Domino reactions in the synthesis of benzothieno[2,3-c]pyridines. New one-pot method of preparing 2-([1]benzothieno-[2,3-c]pyridin-1-yl)benzoic acids and 8,13b-dihydro[1]benzothieno[2',3':3,4]pyrido-[2,1-a]isoindol-5(7h)-ones

Article abstract of DOI:10.1007/s10593-012-1041-z

A series of previously unknown 2-([1]benzothieno[2,3-c]pyridin-1-yl)benzoic acids and 8,13b-dihydro-[1]benzothieno[2',3':3,4]pyrido[2,1-a]isoindol-5(7H)- ones has been synthesized using domino reactions, taking place at the cyclization of 2-[3-oxo-4-(phenylsulfanyl)butyl]-1,3-isoindolinediones in polyphosphoric acid.

Full text of DOI:10.1007/s10593-012-1041-z

Chemistry of Heterocyclic Compounds, Vol. 48, No. 4, July, 2012 (Russian Original Vol. 48, No. 4, April, 2012)
DOMINO REACTIONS IN THE SYNTHESIS OF
BENZOTHIENO[2,3-c]PYRIDINES. NEW ONE-POT
METHOD OF PREPARING 2-([1]BENZOTHIENO-
[2,3-c]PYRIDIN-1-YL)BENZOIC ACIDS AND
8,13b-DIHYDRO[1]BENZOTHIENO[2',3':3,4]PYRIDO-
[2,1-a]ISOINDOL-5(7H)-ONES
V. S. Tolkunov1*, A. B. Eres'ko1, A. I. Khizhan1, A. V. Mazepa2,
G. V. Palamarchuk3, O. V. Shishkin3,4, and S. V. Tolkunov1
A series of previously unknown 2-([1]benzothieno[2,3-c]pyridin-1-yl)benzoic acids and 8,13b-dihydro-
[1]benzothieno[2',3':3,4]pyrido[2,1-a]isoindol-5(7H)-ones has been synthesized using domino
reactions, taking place at the cyclization of 2-[3-oxo-4-(phenylsulfanyl)butyl]-1,3-isoindolinediones in
polyphosphoric acid.
Keywords: 2-([1]benzothieno[2,3-c]pyridin-1-yl)benzoic acids, 8,13b-dihydro[1]benzothieno[2',3':3,4]-
pyrido[2,1-a]isoindol-5(7H)-ones, 2-[3-oxo-4-(phenylsulfanyl)butyl]-1,3-isoindolinediones, cyclization,
domino reaction, polyphosphoric acid .
Benzothieno[2,3-c]pyridines possess a broad spectrum of biological activity [1, 2]. At the present time,
several methods exist for their synthesis. The most widespread methods for obtaining them are based on the
aromatization of 1,2,3,4-tetrahydrobenzothieno[2,3-c]pyridines and 3,4-dihydrobenzothieno[2,3-c]pyridines,
which in turn are synthesized by the Pictet-Spengler and Bischler-Napieralski reactions starting from
2-(benzo[b]thien-3-yl)ethylamines [2-6]. As a rule, these are multistage processes with low final yields of the
desired products. In recent time, domino processes, which involve several sequential reactions and are carried
out without isolating the intermediate products, have been largely developed.
_______
*To whom correspondence should be addressed, e-mail: s_tolkunov@yahoo.com.
1L. M. Litvinenko Institute of Physical-Organic Chemistry and Coal Chemistry, National Academy of Sciences
of Ukraine, 70 R. Luxemburg St., Donetsk 83114, Ukraine.
2A. V. Bogatskii Physicochemical Institute, National Academy of Sciences of Ukraine, 86 Lustdorfska doroga,
Odessa 65080, Ukraine; e-mail: almazepa@rambler.ru.
3NTK "Institute of Monocrystals", National Academy of Sciences of Ukraine, 60 Lenin Ave., Kharkiv 61001,
Ukraine; e-mail: shishkin@xray.isc.kharkov.com
4Kharkov V. N. Karazin National University, 4 Svobody Sq., Kharkiv 61077, Ukraine.
_________________________________________________________________________________________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No 4, pp. 715-720, April, 2012. Original
article submitted February 7, 2012.
666
0009-3122/12/4804-0666©2012 Springer Science+Business Media, Inc.

The aim of the present work was the study of one-pot processes leading to the preparation of
benzothieno[2,3-c]pyridines.
As starting materials, we used 2-[3-oxo-4-(phenylsulfanyl)butyl]-1,3-isoindolinediones 3a-c, obtained
from thiophenols 2a-c and 2-(4-bromo-3-oxobutyl)-1,3-isoindolinedione (1). Two reaction centers are present in
compounds 3a-c, enabling the construction of both the benzo[b]thiophene and the pyridine rings sequentially.
O
Br
O
R
Pyridine
O
N
N
O
S
R
+
O
HS
O
1
2a–c
a R = H, b R = Me, c R = Cl
3a–c
We found that on heating 2-[3-oxo-4-(phenylsulfanyl)butyl]-1,3-isoindolinediones 3a,b in
polyphosphoric acid (PPA) in a medium of chlorobenzene at 100oC for 3 h a series of sequential reactions
occurs leading in the end to benzothieno[2,3-c]pyridine derivatives. Initially the closure of the benzothiophene
ring and the intermediate formation of 2-[(2-benzo[b]thiophen-3-yl)ethyl]-1,3-isoindolinediones 4a,b occur,
which under the reaction conditions undergo cyclization to 5-oxo-7,8-dihydro-5H-[1]benzo-
thieno[2',3':3,4]pyrido[2,1-a]isoindolin-6-ium derivatives 5a,b.
O
O
N+
R
N
H+
PPA
3a,b
R
– H2O
100°C
S
O
S
5a,b
4a,b
H2O
R
– H+
O
N
R
N
COOH
+
S
S
6a,b
a R = H, b R = Me
7a,b
The pyridine ring formation process proceeds via Bischler-Napieralski type reaction. However, upon
work up of the reaction mixture, in place of the expected compounds 5a,b, a mixture of 2-([1]benzothieno[2,3-c]-
pyridin-1-yl)benzoic acids 6a,b and 8,13b-dihydro[1]benzothieno[2',3':3,4]pyrido[2,1-a]-isoindol-5(7H)-ones
7a,b was obtained, which is possibly the result of disproportionation of cations 5a,b.
Three products were isolated on cyclizing 2-[3-oxo-4-(4-chlorophenylsulfanyl)butyl]-1,3-isoindoline-
dione (3c), namely 2-(6-chloro[1]benzothieno[2,3-c]pyridin-1-yl)benzoic acid (6c) (42%), 2-[(2-benzo[b]thiophen-
3-yl)ethyl]-1,3-isoindolinedione (4c) (10%) and an unknown product with molecular mass 483, the composition of
which is to be determined. The structure of compound 4c was confirmed by an counter synthesis from 2-(5-chlo-
ro[1]benzothiophen-3-yl)ethylamine (8) and phthalic anhydride. 10-Chloro-8,13b-dihydro[1]benzo-thieno-
[2',3':3,4]pyrido[2,1-a]isoindol-5(7H)-one (7c) was not detected in the reaction products.
667

O
N
Cl
N
PPA
COOH
3c
+
Cl
100°C
S
O
S
O
4c
NH2
O
Cl
O
4c
S
8
Fig. 1. Molecular structure of compound 7a with representation of atoms by ellipsoids of thermal
vibrations with 50% probability.
8,13b-Dihydro[1]benzothieno[2',3':3,4]pyrido[2,1-a]isoindol-5(7H)-one (7a) was identical in physico-
chemical properties to the compound obtained previously in [4]. The structure of compound 7a was proved by
X-ray structural analysis (Fig. 1). The tetrahydropyridine ring has a "distorted half-chair" conformation
(parameters of folding, S = 0.75, Θ = 35.33, and Ψ = 26.03 [7]). The C(12) and N(1) atoms deviate from the
plane of the remaining ring atoms by 0.39 and -0.26 Å respectively. The unflattening of the ring is also aided by
the steric repulsion between the bicyclic fragments (shortened intramolecular contact S(1)···C(6) 3.44 Å, sum of
van der Waals radii 3.55 Å [8]).
1
In the H NMR spectra of 2-([1]benzothieno[2,3-c]pyridin-1-yl)benzoic acids 6a-c, the signals for the
methylene group, characteristic of the starting compounds 3a-c, were missing, and only signals for the aromatic
protons were observed. Signals of the pyridine ring protons were displayed as doublets in the 8.1 and 8.6 ppm
region with coupling constant J = 5.2 Hz. The 1H NMR spectra of 8,13-dihydro[1]benzothieno[2',3':3,4]pyrido-
[2,1-a]isoindol-5(7H)-ones 7a,b and 1-aryl-1,2,3,4-tetrahydrobenzothieno[2,3-c]pyridines were close in the
aliphatic part [6]. Each proton of the CH2CH2N fragment was observed as a separately standing multiplet.
In summary, a new one-pot method has been developed for preparing substituted 2-([1]benzothieno-
[2,3-c]pyridin-1-yl)benzoic acids and 8,13b-dihydro[1]benzothieno[2',3':3,4]pyrido[2,1-a]isoindol-5(7H)-ones,
based on domino reactions proceeding on cyclization of 2-[3-oxo-4-(phenylsulfanyl)butyl]-1,3-isoindolinedione in
polyphosphoric acid. 8,13b-Dihydro[1]benzothieno[2',3':3,4]pyrido[2,1-a]isoindol-5(7H)-ones are heteroanalogs of
alkaloid nuevamine [9], consequently, the procedure developed by us may be used in the synthesis of substances
possessing biological activity.
668

EXPERIMENTAL
1
13
The H and C NMR spectra were recorded on a Bruker DRX-400 spectrometer (400 and 100 MHz
respectively) in DMSO-d6, internal standard was TMS. The mass spectra were recorded on a MX1321
spectrometer using direct insertion of sample, ionization was by electron impact, ionizing voltage 70 eV,
temperature of ionization chamber 220oC. Ions the intensity of which exceeded 5% are given. Data of elemental
analysis were obtained on a Vario MICROcube CHN analyzer. Analysis of sulfur content was performed by
titration of sulfate anion after combustion in oxygen. Melting points were determined on a Boetius hot stage
apparatus.
2-[3-Oxo-4-(phenylsulfanyl)butyl]-1,3-isoindolinediones 3a-c (General Method). Pyridine (1.5 ml)
was added to a solution of bromo ketone 1 (10 mmol) and thiophenol 2a-c (11 mmol) in 2-PrOH (30 ml). The
mixture was refluxed for 1 h, cooled, the precipitated crystals were filtered off, washed with water, and with
cold 2-PrOH. The product was crystallized from 2-PrOH.
2-[3-Oxo-4-(phenylsulfanyl)butyl]-1,3-isoindolinedione (3a). Yield 3.19 g (98%); mp 94-95oC. 1H NMR
spectrum, δ, ppm (J, Hz): 3.02 (2H, t, J = 7.2, NCH2CH2); 3.82 (2H, t, J = 7.2, NCH2CH2); 3.86 (2H, s,
13
COCH2S); 7.14 (1H, t, J = 8.0, H-4'); 7.22-7.27 (4H, m, H-2',3',5',6'); 7.77-7.83 (4H, m, H-4,5,6,7). C NMR
spectrum, δ, ppm: 202.5; 202.5; 167.5; 134.2; 132.2; 129.1; 129.0; 126.4; 123.2; 43.3; 38.5; 33.1. Mass
spectrum, m/z (Irel, %): 326 (5), 325 [M]+ (27), 202 (35), 161 (14), 160 (100), 130 (5), 123 (22), 109 (6), 104 (6),
77 (9), 76 (9), 55 (14), 51 (6), 45 (22), 41 (5). Found, %: C 66.02; H 4.83; N 4.14; S 10.00. C18H15NO3S.
Calculated, %: C 66.44; H 4.65; N 4.30; S 9.85.
2-{[4-(4-Methylphenyl)sulfanyl]-3-oxobutyl}-1,3-isoindolinedione (3b). Yield 3.26 g (96%); mp
1
97-98oC. H NMR spectrum, δ, ppm (J, Hz): 2.28 (3H, s, CH3); 2.99 (2H, t, J = 7.2, NCH2CH2); 3.75 (3H, s,
COCH2S); 3.79 (2H, t, J = 7.2, NCH2CH2); 7.02 (2H, d, J = 8.0, H-3',5'); 7.15 (2H, d, J = 8.0, H-2',6');
7.74-7.80 (4H, m, H-4,5,6,7). 13C NMR spectrum, δ, ppm: 200.2; 166.8; 135.6; 133.5; 131.5; 130.7; 129.2;
129.1; 122.5; 43.2; 37.7; 32.4; 20.4. Mass spectrum, m/z (Irel, %): 340 (7), 339 [M]+ (34), 203 (5), 202 (37), 161
(10), 160 (100), 138 (7), 137 (38), 130 (6), 123 (6), 105 (5), 91 (8), 77 (11), 76 (6), 55 (9), 45 (20). Found, %:
C 67.43; H 5.19; N 4.18; S 9.28. C19H17NO3S. Calculated, %: C 67.24; H 5.05; N 4.13; S 9.45.
2-{[4-(4-Chlorophenyl)-2-oxo-sulfanyl]butyl}-1,3-isoindolinedione (3c). Yield 3.24 g (90%); mp 96-
97oC. 1H NMR spectrum, δ, ppm (J, Hz): 3.00 (2H, t, J = 7.2, NCH2CH2); 3.81 (2H, t, J = 7.2, NCH2CH2); 3.85
(2H, s, COCH2S); 7.18-7.24 (4H, m, H-2',3',5',6'); 7.74-7.80 (4H, m, H-4,5,6,7). 13C NMR spectrum, δ, ppm: 201.4;
166.8; 133.4; 131.5; 131.2; 129.7; 128.4; 122.5; 42.6; 37.8; 32.3. Mass spectrum, m/z (Irel, %): 361 (8), 360 (6), 359
[M]+ (20), 203 (7), 161 (10), 160 (100), 157 (9), 130 (7), 104 (5), 77 (9), 76 (9), 55 (11), 45 (15). Found, %: C 60.23;
H 3.76; Cl 9.67; N 3.74; S 9.13. C18H14ClNO3S. Calculated, %: C 60.08; H 3.92; Cl 9.85; N 4.89; S 8.91.
2-([1]Benzothieno[2,3-c]pyridin-1-yl)benzoic Acids 6a-c and 8,13b-Dihydro[1]benzothieno-
[2',3':3,4]pyrido[2,1-a]isoindol-5(7H)-ones 7a,b (General Method). A solution of the corresponding
isoindolinedione 3a-c (6.15 mmol) in chlorobenzene (10 ml) was added to PPA (20 g), and the mixture was
stirred for 3 h at 100oC. The still warm mixture was then poured into water (150 ml), stirred for 2 h, and left
overnight. The solid acid 6a-c was filtered off. The filtrate was extracted with CH2Cl2 (100 ml), washed with
water (100 ml), and with 5% NaOH solution (20 ml). On acidification of the alkaline solution an additional
amount of acid 6a-c was obtained. The organic layer was evaporated in vacuum, and compounds 7a,b were
obtained. Compounds 6a-c and 7a,b were crystallized from MeCN.
2-([1]Benzothieno[2,3-c]pyridin-1-yl)benzoic Acid (6a). Yield 0.9 g (48%); mp 273-274oC (decomp.).
1H NMR spectrum, δ, ppm (J, Hz): 7.51-7.68 (5H, m, H-4,5,6,6',7'); 7.92 (1H, d, J = 8.0, H-3); 8.0 (1H, d, J = 8.0,
H-8'); 8.13 (1H, d, J = 5.2, H-4'); 8.38 (1H, d, H-5'); 8.62 (1H, d, J = 5.2, H-3'); 12.36 (1H, br. s, COOH).
13C NMR spectrum, δ, ppm: 167.5; 154.1; 143.3; 141.3; 140.2; 139.9; 134.1; 133.8; 131.7; 130.6; 129.9; 129.1;
128.4; 128.2; 127.4; 123.0; 122.5; 114.2. Mass spectrum, m/z (Irel, %): 305 [M]+ (10), 288 (5), 263 (5), 262 (21),
261 (100), 260 (43), 259 (15), 131 (7), 130 (24), 116 (5). Found, %: C 70.64; H 3.73; N 4.65; S 10.34.
C18H11NO2S. Calculated, %: C 70.80; H 3.63; N 4.59; S 10.50.
669

2-(6-Methyl[1]benzothieno[2,3-c]pyridin-1-yl)benzoic Acid (6b). Yield 0.9 g (46%); mp 271-272oC
1
(decomp.). H NMR spectrum, δ, ppm (J, Hz): 2.53 (3H, s, 6'-CH3); 7.39 (1H, d, J = 8.0, H-7'); 7.58 (1H, t,
J = 8.0, H-4); 7.60-7.67 (2H, m, H-5,6); 7.77 (1H, d, J = 8.0, H-3); 8.00 (1H, d, J = 8.0, H-8'); 8.07 (1H, d, J = 5.2,
H-4'); 8.16 (1H, s, H-5'); 8.60 (1H, d, J = 5.2, H-3'); 12.4 (1H, br. s, COOH). 13C NMR spectrum, δ, ppm: 168.8;
155.3; 144.4; 142.4; 141.1; 138.5; 135.7; 135.2; 132.9; 131.8; 131.2; 131.1; 130.3; 129.4; 124.2; 123.4; 115.3;
22.1. Mass spectrum, m/z (Irel, %): 319 [M]+ (9), 302 (6), 277 (7), 276 (19), 275 (100), 274 (26), 273 (11), 272 (6),
260 (6), 259 (5), 138 (10), 137 (13). Found, %: C 71.66; H 4.19; N 4.26; S 10.21. C19H13NO2S. Calculated, %:
C 71.45; H 4.10; N 4.39; S 10.04.
2-(6-Chloro[1]benzothieno[2,3-c]pyridin-1-yl)benzoic Acid (6c). Yield 0.88 g (42%); mp 266-267oC
1
(decomp.). H NMR spectrum, δ, ppm (J, Hz): 7.54-7.68 (4H, m, H-4,5,6,7'); 7.93 (1H, d, J = 8.0, H-3); 8.01
(1H, d, J = 8.0, H-8'); 8.20 (1H, d, J = 5.2, H-4'); 8.49 (1H, d, J = 2.0, H-5'); 8.65 (1H, d, J = 5.3, H-3'); 12.36
(1H, br. s, COOH). 13C NMR spectrum, δ, ppm: 168.1; 155.1; 144.2; 141.0; 140.4; 139.1; 136.1; 135.6; 132.3;
131.4; 130.9; 130.6; 129.8; 129.2; 129.0; 124.6; 123.6; 115.3. Mass spectrum, m/z (Irel, %): 339 [M]+ (6), 298 (7),
297 (36), 296 (25), 295 (100), 294 (16), 261 (5), 260 (20), 259 (17), 148 (5), 147 (7), 130 (15), 129 (10), 116
(5), 44 (7). Found, %: C 63.39; H 2.73; Cl 10.28; N 4.19; S 9.61. C18H10ClNO2S. Calculated, %: C 63.63;
H 2.97; Cl 10.43; N 4.12; S 9.44.
On evaporating the organic extract remaining after the isolation of acid 6c, a mixture of products was
obtained from which 2-[2-(5-chlorobenzo[b]thiophen-3-yl)ethyl]-1,3-isoindolinedione (4c) was isolated by
1
fractional crystallization from MeCN. Yield 0.21 g (10%); mp 189-191oC. H NMR spectrum, δ, ppm (J, Hz):
3.18 (2H, t, J = 7.6, CH2CH2N); 3.95 (2H, t, J = 7.6, CH2CH2N); 7.30 (1H, dd, J = 8.0, J = 1.6, H-6'); 7.47 (1H,
s, H-2'); 7.78-7.85 (5H, m, H-4,5,6,7,7'); 7.88 (1H, d, J = 1.6, H-4'). Mass spectrum, m/z (Irel, %): 343 (9), 342
(11), 341 [M]+ (25), 196 (37), 195 (6), 194 (100), 183 (7), 181 (20), 161 (6), 160 (62), 159 (10), 133 (7), 115
(8), 105 (8), 104 (10), 102 (8), 77 (18), 76 (10), 51 (5), 45 (6). Found, %: C 63.44; H 3.39; Cl 10.52; N 4.26;
S 9.13. C18H12ClNO2S. Calculated, %: C 63.25; H 3.54; Cl 10.37; N 4.10; S 9.38.
Compound 4c was also obtained by the following procedure. A solution of 2-(5-chloro[1]benzothiophen-
3-yl)ethylamine (8) (2.12 g, 10 mmol) and phthalic anhydride (1.63 g, 11 mmol) in toluene (150 ml) was refluxed
for 12 h in a flask fitted with a Dean-Stark head. The solution was evaporated and the residue crystallized from
MeCN. Yield 2.5 g (73%). The product was identical with product 4c obtained by the cyclization of compound 3c.
8,13b-Dihydro[1]benzothieno[2',3':3,4]pyrido[2,1-a]isoindol-5(7H)-one (7a). Yield 0.48 g (27%);
1
mp 194-195oC (mp 193-195oC [4]). H NMR spectrum, δ, ppm (J, Hz): 2.74-2.83 (1H, m,) and 2.97-3.04 (1H,
m, 8-CH2); 3.42-3.53 (1H, m,) and 4.63-4.68 (1H, m, 7-CH2); 6.03 (1H, s, H-13b); 7.35 (2H, m, H-10,11); 7.53
(1H, t, J = 8.0, H-3); 7.65 (1H, d, J = 8.0, H-9); 7.69 (1H, t, J = 8.0, H-2); 7.74 (1H, d, J = 8.0, H-12); 7.86 (1H,
13
d, J = 8.0, H-1); 7.89 (1H, d, J = 8.0, H-4). C NMR spectrum, δ, ppm: 167.0; 144.3; 138.5; 138.4; 134.1;
132.3; 132.2; 129.1; 129.0; 125.2; 124.9; 123.9; 123.7; 122.9; 121.9; 58.2; 36.8; 24.4. Mass spectrum, m/z (Irel, %):
293 (6), 292 (22), 291 [M]+ (98), 290 (100), 289 (5), 288 (9), 263 (5), 262 (11), 235 (5), 234 (8), 182 (19), 145
(9), 131 (5), 130 (13), 117 (18), 104 (5), 45 (10). Found, %: C 74.38; H 4.59; N 4.74; S 11.00. C18H13NOS.
Calculated, %: C 74.20; H 4.50; N 4.81; S 11.00.
10-Methyl-8,13b-dihydro[1]benzothieno[2',3':3,4]pyrido[2,1-a]isoindol-5(7H)-one (7b). Yield 0.49 g
1
(26%); mp 160-161oC. H NMR spectrum, δ, ppm (J, Hz): 2.45 (3H, s, 6'-CH3); 2.75-2.84 (1H, m) and
2.93-3.00 (1H, m, 8-CH2); 3.40-3.48 (1H, m) and 4.67-4.73 (1H, m, 7-CH2); 5.92 (1H, s, H-13b); 7.12 (1H, d,
J = 8.0, H-11); 7.40 (1H, s, H-9); 7.50 (1H, t, J = 8.0, H-2); 7.64 (1H, t, J = 8.0, H-3); 7.68 (1H, d, J = 8.0,
H-12); 7.73 (1H, d, J = 8.0, H-1); 7.81 (1H, d, J = 8.0, H-4). 13C NMR spectrum, δ, ppm: 168.5; 145.9; 140.2;
137.1; 135.9; 135.7; 134.1; 133.6; 130.8; 130.4; 128.4; 125.6; 125.2; 124.3; 123.5; 59.8; 38.4; 25.9; 23.0. Mass
spectrum, m/z (Irel, %): 307 (9), 306 (19), 305 [M]+ (100), 304 (90), 303 (5), 302 (10), 290 (13), 277 (5), 276
(12), 234 (6), 182 (20), 153 (6), 152 (7), 137 (8), 131 (5), 130 (10), 124 (11), 123 (6), 117 (6). Found, %:
C 74.86; H 4.88; N 4.67; S 10.41. C19H15NOS. Calculated, %: C 74.73; H 4.95; N 4.59; S 10.50.
X-Ray Structural Investigation of Compound 7a. Crystals were monoclinic, C18H13NOS, at 293 K:
a = 13.735(1), b = 8.382(1), c = 12,167(1) Å, β = 98.28(1)o, V = 1386.2(2) Å3, Mr = 582.71, Z = 4, space group
670

P21/c, dcalc = 1.396 g/cm3, μ(MoKα) = 0.231 mm-1, F(000) = 608. The parameters of the unit cell and the
intensities of 23531 reflections (3991 independent, Rint = 0.063) were determined on an Xcalibur 3
diffractometer (MoKα radiation, CCD detector, graphite monochromator, ω scanning, 2θmax = 60o).
The structure was solved by the direct method and refined by the least squares method on F2 in a full-
matrix anisotropic approximation for the non-hydrogen atoms using the SHELXTL software set [10]. The
positions of the hydrogen atoms were made apparent from an electron density difference synthesis and were
refined isotropically. Final values of the probability factors were wR2 = 0.079 on 3970 reflections (R1 = 0.037 on
1974 reflections with F > 4σ(F), S = 0.776). The atomic coordinates, geometric parameters and crystallographic
data of compound 7a have been deposited in the Cambridge Crystallographic Data Center (deposition CCDC
863589).
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