Synthesis of unsymmetrically substituted meso-phenylporphyrins by Suzuki cross coupling reactions

Article abstract of DOI:10.1039/b201622b

The synthesis of unsymmetrically substituted meso-phenylporphyrins by Suzuki cross coupling reactions was discussed. The problems of product contamination, due to deboronylation encountered with electron deficient boronic acids, were overcomed with the use of boronic esters. The unsymmetrically substituted triphenylporphyrins were found to be accessed via partial debromination in situ.

Full text of DOI:10.1039/b201622b

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Synthesis of unsymmetrically substituted meso-phenylporphyrins
by Suzuki cross coupling reactions
Baolu Shi and Ross W. Boyle*
1
Department of Chemistry, University of Hull, Cottingham Road, Hull, UK HU6 7RX
Received (in Cambridge, UK) 13th February 2002, Accepted 17th April 2002
First published as an Advance Article on the web 8th May 2002
Unsymmetrically substituted tetraphenylporphyrins, including A2B2 and AAЈB2 types can be synthesised by
bromination of 5,15-diphenylporphyrins followed by palladium catalysed Suzuki coupling to arylboronic acids and
esters. Unsymmetrically substituted triphenylporphyrins are also accessed via partial debromination in situ.
however, been subjected to Suzuki couplings with arylboronic
Introduction
acids. A study was undertaken, therefore, to determine how
facile and widely applicable such a reaction would be, for the
synthesis of unsymmetrically substituted meso-arylporphyrins.
Initial investigations involved determining which of the
many combinations of solvent and base reported for Suzuki
couplings9 would be most convenient and applicable. Coupling
of 5,15-dibromo-10,20-diphenylporphyrin (Scheme 1: 1; R = R1
= H)18 with 4-methoxybenzeneboronic acid (Scheme 1: 2;
R2 = 4-OMe) was tested with a variety of solvent and base
combinations. The previously reported requirement for zinc
chelation of the porphyrin18 was also examined. At reflux
temperatures, lower boiling solvents, such as THF, required the
use of stronger bases in order to obtain acceptable yields
of the desired coupled products. Higher boiling solvents, such
as toluene and DMF, in combination with weaker bases, gave
products, but also in many cases led to unacceptably low yields.
The combination of higher boiling solvents and weaker bases
gave significant amounts of porphyrin debromination for all
arylboronic acids tested, producing mixtures of bis- and mono-
coupled products. Trace amounts of the corresponding, fully
debrominated, DPP were also detected. Conditions for bis-
coupling were optimised using THF as solvent and potassium
phosphate as base. These conditions gave good yields (74–78%)
of the tetraaryl A2B2 product (Scheme 1: 4; R = R1 = H, R2 =
4-OMe) (Table 1), the major by-product being the corre-
sponding triaryl A2B product (Scheme 1: 12; R = R1 = H,
R2 = 4-OMe). Use of the zinc chelate of 5,15-dibromo-10,20-
diphenylporphyrin resulted in no coupling due to efficient trans-
metallation with palladium, a phenomenon not encountered
with the analogous metal free porphyrin. Optimised conditions
were then applied to a wider range of arylboronic acids, bearing
electron releasing and withdrawing groups, and also the
sterically hindered 2,4,6-trimethylbenzeneboronic acid. Steri-
cally unencumbered (Scheme 1: 2; R2 = H or 4-Me), electron
Synthetic routes to unsymmetrically substituted meso-aryl-
porphyrins are of great interest due to the potential of such
compounds for use in photodynamic therapy,1,2 optoelectronic
devices3,4,5 and the construction of photoactive bioconjugates.6
We have recently reported methods for synthesising such com-
pounds, which do not involve “mixed” condensations, thus
leading to single unsymmetrically substituted products. Two of
these methods rely upon palladium catalysed Heck and Stille
couplings on halogenated meso-arylporphyrins.7,8 We have now
expanded this methodolgy to include Suzuki couplings9 on
meso-brominated, symmetrically and unsymmetrically sub-
stituted 5,15-diphenylporphyrins (DPPs). Several examples of
Suzuki couplings on porphyrins have previously been reported,
however these have involved coupling of arylboronic acids to
porphyrins halogenated at either the β positions10–13 or on a
meso-phenyl ring.14 An example of Suzuki type couplings in
which the porphyrin represents the arylboronic acid coupling
partner has also been reported.15 Suzuki couplings between
arylboronic acids and meso-halogenated 5,15-diphenyl-
porphyrins had not, however, been reported. It was decided,
therefore, to conduct a detailed study of the viability of this
type of reaction for fabrication of unsymmetrically substituted
meso-tetraphenylporphyrins. During the course of our studies a
communication was published reporting this type of reaction
on symmetrically substituted DPPs,16 however, in this case it
was only possible to use inert alkyl substituents on the starting
DPPs. The method reported here allows more useful, and
unsymmetrically, substituted DPPs to be employed. We have
also investigated the effect of substitution on the arylboronic
acids in relation to two significant reactions, which compete
with bis-coupling. These are, firstly, the deboronylation of the
arylboronic acid, previously reported by Suzuki,17 but also
the unreported debromination of the bis-brominated DPP.
The latter process gives access to unsymmetrically substituted
meso-triarylporphyrins in yields of up to 24%. Conditions
for minimising these side reactions are reported which, unlike
those previously communicated, utilise low boiling solvents
and do not require degassing by freeze–thaw cycles, making
bis-coupling much more facile and widely applicable.
Table 1
Entry
R
R1
R2
Yield (%)
4
5
H
H
H
H
H
H
H
H
4-OCH3
4-CH3
H
4-C(O)CH3
3-CHO
4-OCH3
4-OCH3
4-OCH3
2,4,6-Me
74
72
75
77
78
73
77
78
24
6
Results and discussion
7
In previous studies we have investigated various palladium
catalysed coupling reactions on DPPs substituted at the meso-
positions with iodo7 and/or bromo8 groups; this has allowed
the independent introduction of ethynyl and vinyl substituents
at these positions. Porphyrin substrates of this type had not,
8
H
4-CH3
4-C(O)OCH3
4-C(O)OCH3
H
H
4-CH3
4-C(O)OCH3
4-NO2
H
9
10
11
12
DOI: 10.1039/b201622b
J. Chem. Soc., Perkin Trans. 1, 2002, 1397–1400
This journal is © The Royal Society of Chemistry 2002
1397

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Scheme 1 Reagents and conditions: (i) K3PO4, Pd(PPh3)4, THF reflux, 7 h.
rich (Scheme 1: 2; R2 = 4-OMe) and sterically hindered (Scheme
Finally, it was determined if meso-triarylporphyrins could be
1: 2; R2 = 2,4,6-Me) boronic acid gave good yields (>70%) of
bis-coupled A2B2 tetraphenylporphyrins (Table 1). In the case
of two electron deficient arylboronic acids, 3-formyl (Scheme 1:
2; R2 = 3-CHO) and 4-acetyl (Scheme 1: 2; R2 = C(O)Me)
and the sterically hindered 2,4,6-trimethylbenzeneboronic acid
however, products were heavily contaminated with the corre-
sponding benzene derivatives, resulting from extensive deboron-
ylation. Analysis indicated the by-products, other than the
A2B2 tetraphenylporphyrins, were a mono-coupled product and
DPP, resulting from debromination of the porphyrin com-
ponent. Deboronylation was also found to be problematic in
cases where the resulting benzene derivative coeluted with the
desired porphyrin product. To address the latter problem the
relevant boronic acids were converted to the corresponding
cyclic neopentyl glycol† esters (Scheme 1: 3; R2 = 3-CHO or
4-C(O)Me or 2,4,6-Me). The coupling reactions using the
neopentyl esters, as opposed to boronic acids, for the electron
deficient benzeneboronic neopentyl esters, suppressed deboro-
nylation, thus allowing purification of the desired porphyrin
product in good yields.
obtained in acceptable yields by in situ debromination of
the porphyrin. Consequently 5,15-dibromo-10,20-diphenyl-
porphyrin was treated with 2,4,6-trimethylbenzeneboronic acid
using optimised conditions. In this way, 5-(2,4,6-trimethyl-
phenyl)-10,20-diphenylporphyrin (Scheme 1: 12; R = R1 = H,
R2 = 2,4,6-trimethyl) was obtained in 24% yield.
In summary, an optimised method is described for obtaining
unsymmetrically substituted meso-tetraarylporphyrins of the
A2B2 and AAЈB2 types by Suzuki cross coupling reactions.
Using the same conditions A2B meso-triarylporphyrins can
also be accessed as a major by-product in yields up to 24%.
Problems of product contamination due to deboronylation,
encountered with electron deficient boronic acids, can be over-
come with the use of boronic esters. Finally, a core structure
bearing three useful functional groups, which can be reacted
independently to generate combinatorial diversity, has been
synthesised using this route.
Experimental
Previous experiments were restricted to DPPs without sub-
stituents on the phenyl groups, however, as we were interested
in these reactions as part of an ongoing program to develop
combinatorial methods in porphyrin chemistry;19 we decided
to explore how many points of potential diversification could
be introduced onto a meso-arylporphyrin using this method.
Initially, we investigated if the reaction conditions would
tolerate the presence of the synthetically versatile, but hydro-
lyticallysensitive, methoxycarbonylgroup. 5,15-Bis-(4-methoxy-
carbonylphenyl)porphyrin was brominated18 at the available 10
and 20 positions (Scheme 1: 1; R = R1 = 4-C(O)OMe) and then
subjected to Suzuki cross coupling with 4-methoxybenzene-
boronic acid, under our optimised conditions. The desired
product 5,15-bis(4-methoxyphenyl)-10,20-bis(4-methoxycar-
bonylphenyl)porphyrin (Scheme 1: 10; R = R1 = 4-C(O)OMe,
R2 = 4-OMe) was obtained in 77% yield (Table 1). It was next
decided to attempt the synthesis of a highly unsymmetrically
substituted AAЈB2 type porphyrin, anticipating that this could
give access to a core porphyrin with three independently
reactive points of diversification, for use in our combinatorial
studies. 5-(4-Nitrophenyl)-15-(4-methoxycarbonylphenyl)por-
phyrin was brominated18 (Scheme 1: 1; R = 4-NO2, R1 = 4-
C(O)OMe) and cross coupled with 4-methoxybenzeneboronic
acid to give 5,15-bis(4-methoxyphenyl)-10-(4-nitrophenyl)-
20-(4-methoxycarbonylphenyl)porphyrin (Scheme 1: 11; R =
4-NO2, R1 = 4-C(O)OMe, R2 = 4-OMe) in 78% yield (Table 1).
2,2-Dimethylpropane-1,3-diol and 2,4,6-trimethylbenzene-
boronic acid were purchased from Avocado Research
Chemicals Ltd, UK. All other reagents were purchased
from Lancaster Synthesis Ltd, UK. THF was distilled from
sodium and benzophenone. TLC was performed with Merck
aluminium plates coated with silica gel 60 F254. Chroma-
tography was performed using Fluorochem Silica Gel 35–70 µ,
60 Å. All purified compounds were found to contain only one
component by TLC analysis. Melting points were recorded on a
Gallenkamp melting point instrument and are uncorrected. UV
spectra were measured in dichloromethane on an Agilent 8453E
UV–visible spectrometer. 1H and 13C NMR spectra were
recorded on either JEOL JNM-LA400 or JEOL JNM-GX270
NMR spectrometers. Chemical shifts δ are quoted in ppm
relative to the SiMe4 signal as internal standard. Coupling
constants are given in Hz. Low resolution mass spectra were
recorded on a Shimadzu GCMS-QP5050 mass spectrometer.
Accurate mass spectra were carried out at the EPSRC National
Mass Spectrometry Service Centre, University of Wales,
Swansea.
General procedure for Suzuki coupling reactions
To a stirred slurry of K3PO4 (20 eq.) in anhydrous THF was
added porphyrin (1 eq.), benzeneboronic acid or benzene-
boronic acid neopentyl glycol cyclic ester (10 eq.) and Pd(PPh3)4
(0.1 eq.). The reaction was kept under reflux at 85 ЊC for 7 hours
and protected from light. After completion, the solvent was
evaporated and the residue was dissolved in CH2Cl2. This
mixture was washed with saturated NaHCO3, H2O, and brine
† The IUPAC name for neopentyl glycol is 2,2-dimethylpropane-1,3-
diol.
1398
J. Chem. Soc., Perkin Trans. 1, 2002, 1397–1400

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then dried by Na2SO4. The organic solvent was evaporated and
the crude product was purified by flash chromatography to
produce a purple solid.
porphyrin (31 mg, 0.05 mmol), K3PO4 (212 mg, 1 mmol),
3-formylbenzeneboronic acid neopentyl glycol cyclic ester
(109 mg, 0.5 mmol) and Pd(PPh3)4 (5.8 mg, 0.005 mmol) in
THF (20 ml) gave a purple solid (26 mg, 78%); column chroma-
tography (silica, 20% hexane in dichloromethane; Rf = 0.35);
mp >350 ЊC (decomp.); λmax(CH2Cl2)/nm (log (ε/dm3 molϪ1
cmϪ1)) 419 (5.8), 514 (4.2), 550 (3.8), 591 (3.7) and 642 (3.4);
δH (400 MHz, CDCl3) Ϫ2.78 (2H, br s, NH), 7.76–7.80 (6H,
m, 10,20-Ar-3,4,5H), 7.93–7.97 (2H, t, J = 7.6, 5,15-Ar-5H),
8.21–8.23 (4H, m, 10,20-Ar-2,6H), 8.32–8.35 (2H, m, 5,15-Ar-
6H), 8.48–8.50 (2H, m, 5,15-Ar-4H), 8.71 (2H, br s, 5,15-
Ar-2H), 8.76–8.77 (4H, d, J = 4.8, β-pyrrole H), 8.88–8.89 (4H,
d, J = 4.8, β-pyrrole H) and 10.32 (2H, s, CHO); δC (100 MHz,
CDCl3) 118.4, 120.8, 126.8, 127.6, 127.9, 128.9, 134.6, 135.0,
135.2, 139.8, 141.9, 143.2 and 192.6; HRMS (EI) calc. for
C46H30N4O2 670.2369, found 670.2358.
5,15-Bis(4-methoxyphenyl)-10,20-diphenylporphyrin
(4).
Following the general procedure 5,15-dibromo-10,20-diphenyl-
porphyrin (31 mg, 0.05 mmol), K3PO4 (212 mg, 1 mmol), 4-
methoxybenzeneboronic acid (76 mg, 0.5 mmol) and Pd(PPh3)4
(5.8 mg, 0.005 mmol) in THF (20 ml) gave a purple solid
(25 mg, 74%); column chromatography (silica, 50% hexane
in dichloromethane, Rf = 0.23); mp >350 ЊC (decomp.);
λmax(CH2Cl2)/nm (log (ε/dm3 molϪ1 cmϪ1)) 420 (5.8), 516 (4.5),
553 (4.3), 594 (4.2) and 649 (4.2); δH (400 MHz, CDCl3) Ϫ2.77
(2H, br s, NH), 4.09 (6H, s, OCH3), 7.27–7.30 (4H, m, 5,15-Ar-
3,5H), 7.76–7.78 (6H, m, 10,20-Ar-3,4,5H), 8.11–8.14 (4H, m,
5,15-Ar-2,6H), 8.21–8.23 (4H, m, 10,20-Ar-2,6H) and 8.83–
8.88 (8H, m, β-pyrrole H); δC (100 MHz, CDCl3) 55.7, 112.3,
120.0, 120.1, 126.8, 127.8, 131.0, 134.6, 135.7, 142.3 and 159.5;
HRMS (EI) calc. for C46H34N4O2 674.2682, found 674.2672.
5,15-Bis(4-methoxyphenyl)-10,20-(4-methylphenyl)porphyrin
(9). Following the general procedure 5,15-dibromo-10,20-bis-
(4-methylphenyl)porphyrin (20 mg, 0.031 mmol), K3PO4
(131 mg, 0.62 mmol), 4-methoxybenzeneboronic acid (47 mg,
0.31 mmol) and Pd(PPh3)4 (3.6 mg, 0.0031 mmol) in THF
(15 ml) gave a purple solid (16 mg, 73%); column chroma-
tography (silica, dichloromethane; Rf = 0.91); mp >350 ЊC
(decomp.); λmax(CH2Cl2)/nm (log (ε/dm3 molϪ1 cmϪ1)) 421 (5.7),
517 (4.2), 554 (4.0), 592 (3.7) and 649 (3.7); δH (400 MHz,
CDCl3) Ϫ2.77 (2H, br s, NH), 2.71 (6H, s, CH3), 4.10 (6H, s,
OCH3), 7.28–7.30 (4H, m, 5,15-Ar-3,5H), 7.55–7.57 (4H, m,
10,20-Ar-3,5H), 8.09–8.14 (8H, m, 5,10,15,20-Ar-2,6H) and
8.86 (8H, s, β-pyrrole H); δC (67.8 MHz, CDCl3) 21.6, 53.5,
112.2, 127.4, 127.6, 130.9, 134.6, 135.6, 137.4, 139.3 and 164.0;
HRMS (EI) calc. for C48H38N4O2 702.2995, found 702.2993.
5,15-Bis(4-methylphenyl)-10,20-diphenylporphyrin
(5).
Following the general procedure 5,15-dibromo-10,20-diphenyl-
porphyrin (31 mg, 0.05 mmol), K3PO4 (212 mg, 1 mmol), 4-
methylbenzeneboronic acid (68 mg, 0.5 mmol) and Pd(PPh3)4
(5.8 mg, 0.005 mmol) in THF (20 ml) gave a purple solid
(23 mg, 74%); column chromatography (silica, 30% hexane
in dichloromethane; Rf = 0.88); mp >350 ЊC (decomp.);
λmax(CH2Cl2)/nm (log (ε/dm3 molϪ1 cmϪ1)) 418 (5.7), 515 (4.2),
550 (3.9), 590 (3.7) and 647 (3.5); δH (400 MHz, CDCl3) Ϫ2.77
(2H, br s, NH), 2.69 (6H, s, CH3), 7.53–7.55 (4H, d, J = 7.8,
5,15-Ar-3,5H), 7.71–7.78 (6H, m, 10,20-Ar-3,4,5H), 8.08–8.10
(4H, m, 10,20-Ar-2,6H), 8.18–8.23 (4H, m, 5,15-Ar-2,6H)
and 8.82–8.87 (8H, m, β-pyrrole H); δC (67.8 MHz, CDCl3)
21.6, 120.0, 120.3, 126.7, 126.8, 127.5, 127.7, 131.1, 134.6,
134.7, 137.4, 139.3 and 142.3; HRMS (EI) calc. for C46H34N4
642.2783, found 642.2784.
5,15-Bis(4-methoxyphenyl)-10,20-bis(4-methoxycarbonyl-
phenyl)porphyrin (10). Following the general procedure 5,15-di-
bromo-10,20-bis(4-methoxycarbonylphenyl)porphyrin (28 mg,
0.038 mmol), K3PO4 (161 mg, 0.76 mmol), 4-methoxybenzene-
boronic acid (58 mg, 0.38 mmol) and Pd(PPh3)4 (4.4 mg, 0.0038
mmol) in THF (15 ml) gave a purple solid (23 mg, 77%);
column chromatography (silica, dichloromethane; Rf = 0.17);
mp >350 ЊC (decomp.); λmax(CH2Cl2)/nm (log (ε/dm3 molϪ1
cmϪ1)) 420 (5.8), 517 (4.5), 553 (4.2), 592 (4.0) and 649 (3.9); δH
(400 MHz, CDCl3) Ϫ2.79 (2H, br s, NH), 2.50 (6H, s,
C(O)OCH3), 4.10 (6H, s, OCH3), 7.29–7.31 (4H, m, 5,15-Ar-
3,5H), 7.49–7.51 (4H, m, 10,20-Ar-3,5H), 8.11–8.13 (4H, m,
5,15-Ar-2,6H), 8.21–8.23 (4H, m, 10,20-Ar-2,6H) and 8.85–
8.89 (8H, m, β-pyrrole H); δC (100 MHz, CDCl3) 21.4, 55.6,
112.3, 118.9, 119.9, 120.1, 131.1, 134.5, 135.4, 135.6, 139.8,
150.6, 159.5 and 169.6; HRMS (EI) calc. for C50H38N4O6
790.2791, found 790.2789.
5,10,15,20-Tetraphenylporphyrin (6). Following the general
procedure 5,15-dibromo-10,20-diphenylporphyrin (31 mg,
0.05 mmol), K3PO4 (212 mg, 1 mmol), benzeneboronic acid
(61 mg, 0.5 mmol) and Pd(PPh3)4 (5.8 mg, 0.005 mmol) in THF
(20 ml) gave a purple solid (23 mg, 75%); column chroma-
tography (silica, 40% hexane in dichloromethane; Rf = 0.75);
mp >350 ЊC (decomp.); λmax(CH2Cl2)/nm (log (ε/dm3 molϪ1
cmϪ1)) 417 (5.7), 514 (4.3), 549 (4.0), 589 (3.7) and 645(3.6);
δH (400 MHz, CDCl3) Ϫ2.77 (2H, br s, NH), 7.74–7.77 (12H,
m, 5,10,15,20-Ar-3,4,5H), 8.20–8.23 (8H, m, 5,10,15,20-Ar-
2,6H) and 8.85 (8H, m, β-pyrrole H); δC (100 MHz, CDCl3)
120.2, 126.8, 127.8, 131.4, 134.7 and 142.3; HRMS (EI) calc.
for C44H30N4 614.2470, found 614.2470.
5,15-Bis(4-acetylphenyl)-10,20-diphenylporphyrin (7). Follow-
ing the general procedure 5,15-dibromo-10,20-diphenylpor-
phyrin (31 mg, 0.05 mmol), K3PO4 (212 mg, 1 mmol), 4-acetyl-
benzeneboronic acid neopentyl glycol cyclic ester (116 mg,
0.5 mmol) and Pd(PPh3)4 (5.8 mg, 0.005 mmol) in THF (20 ml)
gave a purple solid (27 mg, 77%); column chromatography
(silica, dichloromethane; Rf = 0.36); mp >350 ЊC (decomp.);
λmax(CH2Cl2)/nm (log (ε/dm3 molϪ1 cmϪ1)) 419 (5.5), 515 (4.1),
551 (3.8), 590 (3.6) and 645 (3.5); δH (400 MHz, CDCl3) Ϫ2.79
(2H, br s, NH), 2.89 (6H, s, C(O)CH3), 7.73–7.80 (6H, m, 10,20-
Ar-3,4,5H), 8.20–8.22 (4H, m, 5,15-Ar-3,5H), 8.31–8.38 (8H,
m, 5,10,15,20-Ar-2,6H), 8.79–8.80 (4H, d, J = 4.8, β-pyrrole H)
and 8.87–8.88 (4H, d, J = 4.8, β-pyrrole H); δC (100 MHz,
CDCl3) 27.0, 118.9, 120.7, 126.7, 126.8, 127.9, 131.7, 134.6,
134.8, 136.4, 141.9, 147.2 and 198.3; HRMS (EI) calc. for
C48H34N4O2 698.2682, found 698.2680.
5,15-Bis(4-methoxyphenyl)-10-(4-nitrophenyl)-20-(4-methoxy-
carbonylphenyl)porphyrin (11). Following the general procedure
5,15-dibromo-10-(4-nitrophenyl)-20-(4-methoxycarbonylphenyl)-
porphyrin (24 mg, 0.033 mmol), K3PO4 (141 mg, 0.66 mmol),
4-methoxybenzeneboronic acid (50 mg, 0.33 mmol) and Pd-
(PPh3)4 (3.8 mg, 0.0033 mmol) in THF (15 ml) gave a purple
solid (20 mg, 78%); column chromatography (silica, dichloro-
methane; Rf = 0.54); mp >350 ЊC (decomp.); λmax(CH2Cl2)/nm
(log (ε/dm3 molϪ1 cmϪ1)) 422 (5.6), 518 (4.3), 552 (4.0), 592 (3.7)
and 649 (3.6); δH (400 MHz, CDCl3) Ϫ2.78 (2H, br s, NH), 2.50
(3H, s, C(O)OCH3), 4.10 (6H, s, OCH3), 7.27–7.31 (4H, m,
5,15-Ar-3,5H), 7.48–7.52 (2H, m, 20-Ar-3,5H), 8.09–8.13 (4H,
m, 5,15-Ar-2,6H), 8.20–8.23 (2H, m, 10-Ar-3,5H), 8.37–8.40
(2H, m, 20-Ar-2,6H), 8.61–8.64 (2H, m, 10-Ar-2,6H), 8.72–8.73
(2H, br d, J = 5.8, β-pyrrole H) and 8.87–8.92 (6H, m, β-pyrrole
H); δC (100 MHz, CDCl3) 55.6, 112.4, 116.7, 120.0, 120.6,
121.9, 131.2, 131.9, 134.2, 135.2, 135.4, 135.6, 139.6, 147.7,
149.3, 150.7, 159.6 and 169.6; HRMS (EI) calc. for C48H35N5O6
777.2587, found 777.2578.
5,15-Bis(3-formylphenyl)-10,20-diphenylporphyrin
(8).
Following the general procedure 5,15-dibromo-10,20-diphenyl-
J. Chem. Soc., Perkin Trans. 1, 2002, 1397–1400
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General method for synthesis of benzeneboronic acid neopentyl
glycol cyclic esters20
λmax(CH2Cl2)/nm (log (ε/dm3 molϪ1 cmϪ1)) 412 (5.9), 508 (4.6),
541 (4.1), 583 (4.1) and 638 (3.9); δH (400 MHz, CDCl3) Ϫ2.90
(2H, br s, NH), 1.82 (6H, s, Ar-2,6-CH3), 2.63 (3H, s, Ar-4-
CH3), 7.28 (2H, s, 5-Ar-3,5H), 7.76–7.79 (6H, m, 10,20-Ar-
3,4,5H), 8.23–8.27 (4H, m, 10,20-Ar-2,6H), 8.74–8.75 (2H, d,
J = 4.8, β-pyrrole H), 8.85–8.87 (2H, d, J = 4.8, β-pyrrole H),
9.00–9.01 (2H, d, J = 4.5, β-pyrrole H), 9.32–9.33 (2H, d,
J = 4.5, β-pyrrole H) and 10.20 (1H, s, meso H); HRMS (EI)
calc. for C41H32N4 580.2627, found 580.2626.
benzeneboronic acid (1 eq.) and 2,2-dimethylpropane-1,3-diol
(1.1 eq.) in anhydrous THF (5 ml mmolϪ1) was stirred for 10
min at room temperature. The solvent was evaporated and the
residue was dissolved in CH2Cl2, washed with water, dried by
Na2SO4 and concentrated in vacuo. A small amount of hexane
was added and the mixture was sonicated to produce a suspen-
sion. This suspension was evaporated to produce a solid.
Acknowledgements
4-Acetylbenzeneboronic acid neopentyl glycol cyclic ester
(2, R ؍ 4-C(O)CH3). 4-Acetylbenzeneboronic acid (164 mg,
1 mmol) and 2,2-dimethylpropane-1,3-diol (120 mg, 1.1 mmol)
in THF (5 ml) gave a brown solid (176 mg, 76%); mp 88 ЊC;
δH (400 MHz, CDCl3) 1.03 (6H, s, C(CH3)2(OCH2)2), 2.61 (3H,
s, C(O)CH3), 3.79 (4H, s, C(CH3)2(OCH2)2) and 7.89–7.91 (4H,
m, Ar); δC (100 MHz, CDCl3) 22.0, 26.8, 32.0, 72.5, 127.3,
134.1, 138.7 and 198.7; HRMS (ES) calc. for C13H18BO3
233.1349, found 233.1349.
The authors wish to thank the Wellcome Trust for financial
support (059572) and the EPSRC Mass Spectrometry Service,
Swansea for analyses. BS thanks the Department of Chemistry,
University of Hull for a studentship.
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1400
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