C.-Y. Yu et al. / Tetrahedron Letters 58 (2017) 3854–3858
3855
sulfoxide pyrolysis. The synthetic methodologies for the prepara-
tion of naphthalenophanes and naphthalenophanedienes are very
similar to those of the [2.2]paracyclophane families.
to the oxygen atom. The methylene hydrogens are diastereotopic
since the naphthalenophane is planar chiral. The signals below
2.00 ppm were assigned to the rest of the hydrogens of the long
alkyl chains.
Although alkyl and alkoxy-substituted [2.2]paracyclophane-
1
,9-dienes have been reported, no examples of tetraalkoxy-substi-
In order to obtain a single crystal of 3, a saturated hexane solu-
tion was slowly evaporated at room temperature. The solid state
structure of 3 shows that the dithianaphthalenophane bridges
adopt the chair conformation (Fig. 2). In general, the large distor-
tion in the naphthyl rings indicates a deviation from planarity.
The intramolecular distance between two corresponding carbons
of the naphthyl rings is presented here instead of deviation from
angles of the plane in the naphthyl rings. The intramolecular dis-
tance between the carbon atoms that are connected through the
bridge is shorter (3.30 Å) than the other interatomic distances
between the two naphthyl rings (3.56, 3.43 and 3.42 Å). The aver-
age distance from C(aryl) to C(methylene) (1.52 Å) is comparable
to that in toluene. The angle between C-S-C (103.1°) is comparable
tuted naphthalenophanedienes are available, possibly due to the
tedious and time consuming preparation and purification steps.
Tetraalkoxy-substituted naphthalenophanedienes with strongly
distorted naphthyl rings are one of the essential requirements for
the preparation of soluble naphthylenevinylene homopolymers
and block copolymers with controllable molecular weights, poly-
dispersity, and end groups through ROMP. Herein, we report the
synthesis, characterization, and solid state structures of tetraocty-
loxy-substituted dithia[3.3]naphthalenophane and tetraoctyloxy-
substituted [2.2]naphthalenophane-1,13-diene.
Results and discussion
3
1
to that of dithiacyclophanes.
The benzyne Stevens rearrangement reaction was carried out by
the slow addition of tetrabutylammonium fluoride trihydrate in
THF to a solution of 2-(trimethysilyl)phenyl trifluoromethanesul-
fonate and 3. The crude compound was purified by column chro-
matography to give a white semi-solid in 68% yield. Application
of the benzyne Stevens rearrangement proceeded with relatively
The synthetic route towards tetraoctyloxy-substituted naph-
thalenophanedienes 8 and 9 is shown in Scheme 1. Compound 1
was synthesized using a modification of previously established
synthetic methodology (see ESI).30 (1,5-bis(Octyloxy)naph-
thalene-2,6-diyl)dimethanethiol 2 was prepared by the reaction
of 1 with thiourea to form the corresponding bis(isothiouronium)
salt, followed by treatment with a potassium hydroxide solution
and neutralization with an acidic solution. A relatively high yield
2
4
high yield compared to traditional methods. The benzyne Ste-
vens rearrangement products contained large number of
a
stereoisomers due to migration of the phenyl sulfides on the ether
carbon of the thioether bond. Compounds 4 and 5 were therefore
very difficult to characterize by NMR spectroscopy due to the large
numbers of overlapping signals. High resolution mass spectrome-
try (HRMS) gave a molecular ion of 1037.6511 for 4 and 5 (calcu-
(
90%) was obtained for compound 2 after purification by flash col-
umn chromatography. Tetraoctyloxy-substituted dithia[3.3]naph-
thalenophane 3 was prepared by the very slow addition (3 d) of
an equimolar amount of 1 and 2 in 1,4-dioxane to a solution of
potassium hydroxide in ethanol under high dilution conditions at
room temperature. The slow addition of starting materials under
high dilution conditions for the cyclization reaction can help avoid
side-reactions and diminish the formation of linear oligomers and
polymers. Purification of the crude compound using flash column
chromatography gave the desired dithianaphthalenophane 3 in
+
lated for [MH] 1037.6515). Compounds 4 and 5 were then
2 2
oxidized by the addition of H O (35% w/w) to an acetic acid/-
toluene (1:3) solution at 0 °C over a period of 20 min, with subse-
quent stirring for an additional 12 h at room temperature. The
crude compound was obtained without purification to give 6 and
1
7
7
in 99% yield. Again, the H NMR spectrum of compounds 6 and
5
0% yield. It should be noted that only the pseudo-geminal isomer
(see ESI) exhibited a complex range of signals and characteriza-
of tetraoctyloxy substituted dithia[3.3]naphthalenophanes was
obtained after the cyclization reaction. The possible explanation
is due to the relatively high energy barrier for the formation of
tion was not possible. HRMS gave a molecular ion of 1091.6233
+
(
calculated for [MNa] 1091.6233). The mixture of 6 and 7 was
then heated at reflux in anhydrous DMF for 18 h under an argon
stream. The crude compound was then purified by column chro-
matography to give 8 and 9 in an overall yield of 23%. Further sep-
aration of 8 and 9 by multiple fractional recrystallization in hexane
at 5 °C gave 8 in 18% yield. The filtrates from the recrystallization
were collected and dried under vacuum. This gave compound 9
as an oil in 5% yield. The purity of 9 was determined by integration
of the corresponding peaks in the NMR spectrum. This purification
method gave compound 9 in up to 98% purity. HRMS gave a
pseudo-meta diastereomers.
1
The H NMR spectrum of 3 in CDCl
3
is shown in Fig. 1. Two dou-
blets (7.22 and 7.16 ppm, each J = 8.4 Hz, 4 H) correspond to aro-
matic hydrogens in the meta- and ortho- positions relative to the
methylene groups attached to sulfur. Due to the planar chirality
of dithianaphthalenophane, two doublets (4.61 and 3.51 ppm, each
J = 15.0 Hz, 4 H) were observed, corresponding to the thioether
hydrogens. The two doublet of triplets (3.83 and 3.72 ppm, each
J = 9.3, 6.5 Hz, 4 H) correspond to the methylene hydrogens bonded
RO
RO
RO
RO
RO
Ph
Ph
O
S
S
RO
RO
S
OR
OR
OR
OR
O
OR
OR
S
RO
TMS
Br
Ph
Ph
Br
OR
1
KOH
S
OTf
2 2
H O
OR
OR
4
5
6
8
yield: 18%
S
RO
+
DMF, reflux
18 h
1
3
,4-Dioxane, EtOH
d at R. T.
TBAF 3H
THF
2
O
3 2
CH CO H/ Toluene (1:3)
0
OR
o
OR
OR
C then R.T. for 12 h
RO
2
h at R. T.
Ph
O
Ph
SH
RO
RO
RO
RO
RO
RO
3
S
S
S
S
HS
OR
Ph
Ph
O
2
yield: 50%
OR
OR
OR
7
9
yield: 5%
yield: 68%
yield: 99%
Scheme 1. Synthesis of 4,8,16,20-tetraoctyloxy-[2.2]naphthalenophane-1,13-diene 8 and 4,8,18,22-tetraoctyloxy-[2.2]naphthalenophane-1,13-diene 9.