Synthesis of ethyl 2-arylaminoimidazo[2,1-b]benzothiazole-3-carboxylates

Article abstract of DOI:10.1002/jccs.200400196

3-Arylamino-4-ethoxycarbonylisoxazol-5(2H)-ones, substituted on nitrogen with a benzothiazole group, reacts with triethylamine in ethanol under reflux conditions to provide a convenient synthesis of ethyl 2-arylaminoimidazo[2,1-b] benzothiazole-3-carboxyl

Full text of DOI:10.1002/jccs.200400196

Journal of the Chinese Chemical Society, 2004, 51, 1347-1352
1347
Synthesis of Ethyl 2-Arylaminoimidazo[2,1-b]benzothiazole-3-carboxylates
Jabbar Khalafy,* Ali Reza Molla Ebrahimlo and Karim Akbari Dilmaghani
Chemistry Department, Urmia University, Urmia 57159, Iran
3-Arylamino-4-ethoxycarbonylisoxazol-5(2H)-ones, substituted on nitrogen with a benzothiazole group,
reacts with triethylamine in ethanol under reflux conditions to provide a convenient synthesis of ethyl 2-aryl-
aminoimidazo[2,1-b]benzothiazole-3-carboxylates.
Keywords: Isoxazolones; 2-Chlorobenzothiazole; Imidazobenzothiazoles; Base induced rearrangement;
Triethylamine.
INTRODUCTION
The synthesis of isoxazol-5(2H)-one with benzothi-
Base-catalysed rearrangement of isoxazolinyl hetero-
cycle 1a using a solution of sublimed potassium t-butoxide in
dry tetrahydrofuran at 40 °C gave ethyl 2-hydroxy-4-oxo-
4H-pyrimido[2,1-b]benzothiazole-3-carboxylate 4.3
azole substituted on nitrogen 1a has been reported by Prager
and co-workers1 as shown in Scheme I.
S
Scheme I
N
N
OH
O
CO2Et
H
S
R
4
N
N
130oC / 15 min
O
R
S
N
N
O
We have recently reported4 that the reaction of certain
2-aryl-3-arylaminoisoxazolones 5 with triethylamine leads
to the formation of indoles 6 and carbon dioxide, an outcome
that is formally the same as that achieved by photolysis or py-
rolysis5 (Scheme II).
EtO2C
O
O
Cl
EtO2C
1a R=H
It has been reported2 that the 2-benzothiazol-2-yl iso-
xazolones 1a and 2b gave the corresponding imidazobenzo-
thiazoles 2a and 2b respectively on photolysis in ethyl ace-
tate/trifluoroacetic acid, and the acrylate 3 was obtained from
the photolysis of 1a in methanol.
Scheme II
ArHN
Ar
N
TEA / EtOH
N H
O
EtO C
2
N
O
H
CO Et
2
6
5
We have also reported6 that 3-(4-substituted phenyl)-
aminoisoxazol-5(2H)-ones, substituted on nitrogen with a
nitropyridine group, react with triethylamine to give imi-
dazo[1,2-a]pyridines and indoles. With 4-bromophenyl and
* Corresponding author. Fax: (+98)441-3443442; e-mail: jkhalafi@yahoo.com; J.khalafi@mail.urmia.ac.ir

1348 J. Chin. Chem. Soc., Vol. 51, No. 6, 2004
Khalafy et al.
4-methylphenyl group substituents only imidazopyridines
7a-b are formed, but the 4-methoxyphenyl derivative gave a
3:1 mixture of corresponding imidazo[2,1-a]pyridine 7c and
2-pyridylaminoindole 8, respectively.
Scheme III
R
S
S
C
CH(CO2Et)2
NH2OH
N
HN
NaCH(CO2Et)2
EtOH
H
HN
N
O
R
R
R
EtO2C
O
10
11
9
N
O2N
NH
R=H,Br,Me
HN
N
N
OMe
EtO2C
EtO2C
N
H
The rearrangement of 12, as shown in Scheme IV, pro-
ceeded in 45-62% yield in refluxing ethanol for 24 h in the
presence of triethylamine. The reaction pathway leading to
the imidazobenzothiazole is consistent with our earlier sug-
gestion for the formation of imidazopyridines, which is con-
sistent with the electronic requirements of the reaction, as
shown in Scheme V, or with the alternative pathway sug-
gested by Prager and co-workers.9
NO2
8
7a R=Br
7b R=Me
7c R=OMe
Here we describe the synthesis of new N-substituted
derivatives of m-substituted 3-(phenyl)aminoisoxazol-5(2H)-
ones 11 with a benzothiazole group substituted on N-2 12,
and their rearrangement in the presence of triethylamine to
produce ethyl 2-arylaminoimidazo[2,1-b]benzothiazole-3-
carboxylate 13, as shown in Scheme IV.
CONCLUSION
The base catalysed rearrangements of 3-arylaminoiso-
xazolones substituted on nitrogen with a benzothiazole group
appears to be generally applicable to the synthesis of imida-
zobenzothiazoles, which are clearly suitable synthetic inter-
mediates for a series of new planar polycyclic heterocycles
that could be expected to intercalate with DNA.10,11
RESULTS AND DISCUSSION
The required isoxazolones 12 were synthesized by re-
action of 2-chlorobenzothiazole with 2H-isoxazolones 11,
which in turn were made by a modification of the procedure
of Worrall.7,8 Thus, the reaction of the sodium salt of diethyl
malonate in ethanol with arylisothiocyanates 9 gave the
thiocarbamates 10 in high yield, and these were converted to
the corresponding isoxazolone 11 by reaction with 2 equiv of
hydroxylamine (Scheme III).
EXPERIMENTAL
General procedures
Freshly distilled solvents were used throughout, and
anhydrous solvents were dried according to Perrin and
Amareg.12 1H (400 MHz) and 13C (75 MHz) NMR measure-
N-arylation of 11 with 2-chlorobenzothiazole in chlo-
roform or toluene under reflux conditions gave the corre-
sponding N-substituted isoxazolones 12 in fair yield.
Scheme IV

Synthesis of Ethyl 2-Arylaminoimidazo[2,1-b]
J. Chin. Chem. Soc., Vol. 51, No. 6, 2004 1349
Scheme V
ments were recorded on a Brucker 400 spectrometer in deute-
riochloroform with tetramethylsilane as internal standard,
unless otherwise stated. Infrared spectra were recorded on a
Thermonicolet (Nexus670) FT-infrared spectrometer, using
sodium chloride cells, measured as Nujol mulls or films.
Mass spectra were recorded on a Varian Matt 311 spectrome-
ter and relative abundance of fragments are quoted in paren-
theses after the m/z values. Melting points were determined
on a Philip Harris C4954718 apparatus and are uncorrected.
Microanalyses were performed on a Carlo-Erba Analyzer
1104 at the University of Giessen, Germany.
3H, J = 7.1 Hz), 2.70 (q, 2H, J = 7.1 Hz), 4.272 (q, 2H, J = 7.1
Hz), 5.061 (s, 1H), 7.224 (t, 1H, J = 8.06 Hz), 7.361 (bd, 1H, J
= 7.95 Hz), 8.668 (bd, 1H, J = 8.06 Hz), 8.057 (t, 1H, J = 1.9
Hz), 10.833 (bs, NH). FT-IR umax 3296, 1747, 1590, 1541,
1476, 1394, 1168, 1023, 680, 784 cm-1.
Diethyl (3-methylphenyl)thiocarbamoylmalonate (10,
R=Me)
This compound was prepared as described above, using
3-methylphenyl isothiocyanate (1.3 g, 8.7 mmol) and stirring
for a further 1 h after addition of 3-methylphenyl isothiocya-
nate to the diethyl malonate salt to give diethyl (3-methyl-
phenyl)thiocarbamoyl malonate (1.924, 71.25%) as pale yel-
low solid, m.p. 53-54 ºC. 1H NMR d 1.33 (t, 6H, J = 7.2 Hz),
2.38 (s, 3H), 4.29 (q, 2H, J = 7.2 Hz), 4.30 (q, 2H, J = 7.2 Hz),
5.09 (s, 1H), 7.09 (t, 1H, J = 7.8 Hz), 7.55 (bs, 1H), 7.61 (bd,
1H, J = 8 Hz), 10.75 (s, exchanged by D2O addition, 1H, NH).
FT-IR umax 3252, 1752, 1731, 1592, 1556, 1422, 1296, 1148,
1027, 858, 798, 717 cm-1.
Diethyl (3-bromophenyl)thiocarbamoylmalonate (10,
R=Br)
In a 100 mL round-bottomed flask, absolute ethanol (50
mL) was reacted with sodium (2.9 g, 0.126 mol) and after
cooling to room temperature diethyl malonate (20 g, 18.95
mL, 0.126 mol) was added. The reaction mixture was stirred
at room temperature for 15 min; 3-bromophenyl isothiocya-
nate (26.96 g, 0.126 mol) was added and the stirring was con-
tinued for a further 6 h, during which a yellowish white pre-
cipitate of sodium diethyl (3-bromophenyl)thiocarbamoyl-
malonate salt was formed. The salt was collected and washed
with light petroleum ether (b.p. 30-60 ºC) (3 ´ 50 mL) to give
yellow crystals m.p. 157-158 ºC (34.22 g, 70%). The pure salt
was dissolved in water (40-50 mL) and neutralized with
dropwise addition of HCl (10%) to maintain the pH at 7. The
product was extracted with chloroform and the extract was
washed with water (3 ´ 50 mL) and dried over anhydrous
Na2SO4. Removal of solvent gave (10, R=Br) as a yellow oil
(25.5 g, 68%). 1H NMR d 1.292 (t, 3H, J = 7.1 Hz), 1.295 (t,
Ethyl 3-(3-bromophenyl)amino-5-oxo-2,5-dihydroiso-
xazol-4-carboxylate (11, R=Br)
To a solution of hydroxylamine hydrochloride (2 g,
28.8 mmol) in water (8 mL), potassium bicarbonate (2.8 g, 28
mmol) was added slowly. Ethanol (32 mL) was added and the
resulting potassium chloride was filtered off.
Diethyl (3-bromophenyl) thiocarbamoylmalonate (3.4
g, 9 mmol) was added to the filtrate and the mixture refluxed
for 24 h. The reaction mixture was acidified with dilute hy-
drochloric acid and the white precipitate was collected by
vacuum filtration. The white solid was recrystallized from

1350 J. Chin. Chem. Soc., Vol. 51, No. 6, 2004
Khalafy et al.
ethanol to give the desired product (2.51 g, 85%) as colourless
crystals m.p. 100-102 ºC. Anal. Calc for C12H11BrN2O4.H2S:
C, 41.73; H, 3.19; N, 8.11%; found: C, 41.87; H, 3.22; N,
1.34 Hz), 7.39 (t, 1H, J = 1.92 Hz), 7.44 (td, 1H, J1 = 7.64 Hz,
J2 = 1.29 Hz), 7.69 (dd, 1H, J1 = 8.15 Hz, J2 = 0.96 Hz), 7.79
(dt, 1H, J1 = 7.8 Hz, J2 = 0.97 Hz), 10.17 (s, 1H, NH). 13C
NMR d 14.31, 61.17, 79.20, 121.03, 121.63, 122.63, 122.99,
125.74, 126.04, 127.10, 129.51, 130.38, 133.35, 138.02,
149.10, 157.07, 161.23, 163.02, 163.81. FT-IR umax 3206,
1775, 1712, 1572, 1475, 1441, 1381, 1227, 1178, 1051, 956,
766 cm-1; MS m/z (%) 461 (M+, 12%), 459 (M+, 11%), 417
(82), 415 (71), 371 (48), 369 (40), 334 (25), 294 (28), 291
(27), 290 (100), 262 (30), 224 (27), 177 (33), 161 (34), 150
(40), 135 (26), 134 (33), 108 (29), 44 (65) and HRMS m/z
458.98883 (C19H14BrN3O4S requires 458.98884).
1
8.18%. H NMR (D6-DMSO+CDCl3) d 1.38 (t, 3H, J = 7.1
Hz), 4.37 (q, 2H, J = 7.1 Hz), 6.15 (bs, 1H, NH), 7.23 (dt, 1H,
J1 = 8.2 Hz, J2 = 1.8 Hz), 7.28 (t, 1H, J = 7.8 Hz), 7.33 (dt, 1H,
J1 = 7.8 Hz, J2 = 1.6 Hz), 7.51 (t, 1H, J = 1.8 Hz), 9.38 (bs, 1H,
NH),13C NMR(D6-DMSO+CDCl3) d 14.49, 60.26, 75.21,
119.80, 122.92, 123.82, 128.24, 130.95, 137.58, 162.85,
165.37, 166.72. FT-IR umax 3512, 3297, 1710, 1701, 1590,
1478, 1413, 1323, 1203, 1116, 1011, 794, 734 cm-1; MS m/z
(%) 328 (M+, 66%), 326 (M+, 68%), 282 (81), 280 (70), 201
(26), 197 (16), 171 (26), 157 (36), 91 (31), 90 (32), 76 (21),
63 (24), 45 (19), 44 (100), 40 (47), 36 (23) and HRMS m/z
325.99021 (C12H11BrN2O4 requires 325.99022).
Ethyl 2-(benzothiazol-2-yl)-3-(3-methylphenyl)amino-5-
oxo-2,5-dihydro-4-carboxylate (12, R=Me)
This compound was prepared as described above, using
the corresponding isoxazolone (11, R=Me) (70 mg, 0.27
mmol) and 2-chlorobenzothiazole (45.8 mg, 0.27 mmol) to
give the desired product as white prisms (50 mg, 50%) after
recrystalization from ethanol, m.p. 159-161 ºC. Anal. Calc
for C20H17N3O4S: C, 60.74, H, 4.33, N, 10.62%; found: C,
60.49; H, 4.14; N, 10.93%. 1H NMR d 1.3 (t, 3H, J = 7.1 Hz),
2.19 (s, 3H), 4.28 (q, 2H, J = 7.1 Hz), 6.85 (bd, 1H, J = 7.47
Hz), 6.98 (bd, 1H, J = 8.1 Hz), 7.00 (bs, 1H), 7.08 (t, 1H, J =
7.6 Hz), 7.36 (td, 1H, J1 = 8.1 Hz, J2 = 0.94 Hz), 7.42 (td, 1H,
J1 = 7.6 Hz, J2 = 0.85 Hz), 7.69 (bd, 1H, J = 8 Hz), 7.77 (dd,
1H, J1 = 7.9 Hz, J2 = 0.65 Hz), 10.07 (s, exchanged by D2O
addition, 1H, NH). 13C NMR d 14.31, 21.11, 60.95, 78.64,
119.63, 121.57, 123.09, 123.23, 125.97, 126.94, 127.33,
129.01, 133.67, 136.44, 139.30, 149.18, 157.33, 161.87,
Ethyl 3-(3-methylphenyl)amino-5-oxo-2,5-dihydroiso-
xazol-4-carboxylate (11, R=Me)
The compound was prepared as described above using
diethyl (3-methylphenyl)thiocarbamoylmalonate (1.1 g, 3.5
mmol) and refluxing for 24 h to give the desired product as
colourless crystals (0.7 g,75%), m.p. 109-111 ºC. 1H NMR
(D6-DMSO+CDCl3) d 1.38 (t, 3H, J = 7.1 Hz), 2.37 (s, 3H),
4.35 (q, 2H, J = 7.1 Hz), 7.02 (bd, 1H, J = 7.6 Hz), 7.07 (bd,
1H, J = 7.9 Hz), 7.1 (bs, 1H), 7.27 (t, 1H, J = 7.8 Hz), 9.31 (s,
1H, NH). 13C NMR (D6-DMSO+CDCl3) d 14.53, 21.34,
60.17, 74.82, 118.19, 121.82, 126.42, 129.47, 135.90,
139.75, 163.35, 165.64, 166.66. FT-IR u
3519, 3316,
max
1710, 1678, 1578, 1324, 1226, 1169, 1113, 1000, 795, 725
cm-1.
163.49. FT-IR u
3204, 1774, 1705, 1576, 1514, 1443,
max
Ethyl 2-(benzothiazol-2-yl)-3-(3-bromophenyl)amino-5-
oxo-2,5-dihydro-4-carboxylate (12, R=Br)
1382,1232, 958, 767 cm-1.
Ethyl 3-(3-bromophenyl)amino-5-oxo-2,5-dihydroiso-
xazol-4-carboxylate (100 mg, 0.3 mmol) and 2-chlorobenzo-
thiazole (51 mg, 0.3 mmol) were refluxed in chloroform or
toluene (5 mL) for 48 h. The solvent was removed under re-
duced pressure. On addition of n-hexane (10 mL) to the resi-
due (colourless oil) a white precipitate was formed. The pre-
cipitate was filtered and recrystallized from ethanol to give
ethyl 2-(benzothiazol-2-yl)-3-(3-bromophenyl)amino-5-oxo-
2,5-dihydro-4-carboxylate as white prisms (84.4 mg, 60%)
m.p. 153-155 ºC. Anal. Calc for C19H14BrN3O4S: C, 49.56, H,
3.04, N, 9.13%; found: C, 49.56; H, 2.71; N, 9.02%. 1H NMR
d 1.32 (t, 3H, J = 7.1 Hz), 4.30 (q, 2H, J = 7.1 Hz), 7.08 (t, 1H,
J = 7.9 Hz), 7.14 (dt, 1H, J1 = 8.65 Hz, J2 = 1.59 Hz), 7.20 (dt,
1H, J1 = 7.79 Hz, J2 = 1.55 Hz), 7.38 (td, 1H, J1 = 7.6 Hz, J2 =
Ethyl 2-(benzothiazol-2-yl)-3-(phenyl)amino-5-oxo-2,5-
dihydro-4-carboxylate (12, R=H)
This compound was prepared as described above, using
the corresponding isoxazolone (11, R=H)7 (100 mg, 0.4
mmol) and 2-chlorobenzothiazole (67.85 mg, 0.4 mmol) to
give the desired product as white prisms (100 mg, 65%) after
recrystalization from ethanol, m.p. 141-142 ºC. Anal. Calc
for C19H15N3O4S: C, 59.83, H, 3.96, N, 11.02%; found: C,
60.00; H, 3.72; N, 11.05%. 1H NMR d 1.29 (t, 3H, J = 7.1 Hz),
4.27 (q, 2H, J = 7.1 Hz), 7.04-7.08 (m, 1H), 7.18-7.23 (m,
4H), 7.35 (td, 1H, J1 = 7.6 Hz, J2 = 1.3 Hz), 7.40 (td, 1H, J1 =
7.6 Hz, J2 = 1.3 Hz), 7.65 (dd, 1H, J1 = 7.9 Hz, J2 = 0.88 Hz),
7.76 (dd, 1H, J1 = 7.75 Hz, J2 = 1 Hz), 10.15 (s, exchanged by
D2O addition, 1H, NH). 13C NMR d 14.30, 60.97, 78.72,

Synthesis of Ethyl 2-Arylaminoimidazo[2,1-b]
J. Chin. Chem. Soc., Vol. 51, No. 6, 2004 1351
121.56, 122.48, 123.01, 125.92, 126.54, 126.93, 129.20,
133.47, 136.72, 149.12, 157.23, 161.68, 163.35, 163.99.
FT-IR umax 3190, 1782, 1686, 1569, 1497, 1456, 1442, 1378,
1282, 1224, 1177, 950, 765 cm-1.
1417, 1374, 1281, 1167, 1156, 1087, 752 cm-1.
Ethyl 2-(phenyl)aminoimidazo[2,1-b]benzothiazole-3-car-
boxylate (13, R=H)
The isoxazolone (12, R=H) (100 mg, 0.2624 mmol) and
triethylamine (0.13 mL) were refluxed in ethanol (10 mL) for
24 h. The reaction mixture was left to cool to rt, and the re-
sulting precipitate was collected to give ethyl 2-(3-methyl-
phenyl)aminoimidazo[2,1-b]benzothiazole-3-carboxylate
(13, R=H) as cream crystals (55 mg, 62%), m.p. 157-159 ºC.
Anal. Calc for C18H15N3O2S: C, 64.08; H, 4.48; N, 12.45%;
found: C, 63.79; H, 4.48; N, 12.50%. 1H NMR d 1.53 (t, 3H, J
= 7.1 Hz), 4.50 (q, 2H, J = 7.1 Hz,), 7.00 (bt, 1H, J = 7.4 Hz),
7.25-7.369 (m, 2H), 7.31 (td, 1H, J1 = 7.3 Hz, J2 = 1 Hz), 7.65
(dd, 1H, J1 = 7.2 Hz, J2 = 0.75 Hz), 7.63 (bd, 2H, J = 7.7 Hz),
7.43 (td, 1H, J1 = 7.3 Hz, J2 = 1.2 Hz), 8.56 (bs, exchanged by
D2O addition 1H, NH), 8.83 (bd, 1H, J = 6.6 Hz). 13C NMR d
14.69, 60.50, 116.81, 118.32, 121.85, 123.50, 124.37,
126.38, 128.67, 129.11, 134.46, 140.32, 151.99, 160.34.
FT-IR umax 3309, 1644, 1601, 1569, 1494, 1463, 1422, 1370,
1273, 1171, 1087, 1065, 742 cm1.
Ethyl 2-(3-bromophenyl)aminoimidazo[2,1-b]benzo-
thiazole-3-carboxylate (13, R=Br)
The isoxazolone (12, R=Br) (100 mg, 0.217 mmol) and
triethylamine (0.13 mL) were refluxed in ethanol (10 mL) for
24 h. The reaction mixture was left to cool to rt, and the re-
sulting precipitate was collected to give ethyl 2-(3-bromo-
phenyl)amino imidazo[2,1-b]benzothiazole-3-carboxylate
(13, R=Br) as yellow needles (50 mg, 55%), m.p. 158-160 ºC.
Anal. Calc for C18H14BrN3O2S: C, 51.92; H, 3.36; N, 10.06%;
found: C, 51.87; H, 2.99; N, 10.09%. 1H NMR d 1.54 (t, 3H, J
= 7.1 Hz), 4.52 (q, 2H, J = 7.1 Hz), 7.11 (ddd, 1H, J1 = 7.88
Hz, J2 = 1.7 Hz, J3 = 1 Hz), 7.18 (t, 1H, J = 7.95 Hz), 7.34 (td,
1H, J1 = 7.7 Hz, J2 = 1.14 Hz), 7.46 (td, 1H, J1 = 7.9 Hz, J2 =
1.3 Hz), 7.50 (ddd, 1H, J1 = 8 Hz, J2 = 2.1 Hz, J3 = 1 Hz), 7.69
(dd, 1H, J1 = 7.95 Hz, J2 = 0.88 Hz), 7.95 (t, 1H, J = 7.95 Hz),
8.62 (bs, 1H, NH), 8.84 (bd, 1H, J = 8.35 Hz). 13C NMR d
14.71, 60.72, 116.69, 116.89, 120.83, 122.89, 123.62,
124.59, 124.63, 126.48, 128.79, 130.33, 134.34, 141.52,
141.60, 151.77, 160.28. FT-IR umax 3296, 1641, 1607, 1593,
1556, 1457, 1412, 1375, 1292, 1174, 1085, 1062, 753 cm-1;
MS m/z (%) 417 (M+, 70%), 415 (M+, 62%), 317 (11), 369 (9),
290 (100), 289 (23), 263 (15), 262 (21), 161 (15), 160 (12),
134 (13), 130 (12), 102 (10), 40 (18) and HRMS m/z
414.99900 (C18H14BrN3O2S requires 414.99901).
ACKNOWLEDGMENTS
We are grateful to Professor R. H. Prager (Flinders Uni-
versity) for his valuable comments, and to Professor J.
Ipaktschi (Giessen University) for determining the micro-
analysis and mass spectra.
Ethyl 2-(3-methylphenyl)aminoimidazo[2,1-b]benzo-
thiazole-3-carboxylate (13, R=Me)
Received January 27, 2004.
The isoxazolone (12, R=Me) (100 mg, 0.253 mmol)
and triethylamine (0.13 mL) were refluxed in ethanol (10
mL) for 24 h.The reaction mixture was left to cool to rt, and
the resulting precipitate was collected to give ethyl 2-(3-
methylphenyl)aminoimidazo[2,1-b]benzothiazole-3-carbox
ylate (13, R=Me) as yellow needles (0.04 g, 45%), m.p.
123-125 ºC. 1H NMR d 1.53 (t, 3H, J = 7.1 Hz), 2.38 (s, 3H),
4.51 (q, 2H, J = 7.1 Hz), 6.83 (bd, 1H, J = 7.6 Hz), 7.23 (t, 1H,
J = 7.6 Hz), 7.33 (bt, 1H, J = 7.5 Hz), 7.42-7.48 (m, 3H), 7.67
(bd, 1H, J = 7.8 Hz), 8.52 (bs, exchanged by D2O addition,
1H, NH), 8.86 (bd, 1H, J = 7.3 Hz). 13C NMR d 14.73, 21.67,
60.48, 115.54, 116.84, 119.01, 123.53, 123.60, 123.72,
124.36, 126.40, 126.52, 128.98, 134.51, 138.98, 140.23,
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