Bond Rotation in an Aromatic Carbaporphyrin: Allyliporphyrin

Article abstract of DOI:10.1002/chem.201802176

Allyliporphyrin is a carbaporphyrin that has replaced one pyrrole with an allyl group. Dynamic behavior (bond rotation) was observed by variable temperature ¹H NMR and 2D-NOESY NMR spectroscopy and theoretically examined by DFT calculations. These studies revealed that well-defined bond rotation was first observed in the limited space of the carbaporphyrin from 2 through cis-2 and the calculated rotational barrier was low enough, with the relative energy level of cis-2 only 0.65 kcal mol^?1 higher than 2. The synthesized allyliporphyrin (2) is a strongly aromatic macrocycle as indicated by the chemical shifts of its inner NH and CH signals. However, its palladium complex displayed reduced aromaticity due to the tilted thiophene of Pd-2.

Full text of DOI:10.1002/chem.201802176

A Journal of
Accepted Article
Title: Bond Rotation in an Aromatic Carbaporphyrin: Allyliporphyrin
Authors: Jung-Ho Hong, Adil S. Aslam, Min-Sung Ko, Jonghoon Choi,
Yunho Lee, and Dong-Gyu Cho
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To be cited as: Chem. Eur. J. 10.1002/chem.201802176
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Bond Rotation in an Aromatic Carbaporphyrin: Allyliporphyrin**
Jung-Ho Hong, Adil S. Aslam, Min-Sung Ko, Jonghoon Choi, Yunho Lee, and Dong-Gyu Cho*
Dedication ((optional))
Abstract: Allyliporphyrin is a carbaporphyrin that has replaced one
double bonds. Synthetically, allyliporphyrin (2) is a challenging
carbaporphyrin.[8] Thus, the replacement of one pyrrole of
porphyrin with an allyl group (or removal of the two peripheral
carbons of the pyrrole) has not been reported to date. However,
its synthesis could be accomplished by the modified synthetic
routes that our group has developed to obtain meso-fused
carbaporphyrins.[ Other synthetic routes for the target could be
complicated.[10] Herein, we report the detailed synthesis and
general properties of allyliporphyrin supporting [18]annulene
model of porphyrin by removing a different part (1b vs 2).[
Particularly, well-defined bond rotation was first observed in the
limited space of the carbaporphyrin.
pyrrole with an allyl group. Dynamic behavior (bond rotation) was
1
observed by variable temperature H NMR and 2D-NOESY NMR
spectroscopy and theoretically examined by DFT calculations. These
studies revealed that well-defined bond rotation was first observed in
the limited space of the carbaporphyrin from 2 through cis-2 and the
calculated rotational barrier was low enough, with the relative energy
level of cis-2 only 0.65 kcal/mol higher than 2. The synthesized
allyliporphyrin (2) is a strongly aromatic macrocycle as indicated by
the chemical shifts of its inner NH and CH signals. However, its
palladium complex displayed reduced aromaticity due to the tilted
thiophene of Pd-2.
9]
4]
Bond rotations are considered as the most fundamental
movements in molecular machines.[1, 2a] Although bond rotation
of aromatic [18]annulene was reported in the 1960s (Figure 1),[
such primitive motions could not be considered as mechanical
motions due to their undefined bond rotations. While the bond
3]
[
2c,
rotations of isoporphycenes were reported in the late 1990s,
2d]
in the porphyrin skeletons, pyrrole (or its thiophene analogue)
flipping was observed.[2a, 2b] Historically, to support [18]annulene
model of porphyrin, meso-unsubstituted dideazaporphyrin (a
porphyrin without two pyrrolic NHs, 1a) was first synthesized by
two consecutive McMurry coupling reactions.[ Then, the flexible
nature was recognized[5] in the form of meso-substituted
dideazaporphyrin (1b) while synthesized by removing two
4]
Figure 1. Different aspects of allyliporphyrin (2) from 21,23-dideazaporphyrin
(1a and 1b) and structure of [18]annulene
[
6]
tellurium atoms from meso-substituted telluraporphyrin. Its
conformer (trans-1b) was observed in equilibrium[ without a
metal in its core.[7] Although a minimum number of double bonds
between the two pyrroles (or meso-carbons) is necessary to
observe the bond rotation, stepwise bond rotations have not
been proposed due to the complexity from the multiple double
bond rotations and higher symmetry of dideazaporphyrin (1b)
like [18]annulene. Thus, the model compound (2) was designed
to examine stepwise bond rotations in a minimum number of
6]
The syntheses of carbaporphyrin (2) and its Pd-2 were
accomplished as summarized in Scheme 1. Retrosynthetic
analysis of the carbaporphyrin revealed that the condensation
reaction of diol (8) and dipyrromethane affords the target
compound. To obtain diol (8), the oxidation reaction of (Z)-3-
iodo-3-phenylprop-2-en-1-ol[
11]
with
MnO
afforded
2
acrylaldehyde (3) in an 80% yield. The Horner-Wadsworth-
Emmons reaction of acrylaldehyde (3) followed by DIBAL
2
reduction and MnO oxidation afforded dienylaldehyde (6). The
subsequent Suzuki coupling of thiophen-2-ylboronic acid with
dienylaldehyde (6) led to the corresponding dialdehyde (7) in a
63% yield. The key intermediate, diol (8), was obtained via a
Grignard reaction from dialdehyde (7). Finally, a Lewis-acid-
catalyzed [2+2] reaction[ between diol (8) and dipyrromethane
followed by in situ oxidation with chloranil produced the target
macrocycle 2 in a 6.3% yield. The central cavity composed of
[
*]
J.-H. Hong, A. S. Aslam, Min-Sung Ko, Prof. Dr. D.-G. Cho
Department of Chemistry, Inha University
Incheon, 22212, Republic of Korea
E-mail: dgcho@inha.ac.kr
12]
Jonghoon Choi, Prof. Dr. Yunho Lee
Department of Chemistry, Korea Advanced Institute of Science and
Technology (KAIST)
“NNCS”
(nitrogen-nitrogen-carbon-sulfur)
donors
from
Daejeon, 3055-701, Republic of Korea.
allyliporphyrin (2) could result in a square-planar complex with
palladium(II). Such C–H bond activations often facilitate unique
skeleton modifications.[ Thus, the reaction of free bases 2 with
palladium(II) acetate was performed according to Scheme 1.
However, no signals corresponding to the inner NH or CH in the
1H NMR spectrum of the complex indicated palladium
coordination (Pd-2) in the central cavity (Figure S6, ESI).
[
**] This research was supported by the Basic Science Research
Program through the National Research Foundation of Korea (NRF),
funded by the Ministry of Education, Science and Technology (grant
no. NRF-2016R1D1A1A09917824).
13]
Supporting information for this article is given via a link at the end of
the document.((Please delete this text if not appropriate))
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(
a)
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
N
N
N
S
HN
S
HN
S
HN
H17
H17
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
H18 2a
2b H16
cis-2
(b)
Ph
Ph
N
N
H
N
S
NH
S
NH
H H
S
N
H
Ph
Ph
Ph
Ph
Ph
Ph
2x (x = 0)
cis-2'
Figure 2. (a) Detected conformer (cis-2) in equilibrium with its two resonance
structures 2a and 2b of 2. (b) Undetected conformers (cis-2’ and 2 ) and
tau-2
0
possible tautomer (tau-2) of the allyliporphyrin (2) in equilibrium. The bond
rotation was assessed by changing the dihedral angle highlighted in red.
II
Scheme 1. Synthetic scheme of allyliporphyrin (2) and its Pd complex
1
The H NMR spectrum of 2 has characteristics of an aromatic
polypyrrolic molecule evidenced by the internal NH and CH
resonance signals at –2.93 and –5.06 ppm at –50 °C in CDCl
3
.
These values are comparable to those of the two inner NHs of
[
14]
tetraphenylporphyrin (≈ –2.80 ppm) in the same solvent. The
dynamic behavior of allyliporphyrin was easily recognized by the
very broad peripheral signals of protons (H16 and H18) at 25 °C
in Figure 3b. In contrast, the peaks sharpened into two doublet
signals at 10.24 and 10.14 ppm at –25 °C. At the same
temperature, small signals in the aromatic region started to
appear. The 2D nuclear Overhauser effect spectroscopy
(NOESY) spectrum of 2 showed that the small signals
exchanged with the signals of 2 (Figure S1, ESI). For example,
the small signal (H18cis-2) at 9.20 ppm exhibited an exchange
cross-peak with H18 while the H16 signal at 10.14 ppm
exhibited an exchange cross-peak with H16cis-2 at –5.14 ppm
(Figure S2, ESI). In addition, the small signal (dd, J = 15.1, 10.9
Hz, H17cis-2) at 9.92 ppm exhibited an exchange cross-peak with
H17 of 2 at –5.21 ppm, although the signal (H17cis-2) was more
clearly resolved at –50 °C. The two coupling constants of H17cis-2
signal indicated that H17cis-2 should have cis and trans-double
bond connectivity. Thus, the predicted exchanged structure
should be cis-2, as shown in Figure 2. From the exchanged
peaks, most important signals of 2 were absolutely assigned, as
shown in Figure 3. In addition, another small signal behaving
differently from those of cis-2 was clearly observed at 10.76 ppm
1
Figure 3. Expansion of key areas (a) of the H NMR spectrum of 2 at -50 °C in
1
CDCl
3
, (b) stacked spectra of 2 at various temperatures in CD
NMR spectrum of 2 at 120 °C in o-dichlorobenzene-d
2
Cl
2
, and (c)
H
4
.
(Figure 3a). For instance, the diagonal signals were not clearly
observed at –25 °C and their exchange cross-peaks (H18 and
H16) were clearly observed in the 2D NOESY spectra of 2
peak at 10.76 ppm were not detected due to the overlap of the
expected small peak sets with larger signals. Although it is
difficult to deduce a reasonable structure from the limited
information from the signal at 10.76 ppm, the allyl group should
adopt a structure similar to that of 2. Thus, another conformer
derived from the signals could be related to the NH tautomer of
(Figure S1, ESI). In contrast, all signals arising from cis-2 had
clear diagonal peaks with exchange cross-peaks at –25 °C,
although the intensity of the cross-peaks became very weak at –
50 °C (Figure S3, ESI). The observed coupling constants of the
two doublet peaks at 10.76 ppm (J = 13.7 and J = 13.2 Hz,
respectively) were similar to those of H16 (d, J = 13.8 Hz) and
H18 (d, J = 13.6 Hz) measured for 2. Other signals related to the
2
or 2
x
(x denotes both the dihedral angles in Figure 2). The
dynamic behavior of the allyliporphyrin was also studied by
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increasing the temperature in a o-dichlorobenzene-d
instead of the typical low boiling point NMR solvent (CDCl
4
solvent
). As
respectively, from the energy of 2, although the two values are
relatively similar. These calculations indicate that cis-2 is likely
more abundant than cis-2’ at equilibrium at 25 C. In addition,
3
o
the temperature increased, the two broad H18 and H16 signals
observed at 25 °C became much broader and gradually shifted
to a higher magnetic field (Figure 3c and S5, ESI). The two inner
protons (NH at –3.19 and CH at –5.40 ppm) individually became
much broader at 40 °C. The inner CH signal slowly disappeared
at 70 °C although the inner NH signal was clearly visible even at
x
the energy levels of 2 (Figure 2) were examined by changing
both dihedral angles at the same time in 2. These restricted
rotations enabled the allyl group to rotate at an angle with
respect to the macrocyclic mean plane defined as C5, C10, C15,
0
and C19 in Figure 4. The energy level of 2 (19.91 kcal/mol, two
1
(
1
20 °C (Figure 3c). Similarly, one of the two peripheral signals
H18 and H16) appeared at 9.77 ppm (d, J = 13.2 Hz, 1H) at
20 °C (Figure S5b, ESI). Thus, we concluded that the C17–C16
protons in the macrocycle, Figure 2) is similar to that of cis-2’.
However, the rotational barrier going from 2 to 290 was estimated
to be 57.73 kcal/mol. This value is slightly lower than the
calculated energy of the 90° twisted triplet 2-butene diradical
relative to the energy of trans-2-butene (65.7 kcal/mol obtained
from the same B3LYP DFT parameters).[15] Thus, the full rotation
(2 through 290) should be prohibited. The relative energy of the
NH tautomer of 2 is 2.33 kcal/mol higher than that of 2 (Figure
S16, ESI). The NH tautomer is likely more dominant at
bond rotation around C18 and C15 (from 2a to cis-2, Figure 2)
was monitored over a wide temperature range. Unfortunately,
the average signal expected from the proton exchange between
the inner proton and outer proton from the bond rotation was not
observed at higher temperatures. [3a] This could be due to the
expected peak being very broad or overlapping with others at
high temperatures.
equilibrium when compared to cis-2’ and 2
0
. Thus, the signals at
1
1
0.76 ppm (labeled as H18ta and H16ta) in the H NMR spectrum
[
16]
of 2 likely arise from the NH tautomer of 2. Considering the
data discussed above, it can be reasonably concluded that the
60
50
40
30
20
10
0
2
90
bond rotation of
2 mainly occurs through cis-2 at all
temperatures discussed herein.
20
cis-2'
cis-2
2
0
30 60 90 120 150 180 210 240 270 300 330 360
Dihedral Angle (degree)
Figure 4. Relative energy diagrams obtained from the bond rotation of 2; ●●
from 2 through cis-2, ●● from 2 through cis-2’, and ●● from 2 through 2 . All
0
bond rotations were depicted as their dihedral angles shown in Figure 2. Thus,
all three rotations started at different dihedral angles of 2.
Figure 5. X-ray crystal structures of (a) the top view of 2 and (b) Pd-2.
Thermal ellipsoids are scaled to the 50% probability level. Most hydrogen
atoms and disordered components are omitted for clarity.
To confirm the presence of the proposed conformers at
equilibrium, conformers at local energy minima were obtained by
changing the dihedral angle followed by structural optimization
using DFT calculations (relaxed potential energy scan), as
shown in Figure 4. Specifically, cis-2 was obtained by rotating
the C16–C17 bond of 2a to change the dihedral angle between
C17–H17 and C18–H18 bonds while cis-2’ by rotating the C18–
C17 bond of 2b to change the dihedral angle between C16–H16
and C17–H17 bonds. Structurally, both of cis-2 and 2 have
similar flatness (Figure S8 and S9, ESI), and compared to the
3.0
2
Pd-2
2.5
2
.0
.5
1
o
1.0
energy level of 2, cis-2 is only 0.65 kcal/mol higher. ∆G of the
equilibrium from 2 to cis-2 obtained from Van’t Hoff equation
0.5
(
(
1.02 kcal/mol) also supported the DFT calculation as well
Figure S14, ESI). In contrast, a larger energy difference
0.0
3
00
400
500
600
700
between cis-2 and cis-2’ arose from the steric hindrance
between H18 and the longer C–S bond of cis-2’, which also
shifted the allyl group of cis-2’ out of the plane (Figure S9, ESI).
Thus, the energy level of cis-2’ was calculated to be 18.20
kcal/mol higher than that of 2 (Figure 4). The rotation barriers for
cis-2 and cis-2’ were calculated to be 16.28 and 24.60 kcal/mol,
Wavelength (nm)
2 2
Figure 6. UV-Vis absorption spectra of 2 and Pd-2 in CH Cl
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The structures of the allyliporphyrin (2) and its associated Pd
complex (Pd-2) were unambiguously elucidated by X-ray
2’ and 2
0
, were not observed by the spectroscopic studies and
these observations were also supported by DFT calculations. In
addition, allyliporphyrin (2) is a strongly aromatic macrocycle,
judged by the chemical shifts of its inner NH and CH signals,
although its palladium complex displayed reduced aromaticity
due to its tilted thiophene. The current synthesis also supported
[18]annulene model of porphyrin.
crystallography after crystal growth in CH
5
2 2
Cl /MeOH (Figure
).[17] In the solid state, the two molecules of allyliporphyrin
overlapped and aligned at 180°. The disordered components
and protons were omitted for the structural clarity in Figure 5.
Structurally, the thiophene and pyrrole C ring lie flat while the
pyrrole B ring and allyl group are tilted by 10.90, and 17.85°,
respectively, from the macrocyclic mean plane (Figure S20 and
S21, ESI). Some bond distances were quite unusual, such as
the C9–C10 (1.184 Å), C13–C14 (1.207 Å), and C17–C18
Keywords: porphyrin • carbaporphyrin • bond rotation •
allyliporphyrin • aromaticity
(
1.266 Å) bond, which are shorter than typical carbon double
bonds. On the other hand, the C18–C19 (1.625 Å) and C15–C16
1.524 Å) bonds between the allyl group are particularly longer
[1]
a) S. Erbas-Cakmak, D. A. Leigh, C. T. McTernan, A. L. Nussbaumer,
Chem. Rev. 2015, 115, 10081–10206; b) G. S. Kottas, L. I. Clarke, D.
Horinek, J. Michl, Chem. Rev. 2005, 105, 1281–1376.
(
than other bonds, which may reflect a rotation of the allyl group
within a limited angle from 2 to 290. In contrast, the abnormal
bond lengths of 2 were not observed in its Pd complex. For
example, the longest and shortest bonds (C18–C19 and C9–
C10) of 2 changed to 1.401 and 1.402 Å, respectively, for Pd-2.
The two pyrroles and allyl group of Pd-2 were relatively flat
except for the thiophene which was titled 23.98° from the mean
plane (C5, C10, C15, and C19), as shown in Figure S24. This tilt
disturbs the planarity of the molecules and reduced the
aromaticity of Pd-2. The upfield shifted -protons of thiophene in
[2]
a) M. Toganoh, H. Furuta, J. Phys. Chem. A 2009, 113, 13953–13963;
b) E. Pacholska, L. Latos-Grazynski, Z. Ciunik, Angew. Chem. Int. Ed.
2001, 40, 4466-4469; Angew. Chem. 2001, 113, 4598–4601; c) E.
Vogel, P. Scholz, R. Demuth, C. Erben, M. Bröring, H. Schmickler,Y.-D.
Wu, Angew. Chem. Int. Ed. 1999, 38, 2919–2923.; Angew. Chem. 1999,
1
11, 3100–3105; d) E. Vogel, M. Bröring, C. Erben, R. Demuth, J. Lex,
M. Nendel, K. N. Houk, Angew. Chem. Int. Ed. Engl. 1997, 36, 353–
57; Angew. Chem. 1997, 109, 363-367.
3
[3]
[4]
a) F. Sondheimer, Proc. Roy. Soc., Ser. A 1967, 297, 173–204; b) F.
Sondheimer, R. Wolovsky, Y. Amiel, J. Am. Chem. Soc. 1962, 84, 274–
2
84.
T. D. Lash, S. A. Jones, G. M. Ferrence, J. Am. Chem. Soc. 2010, 132,
2786–12787.
1
the H NMR spectrum and nucleus-independent chemical shifts
1
(
NICS) values of Pd-2 as compared to those in 2 further
[
5]
6]
B. Szyszko, M. J. Białek, E. Pacholska-Dudziak, L. Latos-Grażyński,
Chem. Rev. 2016, 117, 2839–2909.
indicated reduced aromaticity of Pd-2 (Figure S6, S17 and S18
in ESI).
[
E. Pacholska-Dudziak, L. Szterenberg, L. Latos-Grażyński, Chem. Eur.
J. 2011, 17, 3500–3511.
The UV-visible absorption spectrum of 2 in CH
2 2
Cl (Figure 6)
shows a characteristically intense Soret band at 422 nm (ε =
[7]
a) E. Pacholska-Dudziak, J. Skonieczny, M. Pawlicki, L. Szterenberg, Z.
Ciunik, L. Latos-Grażyński, J. Am. Chem. Soc. 2008, 130, 6182–6195;
b) E. Pacsholska-Dudziak, A. Gaworek, L. Latos-Grażyński, Inorg.
Chem. 2011, 50, 10956–10965.
5
−1
−1
2.82 × 10 cm M ) accompanied by weak and broad Q-like
bands at 516, 549, and 624 nm. The spectroscopic features of 2
were very similar to those of (meso-unsubstituted)
[
[
8]
9]
a) T. D. Lash, Chem. Rev. 2017. 2313–2446; b) M. Toganoh, H. Furuta,
Chem. Commun. 2012, 48, 937–954; c) M. Stȩpień, L. Latos-Grażyński,
Acc. Chem. Res. 2005, 38, 88–98.
[
18]
carbachlorins. The Soret band of 2 was red shifted by 21 nm
while the Q-like bands of 2 were blue shifted by 27 nm
compared to those of carbachlorins.[18a] Interestingly, both the
Soret and Q-like bands of 2 are very broad compared to those of
other carbaporphyrins.[8] The bands of the Pd complex were red-
shifted compared to those of its free ligands. Typically, the Soret
band of Pd-2 was red shifted by 36 nm from the Soret band of 2.
In addition, the molar absorption coefficient (ε) of Pd-2 was quite
smaller than that of 2. The distorted thiophene in the solid state
likely reduced molar absorption coefficient (ε) of Pd-2. Thus, the
electronic structure and optical properties of 2 and Pd-2 were
studied by time-dependent density functional theory (TDDFT at
B3LYP/6-31G(d, p). TDDFT calculations predicted that the
oscillator strengths of the Soret and Q-like bands of Pd-2
decreased by a half of those of 2 (Figure S11 and S12, ESI).
In summary, to examine bond rotation of aromatic polypyrrolic
macrocycles with a limited number of carbon double bonds,
allyliporphyrin (2) was synthesized. Structurally, allyliporphyrin is
an interesting carbaporphyrin where one pyrrole is replaced with
an allyl group. The dynamic behavior (bond rotation) was
observed by variable temperature 1H NMR and 2D-NOESY
NMR spectroscopy. These studies revealed that bond rotation
a) A. S. Aslam, J.-H. Hong, J.-H. Shin, D.-G. Cho, Angew. Chem. Int.
Ed. 2017, 56, 16247–16251; Angew. Chem. 2017, 129, 16465–16469;
b) J.-H. Hong, A. S. Aslam, M. Ishida, S. Mori, H. Furuta, D.-G. Cho, J.
Am. Chem. Soc. 2016, 138, 4992–4995.
[
[
10] H. Ogawa, N. Sadakari, T. Imoto, I. Miyamoto, H. Kato, Y. Taniguchi,
Angew. Chem. Int. Ed. 1983, 22, 417; Angew. Chem. 1983, 95, 412.
11] C. G. Nasveschuk, T. Rovis, Angew. Chem. Int. Ed. 2005, 44, 3264-
3267; Angew. Chem. 2005, 117, 3328–3331.
[
[
[
12] D. Gryko, J. S. Lindsey, J. Org. Chem. 2000, 65, 2249–2252.
13] B. Szyszko, L. Latos-Grażyński, Chem. Soc. Rev. 2015, 44, 3588–3616.
14] A. D. Cardenal, H. Jeong Park; C. J. Chalker, K. G. Ortiz, D. C. Powers,
Chem. Commun. 2017, 53, 7377–7380.
[15] S. E. Barrows, T. H. Eberlein, J. Chem. Educ. 2005, 82, 1329–1333.
[
16] The obtained plot from Van’t Hoff equation may not be linear if other
equilibriums are possibly involved (see, Figure S15 and S16 in ESI)
17] CCDC 1826402 and CCDC 1826403 (2 and Pd-2, respectively) contain
the supplementary crystallographic data for this paper. These data can
be obtained free of charge from the Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
[
[
18] A similar synthon for allyliporphyrin (2) leads to meso-unsubstituted
allyliporphyrin with more double bonds: a) D. Li, T. D. Lash, J. Org.
Chem. 2014, 79, 7112–7121; b) M. J. Hayes, T. D. Lash, Chem. Eur. J.
1998, 4, 508–511.
2
occurs from 2 through cis-2 in three sp carbons between the
two meso-carbons. The calculated rotational barrier was low and
relative energy level of cis-2 was only 0.65 kcal/mol higher than
that of 2. Two different rotational pathways, represented by cis-
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Jung-Ho Hong, Adil S. Aslam, Min-Sung
Ko, Jonghoon Choi, Yunho Lee, and
Dong-Gyu Cho*
Page No. – Page No.
Bond Rotation in an Aromatic
Carbaporphyrin: Allyliporphyrin
Porphyrinoid: Allyliporphyrin (2) was synthesized that has replaced one pyrrole
with an allyl group. The current studies revealed that well-defined bond rotation
2
occurs from 2 through cis-2 in three sp carbons between the two meso-carbons.
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