ABC-type meso-triaryl-substituted subporphyrins

Article abstract of DOI:10.1002/ejoc.201402435

ABC-Type subporphyrins 5a-5h, which bear three different meso-aryl substituents, were rationally synthesized by condensation of AB-type tripyrranes and aroyl chlorides. ABC-Type subporphyrins 5i and 5j were synthesized by Pd-catalyzed amination reaction of 4-bromophenyl subporphyrins 5e and 5h, respectively. Comparative studies on these ABC-type subporphyrins with A ₃-type subporphyrins and A₂B-type subporphyrins revealed that substituent effects are mostly simple superpositions of individual substituents but cooperative effects are recognized for subporphyrins which bear both electron-donating and electron-withdrawing substituents. Despite extensive attempts, enantiomeric separation of B-methoxy ABC-type subporphyrins was unsuccessful, whereas B-phenylated ABC-type subporphyrins were separated to pure enantiomers. Separated enantiomers showed weak but distinct CD signals reflecting the chiral clockwise/anticlockwise arrangements of the meso-aryl substituents. These results suggest facile racemization through S _N1-type heterolysis of the B-OMe bond in solution. ABC-Type meso-triaryl-substituted subporphyrins were rationally synthesized. Cooperative substituent effects are noted for donor-acceptor-type subporphyrins. Although the chiral resolution has not been successful for B-methoxy ABC-type subporphyrins, the enantiomers of some B-phenyl subporphyrins have been resolved by using chiral HPLC. Copyright

Full text of DOI:10.1002/ejoc.201402435

FULL PAPER
DOI: 10.1002/ejoc.201402435
ABC-Type meso-Triaryl-Substituted Subporphyrins
Kota Yoshida,[a] Hirotaka Mori,[a] Takayuki Tanaka,[a] Tadashi Mori,*[b] and
Atsuhiro Osuka*[a]
Keywords: Synthetic methods / Porphyrinoids / Chirality / Conformational analysis
ABC-Type subporphyrins 5a–5h, which bear three different
meso-aryl substituents, were rationally synthesized by con-
densation of AB-type tripyrranes and aroyl chlorides. ABC-
electron-donating and electron-withdrawing substituents.
Despite extensive attempts, enantiomeric separation of
B-methoxy ABC-type subporphyrins was unsuccessful,
Type subporphyrins 5i and 5j were synthesized by Pd-cata- whereas B-phenylated ABC-type subporphyrins were sepa-
lyzed amination reaction of 4-bromophenyl subporphyrins 5e
and 5h, respectively. Comparative studies on these ABC-type
subporphyrins with A3-type subporphyrins and A2B-type
subporphyrins revealed that substituent effects are mostly
simple superpositions of individual substituents but coopera-
tive effects are recognized for subporphyrins which bear both
rated to pure enantiomers. Separated enantiomers showed
weak but distinct CD signals reflecting the chiral clockwise/
anticlockwise arrangements of the meso-aryl substituents.
These results suggest facile racemization through SN1-type
heterolysis of the B–OMe bond in solution.
In contrast, subporphyrins adopt domed, bowl-like struc-
tures, which leads to a situation whereby ABC-type subpor-
phyrins are chiral, given no flip-flop bowl inversion.
Whereas enantiomeric separation of B-methoxy ABC-type
subporphyrins has been unsuccessful, B-phenylated ABC-
type subporphyrins have been separated into each enantio-
merically pure form.
Introduction
Subporphyrins are ring-contracted porphyrins that con-
sist of three regularly connected pyrroles and three methine
carbons encompassing a 14π-aromatic electronic network.[1]
Following our first report of the synthesis of tribenzosub-
porphines in 2006,[2] Kobayashi and ourselves reported in-
dependently the synthesis of A3-type meso-triaryl-substi-
tuted subporphyrins.[3,4] Different from meso-aryl-substi-
tuted porphyrins, meso-aryl-substituted subporphyrins ex-
perience remarkably large substituent effects on optical and
electronic properties owing to negligible rotational barriers
of meso-aryl substituents.[5] Quite recently, we developed a
stepwise synthetic route to A2B-type meso-triarylsubpor-
phyrins through an A2-type tripyrrane precursor.[6] Such
A2B-type subporphyrins were also prepared by transition-
metal-catalyzed cross-coupling reactions of meso-bromo-
substituted subporphyrins.[7] In this paper, we report the
synthesis of ABC-type meso-triaryl-substituted subporphy-
rins through condensation of AB-type tripyrranes and aroyl
chlorides. ABCD-type porphyrins possessing four different
meso-aryl groups have been prepared through an elegant
route developed by Lindsey et al.[8] However, these mol-
ecules are usually achiral as a result of a plane of symmetry.
Results and Discussion
Synthesis
In the present synthesis, nonsymmetrical AB-type tripyrro-
methanes were used as key precursors of ABC-type meso-
triaryl subporphyrins. 5-(4-tert-Butylphenyl)-10-phenyltri-
pyrrane (4a) was prepared as shown in Scheme 1. 1-Benzoyl-
5-(4-tert-butylphenyl)dipyrromethane (3a) was prepared
with an existing procedure by using phenylmagnesium
bromide instead of ethylmagnesium bromide.[8f] Benzoyl di-
pyrromethane 3a was reduced with NaBH4 and then re-
acted with pyrrole to furnish the AB-type tripyrrane 4a.[7]
In a similar manner, 5-(4-methoxyphenyl)-10-phenyltripyrr-
ane (4b) and 5-(4-bromophenyl)-10-phenyltripyrrane (4c)
were prepared. AB-type tripyrranes 4a–4c were converted
into their borane–triethylamine complexes, which were then
condensed with 10 equiv. of the appropriate aroyl chlorides
under previously reported conditions.[6] Fractions of sub-
porphyrin and subchlorin that were eluted closely in col-
umn chromatography were collected and subjected to oxi-
dation with activated MnO2 to convert subchlorin into sub-
porphyrin. Then, the axial ligand was quantitatively con-
verted into the methoxy group by stirring a solution of sub-
[a] Department of Chemistry, Graduate School of Science, Kyoto
University,
Sakyo-ku, Kyoto 606-8502, Japan
E-mail: osuka@kuchem.kyoto-u.ac.jp
[b] Department of Applied Chemistry, Graduate School of
Engineering, Osaka University,
2-1 Yamada-oka, Suita 565-0871, Japan
E-mail: tmori@chem.eng.osaka-u.ac.jp
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201402435.
Eur. J. Org. Chem. 2014, 3997–4004
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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K. Yoshida, H. Mori, T. Tanaka, T. Mori, A. Osuka
FULL PAPER
Scheme 1. Synthesis of the AB-type tripyrromethane 4a.
Scheme 2. Synthesis of the ABC-type subporphyrins 5a–5h.
Table 1. ABC-type subporphyrins 5a–5h.
porphyrin in dichloromethane and methanol at 50 °C for
about 15 min. Repeated separations by silica gel column
chromatography gave subporphyrins 5a–5h in 3.2–24% iso-
lated yields (Scheme 2 and Table 1). Subporphyrins 5i and
5j were synthesized by Pd-catalyzed amination reaction of
subporphyrins 5e and 5h in 38 and 50% yields, respectively
(Scheme 3 and Table 2).
Scheme 3. Synthesis of the ABC-type subporphyrins 5i and 5j.
Table 2. Reaction conditions for Pd-catalyzed amination reaction.
Product
X (equiv.)
Y (equiv.)
Time
Yield [%]
5i
5j
2.0
1.2
2.0
1.4
2 d
10 h
38
50
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ABC-Type meso-Triaryl-Substituted Subporphyrins
X-ray Crystallographic Analyses
1H NMR Spectra
1
The H NMR spectra of the ABC-type subporphyrins
The structures of subporphyrins 5g, 5h, 5i, and 5j were
determined by single-crystal X-ray diffraction analysis. All
subporphyrins show bowl-shaped structures with bowl
depths (defined by the distance from the central boron atom
to the mean plain of the peripheral six β-carbons) of 1.33,
1.32, 1.35, and 1.29 Å, respectively. The phenyl and 2-thi-
enyl groups in 5g are severely disordered in the crystal
structure and all three meso-aryl groups are also severely
disordered in the crystal structure of 5h, whereas such dis-
order is not observed for the crystals of 5i and 5j. The dihe-
dral angle of the 2-thienyl substituent toward the subpor-
phyrin core in 5g is small (37.5°), which is similar to the
reported tri(2-thienyl)-substituted subporphyrin and related
molecules.[9] The 4-(dibenzylamino)phenyl groups in 5i and
5j both display a characteristic structural distortion toward
the quinonoidal form and small dihedral angles (38.7° and
33.4°, respectively), as observed for meso-(4-dibenzyl-
aminophenyl)-substituted subporphyrins.[5b] The crystal
structure of 5i was found as a racemate and the enantiomers
have their concave faces facing each other in an offset man-
ner with the concave face of the adjacent subporphyrin
filled by the dibenzylamino group (Figure 1, b).
5a–5j should exhibit six doublet peaks owing to the pyrrolic
β-protons, reflecting the nonequivalent chemical shifts aris-
ing from their C1 symmetry. Nevertheless, in most cases, it
is hard to distinguish all six doublet peaks owing to severe
1
overlap of the signals. However, the H NMR spectrum of
subporphyrin 5a has six distinct doublet peaks owing to the
β-protons at room temperature as shown in Figure 2. H–
H scalar coupling correlation has been revealed by COSY
measurement (see Figure S10 in the Supporting Infor-
mation).
Figure 2. 1H NMR spectrum of subporphyrin 5a in CDCl3 at room
temperature.
Figure 1. (a) X-ray crystal structure of 5i. (b) A view of the crystal packing of subporphyrin 5i. Thermal ellipsoids represent 30% prob-
ability.
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K. Yoshida, H. Mori, T. Tanaka, T. Mori, A. Osuka
FULL PAPER
Absorption and Fluorescence Spectra
The UV/Vis absorption and fluorescence spectral data of
subporphyrins 5a–5j are listed in Table 3 and UV/Vis ab-
sorption and fluorescence spectra of some of the subpor-
phyrins are shown in Figure 3.
In the absorption spectra of A3-type meso-triaryl subpor-
phyrins, the 4-nitrophenyl group, 2-thienyl group, and 4-
aminophenyl group are known to exert strong substituent
effects on the optical properties of subporphyrins.[4,5b,9]
This is also valid for the present ABC-type subporphyrins,
because when one of these substituents is present, subpor-
phyrins exhibit perturbed absorption and fluorescence spec-
tra similar to those of the corresponding A3-type subpor-
phyrins. The absorption spectra of subporphyrins 5a, 5c,
and 5h that bear a 4-nitrophenyl substituent display Soret-
like bands at 380, 383, and 380 nm, and Q-like bands at
466 and 495 nm, 467 and 498 nm, and 464 and 493 nm,
respectively. The red shifts of Soret-like bands in 5a, 5c, and
5h relative to triphenylsubporphyrin 7a are smaller than
Table 3. Optical properties of subporphyrins 5a–5j and 7a–7f.
Figure 3. (a) UV/Vis absorption spectra of subporphyrins 5a, 5c,
5h, 5i, and 5j in CH2Cl2. (b) Fluorescence spectra of subporphyrins
5a, 5c, 5h, and 5i in CH2Cl2.
[d]
[d]
λabs [nm]
λem
ΦF
(ε [104 m–1 cm–1])
[nm]
5a
380
(6.3)
377 (16.9)
466
(0.8)
46
(1.1)
467
(1.1)
464
(1.3)
462
(1.2)
463
(1.3)
470
(1.0)
464
(1.2)
390
(9.0)
407
(5.5)
461
(1.3)
471
(1.8)
522
(1.7)
394
(8.9)
401
(12.4)
527
495 (0.9)
491 (1.2)
498 (1.3)
491 (1.3)
489 (1.2)
491 (1.4)
501 (1.3)
493 (1.2)
598
0.03
0.14
0.01
0.18
0.05
0.19
0.15
0.06
0.60
Ͻ 0.01
0.14
0.15
0.35
0.59
0.60
0.58
that of tri(4-nitrophenyl) subporphyrin 7b, whereas the cor-
responding red shifts in Q-like bands are similar. Subpor-
phyrin 7b exhibits a fluorescence peak at 543 nm with mod-
erate fluorescence quantum yields (ΦF = 0.15) in CH2Cl2.
In contrast, subporphyrins 5a and 5c emit reddish-orange
fluorescence with peaks at 598 and 602 nm and long tails
that extend out to over 800 nm with small fluorescence
quantum yields (ΦF = 0.03 and 0.01) in CH2Cl2. A possible
explanation for this phenomenon is the different degree of
intramolecular electron transfer from the subporphyrin S1-
state to the meso-4-nitrophenyl group, which is supposed to
trigger a red shift for fluorescence and fluorescence quench-
ing. When the subporphyrin core becomes more electron-
rich, the influence of the 4-nitrophenyl substituent becomes
more important. Observed larger red shifts of the Q-bands
and stronger fluorescence quenching in subporphyrins 5a
and 5c relative to 7b and 5h (the fluorescence peak at
574 nm and ΦF = 0.06) can be accounted for in this way.
As a similar feature, the absorption spectrum of subpor-
phyrin 5i is slightly different from that of mono[(4-dibenz-
ylamino)phenyl]-substituted subporphyrin 7d. Namely, the
Soret-like band of subporphyrin 5i has a peak at 390 nm
and a shoulder at 357 nm, whereas that of subporphyrin 7d
has two peaks at 359 and 394 nm. The fluorescence spec-
trum of 5i is less red-shifted than that of subporphyrin 7d.
It seems likely that the substituent effect of the meso-(4-
dibenzylamino)phenyl group is slightly attenuated by the
5b
529
602
533
528
533
556
574
5c
383
(8.3)
379 (16.2)
5d
5e
376 (16.3)
378 (17.4)
382 (13.6)
5f
5g
5 h
5i
380
(9.9)
357
(4.8)
360
(4.0)
373 (16.6)
470 (1.0) 506 (2.0) 595
5j
512 (1.8)
484 (0.9)
492 (1.6)
603
516
543
603
605
622
633
7a[a]
7b[a]
7c[b]
7d[c]
7e[c]
7f[c]
397 (11.1)
394 (11.9)
359
(5.6)
343
(3.0)
505 (2.1)
518 (2.8)
401 (15.4)
(3.5)
[a] See ref.[4]. [b] See ref.[9]. [c] See ref.[5b]. [d] Excited at the peak top
of each Soret band.
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ABC-Type meso-Triaryl-Substituted Subporphyrins
electron-donating meso-(4-methoxy)phenyl group in 5i. In subporphyrins and thus we converted B-methoxy subpor-
contrast, the absorption spectrum of subporphyrin 5j that phyrins 5b, 5f, and 5i into the corresponding B-phenylated
bears both electron-donating and accepting substituents subporphyrins 6b, 6f, and 6i, respectively, by B-arylation
shows two Soret-like peaks at 360 and 407 nm, and is actu- reaction with phenylmagnesium bromide[15] (Scheme 4).
ally non-fluorescent (ΦF Ͻ 0.01) and its fluorescence peak The UV/Vis absorption spectra and fluorescence spectra of
is red-shifted to 603 nm. These observations strongly sug- subporphyrins 6b, 6f, and 6i are shown in Figure 4 and the
gest that the substituent effect of the 4-nitrophenyl group is relevant data are listed in Table 4.
not simply additive but can be enhanced in combination
Table 4. Optical properties of subporphyrins 6b, 6f, 6i, and 8a.
with other electron-donating meso-substituents.
Enantiomeric Separations
ABC-Type subporphyrins should be chiral, providing
that there is no flip-flop bowl inversion. This molecular chi-
rality is classified as bowl chirality,[10] which is seen for
subphthalocyanine,[11] sumanene,[12] fullerene[13] and car-
bon nanotube systems.[14] Studies on bowl chirality have
[b]
λabs [nm] (ε [104 m–1 cm–1])
λem [nm][b]
ΦF
been extensively explored, because such three-dimensional
chiral π-surfaces can serve as an important motif for molec-
ular recognition and asymmetric catalysis. We thus at-
tempted enantiomeric separation of the ABC-type subpor-
phyrins prepared in this study. However, we failed in our
attempts to resolve the enantiomers of B-methoxy ABC-
type subporphyrins despite extensive efforts with various
chiral columns and eluting solvent systems. Then, it was
suspected that racemization of B-methoxy ABC subporphy-
rins might be triggered by a facile flip-flop bowl inversion
that might be possible through SN1-type heterolysis. We en-
visaged that such heterolysis would be difficult for B-phenyl
6b
6f
388 (14.0)
389 (13.0)
399 (8.9)
385 (13.6)
478 (0.8)
479 (0.8)
538 (2.0)
478 (0.9)
512 (1.6)
513 (1.6)
558
561
608
541
0.28
0.30
0.55
0.16
6i
8a[a]
507 (1.3)
[a] See ref.[15]. [b] Excited at the peak top of each Soret band.
The absorption and fluorescence spectra of subpor-
phyrins 6b and 6f are red-shifted relative to those of subpor-
phyrins 5b and 5f, as for subporphyrin 8a. The Soret-like
band of 6i has a single peak at 399 nm probably as a conse-
quence of attenuation of the substituent effect of the 4-(di-
benzylamino)phenyl group, because the subporphyrin core
is less electron-deficient owing to the electron-donating B-
phenyl group. The fluorescence quantum yields of 6b and
6f are larger than those of 5b and 5f, whereas that of 6i is
slightly lower than that of 5i. We were delighted to see that
the bands of the two enantiomers could be resolved by a
chiral HPLC column (Figure 5). Under these conditions,
Scheme 4. Synthesis of subporphyrins 6b, 6f, and 6i that bear a B-
phenyl group through reaction with Grignard reagents.
Figure 5. Chiral HPLC chromatographic chart of (a) 6f and (b) 6i
(column: CHIRALPAK® IB-3; eluent: THF/n-hexane, 5:95, flow
rate: 2.5 mL/min).
Figure 4. UV/Vis absorption and fluorescence spectra of subpor-
phyrins 6b, 6f, and 6i in CH2Cl2.
Eur. J. Org. Chem. 2014, 3997–4004
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K. Yoshida, H. Mori, T. Tanaka, T. Mori, A. Osuka
FULL PAPER
the enantiomeric separations of 6f and 6i to 6fA and 6fB,
Finally, we obtained single crystals of subporphyrin 6iB,
and to 6iA and 6iB, respectively, have been successfully ac- which revealed the structure as shown in Figure 6 (Table 5).
complished. However, the enantiomeric separation of 6b The chiral unit cell (P1 space group) contains two subpor-
has not been accomplished. All the separated enantiomers phyrins with the same chirality, but the packing structure is
did not undergo racemization even after being heated to similar to that of 5i.[16] The phenyl group is axially attached
reflux for 12 h in toluene, indicating their structural robust- to the boron atom with a B–C bond length of 1.58 and
ness. Enantiomers 6fA and 6fB, and 6iA and 6iB display 1.63 Å. The bowl depth is 1.34 Å, which is similar to those
1
exactly the same H NMR, UV/Vis, and fluorescence spec- of axial methoxy forms.
tra but different circular dichroism (CD) spectra (see the
Supporting Information). Unfortunately, these CD spectra
were extremely weak, probably because the chirality arises
not from the subporphyrin core but mainly comes from the
Summary
ABC-Type meso-aryl-substituted subporphyrins 5a–5j
were synthesized for the first time. Cooperative substituent
effects are observed for donor–acceptor-type subpor-
phyrins. Although the enantiomeric separation has not been
chiral arrangement of the peripheral aryl substituents. In
addition, there are 8 possible conformers with regard to the
meso-aryl substituents (R or S as defined in the Supporting
Information) and each conformer shows quite different
successful for B-methoxy ABC-type subporphyrins, the
Cotton effects, which leads to near cancelation. This effect
enantiomers of B-phenyl-substituted subporphyrins 6f and
was fairly well reproduced by our simulation of the CD
spectrum of 6f, in which the conformer population was
6i have been resolved by using chiral HPLC. These results
suggest a facile racemization of B-methoxy ABC subpor-
weighted by Boltzmann distribution (see Figure S14 in the
phyrins in solution, and also subporphyrins in general.
Supporting Information).
Experimental Section
5-(4-tert-Butylphenyl)-10-phenyltripyrrane (4a): To a suspension
of 1-benzoyl-5-(4-tert-butylphenyl)dipyrromethane (3a; 3.83 g,
10.0 mmol) and NaBH4 (10 equiv.) in dry tetrahydrofuran (THF;
100 mL), MeOH (10 mL) was added dropwise under N2. When the
reaction was over, the reaction was quenched with a saturated
aqueous NH4Cl solution, and the product was extracted with ethyl
acetate. The organic phase was washed with brine, and dried with
anhydrous Na2SO4. The solvent was evaporated, and the residue
was dissolved in pyrrole (20 mL, 288 mmol). A solution of tri-
fluoroacetic acid (TFA; 0.15 mL, 1.96 mmol) in CH2Cl2 (1.5 mL)
was added to the solution at 0 °C under N2. The reaction mixture
was stirred for 15 min, and then was quenched by addition of tri-
ethylamine (0.40 mL, 2.95 mmol). The solution was evaporated un-
der reduced pressure, and the residue was purified by silica-gel col-
umn chromatography (eluent: CH2Cl2/n-hexane, 1:1). The solvent
was evaporated, and the residue dried in a vacuum to afford 4a as
brownish yellow amorphous solids (1.79 g, 41%).
5-(4-Methoxyphenyl)-10-phenyltripyrrane (4b) and 5-(4-bromo-
phenyl)-10-phenyltripyrrane (4c) were prepared in a similar man-
ner.
Methoxo[5-(4-tert-butylphenyl)-10-(4-nitrophenyl)-15-phenylsubpor-
phyrinato]boron(III) (5a): To a suspension of 5-(4-tert-butylphenyl)-
10-phenyltripyrrane (4a; 0.460 g, 1.06 mmol) in 1,2-dichloroben-
zene (40 mL, 26.5 mm) was added triethylamine–borane (470 μL,
3 equiv.), and the resulting mixture was heated at 150 °C for 2 h
under an N2 atmosphere to give triethylamine–tri-N-tripyrrome-
thene–borane in situ. The solution color changed from fluorescent
yellowish to dark orange. The solution was then diluted to 10 mm
in 1,2-dichlorobenzene (106 mL). After the addition of 4-nitroben-
zoyl chloride (10 equiv.) dissolved in 1,2-dichlorobenzene through
a syringe the solution was stirred for 30 min at 150 °C under N2.
The reaction mixture was quenched by addition of pyridine
(12 equiv.), and the resulting solution was heated to reflux under
aerobic conditions for 1 h. The solution was cooled to room tem-
perature and ethylenediamine (10 equiv.) was added to the solution
and the mixture was stirred for 1 h. Then, the solution was poured
Figure 6. X-ray crystal structure of subporphyrin 6iB. Thermal el-
lipsoids represent 30% probability. Solvent molecules are omitted
for clarity.
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ABC-Type meso-Triaryl-Substituted Subporphyrins
Table 5. Crystal data of subporphyrins 5g–5j, 6i and 6iB.
5g
5h
5i
Formula
FW
Crystal system
Space group
a /Å
b /Å
c /Å
C33H24BN3O2S
537.42
(C34H21.9BBrN4O3)2(C6H6)3
C49H39BN4O2
726.65
1484.65
triclinic
monoclinic
P21/c (no. 14)
7.5286(1)
19.5441(4)
17.2428(3)
90
94.6863(12)
90
2528.62(8)
4
triclinic
¯
¯
P1 (no. 2)
P1 (no. 2)
14.179(3)
14.583(4)
17.474(4)
87.480(19)
71.040(15)
89.47(2)
3413.8(15)
2
10.1409(3)
11.8103(4)
15.9675(5)
85.5185(18)
81.5718(19)
77.5712(18)
1845.24(10)
2
α /°
β /°
γ /°
V /Å3
Z
T /K
93
1.412
0.0697
0.2243
93
1.444
0.0884
0.2088
93
1.308
0.0927
0.2976
ρcalcd. /gcm–1
R1 [IϾ2σ(I)]
Rw (all data)
GOF
1.035
1.006
1.046
5j
6i
6iB
Formula
FW
Crystal system
Space group
a /Å
b /Å
c /Å
C48H36BN5O3(C4H10O)
815.75
(C54H41BN4O)2(C6H6)3
1007.04
(C54H41BN4O)2(C6H6)3(CO)0.81
1029.73
triclinic
P 1 (no. 1)
10.152(3)
18.232(4)
18.267(4)
111.06(3)
103.39(4)
104.91(5)
2845(2)
2
triclinic
triclinic
¯
¯
P1 (no. 2)
P1 (no. 2)
12.38(1)
13.401(10)
13.944(10)
96.228(7)
111.405(19)
98.06(3)
2107(3)
2
10.131(6)
17.808(8)
18.298(10)
110.61(8)
105.55(12)
102.97(9)
2785(5)
2
α /°
β /°
γ /°
V /Å3
Z
T /K
93
1.286
0.0707
0.2201
1.090
93
1.201
0.630
0.1976
1.009
93
1.202
0.813
0.2302
ρcalcd. /gcm–1
R1 [IϾ2σ(I)]
Rw (all data)
GOF
1.068
onto a silica pad. Elution with CH2Cl2 removed 1,2-dichloroben-
zene, unreacted aroyl chloride, and some byproducts. Then elution
with MeOH/TFA (20:1) afforded a black fraction. The solution was
neutralized by saturated aqueous NaHCO3, extracted with CH2Cl2,
washed with 1 m HCl, and dried with anhydrous Na2SO4. MeOH
was added to the solution and the mixture was heated at 50 °C.
After 15 min the solvent was evaporated and the residue was puri-
fied by silica-gel column chromatography (eluent: CH2Cl2/n-hex-
ane/EtOAc, 1:4:1). The yellow fraction of subporphyrin and the
red fraction of subchlorin were carefully collected by checking with
TLC. Subchlorins were converted into subporphyrins by MnO2
oxidation. The solution was passed through a Celite pad to remove
MnO2. After the B-OMe form of subporphyrins was converted into
the B-OH form by washing with 1 m HCl, the solution was washed
with NaHCO3 aq., and dried with anhydrous Na2SO4. The solvent
was evaporated and the residue was purified by silica-gel column
chromatography (eluent: CH2Cl2/n-hexane/EtOAc, 1:4:1, followed
by MeOH/TFA, 20:1). The solution was neutralized with saturated
aqueous NaHCO3, extracted with CH2Cl2, washed by brine, and
dried with anhydrous Na2SO4. MeOH was added to the solution
and the mixture was heated at 50 °C to convert the B-OH form
into the B-OMe form. The solvent was evaporated, and the residue
was purified by silica-gel column chromatography (eluent: CH2Cl2/
ABC-Type subporphyrins 5b–5h were prepared in a similar man-
ner.
CCDC-983700 (for 5g), -983701 (for 5h), -983702 (for 5i), -983703
(for 5j), -983704 (for 6i), and -983705 (for 6iB) contain the supple-
mentary 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.
Supporting Information (see footnote on the first page of this arti-
cle): The Supporting Information for this article contains NMR
spectra of all compounds; UV-Vis and fluorescence spectra of Sub-
porphyrin 5a-5j; X-ray Crystal structures of Subporphyrins 5g, 5h,
and 5j; An analysis of the crystal data of Subporphyrins 6i (Race-
mic) and 6iB (Enantiomeric Pure); and CD spectra for Subporphy-
rins 6fA and 6iA and the calculated CD spectra for Subporphyrin
6f.
Acknowledgments
This work was supported by the Japanese Ministry of Education,
Culture, Sports, Science and Technology (MEXT) through Grants-
in-Aid [grant number 25220802 (S)] for Scientific Research. The
n-hexane/EtOAc, 1:4:1). Recrystallization from CH2Cl2/n-hexane authors thank Daisel people (Mr. Miyamoto) for their help in find-
afforded pure subporphyrins as orange solids (48.0 mg, 7.5%). ing conditions for the optical separation of subporphyrins. H. M.
Eur. J. Org. Chem. 2014, 3997–4004
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
4003

K. Yoshida, H. Mori, T. Tanaka, T. Mori, A. Osuka
FULL PAPER
2000, 65, 7323; d) D. K. Dogutan, S. H. H. Zaidi, P.
Thamyongkit, J. S. Linsey, J. Org. Chem. 2007, 72, 7701; e)
M. O. Senge, Y. M. Shaker, M. Pintea, C. Ryppa, S. S.
Hatscher, A. Ryan, Y. Sergeeva, Eur. J. Org. Chem. 2010, 237;
f) J. S. Lindsey, Acc. Chem. Res. 2010, 43, 300; g) M. O. Senge,
Chem. Commun. 2011, 47, 1943.
acknowledges the Japan Society for the Promotion of Science
(JSPS) for a Fellowship for Young Scientists.
[1] a) Y. Inokuma, A. Osuka, Dalton Trans. 2008, 2517; b) T.
Torres, Angew. Chem. Int. Ed. 2006, 45, 2834; Angew. Chem.
2006, 118, 2900; c) A. Osuka, E. Tsurumaki, T. Tanaka, Bull.
Chem. Soc. Jpn. 2011, 84, 679; d) C. G. Claessens, D. González-
Rodríguez, M. S. Rodríguez-Morgade, A. Medina, T. Torres,
Chem. Rev., DOI: 10.1021/cr400088w.
[9] a) S. Hayashi, Y. Inokuma, S. Easwaramoorthi, K. S. Kim, D.
Kim, A. Osuka, Angew. Chem. Int. Ed. 2010, 49, 321; Angew.
Chem. 2010, 122, 331; b) S. Hayashi, Y. Inokuma, A. Osuka,
Org. Lett. 2010, 12, 4148.
[2] Y. Inokuma, J. H. Kwon, T. K. Ahn, M.-C. Yoo, D. Kim, A.
Osuka, Angew. Chem. Int. Ed. 2006, 45, 961; Angew. Chem.
2006, 118, 975.
[3] a) N. Kobayashi, Y. Takeuchi, A. Matsuda, Angew. Chem. Int.
Ed. 2007, 46, 758; Angew. Chem. 2007, 119, 772; b) Y. Takeu-
chi, A. Matsuda, N. Kobayashi, J. Am. Chem. Soc. 2007, 129,
8271.
[4] Y. Inokuma, Z. S. Yoon, D. Kim, A. Osuka, J. Am. Chem. Soc.
2007, 129, 4747.
[5] a) Y. Inokuma, S. Easwaramoorthi, S. Y. Jang, K. S. Kim, D.
Kim, A. Osuka, Angew. Chem. Int. Ed. 2008, 47, 4840; Angew.
Chem. 2008, 120, 4918; b) Y. Inokuma, S. Easwaramoorthi,
Z. S. Yoon, D. Kim, A. Osuka, J. Am. Chem. Soc. 2008, 130,
12234.
[6] T. Tanaka, M. Kitano, S. Hayashi, N. Aratani, A. Osuka, Org.
Lett. 2012, 14, 2694.
[7] M. Kitano, S. Hayashi, T. Tanaka, H. Yorimitsu, N. Aratani,
A. Osuka, Angew. Chem. Int. Ed. 2012, 51, 5593; Angew. Chem.
2012, 124, 5691.
[8] a) D. M. Wallace, K. M. Smith, Tetrahedron Lett. 1990, 31,
7265; b) C.-H. Lee, F. Li, K. Iwamoto, J. Dadok, A. A.
Bothner-By, J. S. Lindsey, Tetrahedron 1995, 51, 11645; c) P. D.
Rao, S. Dhanalekshmi, B. J. Littler, J. S. Lindsey, J. Org. Chem.
[10] A. Szumna, Chem. Soc. Rev. 2010, 39, 4274.
[11] a) C. G. Claessens, T. Torres, Tetrahedron Lett. 2000, 41, 6361;
b) S. Shimizu, A. Miura, S. Khene, T. Nyokong, N. Kobayashi,
J. Am. Chem. Soc. 2011, 133, 17322; c) I. Sánchez-Molina, B.
Grimm, R. M. K. Calderon, C. G. Claessens, D. M. Guldi, T.
Torres, J. Am. Chem. Soc. 2013, 135, 10503.
[12] S. Higashibayashi, H. Sakurai, J. Am. Chem. Soc. 2008, 130,
8592.
[13] C. Thilgen, F. Diederich, Chem. Rev. 2006, 106, 5049.
[14] a) E. M. Pérez, N. Martín, Org. Biomol. Chem. 2012, 10, 3577;
b) C. Wang, K. Takei, T. Takahashi, A. Javey, Chem. Soc. Rev.
2013, 42, 2592.
[15] S. Saga, S. Hayashi, K. Yoshida, E. Tsurumaki, P. Kim, Y. M.
Sung, J. Sung, T. Tanaka, D. Kim, A. Osuka, Chem. Eur. J.
2013, 19, 11158.
[16] In this paper we do not discuss the absolute configuration of
6iB because; (i) the CD spectrum is very weak and we could
not obtain distinct mirror-image CD signals, and (ii) the X-ray
diffraction data of 6iB can not be used to determine the abso-
lute configuration for this molecule owing to the absence of
heavy atoms.
Received: April 17, 2014
Published Online: May 27, 2014
4004
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© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2014, 3997–4004