A functionalized spiro[chlorin-porphyrin]-type 'dimer' dizinc complex from rapid [4+2] self-cycloaddition of a conjugated [β,β′- bis(methylene)porphyrinato]zinc

Article abstract of DOI:10.1002/hlca.201100385

Thermal extrusion of SO₂ from β,β′- sulfolenoporphyrins is an effective method for in situ generation of β,β′-bis(methylene)porphyrin which remained unobserved in typical synthetic applications but underwent quickly efficient [4+2]-cycloaddition reactions with dienophiles.We now report the thermal extrusion of SO₂ from the symmetrical (tetra-β,β′- sulfolenoporphyrinato)zinc 1·Zn in the absence of a dienophile (Scheme). In the event, the thermally in situ generated conjugated diene underwent a [4+2] self-cycloaddition, to give the {spirobi[tri-β,β′- sulfolenoporphyrinato]}dizinc 4·2Zn. This chiral (racemic) spirobiporphyrinoid dizinc complex represents the combination of the closely positioned and interacting chromophores of a (porphyrinato)zinc and of a (β-methylene-β,β′-dihydroporphyrinato)zinc. It carries six sulfoleno moieties that are still available for further SO₂ extrusion and cycloaddition reactions. Copyright

Full text of DOI:10.1002/hlca.201100385

Helvetica Chimica Acta – Vol. 95 (2012)
211
A Functionalized Spiro[chlorin-porphyrin]-Type ꢀDimerꢁ Dizinc Complex
from Rapid [4 þ 2] Self-cycloaddition of a Conjugated [b,b’-
Bis(methylene)porphyrinato]zinc
by Srinivas Banalaa)1), Paul Sintica)2), and Bernhard Krꢂutler*a)
a) Institute of Organic Chemistry, University of Innsbruck, Innrain 52a, A-6020 Innsbruck
(phone: þ 43-512-5075200; fax: þ 43-512-5072892; e-mail: bernhard.kraeutler@uibk.ac.at)
Thermal extrusion of SO2 from b,b’-sulfolenoporphyrins is an effective method for in situ generation
of b,b’-bis(methylene)porphyrin which remained unobserved in typical synthetic applications but
underwent quickly efficient [4 þ 2]-cycloaddition reactions with dienophiles.We now report the thermal
extrusion of SO2 from the symmetrical (tetra-b,b’-sulfolenoporphyrinato)zinc 1 · Zn in the absence of a
dienophile (Scheme). In the event, the thermally in situ generated conjugated diene underwent a [4 þ 2]
self-cycloaddition, to give the {spirobi[tri-b,b’-sulfolenoporphyrinato]}dizinc 4 · 2Zn. This chiral (race-
mic) spirobiporphyrinoid dizinc complex represents the combination of the closely positioned and
interacting chromophores of a (porphyrinato)zinc and of a (b-methylene-b,b’-dihydroporphyrinato)zinc.
It carries six sulfoleno moieties that are still available for further SO2 extrusion and cycloaddition reactions.
Introduction. – Natural porphyrinoids, such as hemes, chlorophylls, corrins, and
corphins, are ubiquitous pigments and probably Natureꢀs most versatile cofactors
[1][2]. Porphyrins and chlorins have obtained special attention also as catalysts (see,
e.g., [3]), as mimics for artificial ꢁphoto-reaction centersꢀ [4], and as well-structured
building blocks in multi-porphyrin assemblies [5][6].
For the purpose of the synthesis of suitably functionalized porphyrins and chlorins,
b,b’-sulfolenopyrroles [7], b,b’-sulfolenoporphyrins [8][9], and b,b’-sulfolenochlorins
[10][11] were designed and used as thermal precursors of reactive dienes (Fig. 1)
(sulfolene ¼ 2,5-dihydrothiophene 1,1-dioxide). We have introduced the symmetrical
tetra-b,b’-sulfolenoporphyrin (¼ 5,11,17,23-tetratis[3,5-bis(1,1-dimethylethyl)phenyl]-
7,9,13,15,19,21-hexahydro-1H,3H,25H,27H-tetrathieno[3,4-b :3’,4’-g :3’’,4’’-l :3’’’,4’’’-q]-
phorphine 2,2,8,8,14,14,20,20-octaoxide; 1 · 2 H) as a versatile building block that
carries four reactive sulfone groups, and which was applied for the synthesis of
porphyrins carrying up to four fullerene units [12][13]. More recently, the ZnII complex
1 · Zn was also used to generate a new type of ꢁblackenedꢀ porphyrins, by attaching up to
four conjugated benzoquinone units at the pyrrolic b-positions [14].
The mono-b,b’-sulfolenoporphyrin 2 was synthesized by Gunter and co-workers and
was tested in thermal reactions in the presence or absence of a dienophile [8][15]:
Thermolysis of 2 gave the spiro[chlorinporphyrin]-type dimer 3 by [4 þ 2]-self-
cycloaddition of the elusive b,b’-bis(methylene)porphyrin that was generated from 2 by
1
)
)
Present address: Technische Universitꢄt Berlin, Institut fꢃr Chemie, FG Organische Chemie,
Strasse des 17. Juni 124/TC 2, D-10623 Berlin.
Present address: Silverbrook Research Pty Ltd., North Ryde, NSW 2113, Australia.
2
ꢂ 2012 Verlag Helvetica Chimica Acta AG, Zꢃrich

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Fig. 1. Porphyrins 1 · 2 H, 1 · Zn (systematic atom numbering), and 2, and spiro ꢀdimerꢁ 3
SO2 loss. We have used the symmetrical tetra-b,b’-sulfolenoporphyrin 1 · 2 H, as well as
several of its metal complexes (e.g., 1 · Zn) [12], as building blocks for the assembly of
multi-modular porphyrinoid arrays [13]. To explore the reactivity of sterically hindered
1, we have also set out on an investigation of the thermally accessible b,b’-
bis(methylene)porphyrin itself, that could be generated by thermolysis of 1 · Zn.
However, in the absence of an added dienophile, the thermally in situ generated
(apparently strongly hindered) b,b’-bis(methylene)porphyrin derivatives did not
accumulate in solution, and they ꢁdimerizedꢀ to a spiro[chlorin-porphyrin]-type
compound, which carried six sulfoleno units ready for selective further transformations.
Results and Discussion. – Preparation of Spiro[chlorin-porphyrin]-Type ꢀDimerꢁ
Complex 4 · 2Zn. Upon heating a solution of (tetra-b,b’-sulfolenoporphyrinato)zinc 1 ·
Zn in 1,2-dichlorobenzene at 1408 for 2 h, ca. 30% of the starting material decomposed
to give a major new compound, according to TLC analysis (Scheme). Separation of the
mixture by prep. TLC allowed the recovery of 71% of 1 · Zn and yielded a major
nonpolar green product, 4 · 2Zn, isolated in ca. 17% yield (i.e., 59% based on the
conversion of 1 · Zn). Several more polar fractions that may represent higher oligomers
were not analyzed further.
The UV/VIS spectrum of the new green product 4 · 2Zn exhibited distinctive
features of a porphyrinoid compound. However, it displayed a split Soret band with two
almost equally intense absorptions with maxima at 425 and 440 nm, which reflect the
two interacting tetrapyrrole chromophores (Fig. 2 and Table 1). Weaker absorption
bands with maxima at 553 and 646 nm were also observed, which are characteristic for

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Scheme. Synthesis of the Spiro[chlorin-porphyrin]-Type ꢀDimerꢁ complex 4 · 2Zn via the [b,b’-Bis(me-
thylene)porphyrinato]zinc, an Unobserved Reactive Intermediate Generated from 1 · Zn by Thermolytic
SO2 Extrusion
the superposition of chromophores of a porphyrinatozinc (e.g., 1 · Zn) and of a
chlorinatozinc [16][17], respectively. Upon excitation at 553 or 647 nm, the solution of
4 · 2Zn in CH2Cl2 exhibited strong fluorescence emission at 652 and 713 nm (Fig. 3).
The structure of the new compound 4 · 2Zn was deduced from spectroscopic
analysis as that of a dizinc complex of a spiro[chlorin-porphyrin]-type ꢁdimerꢀ. A FAB-
MS of 4 · 2Zn showed quasimolecular-ion peaks at m/z 2842.4 – 2848.4, corresponding
to a molecular formula C168H200N8O12S6Zn2 (calc. 2841.22). The signals displayed an
isotopic distribution characteristic of the presence of two zinc centers. The base peak
was observed at m/z 2458 – 2463, due to loss of six SO2 groups. Smaller signals were also
found at m/z 2778 – 2784, from loss of one SO2 unit. Further fragmentation into the two
porphyrinoid ꢁmonomersꢀ was not indicated by the MS. The 1H-NMR spectrum
(500 MHz) of 4 · 2Zn exhibited the pattern of an unsymmetric and complex compound.
Signal assignments (Table 2, Fig. 4 and 5,a) were achieved with the help of extensive
analyses by 1H,1H-COSY, ROESY (Fig. 5,b and c), HSQC, and HMQC experiments.
The H-atoms of the three CH2 groups of the cyclohexene ꢁbridgeꢀ between the
porphyrin and chlorin moieties could all be assigned individually: The ꢁisolatedꢀ

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Fig. 2. UV/VIS Spectrum of spiro ꢀdimerꢁ 4 · 2Zn in CH2Cl2 (c ¼ 7.03 · 10ꢀ6 m, CH2Cl2)
Table 1. Pertinent Values from Absorption Spectra (CH2Cl2; l in nm) of the ꢀMonomerꢁ 1 · Zn and the
Spiro[chlorin-porphyrin]-Type ꢀDimerꢁ 4 · 2Zn
1 · Zn
4 · 2Zn
Chlorin-type and Q bands
Soret bands
Other bands
590, 549.5
424
326
646a), 598, 553
440a), 425
325, 250
a) Chlorin-type bands.
CH2(21) group appeared as an AB system at d(H) 2.82 and 4.20; the CH2CH2 group
exhibited m at d(H) 1.92 and 2.08 (CH2(31)), and at 2.78 and 2.94 (CH2(32)). The
exocyclic CH2(31’)¼group at the chlorin moiety gave rise to two s at d(H) 4.92 and 5.46,
which coupled with a C-atom at d(C) 115.1. The signals of the 16 tBu groups appeared
as 13 resolved signals at high field (d(H) 0.2 – 1.5). Likewise, the meso-aryl H-atoms
were distributed between d(H) 6.15 and 7.95, with distinctive upfield shifts for most H-
atoms of four aryl groups that were deduced to be near the linker site of the ꢁdimerꢀ.
The H-atoms of all of these four aryl groups showed strong intra-group NOEꢀs,
allowing for their assignment to a particular aromatic substituent. The 3,5-di(tert-
butyl)phenyl group assigned as that at the 20-position of the porphyrin moiety had most
strongly shifted signals and showed two high-field s at d(H) 0.21 (Me(2052)) and 0.54
(Me(2032)) for the tBu groups , and three low-field resonances at 7.24 (HꢀC(206)), 6.15
(HꢀC(204)), and 7.75 (HꢀC(202)) for the aromatic H-atoms in ortho, para, and ortho
position, respectively. Likewise, the corresponding aromatic group assigned as that at
the 20’-position of the chlorin moiety also had some very strongly upfield-shifted signals

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Fig. 3. Fluorescence emission (—; lexc at 552 nm) and excitation (···· ; lem at 712 nm) spectra of spiro
ꢀdimerꢁ 4 · 2Zn (c ¼ 7.03 · 10ꢀ6 m, CH2Cl2)
Fig. 4. Arbitrary atom numbering used for the spiro[chlorin-porphyrin]-type ꢀdimerꢁ complex 4 · 2Zn
and showed two high-field s at d(H) 0.31 (Me(2052’)) and 1.20 (Me(2032’)) for the tBu
groups, and three low-field resonances, at d(H) 7.03 (HꢀC(202’)), 7.28 (HꢀC(204’)),
and 7.85 (HꢀC(206’)) for the aromatic H-atoms in ortho, para, and ortho positions
(Fig. 5,a).
Compared to the position of the signals of the corresponding H-atoms in the
porphyrinatozinc 1 · Zn, the signals of 4 · 2Zn were shifted upfield by up to 1.29 or
1.19 ppm, as a consequence of the local shielding effect of nearby aromatic groups
(Fig. 6). Four other aryl groups, which were assigned to the outer part of the spiro

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a
1
Table 2. Pertinent H- and 13C-NMR Data (CDCl3; 500 and 125 Mz, resp.) of 4 · 2Zn ). See Fig. 4 for
arbitrary atom numbering.
d(H)
d(C)
d(H)
d(C)
C(2)
C(2’)
54.3
CH2(21)
CH2(31)
CH2(32)
C(4)
2.82 (Ha), 4.20 (Hb)
2.94 (Ha), 2.78 (Hb)
2.08 (Ha), 1.92 (Hb)
41.8
22.9
29.3
CH2(31’)
4.92 (Ha), 5.46 (Hb)
7.63
115.1
C(4’)
153.3b)
126
151.9
35.2
HꢀC(52)
7.95
126.8
150.7
35.4
HꢀC(52’)
C(53)
C(53’)
C(531)
C(531’)
Me(532)
HꢀC(54)
C(55)
1.41
7.84
31.5
Me(532’)
HꢀC(54’)
C(55’)
1.39
7.52
31.6
121.7
151
122.3
149.7
35.4
C(551)
C(551’)
34.6
Me(552)
HꢀC(56)
CH2(71)
C(18)
CH2(181)
HꢀC(202)
C(203)
C(2031)
Me(2032)
HꢀC(204)
C(205)
C(2051)
Me(2052)
HꢀC(206)
1.52
7.64
31.8
Me(552’)
HꢀC(56’)
CH2(71’)
C(18’)
HꢀC(181’)
HꢀC(202’)
C(203’)
C(2031’)
Me(2032’)
HꢀC(204’)
C(205’)
C(2051’)
Me(2052’)
HꢀC(206’)
0.90
7.54
3.77
31.1
128.2
56.4
126.9
56.7
4.22 (Ha), 3.90 (Hb)
137b)
56.3
3.50 (Ha), 3.81 (Hb)
7.75
3.33 (Ha), 3.86 (Hb)
7.03
56.3
130
150.9
34.1
31.6
121.7
151
35.2
30.6
126.2
126.7
151
34.6
0.54
6.15
31.2
1.20
7.28
121.6
150.9
33.9
30.5
126.5
0.21
7.24
0.31
7.85
a) Signal assignments for selected H-atoms and their correlations with directly and indirectly bound C-
atoms (from HSQC and HMBC spectra). b) Tentatively assigned signals.
ꢁdimerꢀ, displayed signals with chemical shifts similar to those found in the porphyrin
ꢁmonomerꢀ 1 · Zn. The unambiguous individual assignment of the signals of the core
part of the spiro ꢁdimerꢀ 4 · 2Zn thus revealed intriguing shifts (mostly upfield) as the
result of anisotropic fields associated with the ring currents of closely positioned
porphyrinoid and 3,5-di(tert-butyl)phenyl moieties (Fig. 6). In contrast, most of the
signals derived for H-atoms at the outer part of the spiro ꢁdimerꢀ were overlapping and
could not be assigned individually.
Discussion. – Several groups have used b,b’-sulfolenoporphyrins as effective
thermal precursors of b,b’-bis(methylene)porphyrins [8 – 15]: Such reactive conjugated
b,b’-diene derviatives of porphyrins have exhibited an excellent reactivity towards
typical dienophiles. As they quickly underwent efficient [4 þ 2] cycloaddition reactions,
the b,b’-bis(methylene)porphyrin remained unobserved in the synthetic applications.
When examining the behavior of the b,b’-bis(methylene)porphyrin (that was generated
from the metal-free meso-unsubstituted sulfolenoporphyrin 2) in the absence of an

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Fig. 5. a) 1H-NMR Chemical shift assignments for the structural section of core part and b) ROESY (H $
H) correlations within the chromophore moieties and c) ROESY interchromophore correlations of 4 · 2Zn

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Fig. 6. 1H-NMR Chemical-shift differences Dd(H) between of 4 · 2Zn and 1 · Zn. Dd ¼ d(4 · 2Zn) ꢀ d(1 ·
Zn) (j Dd j> 0.1 ppm); standard numbers indicate Dd < 0, and bold numbers indicate Dd > 0.
added dienophile, Gunter and co-workers obtained the corresponding DielsꢀAlder
product 3 with another porphyrinꢀs exocylic CH2¼ [8][15].
We expected that the bulky 3,5-di(tert-butyl)phenyl groups at the meso-positions of
tetra-b,b’-sulfolenoporphyrin 1 · Zn would hinder this type of [4 þ 2] cycloaddition
reaction between two b,b’-bis(methylene)porphyrin derivatives, and thus improve their
stability. However, the experiments reported here, and our further studies, confirmed
the [4 þ 2] self-cycloaddition of two b,b’-bis(methylene)porphyrin to be rapid in liquid
solution, even when sterically hindered, and to result in congested unsymmetrical
spiro[chlorin-porphyrin]-type ꢁdimersꢀ efficiently. Thus, when the tetra-b,b’-sulfoleno-
porphyrinato)zinc 1 · Zn was thermolyzed to partial conversion, the dizinc complex 4 ·
2Zn of the hexa-b,b’-sulfolenospiro[corin-porphyrin]-type ꢁdimerꢀ ligand was obtained
in good yield. Further direct thermolysis of 4 · 2Zn in the absence of an added
dienophile was not studied, as it was expected to yield complex higher oligomers.
Unfortunately, attempts to separate the expected two enantiomers of the chiral spiro
ꢁdimerꢀ 4 · 2Zn were unsuccessful.
The structure of the chiral spiro ꢁdimerꢀ was deduced from analysis of an extensive
set of spectral data, taken from UV/VIS, MS, and NMR spectra, in particular. The two
porphyrinoid moieties of these spiro ꢁdimersꢀ were found to be attached to each other
by a short covalent link, which generated a sterically congested arrangement in its
vicinity. As a result of this, significant anisotropic effects were observed for signals in
1
the H-NMR spectra that are assigned to close-by H-atoms (Figs. 5 and 6). The
covalent link, a fused cyclohexene unit, presumably orients the mean planes of the two
porphyrinoid moieties in an almost orthogonal fashion towards each other. As a
consequence, one (or several) of the 3,5-di(tert-butyl)phenyl groups near the linker site
may be positioned close to the other porphyrinoid moiety, experiencing significant
anisotropic effects.
Spiro ꢁdimerꢀ 4 · 2Zn still carries six sulfoleno groups at six pairs of b,b’-positions of
the two porphyrinoid moieties that (presumably) are accessible to typical dienophiles.
Thus, these six functional groups that remain in the ꢁspiro dimerꢀ are expected to offer

Helvetica Chimica Acta – Vol. 95 (2012)
219
the opportunity for attachment of suitable dienophiles in further [4 þ 2] cycloaddition
reactions at the periphery of this spiro ꢁdimerꢀ. The excellent disposition of the dizinc
complex 4 · 2Zn for the generation of conjugated b,b’-bis(methylene)porphyrin
derivatives in solution by SO2 extrusion, as explored earlier with the ꢁmonomericꢀ
(tetra-b,b’-sulfolenoporphyrinato)zinc 1 · Zn [12 – 14], thus provides an excellent
platform for synthetic investigations of subsequent cycloaddition reactions with
dienophiles, such as C60 or benzoquinone. Such follow-up transformations with C60
and the formation of hexafullereno-fused spiro ꢁdimersꢀ have been explored in our
laboratory, due to be reported in a future manuscript.
We are grateful to the Austrian National Science Foundation (FWF; project No. P-17437) for
financial support of this work.
Experimental Part
General. The 1,2-dichlorobenzene (Fluka), CH2Cl2, petroleum ether (40 – 608), MeOH, and toluene
(Acros) were distilled before use. The 3-nitrobenzyl alcohol matrix (NOBA) was a reagent-grade
chemical from Fluka and was used as received. Tetra-b,b’-sulfolenoporphyrins 1 · 2H and 1 · Zn were
synthesized as published [12]. Glassware for all reactions was oven-dried at 1108 and cooled under N2
flow prior to use. Reactions, workup, and chromatography were performed under protection from light
(alumina foil). High vacuum: ca. 0.05 mbar. Column chromatography (CC): silica gel 60 (SiO2; 230 – 400
mesh; Fluka). Prep. TLC: SiO2 60 plates (0.25 mm; Merck). UV/VIS Spectra: U 3000 spectrometer
(Hitachi); 1 mm or 10 mm quartz cells; lmax (log e) in nm. Fluorescence spectra: Varian Cary Eclipse;
excitation (lexc) and emission wavelengths (lem (rel. int.)) in nm. 1H- and 13C-NMR Spectra: Varian-500
spectrometer; at 298 K in CDCl3; d in ppm rel. to CDCl3 solvent (d(H) 7.26 (CHCl3) and d(C) 77.2) as
internal standard, J in Hz. FAB-MS: Finnigan MAT-95; positive-ion mode; NOBA matrix; m/z (rel. %).
{m{{5,5’,11,11’,17,17’,22’,24-Oktakis[3,5-bis(1,1dimethylethyl)phenyl]-7,7’,9,9’,13,13’,15,15’,21,22-dec-
ahydro-19’-methylenesprio[1H,3H,26H,28H-benzo[b]trithieno[3,4-g :3’,4’-l :3’’,4’’-q]porphine-20(19H),
20’(19’H)-[1H,3H,24H,26H]trithieno[3,4-b :3’,4’-g :3’’,4’’-l]phorphine]-kN26,kN27,kN28,kN29 :kN24’,kN25’
,
kN26’,kN27’} 2,2,2’,2’,8,8,8’,8’,14,14,14’,14’-dodecaoxidato(4ꢀ)}}dizinc (4 · 2Zn). A deoxygenated soln. of
(tetra-b,b’-sulfolenoporphyrinato)zinc 1 · Zn (22.5 mg, 15.13 mmol) in 1,2-dichlorobenzene (4.4 ml) was
immersed in a pre-heated oil bath and heated under stirring at 1408. After 2 h, the mixture was removed
from the oil bath and allowed to cool to r.t. under Ar. Upon cooling, the solvent was distilled at 558 under
high vacuum, and the dry mixture was purified by prep. TLC (SiO2, development with 0.6% MeOH/
CH2Cl2). The separated bands were scratched off the TLC plate: The product 4 · 2Zn (top green band)
and the unreacted 1 · Zn (second red band) were each washed off the SiO2 with 3 – 5% MeOH/CH2Cl2
(25 ml) and filtered through a cotton-stuffed pipette. The filtrates containing 4 · 2Zn and 1 · Zn were each
washed with sat. aq. NaHCO3 soln. (3 ꢁ 30 ml) and extracted with CH2Cl2 (50 ml), the extracts filtered
through a plug of dried cotton, and the solvents evaporated. The dry residues were re-dissolved in CH2Cl2
the solns. transferred into small vials, and the solvents evaporated with a N2 flow. The vial contents were
dried at 508 under high vacuum for 12 h: 3.65 mg (17%) 4 · 2Zn and 16.0 mg (71%) of unreacted 1 · Zn. 4 ·
2Zn: UV/VIS (c ¼ 7.03 · 10ꢀ6 m, CH2Cl2): 646 (4.22), 598 (sh, 3.84), 553 (4.28), 440 (5.41), 425 (5.37), 400
(sh, 4.53), 325 (br., 4.23), 250 (3.99) (Fig. 2). Fluorescence emission spectrum (lexc 552 nm, c ¼ 7.03 ·
10ꢀ6 m, CH2Cl2): 652 (1.00), 713 (0.16); excitation spectrum (lem 712 nm): 553 (0.70), 647 (1.00)
(Fig. 3). 1H-NMR: 0.21, 0.31, 0.54, 0.90, 1.20, 1.25, 1.39, 1.41, 1.46, 1.48, 1.51, 1.52, 1.54 (144 H); 1.91 – 1.93
(m); 2.02 – 2.08 (m); 2.75 – 2.81 (m); 2.85 (m); 2.92 – 2.94 (m); 3.32 – 4.24 (m); 4.92 (s, 1 H); 5.46 (s, 1 H);
6.15 (s); 7.03 (s); 7.24 (s); 7.28 (s); 7.29 (s); 7.53 (s); 7.64 – 7.66 (br.); 7.76 (s); 7.78 (s); 7.79 (s); 7.82 (br.);
7.84 (s); 7.85 (s); 7.88 (s); 7.90 (s); 7.94 (br.). MS (C168H200N8O12S6Zn2; calc. 2841.219): 2850.4 (15), 2849.4
(19), 2848.4 (24), 2847.4 (31), 2846.4 (31), 2845.4 (33), 2844.4 (35), 2843.3 (34), 2842.4 (23, [M þ H]þ),
2841.4 (16), 2840.4 (9), 2839.4 (6), 2786.4 (7), 2785.4 (6), 2784.4 (8), 2783.4 (11), 2782.4 (10), 2781.3
(12), 2780.3 (12), 2779.3 (11, [M ꢀ SO2 þ H]þ), 2778.4 (14), 2777.3 (9), 2776.4 (7), 2478.0 (43), 2477.0

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(47), 2476.0 (54), 2475.0 (57), 2474.0 (53), 2473.0 (45), 2472.0 (44), 2471.0 (37), 2466.0 (38), 2465.0 (43),
2464.1 (62), 2463.1 (76), 2462.1 (85), 2461.1 (100), 2460.1 (97), 2459.1 (96, [M ꢀ 6 SO2 þ H]þ), 2458.1
(83), 2457.1 (66), 2456.1 (54), 2455.1 (39).
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Received October 7, 2011