 (d, J ˆ 11.3, HÀC(9)); 5.88 (dd,
3J(2,3) ˆ 6.1, 3J(2,1) ˆ 10.2, HÀC(2)); 5.69 (d, 3J(1,2) ˆ 10.2, HÀC(1)); 3.30 (s, MeOC(O)ÀC(4)); 3.07 (s,
MeOC(O)ÀC(5)). 1H-NMR (600 MHz, CDCl3, in thermal equilibrium with 7% of its DBS isomer 11'): 7.72 (d,
3J(3,2) ˆ 6.2, HÀC(3)); 7.42 (d with f.s., 3J ˆ 6.3, 2 arom. H); 7.22 ± 7.19 (m, 3 arom. H); 7.18± 7.16 ( m, 2 arom.
H); 7.11 ± 7.08( m, 1 arom. H); 7.08± 7.05 ( m, 2 arom. H); 6.72 ± 6.68( m, HÀC(7), HÀC(8)); 6.49 ± 6.46 (m,
HÀC(9)); 6.39 (dd, 3J(2,3) ˆ 6.2, 3J(2,1) ˆ 10.2, HÀC(2)); 5.90 (d, 3J(1,2) ˆ 10.2, HÀC(1)); 3.65 (s,
MeOC(O)ÀC(4)); 3.12 (s, MeOC(O)ÀC(5)). 13C-NMR (150 MHz, CDCl3): 167.26 (s, MeOC(O)ÀC(5));
167.12 (s, MeOC(O)ÀC(4)); 141.77 (d, C(3)); 141.38, 139.54, 138.87, 138.80, 135.82 (5s); 135.52 (d, C(1)); 135.03
(s); 133.58( d, C(9)); 133.23 (d, C(8)); 130.83 (d, C(2)); 130.40 (d, 2 Â enhanced intensity, 2 arom. C); 116.58( d,
2 Â enhanced intensity, 2 arom. C); 116.39 (s); 116.18( d, 2 Â enhanced intensity, 2 arom. C); 116.07 (d, 1 arom.
C); 127.55 (d, 1 arom. C); 127.34 (d, 2 Â enhanced intensity, 2 arom. C); 126.52 (s); 126.46 (d, C(7)); 52.40 (q,
.
‡
‡
MeOC(O)ÀC(4)); 51.85 (q, MeOC(O)ÀC(5)). EI-MS: 423 (27, [M ‡ 1] ), 422 (88, M ), 421 (11), 391 (18),
‡
390 (23), 375 (6), 365 (6), 364 (34), 363 (100, [M À COOMe] ), 363 (24), 362 (57), 361 (9), 349 (13), 348(7),
347 (12), 336 (6), 332 (15), 331 (52), 330 (6), 329 (6), 320 (10), 305 (16), 304 (55), 303 (91), 302 (93), 301 (22),
300 (29), 291 (6), 290 (9), 169 (23), 167 (8), 160 (15), 279 (15), 278 (11), 277 (10), 276 (18), 274 (7), 239 (7), 227
(5), 226 (14), 215 (5), 203 (5), 202 (14), 201 (5), 165 (6), 152 (13), 151 (54), 150 (22), 149 (12), 145 (17), 144 (6),
138(12), 137 (7), 105 (8), 43 (5). Anal. calc. for C 16H22O4 (422.47): C 79.60, H 5.25; found: C 79.26, H 5.29. The
structure of 11 was confirmed by X-ray crystal-structure analysis (cf. Tables 1 and 2).
Data of Dimethyl 6,10-Diphenylheptalene-1,2-dicarboxylate (11'; partially recognized NMR signals in
thermal equilibrium with 93% of its DBS isomer 11): 1H-NMR (600 MHz, CDCl3): 5.76 (d, 3J(5,4) ˆ 6.1,

Helvetica Chimica Acta ± Vol. 88 (2005)
883
HÀC(5)); 3.71 (s, MeOC(O)ÀC(2)); 3.15 (s, MeOC(O)ÀC(1)). 13C-NMR (150 MHz, CDCl3): 167.26 (s,
MeOC(O)ÀC(5)); 52.80 (q, MeOC(O)ÀC(2)); 52.15 (q, MeOC(O)ÀC(1)).
3. X-Ray Crystal-Structure Determination of Compounds 3, 11, and 12 (Tables 1, and 2 and Figs. 1 ± 3)5). ±
All measurements were conducted on a Nonius KappaCCD area detector diffractometer [9] using graphite-
monochromated MoKa radiation (l 0.71073 Š) and an Oxford Cryosystems Cryostream-700 cooler. The data
collection and refinement parameters are given in Table 2, while views of the molecules are shown in Figs. 1 ± 3.
Data reduction was performed with HKL DENZO and SCALEPACK [10]. The intensities were corrected for
Lorentz and polarization effects, but not for absorption. Equivalent reflections, other than the Friedel pairs in 3,
were merged. Each structure was solved by direct methods using SIR92 [11], which revealed the positions of all
non-H-atoms and the non-H-atoms were refined anisotropically.
The molecule in 3 has pseudo Cs symmetry. The atomic coordinates were tested carefully for a relationship
from a higher symmetry space group using the program PLATON [12], but none could be found. Three
electron-density peaks were found near each of C(1) and C(3). These peaks corresponded with the positions
expected if the parent C-atoms were made up from the contributions from disordered CH2 and sp2 CH.
Therefore, each of these peaks was assigned as an H-atom with a site-occupation factor of 0.5. A test refinement
of the positions of these H-atoms showed that they behaved well. For 12, the ester substituent at C(4) is
disordered with the CˆO O-atom and the MeO group occupying two orientations, which differ by a rotation of
ca. 1808 about the C(4)ÀC(ˆO) bond. The best results were obtained when the site-occupation factors of the
two conformations were set to 0.65 and 0.35, resp. In the case of 11, there are two symmetry-independent
molecules in the asymmetric unit. Their conformations differ by a significant rotation of one of the ester
substituents. All of the H-atoms in the structures were placed in geometrically calc. positions and each was
assigned a fixed isotropic displacement parameter with a value equal to 1.2 Ueq of its parent C-atom (1.5 Ueq for
the Me groups of 11).
The structures of 3, and 12 were refined on F using full-matrix least-squares procedures, which minimized
the function Sw(j Fo jÀ j Fc j )2. For 11, the refinement was carried out on F2 by minimizing the corresponding
function based on F2. Corrections for secondary extinction were applied. For 3 and 12, one and five low angle
reflections, resp., were omitted from the final refinement of each structure because the observed intensities of
these reflections were much lower than the calc. values as a result of being partially obscured by the beam stop.
Neutral-atom-scattering factors for non-H-atoms were taken from [13a], and the scattering factors for H-atoms
were taken from [14]. Anomalous dispersion effects were included in Fc [15]; the values for f ' and f'' were those
of [13b]. The values of the mass attenuation coefficients were those of [13c]. All calculations for 11 were
performed using SHELXL97 [16], while the teXsan crystallographic software package [17] was used for the
remaining structures. The crystallographic diagrams were drawn using ORTEPII [18].
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[9] R. Hooft, KappaCCD Collect Software, Nonius BV, Delft, The Netherlands, 1999.
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Appl. Crystallogr. 1994, 27, 435.
5
)
CCDC-219128± 219130 contain the supplementary crystallographic data for this paper. These data can be
obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystal-
lographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: ‡ 441223336033; e-mail:
deposit@ccdc.cam.ac.uk).

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Helvetica Chimica Acta ± Vol. 88 (2005)
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Received December 14, 2004