Synthesis of a class of 5-((5-(pyrrol-2-yl-methylene)-pyrrol-2-yl) methylene)furan-2-ones and the formation of a furanone dipyrrin imino ether

Article abstract of DOI:10.1039/c1nj20415g

A class of α-furanyl dipyrrins 2 were prepared by refluxing THF solutions of DDQ adducts 1 with the appropriate alcohols in the presence of AlCl₃ and further subsequent reaction of the cyano-group results in the formation of an imino ether upon MeOH addition.

Full text of DOI:10.1039/c1nj20415g

View Article Online / Journal Homepage / Table of Contents for this issue
Dynamic Article Links
NJC
Cite this: New J. Chem., 2011, 35, 2483–2487
www.rsc.org/njc
PAPER
Synthesis of a class of 5-((5-(pyrrol-2-yl-methylene)-pyrrol-2-yl)methylene)-
furan-2-ones and the formation of a furanone dipyrrin imino etherw
Ji-Young Shinab and David Dolphin*a
Received (in Gainesville, FL, USA) 12th May 2011, Accepted 17th July 2011
DOI: 10.1039/c1nj20415g
A class of a-furanyl dipyrrins 2 were prepared by refluxing THF solutions of DDQ adducts 1
with the appropriate alcohols in the presence of AlCl3 and further subsequent reaction of the
cyano-group results in the formation of an imino ether upon MeOH addition.
Introduction
2,3-Dichloro-5,6-dicyano-1,4-quinone (DDQ) has been widely
used as a convenient oxidant in the synthesis of polyaryl-
compounds and these oxidative processes have been intensively
studied.1–10 Initial radical formation, to generate resonance
stabilized intermediates, has been considered as the principle
oxidation mechanism when employing DDQ.11,12 On the other
hand, 1,4-benzoquinones bearing electron-withdrawing groups
are strong dienophiles and a few examples are known where
DDQ adducts have been reported as precursors formed during
the aromatization of saturated compounds.13–15
Fig. 1 bDLDAs (1a–1c).
Recently, the formation of unique DDQ-linked products, a
C2 symmetric hexapyrrole16 and bis-dipyrrin linked DDQ
adducts (bDLDAs) were reported (Fig. 1).17 These DDQ-
linked products were isolated during DDQ-oxidations of the
corresponding tripyrromethane and dipyrromethanes under
aerobic conditions. When the dipyrromethane contained
an electron-withdrawing group such as pentafluorophenyl or
2,6-dichlorophenyl at the meso-position, the DDQ adducts
were obtained in reasonable yields. Furthermore, refluxing
these bDLDAs, in the presence of a Lewis acid and nucleo-
philes, produced atypical dipyrrin compounds as shown in
Scheme 1. Compounds 1a and 1b formed, in higher yields than
1c, were further employed in the synthesis of unusual dipyrrin
compounds when reacted with nucleophiles. Thus 2a-1 and
2b-1 were formed when a THF solution of DDQ adducts 1a
and 1b was refluxed in the presence of AlCl3 and methanol.
The mechanism can be rationalized as a ring opening and
Scheme 1 Formation of 2a-1 from 1a.
reclosing process, as shown in Scheme 2. Similarly, 2a-2
was prepared by treatment of 1a with butyl alcohol. The
compounds are unique and their synthetic procedures are
rather facile. In this article, we report crystal structures of
a Department of Chemistry, University of British Columbia, 2036
Main Mall, Vancouver, BC V6T1Z1, Canada.
E-mail: david.dolphin@ubc.ca; Fax: +1 6048229678;
Tel: +1 6048224571
b Division of Advanced Materials Science, Pohang University of
Science and Technology, San 31 Hyojadong, Pohang 790-784,
Republic of Korea. E-mail: jyshin@postech.ac.kr;
Fax: +82 542798138; Tel: +82 542798129
w Electronic supplementary information (ESI) available: NMR spectra
and crystallographic data. CCDC 750127 and 750128. For ESI and
crystallographic data in CIF or other electronic format see DOI:
10.1039/c1nj20415g
Scheme 2 A possible mechanism for the formation of 2 from 1.
c
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2011
New J. Chem., 2011, 35, 2483–2487 2483

View Article Online
the compounds 2a-2 and 2b-1 and formation of a furanone
dipyrrin imino ether 3 as an additional product. Further
treatment of 2a-1 with HCl and MeOH in the presence of
silica gel resulted in the formation of the imino ether 3.
11.23 (bs, 1H, NH), 7.69 (s, 2H, a-CH), 6.86 (s, 4H, b-CH),
6.57 (m, 2H, b-CH), 6.47 (m, 2H, b-CH); dF (282.4 MHz,
CD2Cl2) ꢁ138.53 (d, 2F, J = 23 Hz, o-F), ꢁ139.25 (d, 2F,
J = 23 Hz, o-F), ꢁ152.03 (t, 2F, J = 21 Hz, p-F), ꢁ161.18
(m, 2F, m-F), ꢁ161.48 (m, 2F, m-F); dc (100 MHz, CD2Cl2)
176.7, 157.2, 147.2, 146.6, 144.0, 143.1, 141.3, 139.5, 136.9,
136.1, 131.5, 130.6, 126.9, 122.7, 115.2, 114.0, 61.5; m/z
HRESIMS, calcd. for C38H13N6O2F1035Cl2 ([M + H]+):
845.0317; found 845.0303.
Experimental section
General consideration
All reagents were either prepared following literature methods
or purchased from commercially available suppliers and used
without further purification. Column chromatography was
performed on silica gel.
4,5-Dichloro-1,2-bis-{5-[(4-nitrophenyl)-(1H-pyrrol-2-yl)-
methylene]-5H-pyrrol-2-yl}-3,6-dioxo-cyclohex-4-ene-1,2-dicarbo-
nitrile 1c. (73 mg, 5%) Red solid; dH (400 MHz, CD2Cl2)
11.40 (bs, 2H, NH), 8.34 (d, 4H, J = 7.8 Hz, Ph-H), 7.72
(t, 4H, J = 7.8 Hz, Ph-H), 7.67–7.77 (m, 4H, a-CH), 6.83
(dd, 4H, J = 8.0, 3.4 Hz, b-CH), 6.54 (d, 2H, J = 3.4 Hz,
b-CH), 6.47 (m, 2H, b-CH); dc (100 MHz, CD2Cl2) 176.7,
155.5, 149.4, 146.6, 145.6, 143.0, 142.9, 137.9, 135.5, 132.4,
132.3, 128.2, 123.6, 121.6, 114.9, 114.4, 33.9.
Physical measurements
All NMR spectra of the compounds were measured in
CD2Cl2. 1HNMR, 13CNMR, 19FNMR and 2D-NMR spectra
were recorded using Bruker 300 and 400 spectrometers
1
(CD2Cl2: 5.32 and 54.00 ppm for H and 13C, respectively).
Mass spectra were determined on a time-of-flight (TOF)
spectrometer equipped with an ESI ion source.
General synthetic procedure of compounds 2a-1, 2b-1, and 2b-2
AlCl3 (600 mg) in MeOH (30 mL) was added to a THF
(70 mL) solution of 2a-1 (108 mg, 134.6 mmol). After refluxing
for 2 days, the reaction mixture was poured into water and
extracted with CH2Cl2. The organic layer was dried over
Na2SO4, filtered, and evaporated to dryness. The residue
was column chromatographed on silica gel using CH2Cl2.
The fastest pink fraction was collected and recrystallized from
CH2Cl2 and hexane (20 mg, 30%). Similarly, compounds 2b-1
and 2a-2 were prepared by reactions with MeOH and butyl
alcohol in 36% and 22% yields, respectively.
X-Ray crystallography
The X-ray data were collected on a Bruker X8 APEX II
diffractometer with graphite monochromated Mo-Ka radia-
tion. All data collections were performed at 173 ꢀ 0.1 K.
Corrections were applied for Lorentz and polarization
effects. All structures were solved by direct methods. All
non-hydrogen atoms were refined anisotropically and All
C–H hydrogen atoms were placed in calculated positions but
were not refined. The N–H hydrogen atoms were located in a
difference map and refined isotropically.
(3,4-Dichloro-5-oxo-5H-furan-2-ylidene)-{5-[(2,6-dichloro-
phenyl)-(5-methoxy-1H-pyrrol-2-yl)-methylene]-5H-pyrrol-2-yl}-
acetonitrile 2a-1. (20 mg, 30%) Purple solid; dH (400 MHz,
CD2Cl2) 12.43 (bs, 1H, NH), 7.49 (d, 2H, J = 8.0 Hz, Ph-H),
7.40 (t, 1H, J = 8.0 Hz, Ph-H), 6.99 (m, 1H, J = 4.0 Hz,
b-CH), 6.57 (d, 2H, J = 4.0 Hz, b-CH), 6.32 (d, 2H, J =
4.0 Hz, b-CH), 6.05 (d, 2H, J = 4.0 Hz, b-CH), 4.29 (s, 3H,
Me); dC (100 MHz, CD2Cl2) 178.4, 160.2, 149.8, 145.0, 140.6,
138.8, 137.1, 136.9, 134.2, 131.24, 129.5, 128.8, 124.2, 122.7,
120.7, 118.0, 114.0, 91.9, 58.4; m/z HRESIMS, calcd. for
C22H12N3O335Cl4 ([M + H]+): 505.9633; found 505.9636.
General synthetic procedure of compounds 1a–1c
2,6-Dichlorophenyl, perfluorophenyl, and 4-nitrophenyl
dipyrromethane were prepared by following the original
method.18 DDQ (2.29 g, 10.09 mmol) was added to a CH2Cl2
(150 mL) solution of dichlorophenyl dipyrromethane (1.12 g,
3.85 mmol). After stirring for 2 days, the reaction mixture was
concentrated and column chromatographed on silica gel using
neat CH2Cl2 as an eluent. The desired product 1a followed by
typical oxidized dipyrromethene was isolated first as a red
and second a yellow fraction, in ca. 8% (124 mg) and 30%
(330 mg) yields, respectively. Compounds 1b and 1c were
prepared by the same method in 25% and 5% yields.
(3,4-Dichloro-5-oxo-5H-furan-2-ylidene)-{5-[(5-methoxy-1H-
pyrrol-2-yl)-pentafluorophenyl-methylene]-5H-pyrrol-2-yl}-aceto-
nitrile 2b-1. (26 mg, 36%) Purple solid; dH (400 MHz, CD2Cl2)
12.46 (bs, 1H, NH), 7.02 (m, 1H, J = 3.0 Hz, b-CH), 6.67 (d,
1H, J = 4.9 Hz, b-CH), 6.39 (d, 1H, J = 4.8 Hz, b-CH), 6.17
(d, 1H, J = 3.9 Hz, b-CH), 4.29 (s, 3H, Me); dF (282.4 MHz,
CD2Cl2) ꢁ139.69 (dd, 2F, J = 32, 21 Hz, o-F), ꢁ153.30 (t, 1F,
J = 21 Hz, p-F), ꢁ161.90 (m, 2F, m-F); dC (100 MHz,
CD2Cl2) 136.9, 129.7, 123.6, 120.5, 118.2, 113.9, 113.2, 58.6
(Phenyl-H peaks are broaden due to the C–F couplings).
4,5-Dichloro-1,2-bis-{5-[(2,6-dichlorophenyl)-(1H-pyrrol-2-yl)-
methylene]-5H-pyrrol-2-yl}-3,6-dioxo-cyclohex-4-ene-1,2-dicarbo-
nitrile 1a. (124 mg, 8%) red solid; dH (400 MHz, CD2Cl2)
11.18 (bs, 2H, NH), 7.64 (m, 2H, a-CH), 7.55–7.40 (m, 6H,
J = 8.0 Hz, Ph-H), 6.79 (d, 2H, J = 4.3 Hz, b-CH), 6.73
(d, 2H, J = 4.3 Hz, b-CH), 6.42 (m, 4H, b-CH); dC (100 MHz,
CD2Cl2) 176.7, 156.0, 146.8, 142.8, 141.8, 136.7, 136.0, 135.7,
134.9, 134.2, 131.6, 131.5, 128.8, 128.7, 126.2, 122.0, 114.6,
114.3, 30.3; m/z HRESIMS, calcd. for C38H19N6O235Cl535Cl
([M + H]+): 802.9691; found 802.9671.
{5-[(5-Butoxy-1H-pyrrol-2-yl)-(2,6-dichloro-phenyl)-methylene]-
5H-pyrrol-2-yl}-(3,4-dichloro-5-oxo-5H-furan-2-ylidene)-aceto-
nitrile 2a-2. (16 mg, 22%) Purple solid; dH (400 MHz, CD2Cl2)
12.5 (bs, 1H, NH), 7.48 (d, 2H, J = 8.6 Hz, Ph-H), 7.39
(t, 1H, J = 7.9 Hz, Ph-H), 6.99 (m, 1H, b-CH), 6.55 (d, 1H,
4,5-Dichloro-3,6-dioxo-1,2-bis-{5-[pentafluorophenyl-(1H-
pyrrol-2-yl)methylene]-5H-pyrrol-2-yl}-cyclohex-4-ene-1,2-dicarbo-
nitrile 1b. (407 mg, 25%) Red solid; dH (400 MHz, CD2Cl2)
c
2484 New J. Chem., 2011, 35, 2483–2487
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2011

View Article Online
J = 5.0 Hz, b-CH), 6.32 (d, 1H, J = 4.7 Hz, b-CH), 6.03
(m, 1H, b-CH), 4.68 (t, 2H, J = 5.9 Hz, OCH2CH2CH2CH3),
1.85 (m, 2H, OCH2CH2CH2CH3), 1.54 (m, 2H, OCH2CH2-
CH2CH3), 1.00 (t, 3H, J = 7.4 Hz, OCH2CH2CH2CH3); dC
(100 MHz, CD2Cl2) 178.0, 160.1, 150.2, 145.1, 140.6, 138.7,
136.9, 134.3, 131.2, 129.3, 128.8, 123.7, 123.1, 122.3, 120.6,
118.0, 114.0, 91.9, 71.1, 31.4, 20.0, 14.2.
Synthesis of 2-(3,4-dichloro-5-oxo-5H-furan-2-ylidene)-2-{5-
[(2,6-dichloro-phenyl)-(5-methoxy-1H-pyrrol-2-yl)-methylene]-
5H-pyrrol-2-yl}-acetimidic acid methyl ester (3)
HCl was added to a MeOH and CH2Cl2 (1 : 1) solution of
compound 2-1 (20 mg, 19.8 mmol) until the pH value of the
solution reached 5. The resulting solution was stirred for 2 days
and evaporated to remove the solvent. Compound 3 was
separated by column chromatography on silica gel using
10% MeOH in CH2Cl2 as an eluent. (9.8 mg, 46%), yellowish
red solid; dH (400 MHz, CD2Cl2) 12.15 (bs, 1H, NH), 7.90 (bs,
1H, NH), 7.52 (d, 2H, J = 8.8 Hz, Ph-H), 7.45 (t, 1H, J = 7.8 Hz,
Ph-H), 7.02 (d, 1H, J = 4.4 Hz, b-CH), 6.63 (d, 1H,
J = 4.9 Hz, b-CH), 6.52 (d, 1H, J = 5.4 Hz, b-CH), 5.91
(d, 1H, J = 4.4 Hz, b-CH), 3.94 (s, 3H, Me), 3.82 (s, 3H, Me);
m/z HRESI (+)MS, calcd. for [C23H14N3O435Cl4]+: 535.9895;
found 537.9883.
Fig. 3 ORTEP views of 2a-2 with thermal ellipsoids shown at 50%
probability. Intramolecular hydrogen bonds are denoted with dashed
lines.
red-colored solutions gradually changed to purple as the
reaction progressed. TLC monitoring of the reactions showed
several unstable by-products most of which were found to
have decomposed after washing with water and extraction
with CH2Cl2. When bulky aryl alcohols, such as 2,3,4,5-
tetrachlorophenol and 2,3-difluorophenol, were employed,
much of the starting material (DDQ-adduct) was converted
to the a-free dipyrromethene and eluted as the first red
fraction during column chromatography on silica gel. The
desired bright purple fractions were separated using a gradient
elution with increasing amounts of MeOH in CH2Cl2. On the
other hand, alkyl chain alcohol adducts were obtained in
higher yields without the formation of decomposed dipyrrins.
In these cases, the furanyl compounds were easily separated
using neat CH2Cl2 during column chromatography owing to
their relatively low polarity.
Results and discussion
Compounds 1a–1c were prepared by treating saturated
CH2Cl2 solutions of pentafluorophenyl, 2,6-dichlorophenyl,
and 4-nitrophenyl substituted dipyrromethanes with 2 equiva-
lents of DDQ. The solubility of compound 1a in typical
organic solvents is lower than 1b and much of the former
was lost during column chromatography on silica gel (the yield
was 8% versus 25% for 1b). 1c was also obtained in a yield of
5%.19 1H NMR spectra of bDLDAs (1a–1c) are shown in
Fig. 2. The amino-Hs on the pyrrole rings of all the DDQ
adducts are highly downfield-shifted as a result of the intra-
molecular hydrogen-bonding (11.18, 11.23, and 11.40 ppm for
1a, 1b, and 1c, respectively).
A possible mechanism is shown in Scheme 2. Nucleophilic
attack by the alcohol followed by rearrangement leads to ring
opening (at the sp3C–sp3C bond of the DDQ moiety) in the
presence of a Lewis acid. Nucleophilic ring-closing of the keto-O
and bond cleavage between the keto-C and sp3C result in the
formation of the final keto-furanyl dipyrrin 2.
1a and 1b were each separately refluxed overnight in THF
with methanol, n-butyl alcohol, n-octyl alcohol, or n-hexyl
thiol in the presence of AlCl3. During these reactions the
Fortunately, single crystals of 2a-2 (Fig. 3) and 2b-1 (Fig. 4)
were successfully grown by vapor addition of hexane into
a CH2Cl2 solution.z The crystal structure of 2b-1 (Fig. 4),
having a methoxy group, shows a similar structure to that of
2a-1 which we reported earlier.17 On the other hand, the
crystal structure of 2a-2 exhibits a different configuration from
that of compounds 2a-1 and 2b-1 (Fig. 5). While the O atom in
the ring is oriented towards the nitrogens of the dipyrrin
z Crystal data of 2a-2: C25H17Cl4N3O3, T = 173 K, M = 549.22,
%
triclinic, P1 (no. 2), a = 7.5524(4) A, b = 12.9084(7) A, c =
13.1120(7) A, a = 102.326(2)1, b = 94.333(2)1, g = 98.378(2)1, V =
1227.94(11) A3, Dc = 1.485 gcm-3, Z = 2, R1 = 0.0409 [I > 2.00s(I)],
wR2 = 0.1179 (all data), GOF = 1.075, CCDC 750127.
Crystal data of 2b-1: C22H8Cl2F5N3O3, T = 173 K, M = 528.21,
%
triclinic, P1 (no. 2), a = 7.0689(13) A, b = 9.6348(19) A, c =
16.074(3) A,a = 94.959(7)1, b = 95.467(7)1, g = 106.429(7)1, V =
1037.9(3) A3, Dc = 1.690 g cmꢁ3, Z = 2, R1 = 0.0347 [I > 2.00s(I)],
wR2 = 0.1019 (all data), GOF = 0.990, CCDC 750128.
Fig. 2 1H NMR spectra of bDLDAs in CD2Cl2; DDQ adducted (a)
4-nitrophenyl, (b) pentafluorophenyl, and (c) 2,6-dichlorophenyl
dipyrrins.
c
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2011
New J. Chem., 2011, 35, 2483–2487 2485

View Article Online
Scheme 3 Formation of 3 from 2a-1.
Fig. 4 ORTEP views of 2b-1 with thermal ellipsoids shown at 50%
probability. Intramolecular hydrogen bonds are denoted with dashed
lines.
1
Fig. 7 Comparison of the H NMR spectra of 2a-1(a) and 3(b).
solution of 3 afforded a broad singlet and a sharp singlet
for the peaks of the newly formed NH and methoxy groups,
in the 1H NMR spectrum (Fig. 7). The original methoxy-
group and the other b-Hs become shielded as a result of the
stronger electron-withdrawing group, resulting in their
upfield-shifts while the neighboring b-Hs’ peaks are shifted
downfield.
Fig. 5 Comparison of the different orientations of (a) 2a-2, (b) 2a-1
and (c) 2b-1.
moiety in the latter, the former has the cyclic ring inverted and
facing in the opposite direction. This results first from
the inclusion of a longer alkyl chain which produces an
intramolecular CH–N hydrogen-bond between the meso-
cyano-N atom and the butoxy-1CH2 group. This H-bond
formation renders the original N–Hꢂ ꢂ ꢂO hydrogen-bond
weaker, allowing rotation of the furanyl ring to generate a
new hydrogen-bond (C–Hꢂ ꢂ ꢂO) between the furanyl-O and
b-CH on the neighboring pyrrole ring (Fig. 3). Disruption
of the initial N–Hꢂ ꢂ ꢂO hydrogen-bond causes the NH peak to
be sharper in its 1H NMR spectrum (Fig. 6). Similarly, the
1CH2-peaks of the alkyl chain are shifted down-field
(4.68 ppm).
Conclusions
In summary, variously substituted furanone dipyrrins have
been prepared using a facile synthetic method. Their imino
ethers were obtained by further treatment of compound 2a-1
with an acid and MeOH in the presence of HCl. These
compounds are expected to be useful as building blocks in
developing fully-conjugated pathways and enhancing planarity
throughout the main skeleton of interesting heterocyclic
compounds.
2a-1 was converted to compound 3 by MeOH addition in
the presence of a minute amount of HCl. As in a Pinner
reaction,20 the cyano group was converted to an imino ether
via imino ether hydrolysis. The high resolution mass spectrum
Acknowledgements
Financial support for this work was provided by the Natural
Sciences and Engineering Research Council (NSERC) of
Canada. We thank Dr Brian O. Patrick from the X-ray
crystallography laboratory of the Department of Chemistry
at UBC.
of
3 confirms the structure described in Scheme 3
(C23H14N3O435Cl4; calculated and found masses are (m/z)
535.9895 and 537.9883, respectively). In addition, a CD2Cl2
Fig. 6 1H NMR spectrum of 2a-2 in CD2Cl3; solvent impurities are identified by *.
c
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2011
2486 New J. Chem., 2011, 35, 2483–2487

View Article Online
12 J. H. P. Utley and G. G. Rozenberg, J. Appl. Electrochem., 2003,
33, 525–532.
Notes and references
1 D. Walker and J. D. Hiebert, Chem. Rev., 1967, 67, 153–195.
2 J. S. Lindsey, I. C. Schreiman, H. C. Hsu, P. C. Kearney and
A. M. Marguerettaz, J. Org. Chem., 1987, 52, 827–836.
3 L. Yu, K. Muthukumaran, I. V. Sazanovich, C. Kirmaier,
E. Hindin, J. R. Diers, P. D. Boyle, D. F. Bocian, D. Holten
and J. S. Lindsey, Inorg. Chem., 2003, 42, 6629–6647.
4 G. R. Geier III, J. F. B. Chick, J. B. Callinan, C. G. Reid and
W. P. Auguscinski, J. Org. Chem., 2004, 69, 4159–4169.
5 L. Capella, P. C. Montevecchi and D. Nanni, J. Org. Chem., 1994,
59, 7379–7382.
13 X. Zhou, M. Kitamura, B. Shen, K. Nakajima and T. Takahashi,
Chem. Lett., 2004, 33, 410–411.
14 M. T. Stone and H. L. Anderson, J. Org. Chem., 2007, 72,
9776–9778.
15 T. Takahashi, K. Kashima, S. Li, K. Nakajima and K.-I. Kanno,
J. Am. Chem. Soc., 2007, 129, 15752–15753.
16 J.-Y. Shin, S. S. Hepperle, B. O. Patrick and D. Dolphin, Chem.
Commun., 2009, 2323–2325.
17 J.-Y. Shin, B. O. Patrick and D. Dolphin, Org. Biomol. Chem.,
2009, 7, 2032–2035.
6 C. Brucker, V. Karunaratne, S. J. Rettig and D. Dolphin, Can. J.
¨
Chem., 1996, 74, 2182–2193.
18 C. H. Lee and J. S. Lindsey, Tetrahedron, 1994, 50, 11427–11440.
19 The observed yields, o-F > o-Cl > p-NO2 can be rationalized as a
result of the effectiveness of the electronic and steric configurations
of the EWGs; J.-Y. Shin, H. Furuta, K. Yoza, S. Igarashi and
A. Osuka, J. Am. Chem. Soc., 2001, 123, 7190–7191; R. Taniguchi,
S. Shimizu, M. Suzuki, J.-Y. Shin, H. Furuat and A. Osuka,
Tetrahedron Lett., 2003, 44, 2505–2507; J.-Y. Shin,
S. S. Hepperle and D. Dolphin, Tetrahedron Lett., 2009, 50,
6909–6912.
7 J. S. Lindsey, The Porphyrin Handbook, ed. K. M. Kadish,
K. M. Smith and R. Guilardm, Academic Press, San Diego, CA,
2000.
8 Z. Gross, N. Galili and I. Saltsman, Angew. Chem., Int. Ed., 1999,
38, 1427–1429.
9 J.-Y. Shin, H. Furuta, K. Yoza, S. Igarashi and A. Osuka, J. Am.
Chem. Soc., 2001, 123, 7190–7191.
10 T. E. Wood and A. Thompson, Chem. Rev., 2007, 107, 1831–1861.
11 G. G. Mohamed, F. A. Nour El-Dien and E. U. Farag, Spectrochim.
Acta, Part A, 2006, 65, 11–19, and its references.
20 L. Kurti and B. Czako, Strategic Applications of Named Reactions
´
¨
in Organic Synthesis, Elsevier Academic Press, San Diego, CA,
2005.
c
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2011
New J. Chem., 2011, 35, 2483–2487 2487