Sulfur-incorporating cyclotriveratrylene analogues: The synthesis of cyclotrithioguaiacylene

Article abstract of DOI:10.1021/jo102324u

Cyclotriguaiacylene 1 is the universal precursor of cryptophanes, and represents an important intermediate for the preparation of functionalized cavitands of the cyclotriveratrylene family. Its thio analogue (cyclotrithioguaiacylene 3) was synthesized by two different routes, involving either the Newman-Kwart or the Pummerer rearrangement. The latter, performed starting from a trisulfoxide precursor, produced a purer compound in higher overall yield.

Full text of DOI:10.1021/jo102324u

NOTE
pubs.acs.org/joc
Sulfur-Incorporating Cyclotriveratrylene Analogues: The Synthesis
of Cyclotrithioguaiacylene
Julien Sanseverino,† Jean-Claude Chambron,*,† Emmanuel Aubert,‡ and Enrique Espinosa‡
†Institut de Chimie Molꢀeculaire de l'Universitꢀe de Bourgogne (ICMUB, CNRS UMR no. 5260), 9 Avenue Alain Savary, BP 47870,
F-21078 Dijon, France
‡CRM2 (CNRS UMR no. 7036), Institut Jean Barriol, Facultꢀe des Sciences et Technologies, Nancy-Universitꢀe, Boulevard des
Aiguillettes, BP 70239, F-54506 Vand!uvre-lꢁes-Nancy, France
S Supporting Information
b
ABSTRACT: Cyclotriguaiacylene 1 is the universal precursor of cryptophanes, and represents
an important intermediate for the preparation of functionalized cavitands of the cyclotrivera-
trylene family. Its thio analogue (cyclotrithioguaiacylene 3) was synthesized by two different
routes, involving either the Newman-Kwart or the Pummerer rearrangement. The latter,
performed starting from a trisulfoxide precursor, produced a purer compound in higher overall yield.
Scheme 1. The Newman-Kwart Route to Cyclotrithio-
guaiacylene (3)
ryptophanes are spherical, hollow, and chiral molecules built
by triple bridging of two (C3)-cyclotriveratrylene (CTV)
C
concave subunits with chains of various nature, usually methylenic.1
Their lipophilic cavity can bind stereospecifically various substrates
by van der Waals and/or cation-π interactions: methane2 and its
halogenated derivatives,3 acetylcholine and related quaternary am-
monium salts,4 and xenon gas.5 With few exceptions, most of the
known cryptophanes are synthesized from cyclotriguaiacylene (1), a
CTV analogue featuring hydroxy functions that alternate with
methoxy substituents.6 Other useful functional groups that could
be incorporated either directly or by a series of chemical transforma-
tions are the halogeno (Br,7 I8), the triflate,9 the amino,10 and the
methylthio (CTV 2)11 substituents. However, the synthesis of the
thio analogue, in which SH groups replace the OH groups of
cyclotriguaiacylene, has not been reported. The significance of this
trithiol CTV derivative (3) stems from the fact that it could be used
to advantage as a building block for the self-assembly of crypto-
phanes using disulfide bond formation, by analogy with systems
made from R-cyclodextrin12 or other tripodal building blocks,13 or
for performing dynamic combinatorial chemistry experiments,14
using the thiol disulfide exchange.15
(Scheme 1). Accordingly, 1 was reacted at first with an excess
of NaH in THF followed by N,N-dimethylthiocarbamoyl chlor-
ide, and the reaction mixture was heated at reflux. The trifunc-
tionalized O-aryl N,N-dimethylthiocarbamate CTV derivative
(4) was separated from the mono- and difunctionalized products
by flash column chromatography and obtained in 30% yield.
Subsequent thermic rearrangement in diphenyl ether at 250 °C
afforded the S-aryl N,N-dimethylthiocarbamate CTV isomer 5 in
90% yield as a brown solid. Cyclotrithioguaiacylene 3 was finally
The Newman-Kwart rearrangement16 is a well-established
method for converting phenols to thiophenols, which was
employed, in particular, for the preparation of p-tert-butylcalix-
[4]arenethiols from p-tert-butylcalix[4]arene.17 Therefore, it
seemed perfectly adapted for the synthesis of 3 from 1
Received: November 27, 2010
Published: February 23, 2011
r
2011 American Chemical Society
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obtained by LiAlH4 reduction of 5 in THF followed by acidic
workup, in 73% yield. However, the purity of the rearranged
products (3 and 5) was not fully satisfactory (Figures S3 and S13,
Supporting Information). Another drawback of this route was
the low yield of the carbamoylation reaction (30%).
Scheme 2. Attempted Direct Preparation of 4
In fact, we had earlier attempted to cleave the carbamate
functions of 5 by hydrolysis in basic conditions (NaOH). As the
reaction did not proceed in pure methanol, we employed a 1:1
mixture of methanol and dichloromethane as solvent
(Scheme 1). Unexpectedly, this reaction resulted in the trans-
protection of the thiol groups of 3, by exchange of the carbamate
functions of 5 with the MOM functions of 6, in 85% yield after
chromatography. Although extensively used for the protection of
alcohols and phenols,18 the MOM group has been very scarcely
employed for the protection of their thio analogues. Classical
conditions involve MOMCl/base in THF.19 Actually, reaction of
3 in the conditions used for the conversion of 5 into 6 also
produced 6, in 90% yield. This suggests that the thiolate
functions released in the hydrolysis of 5 then react with
CH2Cl2/MeOH. Noticeably, a very similar MOM protection
of an arylthiol by reaction with CH2BrCl in methanol in the
presence of powdered KOH and a phase transfer catalyst has
been reported.20 The reaction was suggested to proceed via
methanolysis of the intermediate sulfonium cation resulting from
chloride elimination of the intermediate chloromethyl sulfide.
This roundabout potential route to 3 was quite interesting, as
purification of 6 was very easy, contrary to that of 5. However,
attempts to remove the MOM protection with the established
method (AgNO3/EtOH)19b,19d failed to afford a clean product.
Therefore we sought for other routes.
Scheme 3. The Pummerer Route to Cyclotrithioguaiacylene
singlets for the CH3S protons could be identified, with a
maximum of seven in CDCl3 (Figure S25, Supporting In-
formation). (C3)-CTV's are intrinsically chiral compounds be-
cause of their conical (crown) shape and arrangement of
substituents, and exist as a mixture of P and M conformers.28
Therefore, as three stereocenters are generated by oxidation of
the methyl thioether substituents, 11 is expected to exist in the
form of four pairs of diastereomers, C3-symmetric P,R,R,R/M,S,
S,S and P,S,S,S/M,R,R,R, and asymmetric P,R,R,S/M,S,S,R and
P,R,S,S/M,S,R,R. The CH3S protons show up as one singlet each
for the former, and as three singlets each for the latter. Therefore,
the maximum number of signals for these protons is eight. This
arithmetical analysis shows that m-CPBA oxidation of 2 to
trisulfoxide 11 is likely to produce all the possible diastereomers.
The Pummerer rearrangement was carried out by reaction of 11
with 3 equiv of trifluoroacetic anhydride in CH2Cl2, followed by
aminolysis of the thioacetate intermediate by NEt3/CH3OH. In
this way pure 3 was obtained in 80% yield after purification by
column chromatography as a colorless solid material. In addition
to the expected singlets for the R (6.77 ppm) and R0 (7.21 ppm)
protons, and the pairs of doublets for the equatorial (3.52 ppm)
and axial (4.66 ppm) methylenic protons, its 1H NMR spectrum
showed the signature of the thiol protons as a singlet at 3.72 ppm.
Clearly, trisulfoxide 11 was obtained as a mixture of diaster-
eomers. However, complete oxidation to the trisulfone should
afford a single product. Accordingly, reaction of 2 with 7.5 equiv
of m-CPBA at room temperature afforded trisulfone 12 in 89%
yield (Scheme 4). Its 1H NMR spectrum in CDCl3 showed only
one set of signals, and was left unchanged upon switching to
other solvents. Heating of 12 in C2D2Cl4 up to 110 °C caused a
slight downfield shift of the signals of the cone conformation
and the development of a new set of signals corresponding to
the rarely observed saddle conformation, the most characteristic ones
being the singlet of the methylene protons at 4.06 ppm.29 Interest-
ingly, prolonged heating at 100 °C (Figure 1) did not change the ratio
between the cone and saddle conformers (6:1).
(C3)-CTV0s are synthesized by acid-catalyzed regiospecific
cyclodehydration of 3,4-disubstituted benzyl alcohol
derivatives.21 Procedures developed recently use milder condi-
tions (catalytic Sc(OTf)3 in acetonitrile).9 Both 3- and 4-sub-
stituents must be ortho-para directing, and the former strongly
activating toward electrophilic aromatic substitution (electron-
donor).10 In spite of these limitations, we attempted the direct
formation of CTV 4 from 4-(N,N-dimethylcarbamoylthio)-3-
methoxybenzene methanol (8), obtained in 96% yield by NaBH4
reduction of the known aldehyde (7).11 However, heating of 8 in
HCO2H at 70 °C produced the corresponding ester 9
(Scheme 2). Therefore we finally concentrated our efforts on
presynthesized, sulfur-substituted CTV platforms.
The known methylthio-substituted CTV 2 represents another
interesting and easily accessible starting compound.11 Unfortu-
nately, as reported by Collet and co-workers, attempts to
selectively S-demethylate 2 with Na/HMPA at 100 °C failed.22
We obtained similar results by employing sodium diethylamide
in refluxing HMPT/xylene.22 In addition, reaction with t-BuSNa
in refluxing DMF, which has also been efficiently used for the
cleavage of the C-S bond,23 gave the known O-demethylated
product (10),11 a result that could have been predicted from
precedent.11,25
Sulfoxides, which are obtained by controlled oxidation of
thioethers, are easily converted to thiols by the Pummerer
rearrangement upon reaction with trifluoroacetic anhydride
(TFAA) in the presence of a base (Et3N).26 Accordingly, 2
was reacted with the stoichiometric amount of m-CPBA in
CH2Cl2 at 0 °C (Scheme 3). The trisulfoxide 11 derivative of
2 was obtained in 95% yield as a mixture of diastereomers that
Slow evaporation of CH2Cl2/heptane solutions of trisulfone
12 left X-ray quality needle-shaped colorless crystals. The
ORTEP view of Figure 2 shows the cone-shaped structure of
1
could not be separated by chromatography.27 Indeed, its H
NMR spectrum showed complex patterns. In particular, several
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10% aqueous HCl at 0 °C and extracted into CH2Cl2. The combined
organic layers were concentrated to dryness. Purification of the residue
by flash column chromatography (silica gel; CH2Cl2) afforded 4 (0.500
1
g, 0.75 mmol) in 30% yield. Mp 135-136 °C; H NMR (600 MHz,
CDCl3) δ 3.27 (s, 9H; NCH3), 3.43 (s, 9H; NCH3), 3.65 (d, 2J = 13.8
Hz, 3H; eq-H), 3.78 (s, 9H; OCH3), 4.76 (d, 2J = 13.8 Hz, 3H; ax-H),
6.89 (s, 3H; R-H), 7.04 (s, 3H; R0-H) ppm; 13C NMR (75 MHz,
CDCl3) δ 36.5 (CH2), 38.7 (NCH3), 43.3 (NCH3), 56.4 (OCH3),
114.4 (R-C), 125.3 (R0-C), 131.4 (β0-C), 138.0 (β-C), 141.4 (γ0-C),
150.0 (γ-C), 187.8 (CS) ppm; IR (ATR) ν 1507 (CdS) cm-1; ESI-
HRMS found, 670.20766, 692.19937, calcd for [M þ Hþ] 670.20737
and for [M þ Naþ] 692.18932.
2,7,12-Trimethoxy-3,8,13-tri(N,N-dimethylamino)oxo-
methylthiodihydro-5H-tribenzo[a,d,g]cyclononene (5). A solu-
tion of 4 (0.100 g, 0.15 mmol) in diphenyl ether (50 mL) was heated at
250 °C for 6 h. After cooling to room temperature, the reaction mixture was
poured into pentane (250 mL). The resulting precipitate was isolated by
filtration and purified by flash column chromatography (silicagel, CH2Cl2
then CH2Cl2/CH3OH 95:5) to afford 5 (0.090 g; 0.134 mmol) as a brown
solid in 90% yield. Mp 172-173 °C; 1H NMR (600 MHz, CDCl3) δ 3.00
(br s, 9H; NCH3), 3.09 (br s, 9H; NCH3), 3.69 (d, 2J = 13.8 Hz, 3H; eq-H),
3.85 (s, 9H; OCH3), 4.74 (d, 2J = 13.8 Hz, 3H; ax-H), 6.90 (s, 3H; R-H),
7.45 (s, 3H; R0-H) ppm; 13C NMR (75 MHz, CDCl3) δ 36.4 (CH2), 36.9
(NCH3), 56.3 (OCH3), 113.0 (R-C), 114.9 (γ0-C), 131.2 (β0-C), 139.3
(R0-C), 143.0 (β-C), 158.6 (γ-C), 166.3 (CO); IR (ATR) ν 1658 (CdO)
cm-1; ESI-HRMS found 692.18985, calcd for [M þ Naþ] 692.18932.
2,7,12-Trimethoxy-3,8,13-tri(methoxymethylthio)dihydro-
5H-tribenzo[a,d,g]cyclononene (6). From 5: A solution of NaOH
(0.500 g, 12.5 mmol) in water (2 mL) was added to a solution of 5 (0.100
g, 0.15 mmol) in a mixture of CH2Cl2 and CH3OH (1:1; 60 mL). The
reaction mixture was heated at reflux for 24 h. After cooling to room
temperature, it was quenched by the addition of 5% aq HCl (50 mL).
Extraction with CH2Cl2 (3 ꢀ 50 mL) followed by concentration to
dryness afforded a crude material, which was purified by flash column
chromatography (silicagel, CH2Cl2 then CH2Cl2/CH3OH 98:2) to
afford 6 (0.075 g, 0.127 mmol) in85% yield. From 3: The same procedure
was employed starting from NaOH (0.0065 g, 0.163 mmol) and 3 (0.025
g, 0.055mmol). Afterchromatographic purification6was obtained in 90%
yield (0.029 g, 0.0493 mmol). Mp 129-130 °C; 1H NMR (600 MHz,
CDCl3) δ 3.39 (s, 9H; CH2OCH3), 3.64 (d, 2J = 13.8 Hz, 3H; eq-H), 3.86
(s, 9H; OCH3), 4.72 (d, 2J = 13.8 Hz, 3H; ax-H), 4.83 (d, 2J = 11.4 Hz,
3H; SCH2), 5.01 (d, 2J = 11.4 Hz, 3H; SCH2), 6.83 (s, 3H; R-H), 7.52 (s,
3H; R0-H) ppm; 13C NMR (75MHz, CDCl3) δ 36.5(CH2), 55.9 (CH3),
56.0 (CH3), 76.4 (OCH2), 112.0 (R-H), 122.2 (γ0-H), 131.9 (β0-H),
132.2 (R0-H), 139.4 (β-H), 156.2 (γ-H) ppm; ESI-HRMS found
611.15486, calcd for [M þ Naþ] 611.15662.
Figure 1. Monitoring of the equilibrium between the saddle (s) and the
crown (c) conformations of (C3)-CTV 12 by 1H NMR (600 MHz, 298
K) in C2D2Cl4 after prolonged heating at 100 °C. The peak marked with
an asterisk is due to residual CH2Cl2.
Figure 2. ORTEP view of 12 with two co-crystallized solvent mole-
cules. Ellipsoids are drawn at the 50% probability level. Hydrogen atoms
are omitted for clarity.
Scheme 4. Formation of Trisulfone 12
12 with two co-crystallized CH2Cl2 molecules, one of them being
trapped within the molecular cavity. The hydrogen atoms of the
latter enjoy edge-to-face CH π interactions with the receptor,
3 3 3
their distances to the centroids of the closest phenyl moieties
being both equal to 2.81 Å. In addition, while one of the Cl-atoms
exhibits two CH Cl contacts at 2.97 and 3.21 Å, the other
3 3 3
makes a long O Cl interaction (3.80 Å) with a sulfonyl oxygen
3 3 3
atom (Figure S2, Supporting Information).
2,7,12-Trimethoxy-3,8,13-trimethylsulfinyldihydro-5H-
tribenzo[a,d,g]cyclononene (11). m-CPBA (70-75%, 0.741 g
3.00 mmol) was added to a solution of 2 (0.500 g, 1.00 mmol) in CH2Cl2
(25 mL) at -30 °C. Stirring of the reaction mixture for 6 h at 0 °C was
followed by addition of aqueous NaHCO3 (100 mL). The resulting
aqueous phase was extracted with CH2Cl2 and the combined organic layers
concentrated to dryness. Flash column chromatography of the residue
(silica gel; CH2Cl2/CH3OH, 95:5) afforded 11 (0.520 g, 0.95 mmol) in 95%
yield as a colorless solid, as a mixture of diastereomers (see the Supporting
Information for a copy of the 1H and 13C NMR spectra); ESI-HRMS found
569.11384, calcd for [M þ Naþ] 569.10967. Anal. Calcd for C27H30O6-
This work adds a new member to the family of thiol-
functionalized (C3)-CTV0s.30 It contrasts with the reported
ones by the direct connection of the SH group to the cyclo-
phane backbone. As a result cyclotrithioguaiacylene 3 is highly
preorganized to form a cryptophane capsule by oxidative
dimerization. Studies along these lines will be reported in
due course.
’ EXPERIMENTAL SECTION
S3 5/2H2O (546.73): C, 54.8; H, 6.0; S, 16.3. Found: C, 54.9; H, 5.8; S, 16.1.
2,7,12-Trimethoxy-3,8,13-tri(N,N-dimethylamino)thioxo-
methoxydihydro-5H-tribenzo[a,d,g]cyclononene (4). NaH
(1.80 g, 75.0 mmol) was added to a solution of 1 (1.00 g, 2.45 mmol)
in THF (50 mL) and the resulting mixture heated at reflux for 1 h. After
addition of N,N-dimethylthiocarbamoyl chloride (0.900 g, 7.35 mmol)
at 0 °C, the reaction mixture was heated at reflux for 12 h. This operation
was repeated once. The reaction mixture was quenched by addition of
3
2,7,12-Trimethoxy-3,8,13-trimethylsulfonyldihydro-5H-
tribenzo[a,d,g]cyclononene (12). m-CPBA (70-75%, 0.400 g 1.5
mmol) in CH2Cl2 (20 mL) was added to a solution of 2 (0.100 g, 0.200
mmol) in CH2Cl2 (50 mL) at -20 °C. The mixture was stirred at 0 °C for
6 h, then at room temperature for 12 h. The reaction was quenched by
addition of a saturated aqueous solution of NaHCO3. The organic layer was
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NOTE
separated, and the aqueous layer extracted into CH2Cl2 (3 ꢀ 100 mL). The
combined organic layers were concentrated to dryness, and the resulting
solid purified by column chromatography (silica gel; CH2Cl2/CH3OH
95:5) to afford 12 (0.106 g, 0.178 mmol) in 89% yield as a colorless solid.
Mp 350 °C dec; 1H NMR (600 MHz, CDCl3) δ 3.14 (s, 9H; S(O)2CH3),
3.83 (d, 2J = 13.8 Hz, 3H; eq-H), 3.98 (s, 9H; OCH3), 4.83 (d, 2J = 13.8 Hz,
3H; ax-H), 7.06 (s, 3H; R-H), 7.96 (s, 3H; R0-H) ppm; 13C NMR (75
MHz, CDCl3) δ 36.5 (CH2), 43.1 (S(O)2CH3), 56.8 (OCH3), 113.9 (R-
C), 127.5 (γ0-C), 130.3 (β0-C), 131.2 (R0-C), 147.1 (β-C), 156.2 (γ-C)
ppm; IR (ATR) ν 1287 (SdO), 1139 (SdO) cm-1; ESI-HRMS found
617.09300, calcd for [M þ Naþ] 617.09442. Anal. Calcd for C27H30O9S3
(594.73): C, 54.5; H, 5.1. Found: C, 54.5; H, 5.2.
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CH2Cl2/pentane, 50:50 then 80:20), which afforded 3 (0.200 g,
0.438 mmol) in 80% yield as a colorless solid. Mp 242-244 °C; 1H
NMR (300 MHz, CDCl3) δ 3.52 (d, 2J = 13.8 Hz, 3H; eq-H), 3.72 (s,
3H; SH), 3.87 (s, 9H; OCH3), 4.66 (d, 2J = 13.8 Hz, 3H; ax-H), 6.77
(s, 3H; R-H), 7.21 (s, 3H; R0-H) ppm; 13C NMR (75 MHz, CDCl3) δ
36.4 (CH2), 56.3 (OCH3), 112.3 (R-C), 118.8 (γ0-C), 130.8 (R0-C),
132.0 (β0-C), 138.2 (β-C), 154.0 (γ-C); ESI-HRMS found
479.07836, calcd for [M þ Naþ] 479.07798.
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’ ASSOCIATED CONTENT
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S
Supporting Information. General Experimental Meth-
b
1
ods and additional experimental procedures, copies of H and
13C NMR spectra for all compounds, and a crystallographic
information file (CIF). This material is available free of charge via
the Internet at http://pubs.acs.org.
(27) Very careful column chromatography separations allowed us to
isolate small amounts of symmetrical diastereomers, as shown by H
’ AUTHOR INFORMATION
1
NMR spectroscopy.
(28) Collet, A.; Gabard, J.; Jacques, J.; Cesario, M.; Guilhem, J.;
Pascard, C. J. Chem. Soc., Perkin Trans. I 1981, 1630.
Corresponding Author
*E-mail: jean-claude.chambron@u-bourgogne.fr.
(29) Zimmermann, H.; Tolstoy, P.; Limbach, H.-H.; Poupko, R.;
Luz, Z. J. Phys. Chem. B 2004, 108, 18772.
’ ACKNOWLEDGMENT
(30) (a) van Strijdonck, G. P. F.; van Haare, J. A. E. H.; van der
Linden, J. G. M.; Steggerda, J. J.; Nolte, R. J. M. Inorg. Chem. 1994, 33,
999. (b) van Strijdonck, G. P. F.; van Haare, J. A. E. H.; H€onen, P. J. M.;
van den Schoor, R. C. G. M.; Feiters, M. C.; van der Linden, J. G. M.;
Steggerda, J. J.; Nolte, R. J. M. J. Chem. Soc., Dalton Trans. 1997, 449.
J.S. thanks the MENESR for a doctoral fellowship. We are
grateful to Marcel Soustelle for the elemental analyses, and
Marie-Josꢀe Penouilh for the ESI-HRMS spectra. The XRD
Service of CRM2 is acknowledged for technical support.
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dx.doi.org/10.1021/jo102324u |J. Org. Chem. 2011, 76, 1914–1917