Syntheses of two kinds of dimeric hemicarcerand systems

Article abstract of DOI:10.1039/a705537d

The first dimeric hemicarcerand systems are reported, whose synthesis allows either identical or nonidentical cavities and their guests to be tethered at designed distances from one another.

Full text of DOI:10.1039/a705537d

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Syntheses of two kinds of dimeric hemicarcerand systems
Juyoung Yoon and Donald J. Cram*
Department of Chemistry and Biochemistry, University of California at Los Angeles, Los Angeles, CA 90095-1569, USA
The first dimeric hemicarcerand systems are reported,
whose synthesis allows either identical or nonidentical
cavities and their guests to be tethered at designed distances
from one another.
formed in which each of the two shell closures involved m-xylyl
rather than o-xylyl type reactions, as in 14.2 No evidence for
formation of 14 was obtained. The rates of the product-
determining steps involve formation of the second ether group
which closes to form a 26-membered ring leading to 1 or to form
a 27-membered ring to provide 14. Apparently the former rate
is faster than the latter.
The objective of this research was to establish synthetic
feasibility for the synthesis of hemicarcerands covalently
attached to one another through groups of designable lengths
and saturation, of which 1 and 2 are examples. We reported
earlier that appropriate guests incarcerated in 9 underwent
oxidation and reduction reactions in bulk solution containing a
variety of reducing and oxidizing agents. Electron and water
transfers through shells without physical contact between guest
and reagent were demonstrated.1 These results suggest the
possibility of electron transfers occurring between two or more
designable guests whose hosts of appropriate character are
located at controllable distances from one another. We imagine
the possibility of ultimately preparing robust polymer chains
whose core of guests is conducting, whose proximate shells are
electron-permeable, and whose R groups are insulating. Earlier
papers report the easy synthesis of diol 8,2 and its convertibility
to eight different hosts of general structure 9 that differ only in
their A groups.2–4 This family of hosts forms stable complexes
with over 50 characterized guests representing a wide variety of
structural types.2–5
The final step in the synthesis of 2™6H2O† is formulated in
eqn. (3). The two hemicarceplexes, 12™CHCl3† and
13™CHCl3†, were prepared as follows. The hydroxy group of
3,5-Me2C6H3OH was protected by treating it with BrCH2OMe–
NaH–THF to give 4† (95%), which was brominated with
N-bromosuccinimide (NBS)–CH2Cl2–AIBN to give 6† (40%).
Shell closure of diol 8 with 6 in NMP–Cs2CO3 (40 °C, 2 d) gave
11™CHCl3† (NMP exchange with CHCl3 solvent occurred
during chromatography). Deprotection of the ArOCH2OMe
group of 11™CHCl3 (THF–HCl, 35 °C, 4 h) gave 12™CHCl3.†
Alternatively, 3,5-Me2C6H3OH was treated with excess
Br(CH2)4Br–K2CO3–DMF (50 °C, 4 h) to provide 5 (60%)
1
(characterized only by H NMR), which was brominated with
NBS–CH2Cl2–AIBN to give 7† (40%). Shell closure of diol 8
with 7 in NMP–Cs2CO3 (30 °C, 2 d) resulted in 13™CHCl3†
(72%), NMP again being exchanged for CHCl3 as guest during
chromatography. As indicated in eqn. (3), the DMA–Cs2CO3
catalyzed coupling of 13™CHCl3 and 12™CHCl3 gave
2™6H2O† (82%), the CHCl3 guest of the starting materials
being replaced by water during chromatography with CH2Cl2,
drying and absorbing water from the atmosphere.‡
The synthesis of 1™2NMP† (NMP = N-methylpyrrolidi-
none) and of 1™2DMA† (DMA = dimethylacetamide) was
accomplished by the reaction of tetrabromide 3 with two moles
of diol 8 under the conditions of eqns. (1) and (2), respectively.‡
Earlier, 8 had been shown to react with 1,3-(BrCH2)2C6H4 to
give 10™G, suggesting the possibility that a dimer might be
Corey–Pauling–Koltun model examinations of 1, 2 and 14
provide the following estimates for the respective maximum
and minimum distances the centres of the two cavities can be
3
4
5
6
7
Me
Me
O
1
N C
, R = PhCH CH
2
2
Me
2
Chem. Commun., 1997
2065

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O
O
O
Br
O
A
H
G
OH
H
G
•
9
G, A = (CH2)4
12 •
CHCl3
O
OH
OH
H
H
H
G
O
8
10 •
G
O
Br
O
O
Br
O
OCH2Me
O(CH2)4Br
G
H
G
8
R = PhCH CH
2
2
•
•
11
13
CHCl3
CHCl3
O
O
NMP, Cs2CO3
OH
OH
Br
Br
Br
Br
O
O
O
O
2 H
+
+
H
(1)
H
G
G
H no
H
40 °C, 2 d, 60%
O
O
•
1
2NMP
14
8
8
3
DMA, Cs2CO3
OH
OH
Br
Br
Br
Br
O
O
O
2 H
H
G
H
G
H
(2)
(3)
O
40 °C, 2 d, 62%
•
1
2DMA
3
O
O
Br
O
O
Br
O
O
Br
O
DMA, Cs2CO3
Br
O
O(CH2)4Br
HO
O
(CH2)4
O
H
G
+
G
H
G
G
H
55 °C, 2 d, 82%
•
13
CHCl3
•
•
6H2
12
2
O
CHCl3
gel 60, 70–230 mesh). The shell closures required reagent grade DMA or
NMP, freshly distilled and stored over 3 Å molecular sieves (activated at
320 °C) and degassed just prior to use. The shell closures involved medium
dilution and inert atmospheres, and were similar to those reported in refs. 2
and 5.
from one another: 1, 13–15; 2, 13–26; 14, 12.5–16 Å. For all
three models, low-energy conformations appear to exist in
which the outsides of the two shells contact one another. We
believe it is more likely for electrons to pass from an appropriate
guest in one shell of 1 to a second appropriate guest in the other
shell of 1 than it is for electrons to pass between oxidizing or
reducing agents and incarcerated guests dissolved in dilute
solvent, an observed phenomenon.
1 T. A. Robbins and D. J. Cram, J. Am. Chem. Soc., 1993, 115, 12 199.
2 J. Yoon, C. Sheu, K. N. Houk, C. B. Knobler and D. J. Cram, J. Org.
Chem., 1996, 61, 9323.
3 J. Yoon C. B. Knobler, E. F. Maverick and D. J. Cram, Chem. Commun.,
1997, 1303.
4 J. Yoon and D. J. Cram, Chem. Commun., 1997, 1505
5 T. A. Robbins, C. B. Knobler, D. R. Bellew and D. J. Cram, J. Am. Chem.
Soc., 1994, 116, 111.
Footnotes and References
* E-mail: maverick@chem.ucla.edu
† These new compounds gave C and H elemental analyses within 0.30% of
theory, M+ m/z signals of 80–100% intensity (including guest) in their FAB-
MS and 1H NMR spectra consistent with their structures.
‡ The procedures were patterned after those that are standard in the
literature. All products were purified by chromatography (E. Merck silica
Received in Columbia, MO, USA, 31st July 1997; 7/05537D
2066
Chem. Commun., 1997