An efficient one-pot synthesis of substituted 1h-naphtho[2,1-b]pyrans and 4h-1-benzopyrans (=Chromenes) under solvent-free microwave-irradiation conditions

Article abstract of DOI:10.1002/hlca.201100332

A facile heterogeneous synthesis of 3-amino-1-aryl-1H-naphtho[2,1-b]pyran and 2-amino-4-aryl-4H-1-benzopyran derivatives 3 and 5, respectively, was carried out efficiently by one-pot three-component coupling of an aromatic aldehyde 1, an active methylene compound 2, and naphthalen-2-ol or a phenol 4 in the presence of 5-A molecular sieves under solvent-free microwave-irradiation conditions (Scheme 1 and 2, Tables 1 and 2). The catalyst was recovered and recycled (Table 3). Copyright

Full text of DOI:10.1002/hlca.201100332

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Helvetica Chimica Acta – Vol. 95 (2012)
An Efficient One-Pot Synthesis of Substituted 1H-Naphtho[2,1-b]pyrans and
4H-1-Benzopyrans (¼Chromenes) under Solvent-Free
Microwave-Irradiation Conditions
by Adimulam Chandra Shekhara), Akula Ravi Kumara), Gangaram Sathaiaha), Kengiri Rajua),
Pamulaparthy Shanthan Rao*a), Madabhushi Sridhara), Banda Narsaiaha),
Punnamraju Venkata Satya Surya Srinivasa), and Balasubramanian Sridharb)
a) Fluoroorganics Division, Indian Institute of Chemical Technology, Tarnaka, Hyderabad 500607, India
(phone/fax: þ 91-40-27193185; e-mail: shanthanpp1954@gmail.com)
b) Department of X-ray Crystallography, Indian Institute of Chemical Technology, Tarnaka,
Hyderabad 500607, India
A facile heterogeneous synthesis of 3-amino-1-aryl-1H-naphtho[2,1-b]pyran and 2-amino-4-aryl-
4H-1-benzopyran derivatives 3 and 5, respectively, was carried out efficiently by one-pot three-
component coupling of an aromatic aldehyde 1, an active methylene compound 2, and naphthalen-2-ol or
a phenol 4 in the presence of 5-ꢀ molecular sieves under solvent-free microwave-irradiation conditions
(Scheme 1 and 2, Tables 1 and 2). The catalyst was recovered and recycled (Table 3).
Introduction. – Substituted chromenes (¼ benzopyrans) are important compounds
due to their applications in pigments, cosmetics, and agrochemicals, and also they are
integral part of many natural products [1 – 5] and many therapeutic agents such as
antibacterials [6], antivirals [7], mutagenics [8], and antitumor [9] and CNS-active
agents [10]. Conventional method for the synthesis of substituted chromenes are
mainly based on benzaldehyde, malononitrile, and naphthalen-2-ol by using various
catalysts viz., cetyltrimethylammonium chloride (CTACl) [11], benzyltrimethylammo-
nium chloride (TEBA) [12], K2CO3 [6], g-alumina [13], piperidine [14], TiCl4 [15], 1,8-
diazabicyclo[5.4.0]undec-7-ene (DBU) [16], ceric ammonium nitrate (CAN) [17],
methyltrioctylammonium chloride (Aliquatꢁ 336) [18], or CaNa2P2O7 [19]. However,
all these methods have disadvantages in terms of cost, longer reaction times, complex
workup procedures, and usage of solvents. As a result, they are not environmentally
benign, and hence, there is an urgent need to develop an efficient ecologic method for
the synthesis of benzochromene (¼ naphthopyran) derivatives.
Results and Discussion. – In continuation of our efforts in the synthesis of
heterocyclic bioactive molecules by efficient procedures, we wish to report herein a
three-component one-pot synthesis of 1H-naphtho[2,1-b]pyrans (¼ benzo[f]-
chromenes) 3 from naphthalen-2-ol, an aldehyde 1, and an active methylene compound
2 in the presence of 5-ꢀ molecular sieves (MS) as catalyst under solvent-free
microwave-irradiation (MWI) conditions (Scheme 1). A model reaction was per-
formed with stoichiometric quantities of benzaldehyde (1a), malononitrile (2, X ¼ CN)
and napththalen-2-ol in the presence of a catalytic amount of finely powdered 5-ꢀ
ꢂ 2012 Verlag Helvetica Chimica Acta AG, Zꢃrich

Helvetica Chimica Acta – Vol. 95 (2012)
503
Scheme 1. Synthesis of 1H-Naphtho[2,1-b]pyrans in the Presence of Molecular Sieves and under
Microwave Irradiation
molecular sieves without solvent and under microwave irradiation. The reaction
mixture was cooled, dissolved in AcOEt, and filtered to recover the catalyst.
Concentration of the filtrate afforded the corresponding naphthopyran derivative 3a
in excellent yield (95%; Table 1). Encouraged by this result, the reaction was extended
to various substituted aldehydes 1 and active methylene compounds 2 to give the
corresponding naphthopyran derivatives 3b – 3n mostly in excellent yields (Table 1).
The reaction cascade for the formation of the pyran derivatives 3 involves initial
Knoevenagel reaction, by which the aldehyde 1 reacts with the active methylene
compound 2 to give the benzylidenemalononitrile intermediate (X ¼ CN), followed by
alkylation of naphthalen-2-ol and subsequent cyclization. The 5-ꢀ molecular sieve is an
alkali aluminosilicate, and its role is presumably to act as an acidic dehydrating agent
during the formation of the benzylidene intermediate.
Table 1. Molecular-Sieves-Catalyzed Synthesis of Substituted 1H-Naphtho[2,1-b]pyrans (¼ Benzo-
chromenes)a)
1 (Z)
2 (X)
Product
Power [W]
Time [min]
Yield [%]b)
H
H
H
4-Me
4-Cl
CN
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
3n
540
540
540
720
540
540
540
540
540
720
720
720
720
720
5
9
7
7
4
4
7
8
4
7
8
7
9
95
80
89
85
90
95
90
90
90
88
85
85
85
60
COOEt
CONH2
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
4-F
2,4,6-F
2-CF3
4-NO2
4-MeO
3-MeO
c
)
)
)
d
e
15
a) Reaction conditions: benzaldehyde 1 (1.0 mmol), active methylene compound 2 (1.0 mmol),
naphthalen-2-ol (1.0 mmol), 5-ꢀ molecular sieves (0.5 – 1.0 g weight-equiv. rel. to naphthalen-2-ol).
c
e
b) Yield of isolated product 3. ) Naphthalene-1-carboxaldehyde. d) Thiophen-2-carboxaldehyde. ) Cin-
namaldehyde.

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Helvetica Chimica Acta – Vol. 95 (2012)
The above described condensation reaction proceeded well also with phenols 4
under 5-ꢀ MS catalysis producing the corresponding 4H-1-benzopyrans 5 in 70 – 80%
yield (Scheme 2 and Table 2).
Scheme 2. Synthesis of 4H-1-Benzopyrans in the Presence of Molecular Sieves and under Microwave
Irradiation
Table 2. Synthesis of 4H-Benzopyrans in the Presence of Molecular Sieves under Microwave Irradiationa)
2 (X)
4 (Y)
Product
Time [min]
Yield [%]b)
CN
H
H
H
Me
Me
Me
Br
Br
Br
5a
5b
5c
5d
5e
5f
5g
5h
5i
4
6
9
4
8
10
4
5
80
80
75
75
70
70
80
80
80
CONH2
COOEt
CN
CONH2
COOEt
CN
CONH2
COOEt
8
a) Reaction conditions: benzaldehyde (1, Z ¼ H; 1.0 mmol), active methylene compound 2 (1.0 mmol),
substituted phenol 4 (1.0 mmol), 5-ꢀ molecular sieves (0.5 – 1.0 g weight equiv. rel. to phenol),
microwave power 540 W. b) Yield of isolated product 5.
The versatility of the reaction was tested by applying substituted aromatic and
heteroaromatic aldehydes. Benzaldehydes 1 having electron-withdrawing or -donating
groups gave the pyran derivatives 3 in good yields in a short reaction time. But in the
case of cinnamaldehyde, the yield of 3n was only 60% (Table 1), possibly due to a
concomitant aldol reaction [20]. The reaction was regioselective with naphthalen-2-ol
giving exclusively the angularly fused regioisomers 3 [1]. The angular fusion of the
naphtho[2,1-b]pyrans 3 was further supported by the X-ray crystal-structure determi-
nation of 3h (Fig.). The optimized reaction conditions for the formation of the naphto-
and benzopyran derivatives was 720 W microwave power and 5 – 7 min reaction time
under solvent-free conditions. We tried different irradiation levels: at lower radiation
power, exclusive formation of the Knoevenagel products was observed, while pyran
derivatives were formed at high irradiation power.
We finally concentrated on the recyclability of the catalyst. The recycled 5-ꢀ
molecular sieves were used for further runs, and it was found that the catalytic activity
was good, as shown by the yields of the product (Table 3).

Helvetica Chimica Acta – Vol. 95 (2012)
505
Figure. X-Ray crystal structure of 3-amino-1-[2-(trifluoromethyl)phenyl]-1H-naphtho[2,1-b]pyran-2-
carbonitrile (3h)
Table 3. Recycling of MS Catalysta)
Run
1
5
95
2
5
90
3
5
90
Time [min]
Yield [%]a)
a) Yield of compound 3a.
In conclusion, we demonstrated a facile and environmentally benign method for the
synthesis of highly functionalized naphtho- and benzopyran compounds by a single-pot
three-component condensation reaction of naphthalen-2-ol or a phenol, an aldehyde,
and an active methylene compound in the presence of 5-ꢀ molecular sieves as catalyst
under solvent-free conditions. The presented method is superior to existing methods for
the preparation of 4H-1-benzopyrans as the yields are high, the catalyst is inexpensive,
and toxic solvents are avoided in this green synthesis.
We are thankful to Dr. J. S. Yadav, Director, IICT, for his constant encouragement, and A. C. S.,
A. R. K., G. S., and K. R. are thankful to the Council of Scientific and Industrial Research (CSIR), India,
for the financial assistance in the form of SRF fellowships.
Experimental Part
General. Column chromatography (CC): silica gel (SiO2; 60 – 120 mesh; Merck). TLC: precoated
SiO2 (60 – 120 mesh); visualization under UV light. M.p.: Casia-Siamia (VMP-AM) melting-point
apparatus; uncorrected. IR Spectra: Perkin-Elmer-240-C FT-IR spectrophotometer; KBr discs; ˜n in cmꢀ1
.
1H- and 13C-NMR Spectra: Bruker-AV spectrometers; at 300 and 75 MHz, resp.; in CDCl3; d in ppm rel.
to Me4Si as internal standard, J in Hz. EI-MS: VG-7070-H instrument; at 70 eV; in m/z. Elemental
analyses (C, H, N): Vario-EL analyzer.

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1H-Naphtho[2,1-b]pyrans (¼ Benzo[f]chromenes) 3 and 4H-1-Benzopyrans (¼Chromenes) 5:
Typical Procedure. To a mixture of benzaldehyde 1 (1.0 mmol), an active methylene compound 2
(1.0 mmol), and naphthalen-2-ol or phenol 4 (1.0 mmol) in a microwave tube, finely powdered 5-ꢀ MS
(0.5 – 1.0 g weight-equiv. rel. to naphthalenol or phenol) was added. The mixture was subjected to
microwave irradiation at moderate power (540 – 720 W) for 5 – 10 min (TLC monitoring). Then AcOEt
was added, the MS filtered, the AcOEt layer washed with H2O, dried (Na2SO4), and concentrated, and
the residue subjected to CC (AcOEt/hexane 5 :95): 3 or 5. The recovered catalyst was washed with
acetone and dried at 1008 to constant weight and used in subsequent reactions. The catalyst activity was
good up to three recycles, the yields of the products being in the range 75 – 85%.
3-Amino-1-phenyl-1H-naphtho[2,1-b]pyran-2-carboxamide (3c): M.p. 210 – 2128. IR: 3476, 3442
(NH2), 1680 (C¼O). 1H-NMR: 4.75 (s, CH); 6.82 (br. s, NH2); 7.04 (br. s, CONH2); 7.16 – 7.40 (m, 5 arom.
H); 7.56 (d, J ¼ 7.7, 1 arom. H); 7.67 (d, J ¼ 7.7, 1 arom. H); 7.75 – 8.13 (m, 4 arom. H). 13C-NMR: 171.0;
151.8; 140.3; 137.2; 133.5; 129.3; 129.1; 128.8; 128.6; 128.4; 128.3; 128.1; 127.0; 127.2; 126.6; 126.3; 122.5;
118.9; 83.8; 38.4. MS: 316 (Mþ), 300 ([M ꢀ NH2]þ), 239 ([M ꢀ Ph]þ). Anal. calc. for C20H16N2O2
(316.12): C 75.93, H 5.10, N 8.86; found: C 75.90, H 5.11, N 8.83.
3-Amino-1-(2,4,5-trifluorophenyl)-1H-naphtho[2,1-b]pyran-2-carbonitrile (3g): M.p. 199 – 2018. IR:
3448, 3339 (NH2), 2187 (CN). 1H-NMR: 5.5 (s, CH); 6.7 (br. s, NH2); 6.9 (d, J ¼ 7.2, 1 arom. H); 7.1 (d,
J ¼ 7.2, 1 arom. H); 7.3 – 7.85 (m, 6 arom. H). 13C-NMR: 179.8; 166.8; 151.8; 150.3; 149.3; 148.6; 146.7;
145.6; 144.3; 141.7; 139.2; 136.9; 133.5; 132.8; 127.2; 125.6; 117.3; 106.8; 59.2; 20.9. MS: 352 (Mþ), 221
([M ꢀ Ph ꢀ 3F]þ). Anal. calc. for C20H11F3N2O (352.08): C 68.18, H 3.15, N 7.95; found: C 68.17, H 3.16,
N 7.93.
3-Amino-1-[2-(trifluoromethyl)phenyl]-1H-naphtho[2,1-b]pyran-2-carbonitrile (3h): M.p. 231 –
1
2338. IR: 3476, 3442 (NH2), 2198 (CN). H-NMR: 5.5 (s, CH); 6.7 (br. s, NH2); 7.05 (d, 1 arom. H);
7.3 – 7.6 ( m, 5 arom. H); 7.7 – 7.9 (m, 4 arom. H). 13C NMR: 161; 148; 145; 133.6; 131.6; 130.8; 130.4; 129.0;
128.3; 127.2; 126.3; 125.1; 123.2; 122.5; 122.4; 122.1; 119.9; 117.3; 115.6; 58.3; 24.8. EI-MS (70 eV): 366
(Mþ), 297 ([M ꢀ CF3]þ), 221 ([M ꢀ Ph ꢀ CF3]þ). Anal. calc. for C21H13F3N2O (366.10): C 68.85, H 3.58,
N 7.65; found: C 68.83, H 3.56, N 7.63.
3-Amino-1-(naphthalen-1-yl)-1H-naphtho[2,1-b]pyran-2-carbonitrile (3l): M.p. 221 – 2238. IR: 3477,
3440 (NH2), 2216 (CN). 1H-NMR: 4.74 (s, CH); 6.82 (br. s, NH2); 7.10 – 8.27 (m, 13 arom. H). 13C-NMR:
177.1; 151.9; 134.2; 133.6; 133.5; 133.4; 132.6; 128.6; 128.4; 128.3; 128.2; 128.1; 126.9; 126.7; 126.4; 125.8;
125.6; 124.2; 123.2; 122.1; 118.9; 117.3; 59.2; 26.0. MS: 348 (Mþ), 221 ([M ꢀ naphthalenyl]þ). Anal. calc.
for C24H16N2O (348.13): C 82.74, H 4.63, N 8.04; found: C 82.75, H 4.60, N 8.01.
2-Amino-4-phenyl-4H-1-benzopyran-3-carboxamide (5b): M.p. 210 – 2128. IR: 3477, 3441 (NH2),
1
1677 (C¼O). H-NMR: 4.82 (s, CH); 5.2 (br. s, NH2); 6.0 (br. s, CONH2); 6.61 – 6.90 (m, 4 arom. H);
7.06 – 7.36 (m, 5 arom. H). 13C-NMR: 171.1; 156.6; 153.1; 140.2; 129.3; 129.2; 128.9; 128.3; 128.2; 128.1;
127.0; 125.0; 123.5; 117.0; 83.8; 40.1. MS: 266 (Mþ), 189 ([M ꢀ Ph]þ). Anal. calc. for C16H14N2O2 (266.11):
C 72.16, H 5.30, N 10.52; found: C 72.19, H 5.27, N 10.51.
Ethyl 2-Amino-4-phenyl-4H-1-benzopyran-3-carboxylate (5c): M.p. 195 – 1978. IR: 3477, 3440
1
(NH2), 1726 (C¼O), 1025 (CꢀOꢀC). H-NMR: 1.32 (t, J ¼ 7.46, MeCH2); 4.20 (q, J ¼ 7.46, MeCH2);
4.74 (s, CH); 6.61 – 6.75 (m, 4 arom. H); 6.89 (br. s, NH2); 7.06 – 7.40 (m, 5 arom. H). 13C-NMR: 167.2;
160.0; 153.1; 140.3; 129.7; 129.3; 128.9; 128.7; 128.2; 127.0; 126.3; 123.5; 120.2; 81.3; 78.9; 61.7; 39.8; 14.2.
MS: 295 (Mþ), 218 ([M ꢀ COOEt]þ). Anal. calc. for C18H17NO3 (295.12): C 73.20, H 5.80, N 4.74; found:
C 73.19, H 5.77, N 4.73.
2-Amino-6-methyl-4-phenyl-4H-1-benzopyran-3-carbonitrile (5d): M.p. 205 – 206. IR: 3440, 3430
1
(NH2), 2216 (CN). H-NMR: 2.35 (s, Me); 4.74 (s, CH); 6.22 (br. s, NH2); 6.49 – 6.70 (m, 3 arom. H);
7.06 – 7.37 (m, 5 arom. H). 13C-NMR: 177.1; 150.1; 140.3; 133.1; 130.8; 129.5; 129.3; 128.4; 128.2; 127.2;
126.3; 120.2; 117.6; 117.3; 59.2; 29.7; 24.6. MS: 262 (Mþ), 247 ([M ꢀ Me]þ), 185 ([M ꢀ Ph]þ). Anal. calc.
for C17H14N2O (262.11): C 77.84, H 5.38, N 10.68; found: C 77.80, H 5.37, N 10.65.
2-Amino-6-methyl-4-phenyl-4H-1-benzopyran-3-carboxamide (5e): M.p. 215 – 2178. IR: 3476, 3434
(NH2), 1660 (C¼O). 1H-NMR: 2.35 (s, Me); 4.74 (s, CH); 6.48 (br. s, NH2); 6.50 – 6.70 (m, 3 arom. H);
6.96 (br. s, CONH2); 7.06 – 7.40 (m, 5 arom. H).13C-NMR: 172.0; 158.8; 152.1; 140.3; 133.7; 129.8; 129.5;
129.3; 128.4; 128.2; 126.3; 122.5; 119.9; 119.7; 117.8; 83.8; 39.4. MS: 280 (Mþ), 203 ([M ꢀ Ph]þ). Anal.
calc. for C17H16N2O2 (280.12): C 72.84, H 5.75, N 9.99; found: C 72.80, H 5.73, N 9.98.

Helvetica Chimica Acta – Vol. 95 (2012)
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Ethyl 2-Amino-6-methyl-4-phenyl-4H-1-benzopyran-3-carboxylate (5f): M.p. 198 – 2008. IR: 3477,
3441 (NH2), 1726 (C¼O), 1010 (CꢀOꢀC). 1H-NMR: 1.30 (t, J ¼ 7.4, MeCH2); 2.40 (s, MeAr); 4.19 (q, J ¼
7.4, MeCH2); 4.74 (s, CH); 6.40 (br. s, NH2); 6.49 – 6.70 (m, 3 arom. H); 7.07 – 7.37 (m, 5 arom. H).
13C-NMR: 167.2; 160.0; 150.1; 140.3; 133.1; 130.8; 129.5; 129.3; 128.4; 128.2; 127.2; 126.3; 120.2; 117.6;
78.9; 62.0; 40.2; 25.2; 14.2. EI-MS (70 eV): 309 (Mþ), 294 ([M ꢀ Me]þ), 264 ([M ꢀ EtO]þ). Anal. calc.
for C19H19NO3 (309.14): C 73.77, H 6.19, N 4.53; found: C 73.75, H 6.20, N 4.50.
2-Amino-6-bromo-4-phenyl-4H-1-benzopyran-3-carbonitrile (5g): M.p. 189 – 1908. IR: 3476, 3440
(NH2), 2216 (CN). 1H-NMR: 4.74 (s, CH); 6.42 (br. s, NH2); 6.50 – 7.37 (m, 8 arom. H). 13C-NMR: 178.2;
152.1; 141.2; 140.3; 133.7; 129.8; 129.5; 129.3; 128.5; 126.3; 122.5; 120.9; 117.8; 117.3; 59.2; 28.7. MS: 326
(Mþ), 328 ([M þ 2]þ), 249 ([M ꢀ Ph]þ). Anal. calc. for C16H11BrN2O (326.01): C 58.74, H 3.39, N 8.56;
found: C 58.72, H 3.40, N 8.55.
2-Amino-6-bromo-4-phenyl-4H-1-benzopyran-3-carboxamide (5h): M.p. 199 – 2038. IR: 3476, 3440
(NH2), 1686 (C¼O). 1H-NMR: 4.75 (s, 1 H); 6.49 (br. s, NH2); 6.50 – 7.07 (m, 3 H); 6.96 (br. s, CONH2);
7.08 (br. s, 2 H); 7.12 – 7.38 (m, 5 H). 13C-NMR: 171.0; 158.8; 152.1; 140.3; 133.7; 129.8; 129.5; 129.3;
128.4; 128.2; 126.3; 122.5; 119.9; 117.8; 83.8; 39.4. MS: 344 (Mþ), 346 ([M þ 2]þ), 267 ([M ꢀ Ph]þ). Anal.
calc. for C16H13BrN2O2 (344.02): C 55.67, H 3.80, N 8.12; found: C 55.65, H 3.77, N 8.10.
Ethyl 2-Amino-6-bromo-4-phenyl-4H-1-benzopyran-3-carboxylate (5i): M.p. 170 – 1728. IR: 3477,
3441 (NH2), 1726 (C¼O), 1075 (CꢀOꢀC). 1H-NMR: 1.30 (t, J ¼ 7.4, MeCH2); 4.19 (q, J ¼ 7.4, MeCH2);
4.74 (s, CH); 6.42 (br. s, NH2); 6.50 – 7.07 (m, 3 arom. H); 7.08 – 7.37 (m, 5 arom. H). 13C-NMR: 168.4;
160.0; 152.1; 141.2; 133.7; 129.8; 129.4; 129.2; 128.4; 128.2; 126.2; 122.5; 120.0; 117.8; 78.0; 61.7; 39.1; 14.2.
MS: 373 (Mþ), 375 ([M þ 2]þ), 328 ([M ꢀ EtO]þ), 296 ([M ꢀ COOEt]þ). Anal. calc. for C18H16BrNO3
(373.03): C 57.77, H 4.31, N 3.74; found: C 57.70, H 4.30, N 3.78.
X-Ray Crystal Structure of 3h. The data were collected at room temperature with a Bruker-Smart-
Apex-CCD diffractometer and graphite monochromated MoKa radiation (l 0.71073 ꢀ) by means of the
w-scan method [21]. Preliminary lattice parameters and orientation matrices were obtained from four
sets of frames. Unit cell dimensions were determined with 5971 reflections in the range 2.45 < q < 27.938.
Integration and scaling of intensity data were accomplished with the SAINT program [21]. The structure
was solved by direct methods with SHELXS97 [22], and refinement was carried out by full-matrix least-
squares technique with SHELXL97 [22]. Anisotropic displacement parameters were included for all
non-H-atoms. The H-atoms attached to N-atoms were located in a difference density map and refined
isotropically. All other H-atoms were positioned geometrically and treated as riding on their parent C-
atoms with CꢀH ¼ 0.93 ꢀ and Uiso(H) ¼ 1.2 Ueq(C). Data: C21H13F3N2O, Mr 366.33, triclinic, space group
¯
P1, a ¼ 8.6016(6) ꢀ, b ¼ 10.0533(7) ꢀ, c ¼ 10.2070(7) ꢀ, a ¼ 101.857(1)8, b ¼ 96.315(1)8, g ¼ 102.062(1)8,
V¼ 833.89(10) ꢀ3, Z ¼ 2, Dcalc. ¼ 1.459 mg mꢀ3, T 294(2) K, m ¼ 0.114 mmꢀ1, F(000) ¼ 376. Data collection
yielded 8006 reflections resulting in 2921 unique, averaged reflections, 2696 with I > 2s(I). Full-matrix
least-squares refinement led to a final R ¼ 0.0366, wR ¼ 0.0979, and g.o.f. ¼ 1.043. CCDC-839725 contains
supplementary crystallographic data for the structure. These data can be obtained free of charge via
http://www.ccdc.cam.ac.uk/data_request/cif.
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Received August 19, 2011