Photodecarboxylative additions of phenoxyacetates to N-methylphthalimide

Article abstract of DOI:10.1016/j.tetlet.2009.09.067

Photoaddition of various phenoxyace tates to N-methylphthalimide affords the corresponding hydrox-yphthalimidines in yields of 21-93%. The diastereoselectivity of the intermolecular addition is studied for a series of 2-substituted phenoxyacetates with lo

Full text of DOI:10.1016/j.tetlet.2009.09.067

Tetrahedron Letters 50 (2009) 6593–6596
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Tetrahedron Letters
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Photodecarboxylative additions of phenoxyacetates to N-methylphthalimide
Fadi Hatoum a, Sonia Gallagher a, Michael Oelgemöller a,b,
*
a Dublin City University, School of Chemical Sciences, Glasnevin, Dublin 9, Ireland
b James Cook University, School of Pharmacy and Molecular Sciences, Townsville, Queensland 4811, Australia
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 9 June 2009
Revised 3 September 2009
Accepted 11 September 2009
Available online 15 September 2009
Photoaddition of various phenoxyacetates to N-methylphthalimide affords the corresponding hydrox-
yphthalimidines in yields of 21–93%. The diastereoselectivity of the intermolecular addition is studied
for a series of 2-substituted phenoxyacetates with low diastereoselectivities being observed. Comparison
experiments with anisole and ether-containing phthalimide confirm that the crucial electron-transfer
step occurs from the carboxylate functionality.
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Photodecarboxylation
Phthalimides
Photochemistry
Addition reactions
Photoinduced electron transfer
As is apparent from several review articles, the phthalimide
chromophore has attracted significant interest in synthetic organic
photochemistry.1 Among the numerous applications, addition
reactions of alkenes, alcohols, ethers, thioethers, alkylbenzenes,
and amines to the phthalimide system have been described.2 We
have intensively studied the photodecarboxylative addition of
derivatives, were identified in the crude NMR spectrum, but no at-
tempt was made to isolate these products. The O-benzyl-derived
carboxylate 2j gave a somewhat lower yield of the corresponding
addition product 3j. In this case, H-abstraction from the benzylic
position may compete with decarboxylation.
The photoreaction involving 2-(4-chloro-2-methylphenoxy)
acetate 2e gave a mixture of the desired compound 3e and a sec-
ond, minor product (30%). Both the 1H and 13C NMR gave two com-
carboxylates,
a-keto carboxylates, and heteroatom-substituted
carboxylates to phthalimides as a versatile alternative to Grig-
nard-additions.3 The developed method has been applied to the
synthesis of arylmethylene-isoindolin-1-ones (I; Fig. 1),4 and in
particular to ‘open analogues’ of aristolactams (II).5 In continuation
of this medicinal chemistry application, we became interested in
the synthesis of aryloxymethylene isosteres of arylmethylene-iso-
indolin-1-ones.
N-Methylphthalimide 1 was chosen as a model compound for
this study and was irradiated (k = 300 25 nm) in aqueous acetone
in the presence of three equivalents of phenoxyacetates 2a–j
(Scheme 1).6 The reaction progress was monitored by TLC analysis
or by passing the departing nitrogen stream through a saturated
barium hydroxide solution until precipitation of barium carbonate
ceased. Following this procedure, the corresponding addition
products 3a–j were isolated in poor to excellent yields of 21–93%
(Table 1).
R4
R1
R2
R1
R2
R3
N
R3
N
O
O
I
aristolactams (II)
Figure 1. Examples of arylmethylene-isoindolin-1-ones.
R2
R2
R1
For all compounds 3, the C–OH group appeared as a character-
istic singlet at around 90 ppm in the 13C NMR spectrum. In some
cases (2c, g, h, and j), larger amounts of the corresponding ‘simple’
decarboxylation products (–CO2H M –H exchange), that is, anisole
O
HO
O
hν
O
CO2K
R1
N
CH3
+
N CH3
R2 R2
acetone/H2O
O
O
1
2a-j
3a-j
* Corresponding author. Tel.: +61 07 4781 4543; fax: +61 07 4781 6078.
E-mail address: michael.oelgemoeller@jcu.edu.au (M. Oelgemöller).
Scheme 1. Additions of phenoxyacetates 2 to N-methylphthalimide 1.
0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.09.067

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F. Hatoum et al. / Tetrahedron Letters 50 (2009) 6593–6596
Table 1
Product yields for the photodecarboxylative additions of 2 to 1
Entry
R1
R2
H
Time (h)
1.5
Conversiona (%)
100
Yield (%)
85
a
Ph
3e
3b
b
c
d
e
f
H
H
H
H
H
1
11
1
100
61b
100
91
93
53 (87c)
Cl
Cl
Cl
Cl
Cl
4.54
4.52
4.50
4.48
4.46
4.44
4.42
71
(ppm)
1
55 (61c,d
51 (64c)
)
Cl
Cl
3e
3
87
3b
g
H
H
4
65b
48 (74c)
21 (72c)
4.54
4.52
4.50
4.48
4.46
4.44
4.42
h
10
29b
(ppm)
Figure 2. 1H NMR comparison: (a) original crude mixture (top), and (b) after
addition of authentic 3b (bottom).
Cl
i
j
Me
H
2
5
73
51 (70c)
genation, whereas the chloro-substituent shows no effect. Similar
photodehalogenation reactions have been described in the
literature.7
Bn
100b
38
The photoreactions involving branched carboxylates 4a–d fur-
nished diastereoisomeric product mixtures 5a–d (Scheme 2).8 In
all cases, two sets of signals were observed in the 1H NMR spectra
which were assigned to the two diastereoisomers. The diastereo-
isomeric ratio (de) was determined by integration of baseline sep-
arated signals in the 1H NMR spectra. Selectivities were low for
compounds 5a–c being 6%; for 5d a higher de of 28% was achieved
Conversion determined by 1H NMR spectroscopy of the crude reaction mixture.
Larger amounts of ‘simple’ photodecarboxylation (PDC) products identified in
a
b
the crude NMR spectrum.
c
Yield based on conversion.
Contains 30% of 3b.
d
plete sets of signals, although overlap within the 1H NMR made a
definite assignment difficult. The purity of the corresponding car-
boxylic acid of 2e was confirmed by NMR spectroscopy, and there-
fore the by-product must have been formed during irradiation.
Based on the 1H NMR spectrum, in particular the aromatic region,
it was assumed that partial dehalogenation (–Cl ? –H exchange) of
3e to 3b had occurred. A mixed NMR was subsequently recorded
with independently synthesized 3b. Following this strategy, all sig-
nals from the by-product in 3e increased in height (Fig. 2 shows
the pair of doublets for the methylene bridge –CH2Ar protons),
thus unambiguously proving that it was indeed identical with
3b. The reason for the partial dehalogenation of 3e remains unclear
at present. However, since this reaction was not observed for the
related 2,4-dichlorinated carboxylic acid 2d, the electronic nature
of the ortho-substituent may play a crucial role in photodehalogen-
ation. The electron-donating methyl group may thus favor dehalo-
O
O
CO2K
R1
N
CH3
+
R2
O
4a-d
1
hν
acetone/H2O
R2
N
R2
R1
R1
O
HO
HO
O
+
CH3
N
O
CH3
O
u-5a-d
l-5a-d
Scheme 2. Additions of branched phenoxyacetates 4 to N-methylphthalimide 1.

F. Hatoum et al. / Tetrahedron Letters 50 (2009) 6593–6596
6595
O
(Table 2). An assignment of the like- and unlike-diastereoisomers
was not made.
3Sens., PETCO
R3
-
O
CO2
R2 R3
2 / 4
O
2
R1
R1
1 +
+
N
CH3
Since phthalimides are known to react with ethers via H-abstrac-
tion,9 N-methylphthalimide 1 was irradiated in the presence of five
equivalents of anisole 6 (Scheme 3). Even after prolonged irradia-
tion of 20 h, no addition product 3a or photoreduction product
was observed. Instead, 1 was recovered in 98% yield.
R2
- CO2
B
1. H+
1. BET
2. H+
A
PETO
D
C
2. C-C
In order to establish the nature of the crucial photoinduced
electron transfer (PET) step,10, that is, whether it occurs from the
carboxylate or the ether functionality, N-methoxymethylphthali-
mide 7 was irradiated in the presence of potassium propionate 8
(Scheme 4). Photodecarboxylative addition occurred smoothly
and after 2 h of irradiation, compound 9 was isolated in a moderate
yield of 51%.11 No cyclization or photoreduction products arising
from competing intramolecular CH-activations were detected.12
Although product formation for phenoxyacetates 2 and 4 can be
explained by two competing electron transfer routes (Scheme 5),
the high oxidation potentials of dialkyl ethers (EOx >2.5 V vs
SCE13) makes electron transfer from the heteroatom (path A) unli-
kely.14,15 Instead, electron transfer most likely occurs from the car-
boxylate functionality (path B), generating an unstable carboxy
R3
R2
R1
O
N
HO
O
hν, 1
O
CO2
R1
O
H
R1
+
CH3
N
CH3
R2 R3
R2 R3
3 / 5
Scheme 5. Mechanistic scenario.
radical that subsequently undergoes decarboxylation.16 The result-
ing carbon-centered radical furnishes the observed addition prod-
ucts 3 and 5 (path C). The detected ‘simple’ decarboxylation
products are formed through back electron transfer (BET) and sub-
sequent protonation of the corresponding carbanions (path D).17
This pathway was only competitive for carboxylates 2c, g, h, and
j, and consequently, the isolated yields for the desired addition
products 3c, g, h, and j remained low due to complete consumption
of the carboxylate. Based on the unsuccessful addition of anisole to
1 it can be concluded that ‘simple’ decarboxylation products, if
formed, do not contribute to the formation of addition products
3 or 5, respectively.
The photoreactivity of N-methoxymethylphthalimide 7 corre-
lates well with photoaddition reactions involving simple carboxyl-
ates.3b,d Incorporation of an ether group into the N-side chain has
no influence on the ethylation and therefore electron transfer must
occur exclusively from the propionate. In contrast, thioether-de-
rived phthalimides are known to completely suppress photode-
carboxylative additions.18
Table 2
Product yields and de ratios for photodecarboxylative additions of 4 to 1
Entry R1
R2
Time
(h)
Conversiona
(%)
dea
(%)
Yield (%)
a
Ph
Me
2
100
99
6
6
87
Cl
b
Me 11
61 (62b)
Cl
c
Me
1
100
6
80
In conclusion, phenoxyacetates readily undergo photodecarb-
oxylative addition to N-methylphthalimide 1. The simple and gen-
eral procedure developed offers a versatile access to 3-alkyl- and
3-arylmethylene-isoindolin-1-one isosteres and this potential
application is currently being investigated. This application is also
currently being transferred to ‘micro-photochemistry’, that is, pho-
tochemical transformations in micro-structured devices.19
O
d
1
95
28
83 (87b)
Conversion and de determined by 1H NMR spectroscopy of the crude reaction
a
mixture.
b
Yield based on conversion.
Acknowledgements
This research project was financially supported by Science
Foundation Ireland (SFI, 07/RFP/CHEF817 and 06/RFP/CHO028)
and Dublin City University (Research Career Start Award 2006).
The authors would like to thank Professor J. Mattay and Dr. M. C.
Letzel (University of Bielefeld, Germany) for providing MS
analyses.
Ph
O
HO
O
hν
O
N
CH3
+
N
CH3
Ph
CH3
acetone/H2O
O
O
3a
References and notes
1
6
1. (a) Oelgemöller, M.; Griesbeck, A. G. In CRC Handbook of Organic Photochemistry
and Photobiology; Horspool, W. M., Lenci, F., Eds., 2nd ed.; CRC Press: Boca
Raton, 2004; pp 1–19. Chapter 84; (b) Oelgemöller, M.; Griesbeck, A. G. J.
Photochem. Photobiol. C: Photochem. Rev. 2002, 3, 109–127; (c) Yoon, U. C.;
Mariano, P. S. Acc. Chem. Res. 2001, 34, 523–533; (d) Coyle, J. D. In Synthetic
Organic Photochemistry; Horspool, W. M., Ed.; Plenum Press: New York, 1984;
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Kanaoka, Y. Acc. Chem. Res. 1978, 11, 407–413; (g) Bartoschek, A.; Griesbeck, A.
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2005, 65, 2221–2257.
3. (a) Kim, A. R.; Lee, K.-S.; Lee, C.-W.; Yoo, D. J.; Hatoum, F.; Oelgemöller, M.
Tetrahedron Lett. 2005, 46, 3395–3398; (b) Oelgemöller, M.; Cygon, P.; Lex, J.;
Griesbeck, A. G. Heterocycles 2003, 59, 669–684; (c) Griesbeck, A. G.;
Oelgemöller, M. Synlett 2000, 71–72; (d) Griesbeck, A. G.; Oelgemöller, M.
Scheme 3. Attempted addition of anisole 6 to 1.
O
HO
OCH3
OCH3
+
hν
N
N
CO2K
acetone/H2O
O
O
7
8
9
Scheme 4. Addition of propionate 8 to N-methoxymethylphthalimide 7.

6596
F. Hatoum et al. / Tetrahedron Letters 50 (2009) 6593–6596
Synlett 1999, 492–494; (e) Griesbeck, A. G.; Oelgemöller, M.; Lex, J. Synlett
2000, 1455–1457; (f) Griesbeck, A. G.; Kramer, W.; Oelgemöller, M. Green
Chem. 1999, 1, 205–207.
m
= 3304, 2983, 2346, 1681, 1618, 1064, 750 cmÀ1. MS (EI, 70 eV, mixture): m/z
(%) = 351 (M+, <1), 333 (M+ÀH2O, <1), 188 (M+ÀC9H8NO
,
23), 162
À
(M+ÀC8H7Cl2O+, 100), 146 (M+ÀC11H12NO3, 8), 77 (C6H5, 8).2 HR-MS (ESI,
positive ions, mixture): calcd [M+H]+: 352.05018 for C17H15Cl2NO3+H+. Found
[M+H]+: 352.05007.
4. (a) Csende, F.; Stáer, G. Curr. Org. Chem. 2005, 9, 1261–1276; (b) Bently, K. W.
Nat. Prod. Rep. 2006, 23, 444–463; (c) Kumar, V.; Poonam; Prasad, A. K.; Parmar,
V. S. Nat. Prod. Rep. 2003, 20, 565–583.
5. (a) Griesbeck, A. G.; Warzecha, K.-D.; Neudörfl, J. M.; Görner, H. Synlett 2004,
2347–2350; (b) Warzecha, K.-D.; Görner, H.; Griesbeck, A. G. J. Phys. Chem. A
2006, 110, 3356–3363; (c) Hatoum, F.; Gallagher, S.; Baragwanath, L.; Lex, J.;
Oelgemöller, M. Tetrahedron Lett. 2009, doi:10.1016/j.tetlet.2009.08.115.
6. General procedure for irradiation: N-methylphthalimide (1.5 mmol) was
9. (a) Roth, H. J.; Schwarz, D. Arch. Pharm. 1976, 309, 52–58; (b) Roth, H. J.;
Hundeshagen, G. Arch. Pharm. 1976, 309, 58–62; (c) Tanabe, M.; Dehn, R. L.;
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Pérez-Inestrosa, E.; García-Segura, R.; Suau, R. Tetrahedron 2002, 58, 7267–
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10. (a) Hoffmann, N. J. Photochem. Photobiol. C: Photochem. Rev. 2008, 9, 43–60; (b)
Oelgemöller, M.; Bunte, J.-O.; Mattay, J. In Synthetic Organic Photochemistry;
Griesbeck, A. G., Mattay, J., Eds.; Marcel Dekker: New York, 2004; pp 267–295.
Chapter 10.
11. Physical and spectral data for 3-ethyl-3-hydroxy-2-(methoxymethyl)-isoindolin-
1-one 9: yellow oil. 1H NMR (400 MHz, CDCl3): d (ppm) = 0.59 (t, 3J = 7.6 Hz, 3H,
CH3), 2.24 (m, 2H, CH2), 3.40 (s, 3H, OCH3), 4.93 (m, 2H, CH2), 5.30 (s, 1H, OH),
7.58 (ddd, 3J = 7.6, 3J = 7.6, 4J = 1.0 Hz, 1H, Harom), 7.65 (d, 3J = 7.6 Hz, 1H, Harom),
7.71 (ddd, 3J = 7.6, 3J = 7.6, 4J = 1.0 Hz, 1H, Harom), 7.75 (d, 3J = 7.2 Hz, 1H, Harom).
13C NMR (100 MHz, CDCl3): d (ppm) = 8.3, 31.2, 57.0, 70.5, 91.9, 123.1, 123.8,
130.1, 133.5, 144.0, 149.0, 166.0.
dissolved in acetone (50 mL).
A solution of the potassium carboxylate
(4.5 mmol) in water (50 mL) was added, and the mixture was irradiated
(Rayonet Photochemical Reactor RPR-200; k = 300 20 nm) at 15–20 °C in a
Pyrex tube (k P300 nm) while purging with a slow stream of nitrogen. The
progress of the reaction was monitored by TLC analysis or by passing the
departing gas stream through a saturated barium hydroxide solution until
precipitation of barium carbonate ceased. Most of the acetone was evaporated
and the remaining solution was extracted with CH2Cl2 (3 Â 50 mL). The
combined organic layers were washed with 5% NaHCO3 (50 mL) and brine
(50 mL), dried over MgSO4, and evaporated. The products were purified by
column chromatography (eluent: n-hexane/EtOAc = 1:1). In some cases, the
pure product precipitated upon evaporation of acetone and was isolated by
vacuum filtration and drying in vacuo instead.
12. (a) Kanaoka, Y.; Migita, Y.; Sato, Y.; Nakai, H. Tetrahedron Lett. 1973, 51–54; (b)
Sato, Y.; Nakai, H.; Wada, M.; Ogiwara, H.; Mizoguchi, T.; Migita, Y.; Hatanaka,
Y.; Kanaoka, Y. Chem. Pharm. Bull. 1982, 30, 1639–1645.
Selected physical and spectral data for 3-hydroxy-2-methyl-3-[(naphthalene-1-
yloxy)methyl]isoindolin-1-one 3h: yellow solid, mp 177–182 °C. 1H NMR
(400 MHz, CDCl3): d (ppm) = 2.91 (s, 3H, NCH3), 4.17 (s, 1H, OH), 4.47 (d,
2J = 9.6 Hz, 1H, CH2), 4.55 (d, 2J = 9.6 Hz, 1H, CH2), 6.79 (d, 3J = 7.3 Hz, 1H,
Harom), 7.32 (m, 2H, Harom), 7.42 (m, 2H, Harom), 7.46 (ddd, 3J = 7.3, 3J = 7.3,
4J = 1.0 Hz, 1H, Harom), 7.55 (ddd, 3J = 7.3, 3J = 7.3, 4J = 1.0 Hz, 1H, Harom), 7.69
(m, 4H, Harom). 13C NMR (100 MHz, CDCl3): d (ppm) = 24.2, 68.8, 89.2, 105.3,
121.6, 121.8, 122.4, 123.6, 125.5, 125.8, 125.9, 126.9, 127.7, 130.4, 131.9, 132.8,
13. Gutenberger, G.; Meggers, E.; Steckhan, E. In Novel Trends in Electoorganic
Synthesis; Torii, S., Ed.; Springer: Tokyo, 1998; pp 367–369.
14. For (
x
-phthalimidoalkoxy)acetic acids, Yoon et al. have recently suggested an
-decarboxylation, see:
electron transfer from the oxygen tether followed by
a
Yoon, U. C.; Lee, C. W.; Oh, S. W.; Kim, H. J.; Lee, S. J. J. Photo. Sci. 2000, 7, 143–
148.
15. PET from oxygen has been postulated for related photoadditions involving
trimethylsilylmethyl ethyl ether. However, the presence of a
a-TMS group
134.7, 145.6, 153.9, 168.3. IR (KBr):
m
= 3295, 2945, 2347, 1676, 1618, 1070,
greatly effects the oxidation potential of the ether oxygen, which decreases by
about 0.5 V.13 Hence, the reactivity order changes to–OCH2TMS > –OCH2
CO2À>–OCH3 and electron transfer indeed occurs from the heteroatom to the
excited phthalimide (a) Yoon, U. C.; Kim, H. J.; Mariano, P. S. Heterocycles 1989,
29, 1041–1064; (b) Yoon, U. C.; Oh, J. H.; Lee, S. J.; Kim, D. U.; Lee, J. G.;
Kang, K.-T.; Mariano, P. S. Bull. Korean Chem. Soc. 1992, 13, 166–172;
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16. The mechanism mirrors that of related photodecarboxylative cyclization
reactions, see: (a) Griesbeck, A. G.; Kramer, W.; Oelgemöller, M. Synlett 1999,
1169–1178; (b) Kramer, W.; Griesbeck, A. G.; Nerowski, F.; Oelgemöller, M. J.
Inf. Rec. 1998, 24, 81–85; (c) Oelgemöller, M.; Griesbeck, A. G.; Kramer, W.;
Nerowski, F. J. Inf. Rec. 1998, 24, 87–94; (d) Griesbeck, A. G.; Henz, A.; Kramer,
W.; Lex, J.; Nerowski, F.; Oelgemöller, M.; Peters, K.; Peters, E.-M. Helv. Chim.
Acta 1997, 80, 912–933.
17. Yokoi, H.; Nakano, T.; Fujita, W.; Ishiguro, K.; Sawaki, Y. J. Am. Chem. Soc. 1998,
120, 12453–12458.
18. (a) Griesbeck, A. G.; Oelgemöller, M.; Lex, J.; Haeuseler, A.; Schmittel, M. Eur. J.
Org. Chem. 2001, 1831–1843; (b) Görner, H.; Oelgemöller, M.; Griesbeck, A. G. J.
Phys. Chem. A 2002, 106, 1458–1464.
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(b) Coyle, E. E.; Oelgemöller, M. Chem. Technol. 2008, 5, T95; (c) Matsushita, Y.;
Ichimura, T.; Ohba, N.; Kumada, S.; Sakeda, K.; Suzuki, T.; Tanibata, H.; Murata,
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874 cmÀ1. MS (EI, 70 eV): m/z (%) = 319 (M+, 6), 301 (M+ÀH2O, 100), 272 (301-
COH, 18), 244 (M+1ÀC6H4, 7), 162 (M+ÀC11H9O, 84), 77 (C6H5, 23). MS (ESI,
positive ions): m/z = 320 (M + H)+, 639 (M2+H)+. HR-MS (ESI, positive ions):
calcd [M+H]+: 320.12812 for C20H17NO3+H+. Found [M+H]+: 320.12783. calcd
[M+Na]+: 342.11006 for C20H17NO3+Na+. Found [M+Na]+: 342.10988.
7. (a) Rollet, F.; Richard, C.; Philichowski, J. F. Photochem. Photobiol. Sci. 2006, 5,
88–94; (b) Yoshimi, Y.; Ishise, A.; Oda, H.; Moriguchi, Y.; Kanezaki, H.; Nakaya,
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2008, 49, 3400–3404.
8. Selected physical and spectral data for 3-[1-(2,4-dichlorophenoxy)ethyl]-3-
hydroxy-2-methylisoindolin-1-one u-/l-5b: yellow solid, mp (mixture) 115–
125 °C. Main diastereoisomer: 1H NMR (400 MHz, CDCl3): d (ppm) = 1.01 (d,
3J = 6.3 Hz, 3H, CH3), 2.97 (s, 3H, NCH3), 4.52 (s, 1H, OH), 4.76 (q, 3J = 6.3 Hz, 1H,
CH), 6.90 (d, 3J = 8.8 Hz, 1H, Harom), 7.13 (dd, 3J = 8.8, 4J = 2.5 Hz, 1H, Harom), 7.31
(d, 4J = 2.5 Hz, 1H, Harom), 7.40 (m, 1H, Harom), 7.47–7.55 (m, 2H, Harom), 7.58 (d,
3J = 7.9 Hz, 1H, Harom). 13C NMR (100 MHz, CDCl3): d (ppm) = 14.8, 25.8, 80.1,
91.3, 116.8, 123.4, 123.9, 125.1, 127.6, 128.2, 130.7, 130.8, 132.4, 132.6, 144.2,
152.4, 168.4. Minor diastereoisomer: 1H NMR (400 MHz, CDCl3): d (ppm) = 0.82
(d, 3J = 6.3 Hz, 3H, CH3), 2.84 (s, 3H, NCH3), 3.15 (s, 1H, OH), 4.72 (q, 3J = 6.3 Hz,
1H, CH), 6.98 (d, 3J = 8.9 Hz, 1H, Harom), 7.14 (dd, 3J = 8.9, 4J = 2.5 Hz, 1H, Harom),
7.34 (d, 3J = 2.5 Hz, 1H, Harom), 7.41 (m, 1H, Harom), 7.47–7.55 (m, 1H, Harom),
7.61 (d, 3J = 7.9 Hz, 1H, Harom), 8.02 (d, 3J = 7.6 Hz, 1H, Harom). 13C NMR
(100 MHz, CDCl3): d (ppm) = 14.9, 24.4, 78.7, 91.2, 116.9, 122.4, 125.3, 125.5,
127.3, 128.1, 130.3, 130.6, 132.0, 132.8, 144.1, 152.8, 168.2. IR (KBr, mixture):