Facile synthesis of novel dispiroheterocylic derivatives through cycloaddition of azomethine ylides with acenaphthenone-2-ylidine ketones

Article abstract of DOI:10.1016/j.tetlet.2012.10.061

The regioselective synthesis of a series of novel dispiropyrrolidines and dispiropyrrolizidines has been accomplished through intermolecular 1,3-dipolar cycloaddition of azomethine ylides obtained from 1,2-diones like isatin and acenaphthenequinone with acenaphthenone-2-ylidine ketone dipolarophiles in methanol under reflux conditions.

Full text of DOI:10.1016/j.tetlet.2012.10.061

Tetrahedron Letters 53 (2012) 7052–7055
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Tetrahedron Letters
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Facile synthesis of novel dispiroheterocylic derivatives through cycloaddition
of azomethine ylides with acenaphthenone-2-ylidine ketones
⇑
⇑
Srinu Lanka, Sathiah Thennarasu , Paramasivan T. Perumal
Organic Chemistry Division, CSIR-Central Leather Research Institute (CSIR-CLRI), Adyar, Chennai 600020, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The regioselective synthesis of a series of novel dispiropyrrolidines and dispiropyrrolizidines has been
accomplished through intermolecular 1,3-dipolar cycloaddition of azomethine ylides obtained from
1,2-diones like isatin and acenaphthenequinone with acenaphthenone-2-ylidine ketone dipolarophiles
in methanol under reflux conditions.
Received 20 July 2012
Revised 8 October 2012
Accepted 14 October 2012
Available online 23 October 2012
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Acenaphthenone-2-ylidine ketone
Azomethine ylide
1,3-Dipolar cycloaddition
Secondary amino acid
Dispiroheterocylic compounds
Highly functionalized pyrrolidines widely occur in natural prod-
ucts and biologically active compounds.1 Spirooxindole ring sys-
tem is the central skeleton of numerous alkaloids and
pharmacologically important compounds.1a Gelsemine, pseudota-
bersonine, morronside, formosanine, informosanine, and mitraph-
ylline are some of the alkaloids containing spirooxindole ring
systems.2,3 Hence, much attention has been paid to the synthesis
of such interesting compounds. Of particular interest are the spiro-
pyrrodinyloxindole ring systems that are found in alkaloids like
horsifiline, spirotryptostatine A and B, elacomine etc.4 The deriva-
tives of spiropyrrolidinyl oxindole have found wide biological
applications such as antimicrobial and antitumoral agents as well
as inhibitors of human NK-1 receptor.5
The 1,3-dipolar cycloaddition of azomethine ylides with olefins
or acetylenic dipolarophiles is an important general method for the
construction of pyrrolidines and pyrrolizidines.6–8 The synthesis of
spiropyrrolidine, spiropyrrolizidine, and spirothiapyrrolizidine
derivatives via 1,3-dipolar cycloaddition reaction of azomethine
ylides derived from 1,2-diones like isatin, acenaphthenequinone,
has been no report on acenaphthenone-2-ylidine ketones12 em-
ployed as dipolarophiles in cycloaddition of azomethine ylides. In
continuation of our research in the area of 1,3-dipolar cycloaddi-
tions,13 herein, we report the synthesis of the dispiro heterocycles
containing the spirooxindole and spiroacenaphthenone ring sys-
tems through the regioselective cycloaddition reaction of azome-
thine ylides derived from isatin or acenaphthenequinone and
secondary amino acids such as sarcosine and
L-proline with the
acenaphthenone-2-ylidene ketone.14
We first investigated the three-component reaction involving
isatin 1a, sarcosine 2, and (E)-2-(2-(4-methoxyphenyl)-2-oxoethy-
lidene)acenaphthylen-1(2H)-one 4a in methanol under reflux. The
reaction afforded highly substituted dispirooxindole 5a as the only
product in 82% yield. When the reaction mixture was analyzed, no
signals corresponding to the other isomer 50a were observed in
both 1H and 13C NMR spectra. We then probed the effect of solvent
for any noticeable change in regioselectivity and yield. Various
other solvents such as ethanol, toluene, and acetonitrile were used
as the reaction medium to optimize the reaction conditions. The
reaction in methanol reached completion in 70 min, with an iso-
lated yield of 82% making methanol the suitable solvent. The for-
mation of the product was identified by mass spectrometry
which showed a HRMS m/z value of 489.1818 (M+H)+. The regiose-
lective addition and the structure of the product 5a were con-
firmed using spectroscopic data.
and ninhydrin, and secondary amino acids like sarcosine,
L-proline,
and
L
-thioproline has been reported.9 The scope of 1,3-dipolar
cycloaddition reaction in the synthesis of spiro compounds has
been broadened by the use of different dipolarophiles.10
Dipolarophiles derived from isatin and acenaphthenequinone
have also been reported.11 To the best of our knowledge, there
The 1H NMR spectrum of 5a displays a singlet at 2.09 ppm
attributable to the –NCH3 protons of the pyrrolidine ring. The sin-
glet at 3.45 ppm could be ascribed to the –OCH3 protons of the
benzoyl ring. While the two triplets at 3.42 and 4.67 ppm could
⇑
Corresponding authors. Tel.: +91 44 24913289; fax: +91 44 24911589.
E-mail addresses: thennarasu@gmail.com (S. Thennarasu), ptperumal@
gmail.com (P.T. Perumal).
0040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2012.10.061

S. Lanka et al. / Tetrahedron Letters 53 (2012) 7052–7055
7053
be expected from the –NCH2 protons of the pyrrolidine ring, the
triplet at 4.90 ppm must represent the pyrrolidine ring proton at-
tached to benzoyl group. The formation of other regioisomer 50a
is ruled out as it would have exhibited a singlet in the 1H NMR
spectrum for both the –NCH2 protons of pyrrolidine ring and the
pyrrolidine ring proton attached to benzoyl group. Thus, the 1H
NMR spectrum of 5a clearly demonstrates the regiochemistry of
the reaction. A broad singlet appeared at d 9.94 ppm due to the
presence of –NH proton (D2O exchangeable) of the oxindole ring.
The 13C NMR spectrum of 5a shows two peaks at 66.4 and
79.4 ppm arising from the two spiro carbons. The pyrrolidine –
NCH3 and –OCH3 resonate at 35.1 and 55.7 ppm, respectively.
The peaks at 176.4, 196.1, and 203.6 ppm indicate the presence
of oxindole, benzoyl, and acenaphthenone carbonyl groups, respec-
tively. The absence of any other peaks in the 13C NMR spectrum is
an evidence to prove the absence of the other regioisomer. The reg-
ioselectivity observed in the formation of 5a may be due to the ste-
ric factors associated with secondary orbital interactions (SOI)
between the dipolarophile 4a and the ylide derived from isatin
1a and sarcosine 2 (Fig. 2).11
Figure 1. ORTEP diagram of compound 5f.
We broadened the scope of this three-component reaction to
different isatins 1a–e, sarcosine 2, and acenaphthenone2-ylidine
ketones 4a–d. The corresponding dispiropyrrolidines 5a–5h were
obtained in good yields (79–87%) under optimized conditions.
The results are summarized in Table 1 (Scheme 1). The regiochem-
ical outcome of the cycloaddition reaction was confirmed by single
crystal XRD analysis of the cycloadduct 5f (Fig. 1).15
A series of dispiropyrrolizidines 7a–7h were obtained under
the comparable reaction conditions (Scheme 2) by substituting
Table 1
Synthesis of dispiropyrrolidine and dispiropyrrolizidine derivatives
Entry
R1
R2
R3
Secondary amino acid
Product
Yielda (%)
Time (min)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
H
H
H
H
H
H
H
H
Cl
H
H
H
H
H
H
H
Cl
H
H
H
4-Methoxy phenyl
4-Bromo phenyl
4-Phenyl phenyl
2-Acetonaphthyl
4-Methoxy phenyl
4-Methoxy phenyl
4-Methoxy phenyl
4-Methoxy phenyl
4-Methoxy phenyl
4-Bromo phenyl
4-Phenyl phenyl
2-Acetonaphthyl
4-Methoxy phenyl
4-Methoxy phenyl
4-Methoxy phenyl
4-Methoxy phenyl
2
2
2
2
2
2
2
2
6
6
6
6
6
6
6
6
5a
5b
5c
5d
5e
5f
5g
5h
7a
7b
7c
7d
7e
7f
82
85
80
87
87
79
82
80
83
84
88
86
86
89
90
87
70
70
70
65
70
85
80
75
80
75
70
65
70
80
80
80
H
CH3
Allyl
Benzyl
H
H
H
H
H
CH3
Allyl
Benzyl
7g
7h
a
Isolated yield.
O
R3
N
N
R3
R2
O
O
O
R1
H
N
O
COOH
R2
R2
O
5a-h
N
2
O
4a-d
MeOH, reflux
N
N
O
O
R1
R1
1a-e
3a-e
R2
R3
N
O
R1
O
5'a-h
Scheme 1. Synthesis of dispiropyrrolidine derivatives.

7054
S. Lanka et al. / Tetrahedron Letters 53 (2012) 7052–7055
R2
N
and singlet at 3.67 ppm stems from –OCH3 attached to benzoyl
group. In 13C NMR spectrum of 7a shows two peaks at d 73.0 and
78.2 arising from the two spiro carbons. The peaks at d 178.5,
196.6, and 199.5 denote the presence of oxindole, benzoyl and ace-
naphthenone carbonyl groups, respectively. The observed mass of
the product HRMS m/z 515.1946 (M+H)+ further confirmed the for-
mation of compound 7a.
O
R3
N
N
R1
R2
O
O
R3
O
Path A
SOI
We further extended this three-component 1,3-dipolar cycload-
dition reaction to azomethine ylides generated from acenaphthen-
N
O
O
O
R1
equinone 8, sarcosine 2, and
L-proline 6 to prepare the
corresponding dispiropyrrolidines 9a–d and dispiropyrrolizidines
10a–d in good yields (83–90%) as shown in Scheme 3 and
Table 2.15
R1
O
N
The 1H NMR spectrum of 9a, displays a triplet at d 5.11 indicat-
ing the presence of pyrrolidine ring proton attached to benzoyl
group. The two triplets appearing in the range d 3.36 and 4.75 arise
from the –NCH2 protons of pyrrolidine ring. The signals at d 67.6
and 82.7 in the 13C NMR spectrum of 9a, are attributed to the pres-
ence of two spiro carbons. While the peak at d 196.3 is ascribed to
N
N
Path B R2
R2
R3
O
R3
N
O
O
R1
O
Table 2
Synthesis of dispiropyrrolidines and dispiropyrrolizidines
R3
Secondary
amino acid
Product
Yielda
(%)
Time
(min)
Figure 2. Mode of approach of azomethine ylide 3a.
Entry
1
2
3
4
5
6
7
8
4-Methoxyphenyl
4-Bromophenyl
4-Phenyl phenyl
2-Acetonaphthyl
4-Methoxy phenyl
4-Bromo phenyl
4-Phenyl phenyl
2-Acetonaphthyl
2
2
2
2
6
6
6
6
9a
9b
9c
9d
10a
10b
10c
10d
85
83
87
87
88
90
88
86
90
90
90
80
90
90
90
80
sarcosine with another secondary amino acid
yields (83–90%) as summarized in Table 1.
L-proline 6 in good
The structure of compound 7a was confirmed by using 1H, and
13C NMR spectra and by mass analysis. While the multiplet at d
1.89–2.63 in the 1H NMR spectrum suggests the presence of pyrrol-
idine ring, the multiplet at d ꢀ4.63–4.67 ppm indicates –NCH2 pro-
ton of pyrrolidine ring. The doublet at d 5.61 (J = 8.6 Hz) points to
the presence of pyrrolidine ring proton attached to benzoyl group
a
Isolated yield.
R3
O
O
R3
R2
O
CO2H
R2
N
O
N
H
6
+
N
MeOH,reflux
O
N
O
R1
1a-e
O
4a-d
R1
7a-h
Scheme 2. Synthesis of dispiropyrrolizidines.
O
R3
N
N
H
CO2H
2
R3
O
O
O
O
9a-d
O
O
+
O
R3
8
4a-d
N
CO2H
N
H
6
O
10a-d
O
Scheme 3. Cycloaddition of dipolarophiles and azomethine yildes derived from acenaphthenequinone.

S. Lanka et al. / Tetrahedron Letters 53 (2012) 7052–7055
7055
9. (a) Kumar, R. R.; Perumal, S.; Senthilkumar, P.; Yogeeswari, P.; Sriram, D.
Tetrahedron Lett. 2008, 64, 2962; (b) Kumar, R. R.; Perumal, S.; Senthilkumar, P.;
Yogeeswari, P.; Sriram, D. Eur. J. Med. Chem. 2009, 44, 3821; (c) Kumar, R. R.;
Rajesh, S. M.; Perumal, S.; Banerjee, D.; Yogeeswari, P.; Sriram, D. Eur. J. Med.
Chem. 2010, 45, 411; (d) Liu, H.; Dou, G.; Shi, D. J. Comb. Chem. 2010, 12, 633; (e)
Bakthadoss, M.; Kannan, D.; Sivakumar, G. Synthesis 2012, 793; (f) Manian, R. D.
R. S.; Jayashankaran, J.; Raghunathan, R. Tetrahedron 2006, 62, 12357.
10. (a) Rao, J. N. S.; Raghunathan, R. Tetrahedron Lett. 2012, 53, 854; (b) Rajkumar,
V.; Aslam, N. A.; Reddy, C.; Babu, S. A. Synthesis 2012, 4095.
11. (a) Sureshbabu, A. R.; Raghunathan, R. Tetrahedron Lett. 2007, 48, 305; (b)
Sureshbabu, A. R.; Raghunathan, R. Tetrahedron Lett. 2007, 48, 6809; (c) Jain, R.;
Sharma, K.; Kumar, D. Tetrahedron Lett. 1993, 2012, 53; (d) Dandia, A.; Jain, A.
K.; Bhati, D. S. Tetrahedron Lett. 2011, 52, 5333; (e) Liu, H.; Dou, G.; Shi, D. J.
Comb. Chem. 2010, 12, 292.
the benzoyl carbonyl group, peaks at d 203.1 and 204.3 character-
ize the carbonyl groups of the two acenaphthenone moieties. The
observed mass of the product HRMS m/z 524.1859 (M+1) further
confirmed the formation of compound 9a.
Both the dipole and dipolarophile used in the present study are
asymmetrical. The reactions were carried out with the E-isomer of
electron-deficient dipolarophiles. The conformation of azomethine
ylide involved in the formation of 5f appears to be in anti-
conformation, as the syn-conformer shows a large steric energy
according to MM2 and DFT calculations (Supplementary data).
The proposed transition state (Fig. 2) appears to favor secondary
attractive orbital interactions and facilitate the regioselective 1,3-
dipolar cycloaddition.16 However, the role of electronic and steric
effects of the substituents in directing the regioselective addition
cannot be ruled out.16c,17 In conclusion, we have reported for the
first time acenaphthenone-2-ylidine ketones as dipolarophiles in
the 1,3-dipolar cycloaddition with azomethine. We have also re-
ported the synthesis of novel dispiropyrrolidine derivatives in good
yields with very high regioselectivity.
12. Synthesis of acenaphthenone-2-ylidine ketones (4a–d):
A mixture of
acenaphthenequin-one (1.82 g, 10 mmol), acetophenone derivatives
(10 mmol) and powdered KOH (0.5 g) in methanol (25 mL) was refluxed at
60 °C for 1 h and the reaction mixture was allowed to stand overnight at room
temperature. The solid formed was separated by filtration and purified by
crystallization from methanol/dichloromethane (2:1) mixture.
13. Karthikeyan, K.; Sivakumar, P. M.; Doble, M.; Perumal, P. T. Eur. J. Med. Chem.
2010, 45, 3446; (b) Karthikeyan, K.; Saranya, N.; Kalaivani, A.; Perumal, P. T.
Synlett 2010, 2751; (c) Bhaskar, G.; Arun, Y.; Balachandran, C.; Saikumar, C.;
Perumal, P. T. Eur. J. Med. Chem. 2012, 51, 79; (d) Lakshmi, N. V.; Thirumurugan,
P.; Perumal, P. T. Tetrahedron Lett. 2010, 51, 64.
14. Typical experimental procedure for 5, 7, 9, 10: A mixture of isatin 1a–e or
acenaphthenequinone 8 (0.5 mmol), sarcosine 2 or L-proline 6 (0.6 mmol), and
Acknowledgments
acenaphthenone-2-ylidine ketones 4a–d (0.5 mmol) in methanol was refluxed
for an appropriate period of time indicated in the text and cooled to room
temperature. The solid formed was separated by filtration, dried and
crystallized from ethanol to obtain the pure products in good yield (79–90%).
Compound (5a): white solid; mp = 210–212 °C; IR (KBr): 3199, 1709, 1676,
One of the authors, S.L., thanks the Council of Scientific and
Industrial Research (CSIR), New Delhi, India for research fellow-
ship. The authors thank D. Muralidharan, Organic Chemistry Divi-
sion, CLRI, Chennai, for critical suggestions.
1600, 1509, 1466 cmꢁ1 1H NMR (500 MHz, DMSO-d6) d: 2.13 (s, 3H), 3.50 (s,
.
3H), 3.42 (t, 1H, i = 8 Hz), 4.67 (t, 1H, J = 8.5 Hz), 4.90 (t, 1H, J = 8.5 Hz), 6.30 (d,
1H, J = 7.64 Hz), 6.44 (d, 2H, J = 8.4 Hz), 6.85 (t, 3H, J = 7.64 Hz), 6.93 (t, 1H,
J = 7.64 Hz), 7.17–7.19 (m, 3H), 7.37–7.38 (m, 2H), 7.52 (t, 1H, J = 7.64 Hz), 7.62
(t, 1H, J = 4.6 Hz), 7.67 (d, 1H, J = 6.88 Hz), 7.92 (d, 1H, J = 7.64 Hz), 9.96 (s, 1H).
13C NMR (125 MHz, DMSO-d6) d: 35.1, 50.1, 54.2, 55.7, 66.4, 79.4, 109.5, 113.5,
121.6, 124.5, 125.0, 125.2, 127.5, 128.2, 128.4, 129.7, 129.8, 130.6, 132.1, 132.2,
134.8, 141.3, 143.3, 162.7, 176.4, 196.1, 203.6. HRMS: m/z 489.1818 (M+H)+
[Calcd 489.1814].
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.tetlet.2012.
10.061.
Compound (5f): white solid mp = 185–187 °C; IR (KBr): 1718, 1667, 1599,
1507, 1466 cmꢁ1 1H NMR (500 MHz, CDCl3) d: 2.3 (s, 3H), 2.64 (s, 3H), 3.54 (s,
.
3H), 3.60 (t, J = 9 Hz, 1H), 4.92–4.97 (m, 2H), 6.22 (d, 1H, J = 7.64 Hz), 6.30 (d,
2H, J = 8.41 Hz), 6.89 (t, 1H, J = 7.64 Hz), 6.97 (t, 1H, J = 6.88 Hz), 7.25–7.33 (m,
4H) 7.40–7.45 (m, 3H), 7.69 (d, 1H, J = 6.88 Hz), 7.73 (d, 1H, J = 8.41 Hz). 13C
NMR (125 MHz, CDCl3)) d:.25.1, 35.4, 49.7, 54.7, 55.2, 66.7, 79.7, 107.2, 113.0,
121.4, 122.2, 123.5, 124.5, 124.8, 127.0, 127.3, 127.9, 129.3, 129.7, 130.7, 131.3,
132.1, 134.1, 141.6, 144.3, 162.5, 174.8, 195.7, 204.4. HRMS: m/z 503.1967
(M+H)+ [Calcd 503.1965].
References and notes
1. (a) Watson, A. A.; Fleet, G. W. J.; Asano, N.; Molyneux, R. J.; Nash, R. J.
Phytochemistry 2001, 56, 265; (b) O’Hagan, D. Nat. Prod. Rep. 1997, 14, 637; (c)
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1986, 29, 1038.
2. (a) Carroll, W. A.; Grieco, P. A. J. Am. Chem. Soc. 1993, 115, 1164; (b) Early, W. G.;
Oh, T.; Overman, L. E. Tetrahedron Lett. 1988, 29, 3785; (c) Ban, Y.; Taga, N.;
Oishi, T. Chem. Pharm. Bull. 1976, 24, 736; (d) Ban, Y.; Seto, M.; Oishi, T. Chem.
Pharm. Bull. 1975, 23, 2605.
3. (a) Ban, Y.; Taga, N.; Oishi, T. Tetrahedron Lett. 1974, 2, 187; (b) Van Tamelen, E.
E.; Yardley, J. P.; Miyano, M.; Hinshaw, W. B., Jr. J. Am. Chem. Soc. 1969, 26, 7333.
4. Hilton, S. T.; Ho, T. C.; Pljevaljcic, G.; Jones, K. Org. Lett. 2000, 2, 2639.
5. (a) Okita, T.; Isobe, M. Tetrahedron Lett. 1994, 50, 11143; (b) Rosenmond, P.;
Hosseini-Merescht, M.; Bub, C. Liebigs Ann. Chem. 1994, 2, 151; (c) Kornet, M. J.;
Thio, A. P. J. Med. Chem. 1976, 19, 892; (d) Edmondson, S.; Danishefsky, S. J.;
Sepp-Lorenzino, L.; Rosen, N. J. Am. Chem. Soc. 1999, 121, 2147; (e) Cravotto, G.;
Giovenzana, G. B.; Pilot, T.; Sisti, M.; Palmisano, M. J. Org. Chem. 2001, 66, 8447.
6. (a) Pearson, W. H. Studies in Natural Products Chemistry In Rahman, A. U., Ed.;
Elsevier: Amsterdam, 1998; p 323. Vol. 1; (b) Bridges, R. J.; Lovering, F. E.;
Humphrey, J. M.; Stanley, M. S.; Blakely, T. N.; Cristofaro, M. F.; Chamberlin, A.
R. Bioorg. Med. Chem. Lett. 1993, 3, 115.
7. (a) Pellissier, H. Tetrahedron Lett. 2007, 63, 3235; (b) Pinho e Melo, T. M. V. D.
Eur. J. Org. Chem. 2006, 2873; (c) Pandey, G.; Banerjee, P.; Gadre, S. R. Chem. Rev.
2006, 106, 4484; (d) Coldham, I.; Hufton, R. Chem. Rev. 2005, 105, 2765; (e)
Rück-Braun, K.; Freysoldt, T. H. E.; Wierschem, F. Chem. Soc. Rev. 2005, 34, 507;
(f) Kanemasa, S. Synlett 2002, 1371.
Compound (7a): white solid; mp = 180–182 °C; IR (KBr): 3324, 1726, 1692,
1602, 1508, 1466 cmꢁ1 1H NMR (500 MHz, DMSO-d6) d: 1.89–1.94 (m, 2H),
.
2.17–2.21 (m, 2H), 2.53–2.63 (m, 2H), 3.67 (s, 3H), 4.63–4.67 (m, 1H), 5.61 (d,
1H, J = 8.6 Hz), 6.14–6.2 (m, 2H), 6.49 (d, 1H, J = 8 Hz), 6.71(d, 2H, J = 8.6 Hz),
6.76 (t, 1H, J = 7.5 Hz), 7.26 (d, 2H, J = 8 Hz) 7.36 (d, 1H, J = 6.88 Hz), 7.41 (t, 1H,
J = 8 Hz), 7.79 (t, 1H, J = 8 Hz), 7.90 (d, 1H, J = 8.6 Hz), 8.01 (d, 1H, J = 8 Hz), 8.06
(d, 1H, J=6.85 Hz),10.45 (s, 1H). 13C NMR (125 MHz, DMSO-d6) d: 30.6, 31.4,
47.3, 54.2, 55.9, 66.7, 73.0, 78.2, 109.7, 113.9, 120.8, 121.4, 125.4, 125.6, 126.1,
128.1, 128.7, 129.6, 130.0, 130.2, 130.4, 132.4, 136.3, 141.3, 142.4, 163.3, 178.5,
196.6, 199.5. HRMS: m/z 515.1946 (M+H)+ [Calcd 515.1971].
Compound (9a): yellow solid; mp = 220–222 °C; IR (KBr): 1715, 1677, 1596,
1466, 1425 cmꢁ1 1H NMR (500 MHz, DMSO-d6) d: 2.51 (s, 3H), 3.52 (s, 3H),
.
3.36 (t, 1H, J = 8.45, 9 15 Hz), 4.75 (t, 1H, J = 8.4, 9 15 Hz), 5.11 (t, 1H, J = 8.45,
9.15 Hz), 6.45 (d, 2H, J = 8.4), 7.24–7.78 (m, 13H),7.93 (d, 1H, J = 7.65), 13C NMR
(125 MHz, DMSO-d6) d: 35.2, 50.6, 54.9, 55.7, 67.9, 82.7, 113.7, 120.4, 121.6,
124.3, 124.8, 125.7, 126.2, 128.1, 128.2, 128.4, 128.8, 129.6, 129.8, 130.1, 130.5,
131.8, 132.0, 132.2, 134.4, 134.5, 140.9, 141.6, 162.8, 196.3, 203.1, 204.3.
HRMS: m/z 524.1859 (M+H)+ [Calcd 524.1856].
15. The detailed X-ray crystallographic data (CCDC number for 5f is 892288) is
available from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge, CB2 1EZ, UK.
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