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Orthorhombic and Monoclinic 2 3 7 8-Tetramethoxythianthrene Small Structural DifferenceЦLarge Lattice Change.

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Orthorhombic and Monoclinic 2,3,7,8-Tetramethoxythianthrene: Small Structural
Difference- Large Lattice Change**
Hans Bock,* Andreas Rauschenbach, Christian
Niither, Zdenek Havlas, Angelo Gavezzotti, and
Guiseppe Filippini
Dedicated to Prof&or Wolfiung Hilger
on tire occusion of 11is 65th birthiluy
Molecular compounds can often be isolated in several crystalline modifications that have only small differences in
lattice or sublimation energies." - 3 1 In
addition to serendipitous discover3a1 frequently crystal growth
ies,",
under skillfully chosen optimal conditions['. 2 b . 3 b , 3cl-f~r instance, from
solution or by sublimation,[2" 3a. 3c1
from strongly polar or less polar sol"entS,[2c,3cl or in the presence of
cation-chelating Iigand~[~~]--enable
certain molecular conformations to be
captured "snapshots" of the molecular
dynamics.
Here we again reportL4"'on 2.3,7,8tetraniethoxythianthrene. which is
obtained from diisopropyl ether as
m o n ~ c l i n i c [ and
~ ~ ] from n-hexane as
orthorhombic crystals.[51 The structural differences on the molecular level
are rather small: comparison reveals
that in the orthorhombic modification
only the methoxy group in the 3-position is twisted by 79" out of the plane
of the adjacent six-membered ring
(Fig. 1, top left). However. the small
perturbation in the skeletal symmetry
from C,, to C , , which does not apply
to the crystallographic site symmetry, formally introduces molecular chirality.
The changes in the crystal lattices on
going from the monoclinic modification containing altogether Z = 12 molecules of three geometries within the
unit cell to the orthorhombic one with
Z = 8 identical molecules can be plausibly discussed by beginning with the
small structural perturbation (Fig. 1,
[*I
top left). As can be seen from the angles in the planar form
(Scheme 1 left), twisting one H,CO group out of the C, plane
brings some steric relief especially between the H centers in ovtho
ring position and the methyl groups, since the 228 pm distance
between them is within twice the van der Waals radii 2rLdWof
240 pm.
In contrast, in both the monoclinic and the tetragonal modifications of tetramethoxyselenanthrene all H 3 C 0 substituents
lie in the C, plane, and a databank search (Cambridge Crystallographic Data Centre),[4c1 in complete agreement with
PM3 calculations,[6b1suggests that for structures containing
methoxy-substituted -phenyl
- rings a planarization should be
energetically favorable. Nevertheless, the conformation of the
Prof. Dr. H . Bock. Dipl.-Chem. A. Raiischenbach. Dip1 -Chem. C. Nither
Fig. 1 Single crystal structures of the polymorphic modifications of 2.3.7,8-tetramethoxythianthrene.Left' orChemische Institutc der Universitit
thorhombic (Phcir. p(300 K ) = 1.437 gcm- 151, with an interplanar angle of 128 between the C , rings, and unit
Marie-Curie-Strasse I 1
cell ( Z = 8) in (1. h. and c direcrions. The shaded circles emphasize the structural distortion by twisting of the
D-60439 Frankfurt am Main (Germany)
methoxy group in 3-position and its effects on the lattice. Right: monoclinic (P2,:n. p(300 K) = 1.395 gcm- [4b])
Telefax: Inr. code +(6Y) 5800-91XK
containing three independent molecules in the asymmetric unit with dihedral angles of 134 , 132', and 127'. and the
unit cell ( Z = 12) in N. h, and c directions.
Dr. Z. Havlas
Institute of Organic Chcmistry and Biochemistrv of the Czech Acadeniv of Sciences
Fleniingovo Nain 1.CS-I6610 Prag (Czech Republic)
orthorhombic tetramethoxythianthrene (Fig. 1, top left) is sup-
'
[*'I
76
Prof. Dr A. Gavezzotti. Dr. G. F'ilippini
Institute of Physical Chemistry, University of Milan
Via Golgi. 1-20133 Milano (Italy)
Interactions in Crystals, Part 4Y The projcct was supported by the A. MesserStiftung, the State of Hesse. thc Deutsche Forschungspemeinschaft, and the
Fonds der Chemischen Industrie. Part 48. H . Bock. 1. Gobel, C Nither. B.
Solouki. A J<>hn.~ / l ? f J l Bw. 1994. 1.77. 1197.
ported by geometry-optimized PM3 hypersurface calculations :
for the experimentally determined twisting of w(CC- OC) =
79"I5I above the O,C,S, plane, the (negative) heat of formation
is predicted to increase by - 3 kJ mol- and the local minimum
Of the rather
potential is found at a torsion
Of
about 80".[61 On the contrary, both the turning of a H,CO
',
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partly in solution already or only on incorporation into the
crystal lattice cannot be answered ; however. the existence of the
2.3.7.8-tetramethoxythianthrene modifications is another example-as is the use of the moiioethyltetramethylcyclopentadienyl ligand in the rapid crystallization of metal sandwich complexes['Obl-of the often useful rule of thumb that reduced
molecular symmetry can promote an energetically favored crystallization.
Recsi\cd: 1:ebru;iry 1 I . 1994
Revised wrsioii: Jul! 15. 1YY4 [Z 6684 IE]
Gel-man versioii . A i i ~ c i i ('/iiwi. 1995. 107. 120
Scheme 1 . Left. Bond angles and H . . . H distance in 2.3.7.8-tetramethoxythianthi-ene. Right. hypothetical C ' . . C distance of about 230 pm in the orthorhombic
lattice (Fig 1 : left) o n attempting to t w i ? t the H,CO group back into the plane of
the six-inemhered ring (cf. text).
substituent below the O,C,S, plane and the dis- or conrotatory
movement of two vicinal methoxy groups (H,CO-CC-OCH,)
require energy.[""] Altogether therefore, tetramethoxythianthrene displays- in close analogy to the polymorphic conformers of tetraisopropyl-p-phenylenediamine[3"1-a delicate
balance between n,/rc-delocaliration of the oxygen lone pair
density and the H/H repulsion especially between H centers of
the ring in ortho-position and of the methyl group (Scheme 1
left).
Though rather small, the structural distortion is nevertheless
connected with a profound lattice change (Fig. I ) , which shall
be rationalized as follows: a hypothetical attempt to twist the
methoxy group of the orthorhombic modification back into the
plane of the phenyl ring, would enforce a nonbonding C . . C
distance of only 230 pm (Scheme 1 right). This would correspond to ;I prohibitive 42% contraction of the usual van der
Waals distance between two methyl groups of 400 pm.17] This
argument explains the increased packing density due to the parallel arrangement of two twisted H,CO substituents, each from
different molecules (Fig. 1. shaded circle in the unit cell second
from top. left). On the other hand, the shortest contact distance
(CH2)H' . ' S resulting from the dense packing is only 281 pm
and, therefore. smaller than the van der Waals radii sum of
I.;'"
+ rgCiw= 130 + 185 = 305 pm by only 8'/0.'~'
Every tetramethoxythianthrene molecule in the orthorhombic modification is surrounded in the a, b plane by six adjacent
ones (Fig. 1 . bottom left), and above and below it in the c
direction are two additional molecules. In contrast, the monoclinic modification (Fig. 1, right) contains relatively loosely
packed pairs of the sulfur heterocycles with mean S . . . S
distances of 398 pm; the third molecule lies perpendicular to
this pair. The density difference at room temperature between
the orthorhombic ( p =1.437 g ~ m - ~and
) the monoclinic
( p = 1.395 gcm- 3)14h1 modifications amounts to 2.6%. As expected.", * ] this is reflected in the lattice o r sublimation energies
calculated by the atom/atom potential approximation,lga.
which predicts -34.7 kJmol-' for the orthorhombic and
- 32.3 kJ m o l ~ for the monoclinic modification of 2,3,7,8-tetrameth~xythianthrene.~~'~
The following proposals are forwarded for discussion of the
crystal growth of the two different modifications:[' - 3 ,
The
monoclinic crystals of lower density and lattice energy should
grow from a solution in the polar diisopropyl ether rather fast
and in a kinetically controlled way. whereas the orthorhombic
crystals with higher density and lattice energy presumably grow
under thermodynamical control from a solution in an unpolar
hydrocarbon. Whether the symmetry change C,, + C , occurs
Keywords: organic solids * polymorphism * structure elucidation
- 2.3,7.8-tetramethoxythianthrene
[ l ] Reviews on crystal investigations of polqmorphic i i x i l e c u l ~ i i -conformers
"Conformational Polymorphism": J. Beriiatein in Orxciiii(. Sdrd Srnic Chivrii \ r r ) (Ed: G . R. Desiraju). Elsevicr. Amsterdam. 1987. pi' 471 517, G R.
Dcsiraju. C r l ~ . w€/ i i g i i r w r i ~ , q(Mnrcr. .Si.r. ,Morioxr.) 1989. 54. pp. 2x5- 301.
and references therein: see HIYO refs [2. 31
[2] Selected recent publications on polymorphism: a ) hih(pyridii1ium)squarale.
M . T. Reetz. S. Hogei-, K. Harms. .Augc,i,.C/ic,irr. 1994, / / / 6 ,193: ,411,yi~ti..C/wri.
fnr. Ed. ErigI. 1994. 33, 1x1; b) lattice energ! calculiition.; tor monoclinic and
orthorhomhic modifications of benzene. naphthalene. and anthracene: J. Bernstein. J, A . R. P. Sarma. A Gave7zotti. C/iiwi. Plrn. Lcrr. 1990. 174. 361: c)
tricycloindane-1.3-dione:J. J. Stezowski. P U. Biedcrmann. T Hildenbrand.
J. A . Dorsch. J. Eckhardt. I. .4granat. J, C/iivn Sol. < ' / i m i Co!riiJiiiri. 1993,
213
[ 3 ] The cryYlals of polymorphic modifications of niolecular conforinci-r grown so
far by the Frankfurt group: a) monoclinic and tricliiiic tetraisopropyl-1,GBbel. C. Nither, Z. Ha\.I;i>,A. Gave//otti. G.
phenylenedkamine (H. Bock. I.
Filippini, Aiigeii. Chrrn. 1993, 10.5. 1x23: A r i p i , . Cliei?i./ / I / Ed. €ti~yI. 1993. 32.
1755;cf. also H Bock. J. Meuret.C Nither. U. Kryniiz. ( h r i i i . Bw. 1994. 127.
5 5 : b) p?eudopolymorphic. orthorhombic. and monoclinic tctriiphenyl-p-henzosemiquinone sodium contaiiiing two o r thrce tetrahydropyran solvent inolecules (H. Bock. A. John. C. Nither. 1 Chiw Soi.. Cheni. C ' o m i i r f i i . 1994, 1939.
c) orthorhombic and triclinic bis(pyridylamiiic). H Bock. H SchOdel. A.
Gavezzotti, G . Filippini. unpublished (cf. H. Bock. P / i i ~ . \ / ~ i i i ~.Sid/iir,
r i i ~ . Silicon
R d . €/.. 1994, 87. 73: see in addition J. E Johnson. R A. Jacobson. Acro
Cri,.uu//oxr. Seer. B 1973, 29. 1669 and G. J. Pyrka. A A . Pinkerton. Aira
Cri.triiNogr. Self. C 1992. 48. 91: d ) isotypic, monoclinic i
phenylendismine with included solvent molecules auch .I\ acetone. cyclopentanone. cyclopent-2-enonc. tetrahydrofuran. or 2.5-dihydrofuran : H. Bock. N.
Nagel. C. Nither. unpublished (cf. H. Bock. M o / . ('r).\r. L . / y C'i:i..\r. 1994. 240.
166).
[4] a ) H. Bock, A. Rauschenbach, K. Ruppert, Z . H;ivl;is. :lfi,qwi. CIwrr. 1991,
103. 706: .4ngr11.C/im. h r . GI. € t i , q / . 1991. 3).714. bl W. Hinrichs. H -1.
Riedel. G. Klar. J. CIimii. Re.\. i s ) 1982. 334. 1 Cheiii. / < I , \ / / IJ 1982. 3501.
c) the thiaseleno and diseleno derivatives crystallize isotypiciilly tetragnnal w i t h
Z = 4 i n P42,ni: M. Ddtze. W. Hinrichs. G . Klar. .I C / i m Rizt. (S,1991. 314;
J C'l7e.m. Rrs. f 2.1) 1991. 2861
[S] The crystal growth of colorless platelets froin ir-hexane c.in he accomplished
after a 24 h Soxhlet-extraction of the raiv product [ I h ] uilder argon a n d slow
evaporation of the solvent at norinal pressure. C,,H,,O,S,(336 4 g m o l ~'1.
(150 K) II = 154Y.0(1). h =752.3(1). ( ' = 2606 4(2) pm. L' = 3037.2 x 10' pm3.
Z = 8. pI,l,id = 1.471 g c r K 3 . if = 0.37 mm-'.orthorhomhic. spacegvup Phcii
(no. 61). Siemens AED-I1 four-circle dilTractometer ( M O ~ , radiation).
,
3405
measured reflection? within 3 < 20 < 50 . of which 2637 iii-e independent. 2097 with I >l.On(/). Structure solution with direct methods and
difference-Fourier-technique (SHELXTL-PC). 207 parameters. All heavy
atoms were refined anisotropically. all H in ideal positions ;mi refined ticcording to the riding model using isotropic displacement parametera.
R = 0.0445. R M = 0.0372, Rg = 0.0394. I I = 1 , u ' ( F ) + (1.0002 F', GOF =
1 3757. ShiftjError <0.0001. residual electron density 0.28 -0.X e A ? Further details of the crystal structure determination may he obtained ltoin the
Fachinformationszentrum Karlsruhe. D-76344 Eggeii~'Leiii-Leopoldsli~if~n
(Germany) on quoting the depository number CSD-58 673.
[6] a ) T h e PM3 calculations (program: 1 .I P. SIi,iiurl. J. ( ' o i i r j i i i r ( % c i f i . 1989. 10.
209) have been performed on the structural data [5] uith partial peomctry
optimization with the program version MOPAC 6.0 (QC'PE N o . 455) o n an
IBM RISC 6000,'320. The PM3 heats of formation (in kJ nrol- I) addition:~lly
calculeted for the rotation of a H ,CO group below the 0 2 C , , S 2plane a n d for
the simultaneous dis- nnd conrotatory rotations of the vicinal substituents. iia
well as the respective minima (or points of inflection) o f tlic torsion angles
(in )amount to +4:(80), +8!X0 and +7)100. b) Cf. W. llummel. K. Huml.
H.-B. Burpi. H e / i ~Chin?.
.
Ai.tu 1988. 71. 1291.
77
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[7] H. Bock. K . Ruppert. C. Nither, Z. Havlas, H.-F: Herrmann. C. And. 1.
Gobel. A. John, J. Meuret. S . Nick. A. Rauschenbach. W. Seiu, T . Vnupel, B
Solouki. Angcn. Cheni. 1992. 104. 564; Angeii.. Chem.h i / . €d. Engl. 1992. 31,
550, and references therein.
[S] Cf.. for example, I. Bar. J. Bernstein. J. P/i?..s. Chrm. 1984, 88, 243. and references therein.
[9] a ) Summary: A. J. Pertsin. A. I . Kitaigorodsky. The Arom-Aioni Po/mtiul
:Me/horl. Springer, 1987; b) G. Filippini. A . Gavezrotti. .4cru C r y t u l h g r .
S K I . B 1993, 49, 868 (optimized parameter set for atomlatom potential approximation calculations of crystal lattice or sublimation energies). The potential is defined exclusively intermolecularly and contains no intraniolecular corrections. Additional lattice vibration calculations yield frequencies within the
h i t s of expectation.
[lo] Cf.. for example. N ) P. J. Fagan. M. D. Ward. Sri. A I ~1992.
.
367, 2X. b) 0. J.
Scherer. Angi~ii..Chiwz. 1990. 102. 1137: Angeu. Cheni. I n / . Ed. Engl. 1990, ZY.
1104.
+
(S)-( )- and (R)-(- )-1,5-Dimethyl-4-phenyl-
1,5-dihydro-2H-pyrrol-2-ones by Carbene Ring
Contraction and Decarboxylation of (2 R, 3 S)( - )- and (2 S, 3 R)-( + )-6-Diazo-3,4-dimethyl-2phenyloxazepane-5,7-diones**
Giorgio Chelucci and Antonio Saba*
The interest in ephedrine enantiomers as chiral auxiliaries
increased after oxazepane-5.7-dione 1 was reported by
Mukaiyama et al.['] The 6-benzylidene derivative of 1 has been
used as a chiral Michael acceptor,[*]a dienophile in asymmetric
Diels-Alder cy~loadditions,[~]
and an unsaturated substrate in
asymmetric cyclopropanation.[" In the course of our studies in
the field of stabilized carbenes and carbenoids generated by
decomposition of a-diazocarbonyl compounds.[51 we have
devoted our attention to the reactivity of
(2 R , 3 S ) - (-)-6-diazo-3,4-dimethyl-2phenyloxazepane-5,7-dione(2) and its
Ph
0 0
enantiomer 2'. Here we wish to report
their catalytic decomposition, which affords exclusively (S)-(+)- and (R)-(-)-
1,5-dimethyl-4-phenyl-1,5-dihydro-2H-
3 : (S)
3' : ( R )
Scheme 1 . a) TsN,. NEt,. CH,CN. room temperature. 24 h (85%): b) 5%
copper(i) triflate or 5 % rhodium(n) acetate dimer. CH,CII. room temperature
(951% 1.
(Table 1). and a single-crystal X-ray diffraction study.['] The
latter confirmed the presence of a single enantiomer in the crystal and consequently the retention of configuration at the carbon bearing the methyl group, which is not involved in the
process.
Ring contraction of heterocyclic a-diazo carbonyl compounds mostly proceed via a ketene (Wolff rearrangement"])
and rarely have any synthetic value.['] In our case. 3 was formed
as a result of a transannular attack in the seven-membered heterocycle by the ketocarbene or ketocarbenoid intermediate. The
regiospecific insertion into the benzylic C-H bond of oxazepane 2 can be ascribed to the greater electron density of this
bond: electronic activation by the lactone oxygen["] and by the
phenyl group makes this bond more susceptible to attack by the
electrophilic carbene species. In addition. it is documented that,
in intramolecular C- H insertion reactions of diazoacetamides,
a five-membered y-lactam ring is more likely to be formed than
the potentially competitive /j-lactam.l' The suggested straightforward mechanism of regiospecific carbene attack followed by
ready CO, extrusion from the resulting unstable bicyclic intermediate is shown in Scheme 2.[Iz1Irradiation of diazo compound 2 with ultraviolet light ( A = 250 nm, in CH,CI,) led to
formation of the same reaction product 3. although in much
lower yield.['31
r
1
Me
[*] Prof. Dr. A . Saba. Dr. G. Chelucci
Dipartimento di Chimica. Facolti di ScienLe
Via Vienna 7. 1-07100 Sassari (Italy)
Tekpdx: I n t . code + (793229-559
78
2 : (2R)(3S)
2' : ( 2 S ) ( 3 R )
:\$&"
pyrrol-2-one (3 and 3').
2
The 6-diazooxazepanediones 2 and 2'
were easily prepared under mild condiScheme 7.
tions by a "diazo transfer" reaction with
p-toluenesulfonyl azide (TSN,);[~]the
starting materials oxazepanediones 1 and 1' were obtained from
(-)-ephedrine and ( + )-ephedrine, respectively. The decomposition reaction of 2 and 2' was carried out in the presence of
catalytic amounts of copper(r) triflate or rhodium(i1) acetate
dimer in CH,CI, at room temperature and was allowed to
proceed until the diazo stretching band in the IR spectrum had
disappeared. After filtration on neutral A1,0,, removal of the
solvent, and crystallization of the residue, the 2-pyrrolones 3
and 3' were obtained in good yield (Scheme 1).
The structure of the ring-contraction product 3 was determined from the mass, 'HNMR, and I3C N M R spectra
[**I
: (2R)(3S)
': ( 2 S ) ( 3 R )
This work was supported by the Ministero dell' Universiti e della Ricerca
Scientifica e Technologica (MURST) (40% of funding). We thank Mauro
Muccdda for experimental assistance.
3
The enantiomerically pure compounds 3 and 3'open access to
biologically active 4,5-disubstituted 2-pyrrolidinones, which can
be considered as precursors to y-aminobutyric acid (GABA) .[I4'
Thus, catalytic hydrogenation of 3 gave a diastereomeric mixture of (4 S , 5 S)-(+)- and (4 R, 5 S)-(-)-I ,5-dimethyl-4-phenyl2-pyrrolidinone ( 4 a and 4b) in a ratio of 5.5:4.5 (Scheme 3).[l5]
The enantiomer 3' was submitted to the same reductive procedure. A roughly 1 : 1 mixture of (4 R,S R)-( -)- and (4S,S R)( + ) - I .5-dimethyl-4-phenyl-2-pyrrolidinone
(4 a' and 4b') were
obtained. The diastereoisomeric pairs 4a/4b and 4a'/4b' were
readily separated by chromatography on silica gel (eluant: hexane/ethyl acetate 8/2), and their configurations confirmed by
N M R spectroscopy. In particular, the resonance for the 5methyl of 4 b (Table 1 ) shows the well-known y-gauche effect in
the I3C N M R spectrum['61andis shifted upfield relative to that
of the diastereoisomer 4 a (A6 = 4). Thus, 4b can be assigned
the cis- and 4 a the tvuns-pyrrolidinone configuration. Since the
carbon bearing the methyl group is unaffected in the reaction,
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