Stereochemistry of the Diels-Alder cyclization of sugar-derived dienes with active dienophiles

Article abstract of DOI:10.1016/S0957-4166(02)00583-9

The high-pressure intermolecular Diels-Alder reactions of sugar-derived dienes with N-phenylmaleimide are described and the crystal structure of a representative adduct is presented. The sugar matrix can be removed from the molecule, allowing the preparat

Full text of DOI:10.1016/S0957-4166(02)00583-9

TETRAHEDRON:
ASYMMETRY
Pergamon
Tetrahedron: Asymmetry 13 (2002) 2223–2228
Stereochemistry of the Diels–Alder cyclization of sugar-derived
dienes with active dienophiles
Sławomir Jarosz,a,* Katarzyna Szewczyk,a Stanisław Sko´ra,a Zbigniew Ciunikb and
Agnieszka Pietrzaka
aInstitute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44, 01-224 Warszawa, Poland
bFaculty of Chemistry, University of Wrocław, F. Joliot-Curie 14, 50-383 Wrocław, Poland
Received 2 August 2002; accepted 24 September 2002
Abstract—The high-pressure intermolecular Diels–Alder reactions of sugar-derived dienes with N-phenylmaleimide are described
and the crystal structure of a representative adduct is presented. The sugar matrix can be removed from the molecule, allowing
the preparation of enantiomerically pure iso-indole derivatives. © 2002 Elsevier Science Ltd. All rights reserved.
1. Introduction
stereospecific transformations on a sugar backbone are
well documented.
One of the most useful methods for the preparation of
cyclohexane derivatives is undoubtedly the Diels–Alder
reaction.1 The intramolecular version of this reaction
leads to bicyclic adducts. For the preparation of enan-
tiomerically pure compounds (being the obvious targets
in stereoselective synthesis), the ‘chiron approach’2 is
particularly useful, especially when sugars are used as
starting materials. Sugars are readily available and con-
tain a number of defined stereogenic centers. Moreover,
Recently, we elaborated a convenient route to enan-
tiomerically pure, highly oxygenated carbobicyclic
compounds (decalins and [4.3.0]nonanes]) from sugar
organotin derivatives. These reactions are based on
the controlled decomposition of sugar allyltin
D-galacto-configured
derivative is shown in Fig. 1), followed by transfor-
reagents3 (1; as an example the
mations of the resulting dienoaldehyde 2 either into
Figure 1. Application of sugar allyltin derivatives in a highly stereoselective synthesis of carbobicyclic derivatives.
* Corresponding author. E-mail: sljar@icho.edu.pl
0957-4166/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(02)00583-9

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S. Jarosz et al. / Tetrahedron: Asymmetry 13 (2002) 2223–2228
bicyclo[4.3.0]nonene4 3 or bicyclo[4.4.0]decene5 (deca-
line, 4) derivatives (Fig. 1). Both types of compound
could be prepared with very high degrees of selectivity.
Herein, the application of the Diels–Alder reaction of
sugar-derived dienes in an inter-molecular mode is
reported.
2. Results and discussion
The dienes 56 and 66—readily prepared from the corre-
sponding sugar allyltin derivatives 7 and 8 (Scheme
1)—were selected for the present study. These com-
pounds have the opposite configuration at the a-posi-
tion to the diene function. Both derivatives were
reacted with the active dienophile, N-phenylmaleimide
9, under high pressure conditions.7
Scheme 2. Reagents and conditions: (i) 9, toluene–benzene,
4:1, 10 kbar, 86%.
Reaction of the diene 5 with dienophile 9 afforded two
(of the four possible) stereoisomers, 10 and 11, in a 4:1
ratio (Scheme 2). The relative configuration between
the newly created stereogenic centers (C3a, C4 and
C7a) was assigned from the NMR spectra; NOESY
experiments conducted on 10 and 11 indicated a cis
relationship between H-1 and H-2 protons in both
compounds. However, precise determination of the
configurations at these centers, i.e. differentiation
between 10/11, was not possible from the NMR experi-
ments. The configuration of these centers in adduct 10
(the major isomer obtained in reaction of 5 with 9) was
therefore determined as 3aS,4R,7aS by X-ray measure-
ments (see Fig. 2). Consequently, the configuration of
the second cis isomer 11 had to be 3aR,4S,7aR.
Reaction of the diene 6 with olefin 9 was performed
analogously and afforded two adducts in a 3:1 ratio.
Again, the cis geometry between the H-3a and H-4
protons in both adducts 12 and 13 was assigned on the
basis of the NOESY experiments. The absolute configu-
ration at the newly created stereogenic centers (C-3a,
C-7 and C-7a) in these two products was eventually
determined by chemical degradation (see Scheme 3)
either to compound 14 or its enantiomer, ent-14.
To prepare the standard derivative 14 of known
configuration at the C-3a, C-4 and C-7a centers, the
sugar component of compound 10 (the structure of
which was determined by X-ray crystallographic analy-
sis) was transformed by a simple sequence of reactions:
Figure 2. X-Ray structure of 10.
Scheme 1. Reagents and conditions: (i) ZnCl2 Ref. 6.

S. Jarosz et al. / Tetrahedron: Asymmetry 13 (2002) 2223–2228
2225
(i) hydrogenolysis, (ii) hydrolysis, (iii) periodate cleavage,
(iv) reduction, and finally (v) acetylation (see Scheme 3
and Section 4) into the achiral acetoxymethylene group.
The thus obtained levorotatory enantiomer 14 ([h]D −12.1
(c 3.6, CHCl3)) served as the standard for determination
of the configuration of adducts 12 and 13.
of 4-acetoxymethyl-2-phenyl-hexahydroisoindole-1,3-
dione (ent-14), since the configuration at the C-4% center
of the diene 6 is opposite to that in the diene 5. However,
to our surprise, the degradation of 13 afforded the
levorotatory compound 14 ([h]D −10.4 (c 1.1, CHCl3)) and
not its enantiomer! (Scheme 3).
The sequence of reactions used for the preparation of 10
was then performed for 13—the major isomer isolated
from reaction of the diene 6 with 9. We expected, that
the degradation should provide dextrorotatory isomer
Careful analysis of the transition states of the cycloaddi-
tion process allows this unexpected result to be explained:
Only the endo addition—leading to the cis adduct—has
to be considered (Fig. 3). In reaction of the xylo-diene
Scheme 3. Reagents and conditions: (i) 9, toluene–benzene, 4:1, 10 kbar, 83%; (ii) H2/Pd; (iii) THF/H2O (4:1), cat. H2SO4, 40°C,
24 h; (iv) NaIO4 then NaBH4; (v) Ac2O, Et3N, CH2Cl2, DMAP.
Figure 3. Transition states for addition of 5 or 6 to 9.

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S. Jarosz et al. / Tetrahedron: Asymmetry 13 (2002) 2223–2228
5 with olefin 9 the corresponding transition states may
be depicted as I and I%. There is an unfavorable coulombic
interaction between the carbonyl oxygen of the dienophile
and the ring oxygen atom of the sugar fragment of the
diene (transition state I). However, in the alternative
transition state I% there is severe coulombic and steric
interaction of the carbonyl oxygen atom of 9 with the
benzyloxy group placed at the C-3% position of the sugar.
Consequently, the reaction proceeds via transition state
I providing the adduct 10 as the major isomer.
substituted-3a,4,7,7a-tetrahydro-iso-indole-1,3-dione
derivatives. Only two (of the four possible isomers) are
formed in a ratio of ca. 4:1. The cis relationship between
all three newly created stereogenic centers in the products
arises from the endo transition states of the cyclization
process. Rather surprisingly, dienes substituted with the
D
-xylo- and L-arabino tetrose units, having the opposite
configuration at the C-a center (5 and 6, respectively),
afforded (as the major products) iso-indole derivatives
with the same absolute configuration at the bicyclic system.
In reaction of the diene 6 (with the opposite configuration
at the C-4 center of the sugar unit) the endo attack of 9
on the diene proceeds via transition state II [no steric
interaction with the C-3(OBn)], to afford the iso-indole
derivative 13 with the same absolute configuration at the
newly created stereogenic centers as 10. The alternative
II% is less favored due to severe coulombic repulsion
between the carbonyl group of 9 and the ring oxygen of
the sugar component of 6.
4. Experimental
4.1. General
NMR spectra were recorded with a Bruker AM 500 or
Varian Gemini 200 spectrometers for solutions in CDCl3
(internal Me4Si) unless otherwise stated. All resonances
wereassignedbyCOSY(1H–1Hand1H–13C)correlations.
Mass spectra [LSIMS (m-nitrobenzyl alcohol was used
as a matrix to which sodium acetate was added) or EI]
were recorded with a AMD-604 (AMD Intectra GmbH,
Germany) mass spectrometer. Specific rotations were
measured with a JASCO DIP Digital Polarimeter for
chloroform solution at rt. Column chromatography was
performed on silica gel (Merck, 70–230 mesh). Organic
solutions were dried over anhydrous magnesium sulfate.
Although the attack of the dienophile onto a diene system
occurring from the side occupied by a ring oxygen atom
(I or II%) faced the same (or similar) coulombic repulsion,
the attack from the opposite side (I% or II) is strongly
influenced by the substituent at the C-3 position of the sugar
ring (see Fig. 3). Therefore, the C-a (to the reacting diene
system) stereogenic center (opposite in 5 and 6) is not as
important, at least in the case of the process described
here.
4.2. Reaction of dienes with N-phenylmaleimide under high
pressure
Reaction of N-phenylmaleimide 9 with the less hindered
diene supported this assumption to some extent. High
pressure cycloaddition of 9 with 156 afforded two cyclo-
adducts, 16 and 17 in equal amounts (Scheme 4).
A solution of the diene6 5, 6, or 15 (2 mmol) and
N-phenylmaleimide (2 mmol) in toluene–benzene mix-
ture (4:1 v/v; 11 mL) was placed in a piston–cylinder
type apparatus8 and kept under 10 kbar hydrostatic
pressure for 24 h. After this time the solvent was
evaporated to dryness and the residue was chro-
matographed using hexane–ethyl acetate, 5:1“3:1) to
afford pure products.
Again, the cis-relationship between the C-4 and C-3a
centers in both adducts was assigned on the basis of
NOESY NMR experiments.†
“ Reaction of 5 with 9 afforded 10 (68%) and 11
(18%).
3. Conclusion
“ Reaction of 6 with 9 afforded 12 (22%) and 13
(61%).
“ Reaction of 15 with 9 afforded 16 (38%) and 17
(34%). This reaction was performed on a 1 mmol
scale.
The high pressure reactions of sugar-derived dienes
(readily obtained from the corresponding sugar allyltin
derivatives) with N-phenylmaleimide provided the 4-
4.2.1. 4-(3%-O-Benzyl-1%,2%-O-isopropylidene-a- -xylo-
D
tetros-4-yl)-2-phenyl-(3aS,4R,7aS)-tetrahydro-iso-indole-
1,3-dione, 10. [h]D −4.2 (c 1.5); mp=186–187°C; 1H
NMR l: 5.99 (m, H-6), 5.96 (d, J1%,2% 3.7, H-1%), 5.68 (dt,
J4,5=J5,7 3.5, J5,6 9.3, H-5), 5.06 (dd, J3%,4% 3.0, J4%,4 11.1,
H-4%), 4.66 (d, J2%,3% 0, H-2%), 4.01 (d, H-3%), 3.61 (dd,
J3a,4 5.3, J3a,7a 9.0, H-3a), 3.30 (m, J7,7a 1.3, H-7a), 2.86
(m, H-4), 2.81 (ddd, J6,7 6.8, J7,7 15.5, H-7), 2.29 (m,
second H-8), 1.55 and 1.34 [C(CH3)2]; 13C NMR l:
178.8 and 176.7 (2×CꢀO), 129.3–126.5 (Carom, C-5,6),
112.1 [C(CH3)2], 104.7 (C-1%), 81.9, 80.9 and 78.4 (C-
2%,3%,4%), 71.8 (CH2Ph), 41.0 and 39.6 (C-7a,3a), 35.2
(C-4), 26.9 and 26.6 [C(CH3)2], 25.0 (C-7); HRMS
(LSIMS) m/z: 476.2077 [C28H30NO6 (M+H+) requires
476.2073]. NOE: H4ꢁH3a, H3aꢁH-7a.
Scheme 4. Reagents and conditions: (i) toluene–benzene, 4:1, 10
kbar, 24 h.
† The absolute configuration was not determined, however, it may be
tentatively assigned as 3aS,4R,7aS to 16 and 3aS,4R,7aS to 17 on
the basis of the similarity of the 1H NMR spectra of the corre-
sponding isomers (16/12 and 17/13; see Section 4).

S. Jarosz et al. / Tetrahedron: Asymmetry 13 (2002) 2223–2228
2227
4.2.2.
4-(3%-O-Benzyl-1%,2%-O-isopropylidene-a-
D
-xylo-
3.27 (m, H-3a and H-7a), 2.82 (m, H-4), 2.77 and 2.23
(2m, both H-7); 13C NMR l: 178.9 and 177.5 (2×CꢀO),
131.7 (C-5), 127.3 (C-6), 78.4 (C-2%), 73.4 and 72.0
(2×CH2Ph), 68.1 (C-1%), 41.3 (C-3a), 40.8 (C-7a), 37.8
(C-4,), 24.6 (C-7); HRMS (LSIMS) m/z: 490.1982
[C30H29O4NNa (M+Na+) requires 490.1994]. NOE:
H4ꢁH3a, H4ꢁH7a.
tetros - 4 - yl) - 2 - phenyl - (3aR,4S,7aR) - tetrahydro - iso-
indole-1,3-dione, 11. [h]D −40.3 (c 1.3); mp=189–190°C;
1H NMR l: 6.13 (dt, J4,5=J5,7 3.4, J5,6 9.3, H-5), 5.99
(m, H-6), 5.97 (d, J1%,2% 4.0, H-1%), 4.79 (dd, J3%,4% 3.1, J4%,4
10.5, H-4%), 4.70 (d, J2%,3% 0, H-2%), 4.37 (d, H-3%), 3.12
(ddd, J7,7a 1.4, and 7.7, J3a,7a 9.1, H-7a), 2.96 (dd, J3a,4
5.7, H-3a), 2.78 (ddd, J6,7 7.0, J7,7 15.4, H-7), 2.76 (m,
H-4), 2.21 (m, H-7), 1.50 and 1.33 [C(CH3)2]; 13C NMR
l: 178.7 and 176.9 (2×CꢀO), 131.7 and 129.3–126.5
(Carom, C-5,6), 111.6 [C(CH3)2], 104.8 (C-1%), 82.4, 81.5
and 80.0 (C-2%,3%,4%), 71.4 (CH2Ph), 40.7 and 40.2 (C-
3a,7a), 35.0 (C-4), 26.8 and 26.3 [C(CH3)2], 24.5 (C-7);
HRMS (LSIMS) m/z: 476.2069 [C28H29NO6 (M+H+)
requires 476.2073]. Anal. calcd for C28H30NO6 (475.54):
C, 70.72; H, 6.15; N, 2.94. Found: C, 70.59; H, 6.18; N,
2.99. NOE: H4ꢁH3a, H3aꢁH-7a.
4.3. Degradation of compound 10, the major isomer
from reaction of 5 with 9
Major stereoisomer 10 (100 mg) was dissolved in ethyl
acetate (10 mL) and hydrogenated under standard con-
ditions (H2/Pd, overnight). The catalyst was filtered off
through Celite and the solvent was evaporated to dry-
ness. The 13C NMR spectrum of the pure intermediate
thus obtained indicated the saturation of the C5ꢁC6
double bond and removal of the benzyl protecting
group from the C-3% position of the sugar moiety. 13C
NMR l: 179.1 and 176.9 (2×CꢀO), 112.3 (CMe2), 104.1
(C-1%), 85.3, 80.0 and 74.1 (C-2%,3%,4%) 41.1, 40.5 and
33.1 (C-4,3a,7a), 27.5 and 27.3 (CMe2), 25.6, 22.6, 20.5
(C-5,6,7).
4.2.3. 4-(Methyl 2%,3%-di-O-benzyl-b-L-arabino-tetrosid-4-
yl)-2-phenyl-3aS,4R,7aS)-tetrahydro-iso-indole-1,3-
dione, 13. [h]D −106.0 (c 1); 1H NMR l: 5.97 (m, H-5,6),
4.98 (s H-1%), 4.72 (dd, J3%,4% 6.1, J4%,4 11.1 H-4%), 4.03 (d,
J2%,3% 1.8, H-2%), 3.73 (dd, H-3%), 3.63 (dd, J4,3a 5.8, J7a,3a
11.1, H-3a), 3.43 (OCH3), 3.26 (m, H-7a), 2.81 and 2.18
(2×m, both H-7), 2.52 (m, H-4); 13C NMR l: 178.9 and
176.2 (2×CꢀO), 129.0–126.5 (C-5,6 and Ph), 106.0 (C-
1%), 88.8, 87.7 and 79.1 (C-2%,3%,4%), 72.1 and 72.0 (2×
CH2Ph), 54.2 (OCH3), 41.4, 41.1 and 39.9 (C-4,3a,7a),
24.9 (C-7); HRMS (LSIMS) m/z: 562.2191
[C33H33NNaO6 (M+Na+) requires 562.2206]. NOE:
H4ꢁH3a, H3aꢁH-7a.
This crude product was dissolved in THF (10 mL),
sulfuric acid (10% solution in water, 2 mL) was added
and the mixture was heated under reflux for 24 h. After
cooling to rt, the acid was carefully neutralized with
triethylamine and mixture was poured into ether (10
mL) and water (10 mL). Sodium periodate (300 mg)
was added, the mixture was vigorously stirred for 1 h
and partition between ether (20 mL) and water (10
mL). The organic lawyer was separated washed with
water, dried and concentrated. The crude product was
dissolved in THF/MeOH (5 mL, 3:1 v/v) and reduced
with sodium borohydride (50 mg) under standard con-
ditions. Acetylation of the crude material with Ac2O/
py, followed by chromatographic purification
(hexane–ethyl acetate, 5:1“3:1) afforded 14 (30 mg).
4.2.4. 4-(Methyl 2%,3%-di-O-benzyl-b-L-arabino-tetrosid-4-
yl)-2-phenyl-(3aR,4S,7aR)-tetrahydro-iso-indole-1,3-
1
dione, 12. [h]D 82.2 (c 1.4); H NMR l: 6.02 (m, H-6),
5.88 (m, H-5), 4.81 (d, J1%,2% 1.8, H-1%), 4.63 (dd, J3%,4% 7.1,
J4%,4 4.9, H-4%), 4.01 (dd, J2%,3% 3.9, H-2%), 3.85 (dd, H-3%),
3.21 (m, H-7a), 3.20 (OCH3), 3.15 (dd, J4,3a 6.8, J3a,7a
9.4, H-3a), 2.77–2.67 (m, H-4,7), 2.29 (m, second H-7);
13C NMR l: 129.4–126.5 (C-5,6 and Ph), 107.3 (C-1%),
88.2, 84.3 and 80.1 (C-2%,3%,4%), 72.2 and 71.9 (2×
CH2Ph), 55.5 (OCH3), 42.1, 39.7 and 37.4 (C-4,3a,7a),
23.3 (C-7); HRMS (LSIMS) m/z: 562.2191
[C33H33NNaO6 (M+Na+) requires 562.2206]. NOE:
H4ꢁH3a, H3aꢁH-7a.
4.3.1. 4-(Acetoxymethyl)-2-phenyl-(3aS,4R),7aS)tetra-
hydro-iso-indole-1,3-dione, 14. [h]D −12.1 (c 3.6), 13C
NMR l: 170.8 (×2) and 170.1 (3×CꢀO), 67.1
(CH2OAc), 44.6 and (2×) 39.8 (C-3a,4,7a), 24.9 and
(2×) 23.9 (C-5,6,7), 21.0 (COCH3); HRMS m/z:
370.1299 [C18H21NO6 [M+HCOOH+Na+) requires
370.1267].
4.2.5. 4-[1%,2%(S)-Di-O-benzyloxyethane-2%-yl)-2-phenyl-
(3aS,4R,7aS)-tetrahydro-iso-indole-1,3-dione, 16. [h]D
−87.3 (c 2.1); H NMR l: 6.00 (m, H-6), 5.88 (m, H-5),
1
4.41 (ddd, J 11.2, 3.1, and 4.0, H-2%), 3.78 (m, H-3a and
H-1%), 3.64 (dd, J1%,1% 10.8, second H-1%), 3.27 (m, H-7a),
2.80 (ddd, J7,7a 1.2 and 7.4 J7,7 15.2, H-7), 2.68 (m, H-4),
2.22 (m, second H-7); 13C NMR l: 179.1 and 177.6
(2×CꢀO), 130.2(C-5), 127.5 (C-6), 77.5 (C-2%), 73.3 and
72.5 (2×CH2Ph), 70.5 (C-1%), 40.5 (C-3a), 40.1 (C-7a),
38.9 (C-4), 25.4 (C-7); HRMS (LSIMS) m/z: 490.1966
[C30H29O4NNa (M+Na+) requires 490.1994]. NOE:
H4ꢁH3a, H4ꢁH7a (weak), H3aꢁH-7a.
4.4. Degradation of compound 13, the major isomer from
reaction of 6 with 9
This reaction was performed as detailed above for
compound 10. The product had identical spectral data
as 14 (13C NMR and MS); [h]D −10.4 (c 1, CHCl3).
4.2.6. 4-[1%,2%(S)-Di-O-benzyloxyethane-2%-yl)-2-phenyl-
(3aR,4S,7aR)-tetrahydro-iso-indole-1,3-dione 17. [h]D
+11.5 (c 2.1); 1H NMR l: 6.04 (dt, J5,6 9.3, J4,5=J5,7 3.2,
H-5), 5.98 (m, H-6), 4.20 (m, H-2%), 3.94 (m, both H-1%),
4.5. Crystal structure data for compound 10
For crystal structure data for compound 10, see Table
1.

2228
S. Jarosz et al. / Tetrahedron: Asymmetry 13 (2002) 2223–2228
Table 1. Crystal structure data for compound 10
References
Empirical formula
Formula weight
Temperature (K)
C28H29NO6
475.52
100(2)
0.71073
Monoclinic
P21
10.9059(7)
5.4735(5)
20.3267(13)
101.067(5)
1190.81(15)
2
1. Reviews: (a) Jenner, G. Tetrahedron 2002, 58, 5185; (b)
Bear, R. B.; Sparks, S. M.; Shea, K. J. Angew. Chem.,
Int. Ed. Engl. 2001, 40, 820; (c) Pindur, U.; Lutz, G.;
Otto, Ch. Chem. Rev. 1993, 93, 741; (d) Herczegh, P.;
Zsely, M.; Szilagyi, L.; Bajza, I.; Kovacs, A.; Batta, G.,
Bognar, R. Cycloaddition Reactions in Organic Chemistry
1992, p. 112 (ACS Symposium Series 494, Guiliano R.
M. Edition); (e) Roush, W. R. Advances in Cycloaddition
1990, 2, 91.
2. (a) Hanessian, S. Total Synthesis of Natural Products:
The Chiron Approach; Pergamon Press: New York, 1983;
(b) Fraser-Reid, B. Acc. Chem. Res. 1996, 29, 57 and
references cited therein.
,
u (A)
Crystal system
Space group
,
a (A)
,
b (A)
,
c (A)
i (°)
−3
,
V (A
Z
)
Dc (Mg m−3
)
1.326
0.093
504
v (mm−1
F(000)
)
3. Kozłowska, E.; Jarosz, S. J. Carbohydr. Chem. 1994, 13,
889.
4. (a) Jarosz, S.; Kozłowska, E.; Jezewski, A. Tetrahedron
1997, 53, 10775; (b) Jarosz, S.; Sko´ra, S. Tetrahedron:
Asymmetry 2000, 11, 1425.
5. Jarosz, S.; Sko´ra, S. Tetrahedron: Asymmetry 2000, 11,
1433.
6. Jarosz, S.; Sko´ra, S.; Szewczyk, K. Tetrahedron: Asym-
metry 2000, 11, 1997.
Crystal size (mm)
Diffractometer
Theta range for data collection (°)
Ranges of h,k,l
0.15×0.15×0.15
Kuma KM4CCD
3.75–28.49
−14“14, −7“7,
−26“26
14909
5521 (0.0180)
94.6%
5521/433
1.031
Reflections collected
Independent reflections (Rint
Completeness to 2q=28.49
Data/parameters
)
Goodness-of-fit (F2)
7. It is known that Diels–Alder reactions are accelerated
under high pressure, see: Jenner, G. Tetrahedron 1997,
53, 2669; Jurczak, J.; Bauer, T.; Jarosz, S. Tetrahedron
1986, 42, 6477.
Final R1/wR2 indices (I\2|I)
Extinction coefficient
0.0283/0.0663
0.0188(17)
0.241/−0.168
−3
,
Largest diff. peak/hole (e A
)
8. (a) Jurczak, J.; Chmielewski, M.; Filipek, S. Synthesis
1979, 41; (b) Jurczak, J.; Gryko, T. D. In Chemistry
under Extreme or Non-Classical Conditions; van
Eldik, R.; Hubbard, C. D., Eds.; Wiley & Sons and
Spektrum Akademischer Verlag Co-Publication, 1997;
Chapter 4.
5. Supplementary material
Crystallographic data (excluding structure factors) for
the structure of 10 have been deposited with the Cam-
bridge Crystallographic Data Centre as supplementary
publication no. CCDC 192616.