Conversion of α,β-unsaturated ketones to 1,5-diones via tandem retro-Aldol and Michael addition using Co(acac)2 covalently anchored onto amine functionalized silica

Article abstract of DOI:10.1016/j.tetlet.2015.02.057

Abstract A new and efficient method has been developed for the conversion of α,β-unsaturated ketones to 1,5-diketones via tandem retro-Aldol and Michael addition in the presence of Co(acac)₂ covalently anchored amine functionalized silica [AS-Co(acac)₂]. The single crystal X-ray crystallography confirms the formation of 1,5-diketones. This method has been proved to be an attractive alternative to existing methodologies under conventional homogeneous catalysis with the frequent troublesome manipulation and work-up. The AS-Co(acac)₂ was found to be highly active and could be recycled for four consecutive runs with slight decrease in activity.

Full text of DOI:10.1016/j.tetlet.2015.02.057

Accepted Manuscript
Conversion of α,β-unsaturated ketones to 1,5-diones via tandem retro-Aldol and
Michael addition using Co(acac)2 covalently anchored onto amine functional-
ized silica
Ravinderpal Kour Sodhi, Satya Paul, Vivek K. Gupta, Rajni Kant
PII:
S0040-4039(15)00328-7
DOI:
http://dx.doi.org/10.1016/j.tetlet.2015.02.057
TETL 45926
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
22 December 2014
12 February 2015
13 February 2015
Please cite this article as: Sodhi, R.K., Paul, S., Gupta, V.K., Kant, R., Conversion of α,β-unsaturated ketones to
1,5-diones via tandem retro-Aldol and Michael addition using Co(acac)2 covalently anchored onto amine
functionalized silica, Tetrahedron Letters (2015), doi: http://dx.doi.org/10.1016/j.tetlet.2015.02.057
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Conversion of α,β-unsaturated ketones to
1,5-diones via tandem retro-Aldol and
Michael addition using Co(acac)2 covalently
anchored onto amine functionalized silica
,a
Ravinderpal Kour Sodhi,a Satya Paul∗ , Vivek K. Guptab and Rajni Kantb
aDepartment of Chemistry, University of Jammu, Jammu-180 006, India
bX-ray Crystallography Laboratory, Department of Physics and Electronics,
University of Jammu, Jammu-180 006, India
R2
O
O
O
AS-Co(acac)2,
aq. NaOH
CHO
+
R1
R2
R1
R1
R2
1,4-dioxane

1
Tetrahedron Letters
journal homepage: www.els evier.com
Conversion of α,β-unsaturated ketones to 1,5-diones via tandem retro-Aldol and
Michael addition using Co(acac)2 covalently anchored onto amine functionalized
silica
,a
Ravinderpal Kour Sodhi,a Satya Paul∗ , Vivek K. Guptab and Rajni Kantb
aDepartment of Chemistry, University of Jammu, Jammu-180 006, India
bX-ray Crystallography Laboratory, Department of Physics and Electronics, University of Jammu, Jammu-180 006, India
ARTICLE INFO
ABSTRACT
Article history:
Received
A new and efficient method has been developed for the conversion of α,β-unsaturated ketones to 1,5-
diketones via tandem retro-Aldol and Michael addition in the presence of Co(acac)2 covalently
anchored amine functionalized silica [AS-Co(acac)2]. The single crystal X-ray crystallography
confirms the formation of 1,5-diketones. This method has been proved to be an attractive alternative to
existing methodologies under conventional homogeneous catalysis with the frequent troublesome
manipulation and work-up. The AS-Co(acac)2 was found to be highly active and could be recycled for
four consecutive runs with slight decrease in activity.
Received in revised form
Accepted
Available online
Keywords:
AS-Co(acac)2
α,β-unsaturated ketones
1,5-diones
2009 Elsevier Ltd. All rights reserved
Retro-Aldol
Michael addition
Heterogeneous catalysis
R2
Introduction
O
O
O
AS-Co(acac)2,
aq. NaOH
The chemistry of chalcones has generated intensive scientific
studies throughout the world. Especially, interest has been
focused on the synthesis and biodynamic activities of chalcones.
Due to the unique structural feature, chalcones have also emerged
as a reliable class of substrates and important precursors in
synthetic chemistry. Their activity is mostly based either on the
Michael acceptor activity of the α,β-unsaturated carbonyl system,
or their radical scavenging or reductive potential which are often
referred to as their antioxidative behaviour.1 Moreover, they have
attracted widespread research interests from organic chemists to
investigate their chemical reactivities in a variety of reactions,
e.g. classical Claisen-Schmidt condensation,2 Suzuki coupling3
and Heck reaction.4
R1
R2
R1
R1
1,4-dioxane
+
CHO
R2
Scheme 1. Conversion of α,β-unsaturated ketones to 1,5-diones via
tandem retro-Aldol and Michael addition.
3.4 and multiplet in the range δ 4.0-4.2 suggesting the presence
of –CH2-CH moiety in the isolated product.Various possibilities
were explored and it was found that in case of α,β-unsaturated
ketones, carbonyl group in conjugation with the olefin double
bond can activate the olefin double bond and cause it to break
into aldehyde and ketone in the presence of alkali, heat and water
(retro-Aldol). Although the retro-aldol reaction is less
widespread, it nevertheless plays an important role in solving
certain synthetic tasks.5 The lack of a general and effective
method for the retro-Aldol reaction is often a restriction for its
more widespread use in organic synthesis. The ketone generated
by retro-Aldol in the presence of alkali and AS-Co(acac)2
undergoes Michael addition on α,β-unsaturated ketone to give
1,5-diketone, structure of which was confirmed by 1H, 13C NMR,
and mass spectral data. Single crystal X-ray crystallography
Epoxy carbonyl compounds are very important intermediates and
can serve as versatile precursors in the synthesis of many natural
products and drug molecules. These are usually prepared via
epoxidation of α,β-unsaturated ketones. In an initial attempt to
evaluate the catalytic activity of AS-Co(acac)2 for the
epoxidation, we examined the reaction in detail using (E)-1,3-
bis(4-chlorophenyl)prop-2-en-1-one as a test substrate in the
presence of aq. NaOH using 1,4-dioxane as solvent (Scheme 1).
During the course of characterization, to our surprise it was found
that the product was quite different from the desired product.
1
further
confirmed
the
formation
of
1,3,5-tris(4-
From the H NMR spectral data, it was found that there was no
peak corresponding to -CH proton of oxirane ring, whereas
chlorophenyl)pentane-1,5-dione. The Michael addition reaction is
one of the most fundamental reactions in the synthesis of 1,5
dicarbonyl compounds. Transition-metal-catalyzed Michael
additional peaks appeared as double-doublets in the range δ 3.2-
———
∗ Corresponding author. Tel.: +91-191-2453969; fax: +91-191-2431365; e-mail: paul7@rediffmail.com

2
Tetrahedron
addition of organometallic species over the last two decades has
investigation of structure-reactivity relationship. Thus, a variety
of chalcones were synthesized and subjected to reaction under the
optimized conditions.29 The reaction led to the desired products
in moderate yields. The moderate yield of isolated products is
due to the fact that some amount of the chalcone undergoes retro-
Aldol to yield ketone and aldehyde, while the other remained as
it is. The left out chalcone act as Michael acceptor and the
enolate ion generated from ketone act as nucleophile. The
reported yield of products is with respect to remaining chalcone,
so products were obtained in low yields.
become an important synthetic tool for constructing carbon
skeletons.6-7 The Michael addition of active methylene
compounds to activated π-systems is one of the oldest and more
useful carbon-carbon bond forming reactions.8-9 Michael addition
of malonate diesters10 or nitroalkanes11 to simple enones have
been reported. Alternatively, in pioneering work by Barbas et al.
and other groups, simple ketones or aldehydes have been added
to activated Michael acceptors such as nitroalkenes or
alkylidenemalonates.12 In contrast, Michael addition reaction of
ketones with chalcones still remain a challenge and are rarely
reported, probably due to the low reactivity and high steric
hindrance of substrate. Diketones are one of the important
synthetic intermediates and desirable starting materials for the
synthesis of numerous heterocycles13-15 and polyfunctional
Table 2. Effect of solvent and temperature on the conversion of
α,β-unsaturated carbonyl compounds to 1,5-diketones
Solvent
Temperature
Time (h)
Yield (%)b
compounds.16-19 Polyfunctionalized derivatives containing
a
Toluene
110 oC
50 oC
100 oC
50oC
82oC
50oC
80oC
80oC
7
7
7
7
7
7
5
7
No reaction
dicarbonyl moiety are valuable intermediates in organic synthesis
since they can be transformed into a plethora of important target
compounds such as cyclopentenones, furans, pyrroles, thiophenes
and other heterocyclic systems.20-27
Water
Traces
10
Water
ter-Butanol
ter-Butanol
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
15
Since we found an unexpected reaction taking place, we set out
to study the scope of the reaction. Toward this goal, we have
varied reaction conditions such as the catalyst, base and the
solvent. Initial investigations for the conversion of α,β-
unsaturated carbonyl compounds to diketones involved the use of
different supported metal catalysts using (E)-1,3-bis(4-
chlorophenyl)prop-2-en-1-one as a test substrate. Out of the
different catalysts tested, AS-Co(acac)2 gave the best results with
maximum yield. The results are summarized in Table 1.
30
30
48
48
aReaction conditions: (E)-1,3-bis(4-chlorophenyl)prop-2-en-1-one
(0.277 g, 1 mmol), 25 equiv. NaOH (2 mL, 0.25 M solution), AS-
Co(acac)n (0.2 g, 1.45 wt% Co) at 80 oC in 1,4-dioxane (10 mL).
bColumn chromatography yields.
Table 1. Comparison of the catalytic activities of different
M(acac)n covalently anchored onto amine functionalized silica
for the synthesis of 1,5-diones
The substituent has significant effect on the reaction efficiency
and reactivity. R1 and R2 bearing chloro, bromo or nitro group on
aromatic ring (Scheme 1) led to the product in good yields
(Table 3, entries 1-3, 5-6), whereas, reactant bearing electron-
donating group took longer time and gave the desired product in
moderate yield (Table 3, entry 4). The structure of 1,3,5-tris(4-
chlorophenyl)pentane-1,5-dione has been confirmed by X-ray
crystallography (Table 3, entry 1, S1).
Entry
Catalyst
Time (h)
Yield (%)b
1
2
3
4
5
6
AS-Co(acac)2
AS-Cu(acac)2
AS-Pd(acac)2
AS-Mn(acac)3
AS-Co(acac)3
AS-Ru(acac)3
5
5
5
5
5
5
48
30
35
40
40
20
aReaction conditions: (E)-1,3-bis(4-chlorophenyl)prop-2-en-1-one
(0.277 g, 1 mmol), 25 equiv. NaOH (2 mL, 0.25 M solution), AS-
M(acac)n [M= Cu, Ru, Pd, Co, Mn and n=2 or 3 (5 mol% metal)] at
80 oC in 1,4-dioxane (10 mL).
bColumn chromatography yields.
The preparation and characterization of AS-Co(acac)2 has
already been reported in our earlier communication.28
The effect of different solvents at different temperatures on the
catalytic activity of AS-Co(acac)2 was investigated. We varied
the solvent used in the reaction to evaluate its role and efficacy.
Among the different solvents tested (toluene, water, tert-butanol,
1,4-dioxane), the reaction proceeded well in 1,4-dioxane at 80
°C in terms of activity and selectivity (Table 2). The reaction
was very sluggish in the absence of base. Next, we tested
different bases (K2CO3, KOH, NaOH) and found that NaOH gave
the best results with maximum conversion. From the above
observation, it appeared that the presence of base is detrimental
for the formation of retro-Aldol product. Having developed
conditions for this unique reaction, the work was focused on the
Fig 1. ORTEP view of 1,3,5-tris(4-chlorophenyl)pentane-1,5-
dione.
Heterocyclic chalcones were also found to be compatible under
the optimized reaction conditions and converted to the
corresponding products in good yields (entries 7,8). Overall,
there is a good substrate scope for the reaction, providing access
to a variety of 1,5-diketones in high selectivities. The separation

3
of 1,5-diketones from the accompanying aromatic aldehydes has
been effectively achieved by column chromatography (Table 3,
S8, S9). Although great efforts have been devoted to the
synthetic and selectivity aspects of Michael reactions catalyzed
by transition metals, less effort has been dedicated to the
mechanistic aspects, which is crucial for their better
understanding. The mechanistic pathway of the reaction can be
explained by the retro-Aldol and Michael addition of ketone on
α,β-unsaturated ketones. The proposed mechanism involves the
retro-Aldol reaction of the α,β-unsaturated ketones, thus breaking
it into aldehyde and ketone. The C=O bond of the chalcone
interacts with the metal catalyst thus weakening the π-bond
followed by nucleophilic attack of enolate ion (generated by the
reaction of base with ketone) to give the desired 1,5-diketone
with the regeneration of the metal catalyst (Fig. 2). Further,
crossover experiment was carried out to study and explore the
mechanistic pathway of the reaction using (E)-3-(4-nitrophenyl)-
1-phenylprop-2-en-1-one and (E)-3-(4-chloro phenyl)-1-(4-
methylphenyl)prop-2-en-1-one as test substrates. The aim of the
experiment was to determine whether the components of each
reactant had an opportunity to exchange with each other i.e. intra
or intermolecular mechanistic path. The structural analysis of the
isolated product confirms the formation of intermolecular cross
product. From the two substrates, 3-(4-chlorophenyl)-1-phenyl-5-
(4-methylphenyl)pentane-1,5-dione was formed exclusively
along with the mixture of two unreacted chalcones. The
formation of the single crossover product can be explained by the
fact that out of the two reacting species, (E)-3-(4-nitrophenyl)-1-
Table 3. AS-Co(acac)2 catalyzed synthesis of 1,5-diketones from
α,β-unsaturated carbonyl compounds via retro-aldol and Michael
additiona
Entry
Product
Aldehyde
Cl
O
O
1
CHO
Cl
Cl
Cl
5h, 48%
25%
O
O
CHO
Br
Br
2
7h, 45%
20%
NO2
CHO
O
O
3
phenylprop-2-en-1-one
in the formation of 4-nitrobenzaldehyde and acetophenone.
However, in case of (E)-3-(4-chlorophenyl)-1-(4-
undergoes retro-Aldol faster resulting
O2N
Cl
Cl
6h, 48%
20%
methylphenyl)prop-2-en-1-one, the presence of electron donating
group reduces the chance of retro-Aldol and thus make the
reaction process slow. In the meantime, the acetophenone in
presence of base generates enolate and undergoes Michael
addition with (E)-3-(4-chloro phenyl)-1-(4-methylphenyl)prop-2-
OCH3
CHO
O
O
en-1-one
to
methylphenyl)pentane-1,5-dione as the product.
give
3-(4-chlorophenyl)-1-phenyl-5-(4-
4
H3CO
F
F
6h, 40%
25%
O
O
Ph
O
NO2
O
Ph
Co(II)
Ph
Ph
CHO
Retro-aldol
O
OH
O
O
5
O
Co(II)
Ph
CH3
OH
Ph
H
+
NO2
O
Ph
O
Co(III)
Ph
Ph
Ph
7h, 45%
20%
Ph
NO2
O
O
Co(III)
O
H2C
Ph
Ph
Ph
H2C
Ph
6
CHO
O
O
Enolate ion
Michael addition
O2N
25%
Fig 2. Proposed mechanism for the synthesis of 1,5-diketones via
6.5h, 45%
retro-Aldol and Michael addition using AS-Co(acac)2.
O
In order to find out the role of AS-Co(acac)2 as the heterogeneous
catalyst, the reaction with (E)-1,3-bis(4-chlorophenyl)prop-2-en-
1-one was carried out in the presence of activated silica, 3-
aminopropyl silica (AMPS) and without using catalyst (Table 4,
entry 1). With AS-Co(acac)2, reaction was completed in 5 h with
48% yield (column chromatography). However, with activated
silica and AMPS, poor results were obtained with negligible
conversion of the reactant. The results are summarized in Table
4, which indicated that the presence of cobalt played an important
role for the desired transformation.
7
O
O
CHO
O
5.5h, 48%
25%

4
Tetrahedron
attractive alternative to conventional homogeneous catalysts with
easy work-up and recyclability.
S
O
O
CHO
8
Cl
Cl
S
5h, 48%
25%
Cl
O
O
9c
Mixtured
H3C
7h, 35%
aReaction conditions:
mmol), 0.025 equiv. NaOH (2 mL, 2.5 M solution), AS-Co(acac)2,
(0.2 g, 1.45 wt% Co) at 80 oC in 1,4-dioxane (10 mL).
bAll the yields refer to column chromatography.
α,β-unsaturated carbonyl compound (1
Fig 3. Recyclability of AS-Co(acac)2. Reaction conditions: (E)-1,3-
bis(4-chlorophenyl)prop-2-en-1-one (0.277 g, 1 mmol), 0.025 equiv.
NaOH (2 mL, 2.5 M solution), AS-Co(acac)2, (0.2 g, 1.45 wt% Co)
at 80 oC in 1,4-dioxane (10 mL) for 5 h.
cCross over experiment: (E)-3-(4-nitrophenyl)-1-phenylprop-2-en-1-
one (1 mmol), (E)-3-(4-chloro phenyl)-1-(4-methylphenyl)prop-2-
en-1-one (1 mmol) as test substrates and reaction conditions as
mentioned above.
Acknowledgments
We thank Director IIIM Jammu for mass spectral data. We
gratefully acknowledge Department of Science and Technology,
Government of India for NMR spectrometer (Bruker Avance III,
400 MHz) under PURSE program to the University of Jammu.
We also thank UGC, New Delhi for financial support (Major
research Project, F-41-281/2012 (SR)).
dMixture: mixture of two chalcones and aldehyde.
Table 4. Comparison of activity of AS-Co(acac)2, activated silica
and AMPS for the conversion of α,β-unsaturated carbonyl
compounds to diketonesa.
References and notes
1. Amslinger, S. ChemMedChem. 2010, 5, 351-356.
2. Claisen, L.; Claparede, A. Chem. Ber. 1881, 14, 2460-
2468.
Entry
Catalyst
Time (h)
Yield (%)b
3. Eddarir, S.; Cotelle, N.; Bakkour, Y.; Rolando, C.
Tetrahedron Lett. 2003, 44, 5359-5363.
4. Wu, X. F.; Neumann, H.; Spannenberg, A.; Schulz, T.;
Jiao, H. J.; Beller, M. J. Am. Chem. Soc. 2010, 132, 14596-
14602.
1
2
No catalyst
5
5
5
Activated silica
10
3
4
Aminopropyl silica
AS-Co(acac)2
5
5
10
48
5. Arigan, Z. S.; Suschitiky, H. J. Chem. Soc. 1961, 2241-
2260.
6. Krause, N.; Hoffmann-Röder, A. Synthesis. 2001, 171-
196.
7. Christoffers, J.; Koripelly, G.; Rosiak, A.; Rössle, M.
Synthesis, 2007, 1279-1300.
8. Jung, M. E. In Comprehensive Organic Synthesis, (Ed.
Trost, B. M.; Fleming, I), Pergamon Press: Elmsford, NY,
1991, 4, 1.
aReaction conditions: (E)-1,3-bis(4-chlorophenyl)prop-2-en-1-one
(0.277 g, 1 mmol), 0.025 equiv. NaOH (2 mL, 2.5 M solution), and
catalyst (0.2 g, 1.45 wt% Co for entry 4; 0.2 g for entries 2-3) at 80
oC in 1,4- dioxane (10 mL).
bColumn chromatography yields.
9. Perlmutter, P. Conjugate Addition Reactions in Organic
Synthesis; Pergamon Press: Elmsford, NY, 1992.
10. Halland, N.; Aburel, P. S.; Jorgensen, K. A. Angew.
Chem., Int. Ed. 2003, 42, 661-665.
11. Corey, E. J.; Zhang, F.-Y. Org. Lett. 2000, 2, 4257- 4259.
12. Betancort, J. M.; Sakthivel, K.; Thayumana- van, R.;
Barbas, C. F. Tetrahedron Lett. 2001, 42, 4441-4444.
13. Hirsch, S. S.; Bailey, W. J. J. Org. Chem. 1978, 43, 4090-
4094.
The recovery and recyclability of AS-Co(acac)2 catalyst was
investigated for the synthesis of 1,5-diketones for four
consecutive runs (Fig. 3) and found that there is a little drop in
the activity of the catalyst upto 4th run. At the end of the reaction,
the catalyst was separated by simple filtration, washed with ethyl
acetate (3×5 mL) and water (3×10 mL), followed by drying
before using in the next run. The amount of Co in the recovered
catalyst was determined by AAS after 4th run. The results showed
that the Co content of the recovered catalyst remains almost
constant. This fact confirmed the strong coordination of
Co(acac)2 with amine functionalized silica.
14. Krohnke, F. Synthesis. 1976, 1-24.
15. Constable, E. C.; Thompson, A. M. W. C. J. Chem. Soc.
Dalton. Trans. 1992, 2947-2950.
16. Potts, K. T. Bull. Soc. Chem. Belg. 1990, 99, 741-768.
17. Butler, I. R.; Mcdonald, S. J.; Michael B. Hursthouse, M.
Conclusion
In conclusion, we have developed a new and efficient approach
for the synthesis of 1,5-diketones from α,β-unsaturated carbonyl
compounds via tandem retro-Aldol and Michael addition
reactions. We believe this is the first report on the synthesis of
1,5-diketones following this strategy. The method provides an
•
B.; Malik, K. M. A. Polyhedron. 1995, 14, 529-539.
18. Gill, N. S.; James, K. B.; Lions, F.; Potts, K. T. J. Am.
Chem. Soc. 1952, 74, 4923-4928.
19. Simon, C.; Constantieux, T.; Rodriguez, J. Eur. J. Org.
Chem. 2004, 4957-4980.
20. Patzel, M.; Liebscher, J. Synthesis, 1995, 879-894.

5
21. Eicher, T.; Hauptmann, S. The Chemistry of Heterocycles,
Georg Thieme Verlag: New York, 1995.
22. Dean, F. M. Adv. Heterocycl. Chem. 1982, 30, 172-175.
23. Sundberg, R. J. In Comprehensive Heterocyclic
Chemistry, Vol. 4, (Ed. Katritzky, A. R.; Rees, C. W),
Pergamon: Oxford, 1984, 329-330.
24. Ellison, R. A. Synthesis. 1973, 397-412.
25. Ho, T. L. Synth. Commun. 1974, 4, 265-287.
26. Stetter, H.; Kuhlmann, H. Org. React. 1991, 40, 407-496.
27. Vashchenko, E. V.; Knyazeva, I. V.; Krivoshey, A. I.;
Vashchenko, V. V. Monatsh Chem. 2012, 143, 1545-1549.
28. Sodhi, R. K.; Paul, S.; Clark, J. H. Green Chem. 2012, 14,
1649-1656.
29. General procedure for the AS-Co(acac)2 catalyzed
conversion of α,β-unsaturated carbonyl compounds to
1,5-diketones
To a mixture of α,β-unsaturated carbonyl compound (1
mmol), 0.025 equiv. NaOH (2 mL, 2.5 M solution) and
AS-Co(acac)2 (0.2 g, 1.45 wt% Co), 1,4-dioxane (10 mL)
o
was added, and the reaction mixture was stirred at 80 C.
After completion of the reaction (monitored by TLC), the
reaction mixture was diluted with ethyl acetate and filtered.
The residue was washed with hot ethyl acetate (30 mL),
followed by distilled water (150 mL). The organic layer
was washed with water and dried over anhydrous Na2SO4.
Finally, the product was obtained after purification by
column chromatography on silica gel (EtOAc-pet. ether).
The recovered catalyst was washed with EtOAc (3×5 mL)
followed by double distilled water (3×10 mL), dried at 100
°C for 2 h and reused for subsequent reactions.
1
The structures of the products were confirmed by H, 13C
NMR and mass spectral data (S10).
Representative
Chlorophenyl)pentane-1,5-dione (Table 3, entry 1). M.p.
spectral
of
1,3,5-tris(4-
o
123-125 C, yield 0.066 g (48%). 1H NMR (400 MHz,
CDCl3): δ 3.26-3.32 (dd, 2H, J= 8 Hz, J= 16 Hz, CH2),
3.45-3.51 (dd, 2H, J= 8 Hz, J= 16 Hz, CH2), 4.01-4.05 (m,
1H, CH), 7.21-7.28 (m, 4H, Harom), 7.44-7.46 (d, 4H, J= 8
Hz, Harom), 7.89-7.91 (d, 4H, J= 8 Hz, Harom). 13C NMR
(100 MHz, CDCl3): 36.41, 44.64, 128.84, 128.86, 129.02,
129.54, 132.56, 134.95, 139.79, 141.96, 196.99. MS (ESI):
430 (M)+, 432.90 (M+2).