Functional paracyclophanes: Synthesis of [2.2] paracyclophanemethyldithiocarbonates using thione-thiol rearrangement of S,O-dithiocarbonates (benzyl Schoenberg rearrangement) at mild conditions

Article abstract of DOI:10.1002/ijch.201100079

A pathway to benzylic [2.2]paracyclophane thiol derivatives was investigated using the benzyl Schoenberg rearrangement. Copyright

Full text of DOI:10.1002/ijch.201100079

Full Paper
DOI: 10.1002/ijch.201100079
Functional Paracyclophanes: Synthesis of
[2.2]Paracyclophanemethyldithiocarbonates Using Thione–
Thiol Rearrangement of S,O-Dithiocarbonates (Benzyl
Schçnberg Rearrangement) at Mild Conditions
Daniel Frank,[a] Martin Nieger,[b] Christian Friedmann,[c] Jçrg Lahann,*[c, d] and Stefan Brꢀse*[a]
Abstract: A pathway to benzylic [2.2]paracyclophane thiol derivatives was investigated using the benzyl Schçnberg rearrange-
ment.
Keywords: [2.2]paracyclophane · S-ligand · solid phase catalysis · sulfur · thione–thiol rearrangement
1. Introduction
[2.2]Paracyclophanes and their derivatives build an excit-
ing class of molecules, which is of great interest for the
areas of polymer science,[1] advanced materials[2,3] and
catalysis.[4]
ethanol or lithium aluminum hydride in dry THF.[13] The
diastereomeric ratio of the resulting products can be
varied by the choice of the reducing agent. The diastereo-
mers were separated using flash chromatography.
Recently, we embarked on the exploration of function-
alized paracyclophanes for the generation of soft-matter
surfaces suitable for reaction at biological interfaces.[5,6]
The versatility of [2.2]paracyclophane chemistry, com-
bined with the processibility of [2.2]paracyclophanes via
chemical vapor deposition polymerization,[2] makes them
ideal precursors for reactive polymer coatings useful in a
wide range of biomedical and biotechnological applica-
tions. Due to their planar chirality, benzylic functionalized
[2.2]paracyclophanes play an important role as ligands in
asymmetric synthesis, for example, the addition of diethyl
zinc to ketones and aldehydes.[7] Although this substance
class is well-explored, there exist only a few examples of
thiol-containing derivatives of [2.2]paracyclophanes.[8]
A straightforward approach towards [2.2]paracyclopha-
nemethylthiols could be based on a thione–thiol rear-
rangement (benzyl Schçnberg rearrangement), but this
rearrangement has only been reported for alkyl and aryl
xanthates under high temperatures and harsh condi-
tions.[9,10]
However, the diastereomers of 2c could not be separat-
ed with common techniques. 4-Formyl[2.2]paracyclophane
(1a) showed an unexpected low reactivity towards
sodium boronhydride, hence lithium aluminum hydride
was used according to literature.[13]
The synthesized alcohols (2b: 2nd eluted diastereomer;
2c: mixture; 2d: 1st eluted diastereomer) were treated
with sodium hydride, carbon disulfide, and methyl iodide
[a] D. Frank, S. Brꢀse
Institute of Organic Chemistry
Karlsruhe Institute of Technology (KIT)
Fritz-Haber-Weg 6, 76131 Karlsruhe, Germany
phone:+49 (0)721 608-4 2902
fax:+49 (0)721 608-4 8581
e-mail: braese@kit.edu
[b] M. Nieger
Laboratory of Inorganic Chemistry, University of Helsinki
FIN-00014 Helsinki, Finland.
[c] C. Friedmann, J. Lahann
Here, we report a convenient route for the preparation
Institute of Functional Interfaces
Karlsruhe Institute of Technology (KIT)
Hermann-von-Helmholtz-Platz 1
76344 Eggenstein-Leopoldshafen, Germany
of
(rac)-4-thiomethyl[2.2]paracyclophane
derivatives
under unusually mild reaction conditions.
The introduction of a carbonyl function to [2.2]paracy-
clophane can easily be achieved via electrophilic substitu-
tion using a Lewis acid, for example, aluminum trichlor-
ide. For representing investigations, the four different car-
bonyl compounds 1a–d were synthesized.[11]
[d] J. Lahann
College of Engineering, University of Michigan
3414 G. G. Brown, 2300 Hayward
Ann Arbor, MI 48109-2136, USA
phone:+1 734 763-7543
The corresponding alcohols 2a–d were synthesized
from 1a–d in good yields using sodium boronhydride in
fax:+1 734 764-7453
e-mail: lahann@umich.edu
Isr. J. Chem. 2012, 52, 143 – 148
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
143

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J. Lahann, S. Brꢀse et al.
Table 1. Used substrates for the electrophilic substitution.
or benzyl bromide to give the desired S,O-dithiocarbon-
ates in moderate to excellent yields.[14]
The aqueous work-up had no effect on the dithiocar-
bonate functionality of compounds 3a-Me and 3a-Bn.
However, a partially rearrangement could be observed
during purification (vide infra).
Moreover, the dithiocarbonate 3b-Me already rear-
ranged during work-up: it reacted immediately with
water or semi-saturated ammonium chloride solution,
which resulted in 30% loss of the product due to a Chu-
gaev-like elimination of the dithiocarbonate. The formed
4-vinyl[2.2]paracyclophane is known in literature.[15,16]
In contrast to all other investigated substances, 3c-Me
did not rearrange, either during work-up or during purifi-
cation, and could be obtained as a pure yellow solid.
The dithiocarbonate 3d-Bn rearranged under the influ-
ence of water or aqueous solutions, which resulted in
quantitative conversion into the corresponding S,S-dithio-
carbonates. A SN1 mechanism, according to the strong
mesomeric stabilization and size of the formed cation,
can be expected. After crystallization from dichlorome-
thane and hexane, crystals were obtained for X-ray dif-
fraction that corroborate the postulated S,S-carbonate
structure (Figure 1).
Entry
Lewis acid
RCOX
Yield (%)
Product
1
2
3
4
TiCl4
AlCl3
AlCl3
AlCl3
Cl2CHOMe
CH3COCl
TFAA
96
1a
1b
1c
1d
56[a]
92
BzCl
75
[a] Cram et al.[12]
Table 2. Used substrates for the reduction.
To ensure that the conditions for the rearrangement
were comparable to the conditions during chromato-
graphical separation, a suspension of silica gel in various
solvents was chosen. To compare this method with anoth-
er set of conditions, the substrates were also added to a
solution acidified with acetic acid or trifluoroacetic acid,
as shown in Table 4.
The diastereomeric ratio of 3c-Me changed during the
rearrangement from 7:10 to 2:13, while the diastereo-
meric ratio of 4c-Me was 3 :10.
Starting materi- Reducing
Reaction
Time
Product Yield
al
agent
(%)
1a
1b
1c
1d
LiAlH4
LiAlH4
NaBH4
LiAlH4
3 d
3 h
20 min
12 h
2a
2b
2c
2d
80
quant.[a]
quant.[b]
92[c]
The results show that silica gel can be used as an effi-
cient catalyst for the thione–thiol rearrangement in non-
polar and aprotic solvents. In a simple work-up proce-
[a] diastereomeric ratio =7:10; [b] diastereomeric ratio =7:10; [c]
diastereomeric ratio =4 :3.
Table 3. Used substrates for the S,O-dithiocarbonate formation.
[a]
Starting material
R’X
Stability towards aqueous solutions
Product
Yield (%)
Product [b]
Yield (%)
2a
2a
2b
2b
2c
2d
MeI
BnBr
MeI
MeI
MeI
BnBr
Stable
Stable
3a-Me
3a-Bn
3b-Me
3b-Me
3c-Me
3d-Bn
quant.
78
22
37
91
4a-Me
4a-Bn
4b-Me
4b-Me
4c-Me
4d-Bn
–
–
Unstable
43[c]
14[e]
–
[d]
–
Stable
Unstable
–
87[f]
[a] S,O-dithiocarbonate; [b] S,S-dithiocarbonate; [c] diastereomeric ratio 2 :11; [d] no aqueous work-up, 65% conversion of the alcohol; [e]
diastereomeric ratio 1:4; [f] diastereomeric ratio 11:20.
144
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Isr. J. Chem. 2012, 52, 143 – 148

Functional Paracyclophanes: Synthesis of [2.2]Paracyclophanemethyldithiocarbonates Using Benzyl Schçnberg Rearrangement
(Sp/R)/(Rp/S) and (Sp/S)/(Rp/R)-(rac)-[2.2]Paracyclophan-4-yl-
(trifluormethyl)methanol (2c)
(rac)-4-Trifluoracetyl[2.2]paracyclophane (2.40 g, 7.89 mmol,
1.00 equiv) was dissolved in 200 mL ethanol and cooled down to
08C. Then sodium boronhydride (310 mg, 8.19 mmol, 1.04 equiv)
was added and the solution was stirred 10 min at 08C afterwards
10 min at room temperature. The conversion was monitored by
TLC. The reaction mixture was quenched with saturated ammo-
nium chloride solution and extracted twice with diethyl ether.
The combined organic phases were washed with brine and dried
over magnesium sulfate. After removal of the solvent under re-
duced pressure the crude product was purified using column
chromatography (hexane :ethyl acetate 4 :1) yielding 2.42 g
(7.84 mmol, quant.) of a yellow, crystalline solid. Mp: 868C. Dia-
stereomeric ratio 10 :7. - Diastereomer A: 1H NMR (500 MHz,
CDCl3): d [ppm]=2.57 (d, J=4.6 Hz, 1H, OH), 2.89–3.25 (m,
7H, HPc), 3.41 (ddd, J=13.9 Hz, 9.9 Hz, 1.9 Hz, 1H, HPc), 5.43–
5.50 (m, 1H, CHOH), 6.45–6.60 (m, 6H, HAr), 6.77 (bs, 1H,
HAr). – 19F NMR (500 MHz, CDCl3): d [ppm]=À78.36 (d, J=
Figure 1. X-ray
structure
of
racemic
S-benzyl-S-(Sp/S)-
([2.2]paracyclophan-4-yl)phenylmethyl dithiocarbonate (4d-Bn).
dure, the suspension can be filtered off with the product
remaining in solution.
1
6.8 Hz, CF3). – Diastereomer B: H NMR (500 MHz, CDCl3): d
The rearrangement can also be catalyzed using a strong
acid in low-polar solvents, but this method might not be
as tolerant to acid-sensitive groups as the method men-
tioned above.
[ppm]=2.20 (d, J=6.9 Hz, 1H, OH), 2.89–3.25 (m, 7H, HPc),
3.60 (ddd, J=13.2 Hz, 9.9 Hz, 3.2 Hz, 1H, HPc), 4.97 (quint., J=
7.1 Hz, 1H, CHOH), 6.39 (d, J=8.1 Hz, 1H, HAr), 6.45–6.60 (m,
6H, HAr). – 19F NMR (500 MHz, CDCl3): d [ppm]=À74.99 (d,
J=7.3 Hz, CF3). 13C NMR (500 MHz, CDCl3): d [ppm]=33.3
(À), 33.6 (À), 34.5 (À), 35.1 (À), 35.2 (À), 35.2 (À), 35.3 (À),
69.7 (+, q, J=31.4 Hz, CHOH), 72.5 (+, q, J=31.4 Hz, CHOH),
124.3 (q, J=282.3 Hz, CF3), 124.8 (q, J=283.0 Hz, CF3), 131.3
(+), 131.3 (+), 132.5 (+), 132.6 (+), 132.6 (+), 132.7 (+), 133.0
(+), 133.5 (+), 133.9 (+), 134.3 (+), 135.3 (+), 136.5 (+), 137.7
(Cquart.), 138.9 (Cquart.), 139.3 (Cquart.), 139.5 (Cquart.), 139.6 (Cquart.),
139.8 (Cquart.), 140.3 (Cquart.), 140.3 (Cquart.). – IR (KBr): n [cmÀ1]=
3545 (vw), 2925 (vw), 2852 (vw), 2349 (vw), 2330 (vw), 2325
(vw), 2161 (vw), 1986 (vw), 1594 (vw), 1498 (vw), 1346 (vw),
1261 (vw), 1166 (vw), 1120 (vw), 1051 (vw), 945 (vw), 903 (vw),
879 (vw), 837 (vw), 798 (vw), 778 (vw), 739 (vw), 718 (vw), 701
(vw), 670 (vw), 665 (vw), 641 (vw), 627 (vw), 599 (vw), 512 (vw),
2. Representative Experimental Procedures
Solvents and chemicals used for reactions were ordered from
VWR and used without further purification. The reactions were
carried out under argon. Thin-layer chromatography (TLC) was
carried out on silica gel plates (Kieselgel 60, F254, Merck) with
detection by UV light.
The compounds 1a-d were synthesized according to literature.[11]
The compounds 2a–b and 2d were synthesized according to liter-
ature.[13]
Table 4. Conversion of S,O-dithiocarbonates into the corresponding xanthates in various solvents.
Starting material
Solvent/Catalyst
t, T
Yield (%)
Product
3a-Me
3a-Me
3a-Me
3a-Me
3a-Me
3a-Bn
3a-Bn
3c-Me
3c-Me
CH2Cl2/TFA[a]
12 h, rt
16 h, rt
12 h, rt
24 h, rt
12 h, rt
12 h, rt
12 h, rt
48 h, 408C
24 h, 908C
50
-
-
4a-Me
4a-Me
4a-Me
4a-Me
4a-Me
4a-Bn
4a-Bn
4c-Me
4c-Me
CH2Cl2/AcOH[a]
[b]
EtOAc/SiO2
[c]
n-Hexane, EtOAc 15:1/SiO2
67
90d)
75
[b]
n-Hexane/SiO2
CH2Cl2/TFA[a]
[b]
n-Hexane/SiO2
n-Hexane/SiO2
n-Heptane
quant.
traces
16
[b]
[a] Two drops of acid in 5 mL dichloromethane; [b] 2.2 g silica gel and 5 mL of solvent; [c] 1.61 g silica gel and 3.2 mL solvent; [d] 10% hy-
drolysis of the S,O-dithiocarbonate.
Isr. J. Chem. 2012, 52, 143 – 148
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145

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J. Lahann, S. Brꢀse et al.
442 (vw), 401 (vw). – MS (70 eV, EI), m/z (%): 306 [M+] (38),
202 [C10H9F3O+] (14), 104 [C8H8+] (100). – EA C18H17F3O
(306.12): calcd: C 70.57, H 5.59, F 18.61, O 5.22, found: C 70.52,
H 5.43.
[ppm]=19.9 (+, CH3), 33.1 (À), 34.2 (À), 34.8 (À), 34.9 (À),
35.2 (À), 35.2 (À), 35.3 (À), 35.5 (À), 75.0 (+, q, J=32.6 Hz, 1H,
CHO), 79.3 (+, q, J=32.8 Hz, 1H, CHO), 124.3 (d, J=282.4 Hz,
CF3), 124.8 (d, J=282.4 Hz, CF3), 126.1 (Cquart.), 128.1(Cquart.),
131.7 (+), 132.1 (+), 132.3 (+), 132.6 (+), 132.6 (+), 132.7 (+),
133.0 (+), 133.0 (+), 134.7 (+), 135.0 (+), 135.4 (Cquart.), 135.5
(Cquart.), 136.9 (Cquart.), 139.1 (Cquart.), 139.4 (Cquart.), 139.4 (Cquart.),
140.1 (+), 140.3 (Cquart.), 140.4 (Cquart.), 216.0 (Cquart., COS2), 216.3
(Cquart., COS2). – 19F NMR (500 MHz, CDCl3): d [ppm]=À75.38
(d, J=6.6 Hz, 3F, CF3), À73.84 (d, J=7.2 Hz, 3F, CF3). – IR
(KBr): n [cmÀ1]=2956 (vw), 1594 (vw), 1497 (vw), 1412 (vw),
1361 (vw), 1270 (w), 1166 (w), 1128 (w), 1055 (w), 966 (vw), 859
(vw), 805 (w), 719 (vw), 707 (w), 691 (vw), 671 (vw), 631 (w), 588
(vw), 530 (vw), 513 (w), 496 (vw). – UV/VIS (CHCl3): lmax [nm]
(A)=235 (3.49), 277 (3.27), 280 (3.53), 282 (3.58), 289 (2.97). –
MS (70 eV, EI), m/z (%): 396 [M+] (2), 336 [C19H19F3S+] (37),
289 [C18H16F3+] (23), 185 [C10H8F3+] (24), 104 [C8H8+] (100), 91
[C2H3S2+] (22). HR-MS (EI): 396.0829 (calculated for [M+],
C20H19OS2F3), 396.0832 (observed). – EA C20H19F3OS2 (396.10):
calcd: C 60.58, H 4.83, S 16.17, found: C 61.52, H 4.92, S 16.82.
S-Methyl-O-((rac)-[2.2]paracyclophan-4-yl)methyl
dithiocarbonate (3a-Me)
(rac)-4-Hydroxymethyl[2.2]paracyclophane (119 mg, 0.50 mmol,
1.00 equiv) (2a) was dissolved in dry THF (10 mL) and cooled to
08C. Sodium hydride suspension (24 mg, 0.60 mmol, 1.20 equiv)
was added and the suspension was stirred at room temperature
for 1 h. The reaction mixture was cooled to 08C and carbon di-
sulfide (64 mL, 1.05 mmol, 2.10 equiv) was added via cannula.
The yellow solution was stirred for 12 h at room temperature,
cooled down to 08C and methyl iodide (38 mL, 0.60 mmol,
1.20 equiv) was added. After stirring for further 6 h at room tem-
perature, the reaction mixture was washed with semi-saturated
ammonium chloride solution and brine. The organic layer was
dried over magnesium sulfate and the solvent was removed
under reduced pressure. The product was obtained (195 mg,
1
quant.) as a colorless waxy solid. H NMR (500 MHz, CDCl3): d
S-Methyl-S-((rac)-[2.2]paracyclophan-4-yl)methyl dithiocarbonate
[ppm]=2.57 (s, 3H, CH3), 2.92 (ddd, J=13.7 Hz, 10.8 Hz, 5.7 Hz,
1H, HPc), 2.97–3.20 (m, 6H, HPc), 3.33 (ddd, J=13.6 Hz, 10.2 Hz,
2.2 Hz, 1H, HPc), 5.37 (d, J=12.3 Hz, 1H, CH2O), 5.60 (d, J=
12.3 Hz, 1H, CH2O), 6.39–6.44 (m, 2H, HAr), 6.49–6.58 (m, 4H,
HAr), 6.62–6.66 (m, 1H, HAr). - 13C NMR (500 MHz, CDCl3): d
[ppm]=19.1 (+, CH3), 33.0 (À), 34.6 (À), 35.0 (À), 35.3 (À),
74.8 (–, CH2O), 129.9 (+), 132.3 (+), 133.1 (+), 133.2 (Cquart),
133.3 (+), 133.4 (+), 134.1 (+), 135.2 (+), 138.8 (Cquart.), 139.2
(Cquart.), 139.5 (Cquart.), 140.2 (Cquart.), 216.0 (Cquart.). IR (ATR): n
[cmÀ1]=3005 (vw), 2922 (w), 2851 (w), 1640 (vw), 1592 (w), 1498
(w), 1438 (w), 1411 (w), 1318 (vw), 1226 (w), 1188 (m), 1052 (m),
961 (w), 935 (w), 894 (w), 863 (m), 795 (m), 773 (w), 716 (m),
643 (w), 622 (w), 588 (w), 571 (w), 509 (w), 492 (w), 447 (vw),
406 (vw) cmÀ1.– m.p.: 488C. – EI-MS [70 eV, m/z (%)]: 328 (10)
[M+], 300 (15) [M+ -C2H4], 221 (100) [C17H17+], 208 (20)
[C16H16+], 164 (29) [C10H12S+], 149 (18) [C9H9S+], 117 (35)
[C9H9+], 104 (95) [C8H8+], 91 (22) [C7H7+]. – HR-MS (EI):
328.0956 (calculated for [M+], C19H20OS2), 328.0953 (observed).
(4a-Me)
S-Methyl-O-((rac)-[2.2]paracyclophan-4-yl)methyl dithiocarbon-
ate (3a) (40.0 mg, 0.12 mmol) was added to a suspension of 2.2 g
silica gel in hexane (5 mL) and stirred for 12 h at room tempera-
ture. The reaction mixture was filtered and rinsed with 10 mL di-
chloromethane. After removal of the solvent a yellow solid was
obtained (38%, 90%) and the yield was ascertained using NMR
spectroscopy.
1H NMR (500 MHz, CDCl3): d [ppm]=2.44 (s, 3H, CH3), 2.85
(ddd, J=13.8 Hz, 10.8 Hz, 6.1 Hz, 1H, HPc), 2.94–3.11 (m, 4H,
HPc), 3.17 (ddd, J=13.2 Hz, 10.8 Hz, 2.0 Hz, 1H, HPc), 3.35 (ddd,
J=13.7 Hz, 10.3 Hz, 2.1 Hz, 1H, HPc), 4.02 (d, J=13.4 Hz, 1H,
CH2S), 4.19 (d. J=13.4 Hz, 1H, CH2S), 6.28 (m, 1H, HAr), 6.41–
6.46 (m, 2H, HAr), 6.48 (cm, 2H, HAr), 6.52 (dd, J=7.8 Hz,
1.8 Hz, 1H, HAr), 6.70 (dd, J=1.9 Hz, 7.8 Hz, 1H, HAr).–
13C NMR (500 MHz, CDCl3): d [ppm]=13.1 (+, CH3), 33.3 (À),
33.7 (À), 34.3 (À), 34.9 (À), 35.3 (À), 129.0 (+), 132.2 (+), 132.2
(+), 133.2 (+), 133.4 (+),135.0 (+), 135.0 (+), 135.2 (+), 138.0
(Cquart.), 139.2 (Cquart.),139.5 (Cquart.), 140.3 (Cquart.), 189.9 (Cquart.
,
S-methyl-O-((rac)-[2.2]paracyclophan-4-yl)(trifluormethyl)methyl
dithiocarbonate (3c-Me)
COS2). – EI-MS [70 eV, m/z (%)]: 328 (5) [M+], 268 (100) [M+
-COS], 253 (70) [C17H17S+], 221 (32) [C17H17+], 220 (69)
[C17H16+], 207 (23) [C16H15+], 164 (53) [C10H12S+], 149 (71)
[C9H9S], 118 (40) [C9H10+], 117 (28) [C9H9+], 104 (46) [C8H8+],
91 (33) [C7H7+]. – HR-MS (EI): 328.0956 (calculated for [M+],
C19H20OS2), 328.0957 (observed). - IR (KBr): n [cmÀ1]=2924
(w), 2850 (vw), 1700 (w), 1634 (m), 1592 (vw), 1498 (w), 1412
(w), 1309 (vw), 1179 (vw), 1132 (w), 1047 (vw), 971 (w), 944
(vw), 907 (w), 868 (w), 847 (m), 794 (w), 751 (vw), 716 (w), 694
(vw), 639 (w), 590 (w), 572 (vw), 511 (w), 486 (w), 411 (vw). -
EA C19H20OS2 (328.10): calcd: C 69.47, H 6.14, O 4.87, S 19.52,
found: C 70.14, H 6.18, S 18.43.
Sodium hydride suspension (48 mg, 1.2 mmol, 1.2 equiv) was
added to a solution of (rac)-[2.2]paracyclophan-4-yl)(trifluorome-
thyl)methanol (306 mg, 1.0 mmol, 1.0 equiv) (2a) in 20 mL dry
THF at 08C. After stirring at room temperatue for 1 h the reac-
tion mixture was cooled to 08C and carbon disulfide (0.13 mL,
2.1 mmol, 2.1 equiv) was added. The solution was warmed to
room temperature and stirred for 12 h. Next methyl iodide
(81 mL, 1.3 mmol, 1.3 equiv) was added at 08C. The solution was
stirred for 3 h and quenched with diethyl ether and water. The
organic layer was washed with brine and dried over magnesium
sulfate. The solvent was removed under reduced pressure and
the crude product was purified using flash chromatography (hex-
ane :ethyl acetate 15 :1). A pale yellow solid was obtained in
91% yield (360 mg, 0.91 mmol). Diastereomeric ratio 7:10. –
1H NMR (500 MHz, CDCl3): d [ppm]=2.72 (s, 3H, CH3), 2.79 (s,
3H, CH3), 2.93–3.10 (m, 7H, HPc), 3.11–3.23 (m, 7H, HPc), 3.53
(ddd, J=13.8 Hz, 6.8 Hz, 5.6 Hz, 1H, HPc), 3.58–3.65 (m, 1H,
HPc), 6.25–6.29 (m, 2H, HAr), 6.33–6.35 (m, 2H, HAr), 6.48–6.11
(m, 9H, HAr), 6.84 (s, 1H, HAr), 7.15 (q, J=7.3 Hz, 1H, CH),
7.55 (q, J=6.3 Hz, 1H, CH). – 13C NMR (500 MHz, CDCl3): d
(Sp/R)/(Rp/S) and (Sp/S)/(Rp/R)-S-Benzyl-S-(rac)-
[2.2]paracyclophan-4-ylphenylmethyldithiocarbonate (4d-Bn)
1.74 g (5.53 mmol, 1.00 equiv) (rac)-[2.2]Paracyclophan-4-ylphe-
nylmethanol were dissolved in 50 mL dry THF and cooled down
to 08C. After the addition of sodium hydride suspension
(270 mg, 6.64 mmol, 1.20 equiv) in small portions, the reaction
mixture was stirred for 1 h at room temperature. The suspension
was cooled to 08C and carbon disulfide (0.75 mL, 11.7 mmol,
146
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Isr. J. Chem. 2012, 52, 143 – 148

Functional Paracyclophanes: Synthesis of [2.2]Paracyclophanemethyldithiocarbonates Using Benzyl Schçnberg Rearrangement
0.89 g, 2.10 equiv) was added dropwise via cannula. The reaction
mixture was vigorously stirred at room temperature for 12 h.
After cooling to 08C benzyl bromide (0.85 mL, 7.19 mmol,
1.23 g, 1.30 equiv) was slowly added. The mixture was stirred for
3 h at room temperature and then quenched with water and di-
ethyl ether. The aqueous phase was separated and extracted with
dichloromethane. The combined organic layers were washed
with brine and dried over magnesium sulfate. After removal of
the solvent under reduced pressure a pale, yellow, slowly harden-
ing solid remained. The residue was purified using column chro-
matography (hexane :ethyl acetate 15 :1) yielding the product as
a yellow solid (2.30 g, 4.81 mmol, 87%). Diastereomeric ratio
20 :11. A separate analysis of the two diastereomers was not pos-
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1
sible. – H NMR (500 MHz, CDCl3): d [ppm]=2.62–2.73 (m, 1H,
HPc), 2.77–3.28 (m, 6H, HPc), 3.48 (ddd, J=2.7 Hz, 10.3 Hz,
14.1 Hz, 1H, HPc), 4.07 (d, J=13.5 Hz, 1H, CH2Ph), 4.19 (d, J=
13.7 Hz, 1H, CH2Ph), 5.82 (s, 1H, CH), 6.52 (dd, J=1.6 Hz,
7.9 Hz, 1H, HAr), 6.97–7.49 (m, 10H, HAr); 2.62–2.73 (m, 1H,
HPc), 2.77–3.28 (m, 7H, HPc), 4.23 (d, J=13.5 Hz, 1H, CH2Ph),
4.33 (d, J=13.7 Hz, 1H, CH2Ph), 5.89–5.92 (m, 1H, CO), 6.14 (s,
1H, HAr), 6.63 (dd, J=1.3 Hz, 8.0 Hz, 1H, HAr), 6.39–6.49 (m,
5H, HAr), 6.97–7.49 (m, 10H, HAr). – 13C NMR (500 MHz,
CDCl3): d [ppm]=33.7 (À), 34.5 (À), 34.7 (À), 34.8 (À), 35.0
(À), 35.2 (À), 35.3 (À), 50.6 (À), 52.8 (À), 127.0 (+), 127.5 (+),
127.6 (+), 127.7 (+), 127.8 (+), 128.5 (+), 128.6 (+), 128.7 (+),
128.8 (+), 128.8 (+), 128.9 (+), 129.0 (+), 129.3 (+), 129.5 (+),
129.8 (+), 130.7 (+), 131.6 (+), 132.3 (+), 132.4 (+), 132.6 (+),
132.7 (+), 132.8 (+), 132.9 (+), 133.0 (+), 133.10 (+), 135.9 (+),
136.4 (Cquart.), 136.6 (Cquart.), 136.7 (Cquart.), 137.2 (Cquart.), 137.4
(Cquart.), 138.6 (Cquart.), 139.3 (Cquart.), 139.4 (Cquart.), 139.4 (Cquart.),
139.7 (Cquart.), 140.0 (Cquart.), 140.2 (Cquart.), 143.1 (Cquart.), 188.3
(Cquart.). - UV/VIS (CHCl3): lmax [nm] (A)=227 (1.59), 232
(2.50). - MS (70 eV, EI), m/z: No M+ peak could be detected.
The structure was verified using X-ray diffraction (Figure 1;
CCDC-830691).
3. Summary
A method for the synthesis of benzylic S,S-[2.2]paracyclo-
phanemethyldithiocarbonates using S,O-dithiocarbonates
was described. The precursors can be prepared in good
yields. The thione–thiol rearrangement leading to the de-
sired products can be catalyzed with silica gel and works
even at room temperature.
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Received: July 26, 2011
Accepted: November 10, 2011
Published online: January 19, 2012
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