Rearrangement of furo[2,3-c]quinoline-2,4(3aH,5H)-diones to furo[3,4-c]quinoline-3,4(1H,5H)-diones

Article abstract of DOI:10.1016/j.tetlet.2007.11.010

Thermally assisted base-catalyzed rearrangement of furo[2,3-c]quinoline-2,4(3aH,5H)-diones 1 to the corresponding furo[3,4-c]quinoline-3,4(1H,5H)-diones 2 is reported, and a mechanism of the transformation is proposed.

Full text of DOI:10.1016/j.tetlet.2007.11.010

Available online at www.sciencedirect.com
Tetrahedron Letters 49 (2008) 90–93
Rearrangement of furo[2,3-c]quinoline-2,4(3aH,5H)-diones
to furo[3,4-c]quinoline-3,4(1H,5H)-diones
b,
a
b
Stanislav Kafka,a, Janez Kosˇmrlj, Antonın Klasek and Andrej Pevec
*
*
´
´
aFaculty of Technology, Tomas Bata University in Zlı´n, 762 72 Zlı´n, Czech Republic
bFaculty of Chemistry and Chemical Technology, University of Ljubljana, 1000 Ljubljana, Slovenia
Received 2 October 2007; revised 23 October 2007; accepted 1 November 2007
Available online 6 November 2007
Abstract—Thermally assisted base-catalyzed rearrangement of furo[2,3-c]quinoline-2,4(3aH,5H)-diones 1 to the corresponding
furo[3,4-c]quinoline-3,4(1H,5H)-diones 2 is reported, and a mechanism of the transformation is proposed.
ꢀ 2007 Elsevier Ltd. All rights reserved.
R1
In recent years, we have explored the reactivity of
quinoline-2,4(1H,3H)-diones, and these studies have
led to a number of interesting products.1–3 For example,
Wittig reaction of 3-hydroxyquinoline-2,4(1H,3H)-
diones with ethyl (triphenylphosphoranylidene)acetate
(Ph3P = CHCO2Et) afforded the desired and expected
(2E)-(3-hydroxy-2-oxo-2,3-dihydroquinolin-4(1H)-yl-
idene)acetates.1k In some cases, furo[3,4-c]quinoline-
3,4(1H,5H)-diones were also formed and isolated as
by-products.2 The formation of these compounds was
tentatively explained through the rearrangement of
intermediately formed furo[2,3-c]quinoline-2,4(3aH,
5H)-diones by the basic Wittig reagent (Ph3P = CH-
CO2Et) or triphenylphosphine. Inter alia we were
intrigued by this rearrangement and decided to study
it in more detail, and report our preliminary results in
this Letter.
O
O
R1
O
R2
R4
R2
R4
O
R3
R3
O
DMAP
cyclohexylbenzene
reflux
N
H
O
N
H
1
2
Scheme 1.
4-dimethylaminopyridine (DMAP, 20 mol %) afforded
the desired products in good yields.
In a general reaction procedure, a mixture of compound
1 (0.5 mmol) and DMAP (20 mol %) in cyclohexyl-
benzene (2 mL) was heated at reflux (ꢀ239 ꢁC) under
an inert atmosphere for 25–120 min. After cooling, the
precipitated compound 2 was filtered under vacuum
and recrystallized from the solvent indicated in Table
1. The yields of analytically pure products, obtained
after the recrystallization, are given in Table 1. Careful
monitoring of the reaction progress was found to be
crucial as additional heating of the reaction mixture,
after starting lactone 1 had been consumed, decreased
the yield of 2. The reaction times and the yields reported
in Table 1 refer to the optimal reaction conditions. It is
interesting to note that, in comparison to 1a–g, com-
pound 1h was the most reactive. Conducting the reac-
tion at 190–205 ꢁC (Table 1, entry 9, conditions C)
resulted in complete consumption of 1h in 4 min, afford-
ing 2h in 52% yield. If conditions A were applied, no 2h
could be detected in the reaction mixture, probable due
to its fast decomposition.
Starting furo[2,3-c]quinoline-2,4(3aH,5H)-diones 1,
required to study the rearrangement shown in Scheme
1, were prepared by known chemistry from 3-hydroxy-
quinoline-2,4(1H,3H)-diones.2–4 To test whether the
base catalyst was essential for the rearrangement, we
initially conducted experiments with lactones 1a,d–f in
boiling cyclohexylbenzene without any additives. No
reaction (data not shown) took place, and after 3 h of
heating, the starting materials were nearly quantitatively
recovered. As shown in Table 1, the addition of
Keywords: Rearrangement; Quinolones; Isocyanate; Mechanism.
*
Corresponding authors. E-mail addresses: kafka@ft.utb.cz; janez.
kosmrlj@fkkt.uni-lj.si
0040-4039/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2007.11.010

S. Kafka et al. / Tetrahedron Letters 49 (2008) 90–93
Table 1. Rearrangement of lactones 1 to furo[3,4-c]quinoline-3,4(1H,5H)-diones 2a
91
Entry
1
R1
R2
R3
R4
Conditions
Time (min)
Yieldb (%)
2, mp (ꢁC, solvent)
1
2
3
4
5
6
7
8
9
1a
1b
1c
1c
1d
1e
1f
n-Bu
n-Bu
n-Bu
n-Bu
Bn
Bn
Bn
Ph
Ph
H
H
H
H
H
H
Me
Me
H
H
H
H
H
H
Me
H
H
H
Me
Me
H
A
A
A
B
A
A
A
A
C
120
90
50
100
25
40
40
40
4
60
41
46
44
53
64
66
47
52
2a, 228–232 (EtOH)
2b, 229–236 (n-BuOH)
2c, 273–278 (EtOH)
2c
H
2d, 289–294 (EtOH)
2e, 288–292 (HOAc)c
2f, 281–283 (HOAc)d
2g, 297–307 (DMF/EtOH)
2h, 335–342 (DMF/EtOH)
Me
Cl
H
1g
1h
Me
Me
a Conditions: (A) DMAP (20 mol %), cyclohexylbenzene (bp 239 ꢁC), reflux; (B) PhCH2NH2 (2.2 equiv), cyclohexylbenzene, reflux; (C) DMAP
(20 mol %), cyclohexylbenzene, bath temperature 190–205 ꢁC.
b Refers to isolated, recrystallized products.
c Lit.2 mp 282–285 ꢁC (HOAc).
d Lit.2 mp 280–284 ꢁC (HOAc).
Confirmation of the structures of furo[3,4-c]quinoline-
3,4(1H,5H)-diones 2 was provided by IR, MS, and
NMR spectra, and in some cases 2D NMR spectra.4
Proton H-1 and carbon C-1 resonances appeared at d
5.87–6.94 ppm and d 78.2–81.7, respectively, and were
characteristic for compounds 2. Single crystal X-ray
structure determination corroborated the structure of
2b (Fig. 1).5 In the crystal, four molecules of 2b are
assembled into a framework by weak N5–HÁ Á ÁO@C3
hydrogen bonds, as shown in Figure 2.
A mechanistic rationalization for the rearrangement is
given in Scheme 2. Base-assisted deprotonation leads
to intermediate resonance stabilized carbanion and
isocyanate group, which after re-combination and sub-
sequent enolization results in the formation of 2. A
Figure 2. The hydrogen bond stacking diagram of four molecules of 2b
depicted in black, blue, red, and green. The hydrogen atoms on carbon
atoms have been omitted for clarity.
similar isocyanate mechanism has been proposed for
the rearrangement of 4-imino-(1H,4H)-3,1-benzox-
azine-2-ones into 2,4-quinazolinediones by Azizian
et al.6 The authors trapped the isocyanate group with
methanol leading to the corresponding methyl carba-
mate. In accordance with the proposed mechanism,
R1
O
O
O
H
H
the authors also reported that the N-methyl derivative
which cannot form an isocyanate did not rearrange.
Our proposed mechanism is in agreement with the fact
O
O
R1
C O
O
R1
H
N
H
O
N
H
O
N
H+
1
H
R1
O
via
enolization
O
N
O
H
2
Scheme 2.
that none of the N-substituted analogues 1 tested
underwent the rearrangement (data not shown), but so
far, attempts to provide further evidence have been
unsuccessful. For example, anticipating that the inter-
mediately formed isocyanate would be trapped as the
corresponding benzylurea derivative, heating of 1c was
conducted in cyclohexylbenzene in the presence of
benzylamine (2.2 equiv). Unfortunately, in comparison
Figure 1. ORTEP plot of 2b from the X-ray crystal structure with
thermal ellipsoids at 30% probability for non-H atoms and open circles
for H-atoms (O: red, N: blue). Crystals of 2b were grown by dissolving
the compound in hot n-butanol followed by slow cooling to room
temperature.

92
S. Kafka et al. / Tetrahedron Letters 49 (2008) 90–93
71.05; H, 6.51; N, 5.13. Compound 1c: mp 226–232 ꢁC
(EtOH); IR (KBr): m 3193, 3136, 3102, 3066, 2979, 2957,
2932, 2876, 2741, 1893, 1863, 1820, 1756, 1691, 1637, 1617,
1495, 1472, 1447, 1417, 1381, 1374, 1357, 1309, 1291, 1269,
1246, 1226, 1205, 1182, 1153, 1142, 1114, 1091, 1068, 1043,
1026, 1009, 963, 949, 934, 904, 888, 864, 831, 815, 789, 750,
to the DMAP experiment (compare entries 3 and 4 in
Table 1), the yield of compound 2c was nearly identical,
and no urea derivative could be found in the reaction
mixture.
In conclusion, furo[2,3-c]quinoline-2,4(3aH,5H)-diones
1 rearranged under heating in the presence of DMAP
into furo[3,4-c]quinoline-3,4(1H,5H)-diones 2 in moder-
ate to good yields. To the best of our knowledge, this is
the first study of such a rearrangement and the scope
and limitations will be the subject of forthcoming
investigations.
1
739, 727, 662, 641, 619, 562, 552, 522, 465, 434 cmÀ1; H
NMR (300 MHz, DMSO-d6): d 0.78 (t, J = 6.7 Hz, 3H),
1.15–1.22 (m, 4H), 1.58–1.69 (m, 1H), 1.92–2.03 (m, 1H),
2.31 (s, 3H), 6.43 (s, 1H), 6.97 (d, J = 8.2 Hz, 1H), 7.31 (dd,
J = 8.2, 1.1 Hz, 1H), 7.53 (br s, 1H), 10.64 (br s, 1H); 13C
NMR (75 MHz, DMSO-d6): d 13.6, 20.1, 21.5, 24.2, 37.0,
86.2, 111.9, 115.2, 116.1, 127.1, 132.5, 133.8, 135.0, 163.8,
166.8, 171.0; Anal. Calcd for C16H17NO3: C, 70.83; H, 6.32;
N, 5.16. Found: C, 71.10; H, 6.40; N, 5.08. Compound 1h:
mp 246–248 ꢁC (benzene); IR (KBr): m 3350–3650 (br),
3238, 3199, 3103, 2955, 2925, 1817, 1770, 1698, 1628, 1618,
1580, 1508, 1461, 1450, 1406, 1384, 1349, 1304, 1254, 1210,
1203, 1112, 1091, 1072, 1064, 1025, 1003, 970, 920, 911, 876,
857, 843, 814, 787, 760, 732, 696, 677, 655, 648, 586, 564,
495, 467, 443, 419 cmÀ1; 1H NMR (300 MHz, DMSO-d6): d
2.18 (s, 3H), 2.47 (s, 3H), 6.73 (s, 1H), 6.93 (d, J = 7.8 Hz,
1H), 7.13 (d, J = 7.8 Hz, 1H), 7.22–7.29 (m, 2H), 7.34–7.41
(m, 3H), 10.16 (br s, 1H); 13C NMR (75 MHz, DMSO-d6):
d 17.2, 19.6, 86.9, 116.0, 122.7, 125.4, 125.8, 129.2, 130.0,
133.8, 134.5, 134.9, 134.9, 161.0, 165.6, 171.0; Anal. Calcd
for C19H15NO3: C, 74.74; H, 4.95; N, 4.59. Found: C,
75.02; H, 5.08; N, 4.49. Compound 2a: IR (KBr): m 3160,
3107, 3050, 2955, 2932, 2868, 1761, 1666,1622, 1564, 1468,
1434, 1404, 1338, 1280, 1236, 1200, 1142, 1025, 815, 768,
689, 658, 634 cmÀ1; 1H NMR (300 MHz, DMSO-d6): d 0.85
(t, J = 7.0 Hz, 3H), 1.15–1.45 (m, 4H), 1.78–1.90 (m, 1H),
2.18–2.30 (m, 1H), 5.91 (dd, J = 7.5, 2.8 Hz, 1H), 7.32 (dd,
J = 7.9, 7.5 Hz, 1H), 7.46 (d, J = 8.3 Hz, 1H), 7.73 (dd,
J = 8.3, 7.5 Hz, 1H), 7.87 (d, J = 7.9 Hz, 1H), 12.13 (br s,
1H); 13C NMR (75 MHz, DMSO-d6): d 13.6, 21.7, 26.1,
33.1, 78.3, 113.3, 114.5, 116.3, 122.6, 125.6, 134.0, 141.7,
156.5, 166.7, 166.9; HRMS calcd for C15H15NO3:
257.1052. Found: 257.1060. Compound 2b: IR (KBr): m
3315–3700 (br), 3150-3315 (br), 3138, 3078, 2956, 2929,
2873, 2863, 1769, 1673, 1619, 1605, 1578, 1500, 1468, 1399,
1344, 1209, 1165, 1139, 1039, 1012, 971, 825, 814, 782, 749,
690, 542, 519, 442 cmÀ1; 1H NMR (300 MHz, DMSO-d6): d
0.84 (t, J = 7.0 Hz, 3H), 1.15–1.45 (m, 4H), 1.78–1.90 (m,
1H), 2.18–2.40 (m, 1H), 2.48 (s, 3H), 5.91 (dd, J = 7.5,
3.0 Hz, 1H), 7.24 (dd, J = 8.0, 7.3 Hz, 1H), 7.58 (d,
J = 7.3 Hz, 1H), 7.71 (d, J = 8.0 Hz, 1H), 11.19 (br s,
1H); 13C NMR (75 MHz, DMSO-d6): d 13.7, 17.7, 21.7,
26.1, 33.2, 78.5, 113.4, 114.2, 122.4, 123.5, 124.9, 135.2,
140.1, 156.8, 166.9, 167.2; Anal. Calcd for C16H17NO3: C,
70.83; H, 6.32; N, 5.16. Found: C, 70.60; H, 6.47; N, 5.13.
Compound 2c: IR (KBr): m 3310–3610 (br), 3155, 3096,
3031, 2954, 2927, 2871, 2860, 1766, 1671, 1601, 1571, 1508,
1466, 1458, 1449, 1392, 1352, 1330, 1289, 1235, 1207, 1191,
1146, 1112, 1051, 1035, 971, 958, 828, 818, 805, 758, 739,
Acknowledgements
This study was supported by the Czech Science
Foundation (Grant No. 203/07/0320), by the Ministry
of Education, Youth and Sports of the Czech Republic
(Project MSM7088352101 and Joint Project Nr 9-06-3)
of Programme KONTAKT, and the Slovenian Research
Agency (Project P1-0230-0103 and Joint Project BI-CZ/
07-08-018). The authors thank Dr. Bogdan Kralj and
ˇ
Dr. Dusˇan Zigon (Mass Spectrometry Center, Jozˇef
Stefan Institute, Ljubljana, Slovenia) for mass spectral
measurements.
References and notes
1. (a) Kosˇmrlj, J.; Kafka, S.; Leban, I.; Grad, M. Magn.
´
ˇ
Reson. Chem. 2007, 45, 700–704; (b) Klasek, A.; Lycka, A.;
Holcˇapek, M.; Hoza, I. J. Heterocycl. Chem. 2006, 43,
´
ˇ
ˇ
1251–1260; (c) Klasek, A.; Lycka, A.; Holcapek, M.; Hoza,
´
I. Tetrahedron 2004, 60, 9953–9961; (d) Klasek, A.;
Mrkvicˇka, V.; Pevec, A.; Kosˇmrlj, J. J. Org. Chem. 2004,
´
ˇ
69, 5646–5651; (e) Klasek, A.; Koristek, K.; Kafka, S.;
´
Kosˇmrlj, J. Heterocycles 2003, 60, 1811–1820; (f) Klasek,
A.; Korˇistek, K.; Lycˇka, A.; Holcˇapek, M. Tetrahedron
´
ˇ
2003, 59, 5279–5288; (g) Klasek, A.; Polis, J.; Mrkvicka, V.;
Kosˇmrlj, J. J. Heterocycl. Chem. 2002, 39, 1315–1320; (h)
´
ˇ
Kafka, S.; Klasek, A.; Polis, J.; Kosmrlj, J. Heterocycles
´
ˇ
2002, 57, 1659–1682; (i) Kafka, S.; Klasek, A.; Kosmrlj, J.
´
ˇ
J. Org. Chem. 2001, 66, 6394–6399; (j) Klasek, A.; Koristek,
K.; Polis, J.; Kosˇmrlj, J. Tetrahedron 2000, 56, 1551–1560;
´ˇ
´
(k) Kafka, S.; Kovar, M.; Klasek, A.; Kappe, T. J.
Heterocycl. Chem. 1996, 33, 1977–1982.
´
ˇ
ˇ
2. Klasek, A.; Koristek, K.; Polis, J.; Kosmrlj, J. Heterocycles
1998, 48, 2309–2326.
´
3. Klasek, A.; Kafka, S. J. Heterocycl. Chem. 1998, 35, 307–
311.
;
700, 665, 639, 572, 509, 483, 447 cmÀ1 1H NMR
4. Spectral and analytical data for new compounds 1b,c,h and
2a–d,g,h are, as follows. Compound 1b: mp 168 ꢁC (EtOH);
IR (KBr): m 3265, 3112, 2963, 2942, 2912, 2869, 1743, 1719,
1632, 1598, 1492, 1465, 1441, 1389, 1351, 1320, 1249, 1233,
1203, 1165, 1140, 1134, 1093, 1072, 1014, 971, 941, 912, 901,
881, 871, 800, 780, 768, 744, 726, 707, 671, 656, 601, 560,
(300 MHz, DMSO-d6): d 0.85 (t, J = 7.0 Hz, 3H), 1.16–
1.45 (m, 4H), 1.77–1.90 (m, 1H), 2.18–2.30 (m, 1H), 2.40 (s,
3H), 5.87 (dd, J = 7.6, 3.0 Hz, 1H), 7.36 (d, J = 8.5 Hz,
1H), 7.56 (dd, J = 8.5, 1.2 Hz, 1H), 7.65 (br s, 1H), 12.06
(br s, 1H); 13C NMR (75 MHz, DMSO-d6): d 13.7, 20.3,
21.8, 26.2, 33.1, 78.3, 113.3, 114.3, 116.2, 124.7, 131.9,
135.5, 139.8, 156.5, 166.5, 167.0; Anal. Calcd for
C16H17NO3: C, 70.83; H, 6.32; N, 5.16. Found: C, 70.63;
H, 6.57; N, 5.03. Compound 2d: IR (KBr): m 3154, 3100,
3047, 3028, 2976, 2938, 2901, 2870, 1777, 1673, 1622, 1603,
1565, 1507, 1472, 1434, 1403, 1337, 1277, 1240, 1195, 1156,
1137, 1056, 1025, 875, 832, 805, 768, 734, 699, 667,
1
527, 441 cmÀ1; H NMR (300 MHz, DMSO-d6): d 0.77 (t,
J = 6.7 Hz, 3H), 1.05–1.25 (m, 4H), 1.59–1.71 (m, 1H),
1.91–2.05 (m, 1H), 2.30 (s, 3H), 6.47 (s, 1H), 7.10 (dd,
J = 7.6, 7.6 Hz, 1H), 7.35 (d, J = 7.4 Hz, 1H), 7.55 (d,
J = 7.4 Hz, 1H), 9.94 (br s, 1H); 13C NMR (75 MHz,
DMSO-d6): d 13.6, 17.4, 21.5, 24.2, 36.5, 86.0, 112.0, 115.7,
123.2, 124.8, 125.2, 134.6, 135.4, 163.9, 167.4, 171.0; Anal.
Calcd for C16H17NO3: C, 70.83; H, 6.32; N, 5.16. Found: C,
625 cmÀ1 1H NMR (300 MHz, DMSO-d6): d 3.24 (dd,
;

S. Kafka et al. / Tetrahedron Letters 49 (2008) 90–93
93
1
J = 14.6, 6.7 Hz, 1H), 3.60 (dd, J = 14.6, 3.6 Hz, 1H), 6.20
(dd, J = 6.7, 3.6 Hz, 1H), 7.05–7.13 (m, 2H), 7.15–7.26 (m,
3H), 7.38 (dd, J = 7.9, 7.5 Hz, 1H), 7.45 (d, J = 8.3 Hz,
1H), 7.75 (dd, J = 8.3, 7.5 Hz, 1H), 8.07 (d, J = 7.9 Hz,
1H), 12.07 (br s, 1H); 13C NMR (75 MHz, DMSO-d6): d
78.2, 113.5, 114.9, 116.2, 122.6, 126.0, 126.8, 128.0, 129.4,
134.0, 135.0, 141.5, 156.3, 165.9, 166.6; HRMS calcd for
C18H13NO3: 291.0895. Found: 291.0903. Compound 2g: IR
(KBr): m 3310–3670 (br), 3159, 3104, 3071, 3029, 3011,
2984, 2935, 2918, 2900, 2871, 2762, 2730, 1778, 1666, 1624,
1607, 1585, 1567, 1510, 1483, 1472, 1458, 1438, 1405, 1353,
1326, 1289, 1266, 1244, 1192, 1157, 1138, 1078, 1057, 1047,
1024, 992, 955, 915, 893, 887, 863, 807, 792, 777, 760, 713,
652, 600, 590, 564, 536, 506, 494, 470, 460, 425 cmÀ1; H
NMR (300 MHz, DMSO-d6): d 2.18 (s, 3H), 2.46 (s, 3H),
6.88 (d, J = 7.5 Hz, 1H), 7.20–7.28 (m, 3H), 7.35–7.44 (m,
4H), 11.13 (br s, 1H); 13C NMR (75 MHz, DMSO-d6): d
17.8, 21.7, 81.7, 114.3, 115.7, 122.6, 125.1, 128.1, 129.3,
129.6, 134.4, 135.0, 136.2, 141.3, 156.3, 165.1, 166.3; Anal.
Calcd for C19H15NO3: C, 74.74; H, 4.95; N, 4.59. Found: C,
74.47; H, 5.04; N, 4.61.
5. Crystal data for 2b: C16H17NO3, M = 271.31, tetragonal,
˚
space group I41/a (No. 88), a = 15.8894(5) A, c =
23.6016(10) A, V = 5958.8(4) A , Z = 16, T = 150(2) K,
3
˚
˚
Dc = 1.210 g cmÀ1
,
l(Mo-Ka) = 0.084 mmÀ1
,
F(000) =
2304, crystal size = 0.18 · 0.18 · 0.15 mm, 5168 reflections
collected, 2623 unique (Rint = 0.0547). The final R1 =
0.0706, wR2 = 0.1609, and for all data R1 = 0.1316,
wR2 = 0.1971. Crystallographic data (excluding structure
factors) for the structure of 2b in this Letter has been
deposited with the Cambridge Crystallographic Data Cen-
tre as supplementary publication number CCDC 659269.
Copies of these data can be obtained, free of charge,
on application to CCDC, 12 Union Road, Cambridge
1
697, 662, 647, 593, 555, 519, 495, 455, 428 cmÀ1; H NMR
(300 MHz, DMSO-d6): d 6.94 (s, 1H), 7.12 (dd, J = 7.5,
7.5 Hz, 1H), 7.26 (d, J = 7.7 Hz, 1H), 7.40–7.50 (m, 6H),
7.64 (ddd, J = 7.7, 7.7, 1.0 Hz, 1H), 12.23 (br s, 1H); 13C
NMR (75 MHz, DMSO-d6): d 79.6, 113.3, 114.7, 116.3,
122.4, 125.5, 128.1, 129.2, 129.8, 134.0, 135.1, 142.0, 156.5,
165.2, 166.9; Anal. Calcd for C17H11NO3: C, 73.64; H, 4.00;
N, 5.05. Found: C, 73.83; H, 4.19; N, 4.92. Compound 2h:
IR (KBr): m 3310–3640 (br), 3182, 3127, 3051, 2975, 2932,
1782, 1668, 1655, 1595, 1569, 1490, 1472, 1454, 1384, 1363,
1328, 1292, 1264, 1244, 1216, 1183, 1161, 1115, 1088, 1042,
1023, 1002, 992, 947, 922, 854, 830, 819, 801, 775, 753, 700,
CB2 1EZ, UK [fax: +44
deposit@ccdc.cam.ac.uk].
0 1223-336033 or e-mail:
6. Azizian, J.; Mehrdad, M.; Jadidi, K.; Sarrafi, Y. Tetra-
hedron Lett. 2000, 41, 5265–5268.