Synthesis and Beckmann rearrangement of novel (Z)-2-organylselanyl ketoximes: promising agents against grapevine anthracnose infection

Synthesis and Beckmann rearrangement of novel (Z)-2-organylselanyl ketoximes: promising agents against grapevine anthracnose infection

Tetrahedron Letters 57 (2016) 5575–5580 Contents lists available at ScienceDirect Tetrahedron Letters journal homepage: www.elsevier.com/locate/tetl...

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Tetrahedron Letters 57 (2016) 5575–5580

Contents lists available at ScienceDirect

Tetrahedron Letters journal homepage: www.elsevier.com/locate/tetlet

Synthesis and Beckmann rearrangement of novel (Z)-2organylselanyl ketoximes: promising agents against grapevine anthracnose infection Bianca Waskow a, Renata A. Mano a, Rafaela X. Giacomini a, Daniela H. Oliveira a, Ricardo F. Schumacher a, Ethel A. Wilhelm a,b, Cristiane Luchese a,b, Lucielli Savegnago b, Raquel G. Jacob a,⇑ a b

Laboratório de Síntese Orgânica Limpa—LASOL, CCQFA, Universidade Federal de Pelotas—UFPel, CEP 96010-900 Pelotas, RS, Brazil Grupo de Pesquisa em Neurobiotecnologia—GPN, CDTec, CCQFA, Universidade Federal de Pelotas—UFPel, CEP 96010-900 Pelotas, RS, Brazil

a r t i c l e

i n f o

Article history: Received 9 August 2016 Revised 11 October 2016 Accepted 20 October 2016 Available online 21 October 2016 Keywords: Organochalcogen (Z)-2-Organylselanyl ketoxime Beckmann rearrangement Anthracnose Antioxidant activity

a b s t r a c t We present here the synthesis of novel (Z)-2-organylselanyl ketoximes by nucleophilic substitution reaction of E/Z mixtures of 2-bromo ketoximes with nucleophilic species of selenium, which were generated in situ by simple cleavage of diorganyl diselenides with NaBH4 using ethanol/THF as solvent. The new 2organylselanyl ketoximes were synthesized in moderate to good yields and with selectivity for the (Z)configuration. The synthesized (Z)-2-arylselanylacetophenone oximes were submitted to the Beckmann rearrangement, furnishing the corresponding N-aryl-2-(selanyl)acetamides. (Z)-1-Phenyl-2(phenylselanyl) ketoxime has antifungal activity against Sphaceloma ampelinum and a good level of antioxidant activity in vitro in DPPH, ABTS, FRAP and lipid peroxidation assays. Ó 2016 Elsevier Ltd. All rights reserved.

Introduction The organochalcogen compounds,1 mainly those containing nitrogen atoms,1d are a special class of molecules that can participate in selective organic reactions and present many pharmaceutical applications. Particularly, organoselenium compounds have attracted great interest due to their biological activities and applicability in organic reactions.1a–c Thereby, the search for novel nitrogen-functionalized organoselenium compounds remains a promising field to be explored. Oximes are important intermediates in organic synthesis, being used as building blocks in the synthesis of pharmaceuticals and agrochemicals.2 Oximes are easily reduced to amines and are further used in the production of plastics, synthetic fibers and pharmaceutical derivatives, or in the synthesis of N-substituted amides by the Beckmann rearrangement.3 This rearrangement is an atom-economic reaction and is an industrially important step in the synthesis of Nylon-6.4 With respect to their biological properties, oximes may act as bactericide, insecticide, herbicide, and fungicide,5–9 with the advantage of often have a low toxicity. They are recognized as ⇑ Corresponding author. Tel.: +55 53 32757178; fax: +55 53 32757354. E-mail address: [email protected] (R.G. Jacob). http://dx.doi.org/10.1016/j.tetlet.2016.10.078 0040-4039/Ó 2016 Elsevier Ltd. All rights reserved.

antidotes for nerve agents6 and can reactivate acetylcholinesterase in the treatment against poisoning by organophosphorus pesticides.6 Oximes have also antioxidant7 and immunosuppressive8 activities, besides other biological properties.9 The traditional method to prepare oximes is the reaction of a carbonyl compound with an excess of hydroxylamine hydrochloride in the presence of a stoichiometric amount of base.10 Recently, green solvent-free approaches,11 or using ultrasound,12 iodine,13 or microwave irradiation14 have been described. The synthesis of 2-alkoxy ketoximes and 2-organylthio ketoximes has been reported in many works.15 These compounds are prepared by nucleophilic substitution reactions of 2-halo ketoximes with their respective nucleophiles. Some of these ketoximes present biological activity and synthetic application.8,15a To the best of our knowledge, the synthesis of 2-organylselanyl ketoximes has not been yet described. The presence of an adjacent organoselenium group could generate or enhance the biological activity of the oxime, besides it could modify its reactivity in classical reactions. Thus, we present here our results on the synthesis of novel (Z)2-organylselanyl ketoximes 3 by nucleophilic substitution reaction of 2-bromo ketoximes 1 with nucleophilic species of selenium. The selenolate anion was generated in situ by simple cleavage of diorganyl diselenide 2 with NaBH4 using ethanol/THF as solvent

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B. Waskow et al. / Tetrahedron Letters 57 (2016) 5575–5580 OH

N R

1

R1 SeSeR 1 2 EtOH/THF, NaBH4 Br 0º C, N2

R, R1 = Alkyl and Aryl

N R

OH Se

3

TsCl (30 mol%) ZnCl2 (30 mol%)

was stirred at room temperature under N2 atmosphere until complete cleavage of the Se–Se bond, which was indicated by a change in color to whitish. Then, the reaction mixture was cooled to 0 °C and a solution of 2-bromo-ketoxime 1a in ethanol (1 mL) was added dropwise. The reaction occurred instantly, affording 1-phenyl-2-(phenylselanyl) ketoxime 3a in 85% yield. NMR studies revealed that (Z)-3a was the only formed isomer, which has the N-OH and CH2Se in the syn configuration. The 1H-chemical shift of the CH2Se group appeared as a singlet at d 4.14 ppm. To extend the scope of this methodology, we explored the reaction of various oximes 1a–g with differently substituted diaryl diselenides 2a–e and dibutyl diselenide 2f. The results shown in Table 2 reveal that the reaction worked well with a range of substituted arylketoximes and diorganyl diselenides, affording the corresponding products in moderate to good yields and high selectivity for the (Z)-isomer. The reactions were not sensitive to the electronic effects of the substituent bearing the aryl group directly attached the [email protected] bond (Table 2, entries 1–4). On the other hand, when ketoximes containing ortho-substituted aryl groups 1e and 1f, and the alkyl group 1g were used, two isomers were observed, but with the (Z)-isomer obtained in a larger amount (Table 2, entries 5–7). The 1H NMR spectrum (CDCl3, 400 MHz) of these compounds showed chemical shifts of the methylene group (CH2Se) as a singlet at d 4.19 ppm, 4.17 ppm and 3.71 ppm for (Z)-isomers 3e, 3f, and 3h, respectively. In the (E)-isomers 3e0 , 3f0 and 3g0 the methylene group appeared at d 3.98 ppm, 3.96 ppm and 3.60 ppm, respectively. These chemical shifts are in agreement with previously reported studies on nucleophilic substitution reactions of 2-bromoketoximes.15b,c When the reaction was performed with substituted diaryl diselenides 2b–e (Table 2, entries 8–11), only the respective (Z)-isomer was obtaining in good yields with no significant difference among electron-donating (4-OMe, 2,4,6-Me3) and electron-withdrawing (4-Cl, 4-F) substituent effects. Finally, dibutyl diselenide 2f was satisfactorily used and produced 1-phenyl-2-(butylselanyl) ketoxime 3l in 87% yield and exclusively in Z-configuration (Table 2, entry 12). A plausible mechanism for the reactions of a mixture of E/Z 2bromo-ketoximes 1 with diorganyl diselenides 2 using EtOH/THF as solvent in the presence of NaBH4 to form the (Z)-ketoxime 3 is depicted on Scheme 2. At first, the nucleophilic selenium species 20 attacks the E/Z 2-bromo-ketoxime 1 to generate the E/Z a-selenooxime 30 . Then, addition of a second equiv of the selenolate 20 to the C–N double bond, generates the intermediate A that, in the case of E-isomer, suffers a rotation to produce intermediate B.15b,c

O R

R1 CH 3CN, reflux, 5 h

N H

Se

R

1

4

Antifungal and antioxidant activities in vitro

Scheme 1. General scheme of the present work.

(Scheme 1).1b The synthetic application in Beckmann rearrangement was also explored. Additionally, a preliminary screening of the new selenooximes 3 for their antifungal potential against Sphaceloma ampelinum and a study on their antioxidant activity in vitro were also performed. Initially, we choose 2-bromo-1-phenylethan-1-one oxime 1a (E/Z mixture in a E/Z ratio = 2:1)15b and diphenyl diselenide 2a as standard starting materials to perform the optimization study, aiming to prepare the respective 1-phenyl-2-(phenylselanyl) ketoxime 3a (Table 1). Firstly, the phenylselenolate anion 2a0 was generated in situ by the reaction of 2a with NaBH4 under N2 atmosphere in EtOH. Then, a solution of 2-bromo-ketoxime 1a was added and the reaction was followed by TLC (Table 1). Initially, we fixed the amount of 1a (1.0 mmol) using ethanol as solvent and evaluated the influence of the temperature on the reaction system (Table 1, entries 1–3). In this case, we observed that the best result was obtained when the reaction was performed at 0 °C, giving the desired product in 65% yield (Table 1, entry 3). Subsequently, the reaction stoichiometry was evaluated (Table 1, entries 4 and 5). This study allowed us to observe that using a slight excess (1.3 mmol) of 2-bromo-ketoxime 1a, the reaction yield increased to 80%. In the next step, considering the better solubility of diphenyl diselenide 2a in nonpolar solvents, we evaluate the use of tetrahydrofuran (THF) as the solvent (Table 1, entry 6); however, no product was formed. Thus, we used a mixture of ethanol/THF (1:1) as the solvent (Table 1, entry 7) and fortunately, the yield increased to 85%. The use of polyethylene glycol 400 (PEG400) as solvent was also evaluated (Table 1, entry 8), however only 30% of the desired product was obtained. Based on the optimization study, the best condition was defined as using diphenyl diselenide 2a (0.6 mmol), NaBH4 (1.2 mmol), 2bromo-ketoxime 1a (1.3 mmol) and 4 mL of solvent (ethanol/THF 1:1) under N2 atmosphere (Table 1, entry 7). In short, NaBH4 was added to a yellowish solution of diphenyl diselenide 1a in a mixture of ethanol/THF (1:1). This heterogeneous reaction mixture

Table 1 Optimization of the synthesis of 3aa N

OH Br

Se

Se 2a

NaBH4, solvent

Se

N2, temperature

1a temperature

2a'

OH N Se (Z)-3a

Entry

Oxime 1a (mmol)

Solvent

Temp. (°C)

Yield (%)

1 2 3 4 5 6 7b 8

1 1 1 1.2 1.3 1.3 1.3 1.3

Ethanol Ethanol Ethanol Ethanol Ethanol THF Ethanol/THF PEG-400

Reflux Rt 0 0 0 0 0 60

50 60 65 70 80 — 85 30

a Reactions performed using diphenyl diselenide 2a (0.6 mmol), NaBH4 (1.2 mmol) in 4 mL of solvent under N2 atmosphere. After cleavage of 2a, the oxime 1a in 1 mL of solvent was added. b A mixture of solvent ethanol/THF 1:1 was used as the solvent.

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B. Waskow et al. / Tetrahedron Letters 57 (2016) 5575–5580 Table 2 Scope and generality on the synthesis of compounds 3 and 30 a N R

Entry

Oxime 1 (Z:E) N

OH

R1 SeSeR1 2 / NaBH4 Ethanol/THF

Br

OH

Se

OH

Se Cl

N

OMe N

Se

OMe N

Se)2

N

Se

Cl

Se)2

Br

N

N

Se

Se)2

Br 1g (50:50)

8

10

OH

OH Br

11

1a (33:67) N

OH

Br 1a (33:67)

N

OH Se

70

3h Me Me

N

Me 2c Cl

Se)2

OMe

OH

3i Me N

Se 3j

Se)2

N

71 Cl

OH Se

2e 3k

Se)2 2e

68 Me

OH

2d

F

Me

Se

Se) 2

Br 1a (33:67) N

12

Se) 2 2b

1a (33:67)

N

87d

Se

MeO

OH Br

OH

3g

Br 1a (33:67) N

9

N

2a

OH

82c

3f

OH

N

OH

2a

1f (50:50)

7

45b

3e

OH

6

OH

2a

1e (50:50) Cl

68

3d

O 2N

Br

5

OH

2a

1d (85:15)

OH

87

3c

Se)2

Br

4

OH

N

2a

OH

78

3b

Se)2

1c (89:11)

N

OH Se

Me

Br

O2 N

85

2a

1b (81:19)

3

N

Se)2

Br

2

Cl

N

Yield (%)

OH

3a

N

N

Product 3

2a

1a (33:67)

Me

R1

Se)2

Br

1

Se (Z)-3

Diselenide 2

OH

OH

R

N 2, 0 ºC

1

N

N

65 F

OH Se

87

3l

a

Reactions performed using diorganyl diselenide 2 (0.6 mmol), NaBH4 (1.2 mmol) in 4 mL of ethanol/THF (1:1) under N2 atmosphere. After cleavage of 2, the solution of oxime 1 in ethanol was added. b Z/E mixture: 93:07. c Z/E mixture: 70:30. d Z:E mixture: 73:27.

Then, elimination of selenolate affords the thermodynamically more stable product (Z)-3. To prove the stated above, firstly we carried out the reaction of the E/Z mixture of 2-bromo-ketoxime 1a with NaBH4 using EtOH/ THF as solvent to confirm the formation of Z-isomer 5a, as

described in the literature15b (Scheme 3, Eq. 1). Based on this result, in a second moment, the compound 5a was generated and after that, phenylselenolate 2a0 was added (Scheme 3, Eq. 2). In this case, the only isolated product was the E-isomer of ketoxime 5b (90% yield). On the other hand, the dropwise addition of a

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HO

N Br

R

HO

R1 Se 2'

N

R

(E/Z)-1

SeR1

R1 Se 2'

HO R

(E /Z)-3'

N

N SeR1

SeR1

R

OH

N

SeR1

R

SeR1

A

OH SeR1

(Z)-3

B

Scheme 2. Proposal mechanism for the formation of (Z)-ketoxime 3.

N

Br

Ph

HO

OH NaBH 4, ethanol / THF N 2, 0 °C

1a (E /Z mixture) N

HO

OH

Br 1a (E/Z mixture)

NaBH 4, ethanol / THF

Ph

N Ph

N 2, 0 °C

OH Br

Ph

1a (2:1 E /Z mixture)

(Eq. 1)

Table 3 Beckmann rearrangement of selanyl ketoximes 3. Synthesis of acetamides 4a–fa

5a (94%) Z isomer N

Ph

5a Z isomer

N N

R 1Se 2a'

OH

Ph

R

OH Se

3

O

TsCl (30 mol%) ZnCl2 (30 mol%)

R

N H

R 1 CH 3CN, reflux, 5 h

Se

R1

4

(Eq. 2)

5b (90 %) Only E isomer

OH OH N N SePh + SePh + Ph R R 5 (35 %) 3' (38%) 3 (27 %) 2:1 (E /Z) E isomer Z isomer

HO R 1 Se 2a' ethanol/THF, N2 , 0 °C

N

Entry

Selanyl ketoxime 3

N

N

(Eq. 3)

Product 4

OH

O

Se

1

N H

3a

Scheme 3. Control experiments.

N

Se

O

Se

N H

3b

Me

N

N H

3d

O 2N

OMe N

OH

OMe

3e

N

3h

N H

3k

N 3g

N H

Se 4e

67 OMe

Se 4f

75 F

F

O

OH Se

65

4d

O

Se

7

Se

OMe

OH

6

64

O

Se

N

N H

OH

5

Se 4c

O

Se

4

75

4b O

Se

3

Se

O2N

OH

97

4a

Me

OH

2

freshly prepared solution of phenylselenolate 2a0 to 2-bromoketoxime 1a, afforded a mixture of products, with isomeric ratio of 1.4:1 of products (Scheme 3, Eq. 3). We believe that this result evidences the SN2 character of the reaction. Still, the increased amount of Z-isomer is in agreement with the mechanism described above. In order to verify the synthetic application of the synthesized 2-(organylselanyl) ketoximes 3, they were subjected to the Beckmann rearrangement. In this context, by reacting the ketoximes 3 with TsCl (30 mol %) and ZnCl2 (30 mol %) in acetonitrile under reflux temperature for 5 h, the respective N-aryl-2-(selanyl)acetamides 4 could be obtained (Table 3).16 As can be seen in Table 3, the 2-(organylselanyl) ketoximes 3 bearing aryl groups directly attached to the [email protected] bond gave the desired acetamides 4a–f in good to excellent yields (Table 3, entries 1–6). Unfortunately, when 1-(phenylselanyl)butan-2-one oxime 3g was used, no product could be observed and the starting material was recovered (Table 3, entry 7). On the other hand, anthracnose caused by the fungus Sphaceloma ampelinum de Bary (anamorph Elsinoe ampelina), is one of the most important fungal diseases of grape.17 It is considered a destructive disease of grapevines grown in humid and warm climates. The pathogen infects all young green tissues of grapevines and it causes significant production losses.18 The use of fungicides to control anthracnose is efficient, but due to their high cost and toxicity, the development of new control agents is required. In this context, as a preliminary study, we evaluated the use of 2-(phenylselanyl) ketoxime 3a and 2-(phenylselanyl)acetamide 4a against S. ampelinum.5 The antifungal effect of 3a and 4a was compared with (E)-acetophenone oxime 5b and 2-bromo-ketoxime 1a. Fig. 1 shows the mycelia growth inhibition of S. ampelinum by compounds 1a, 3a, 4a and 5b. The results demonstrated that compounds 3a and 4a reduced the colony diameter (mm) at all days tested, when compared to the control group. Compound 5b did not reduce the colony diameter at any of the days. Compound 3a caused an inhibition of mycelia growth of S. ampelinum around 100%, 63%, 62%, 60%, 50%, and 46% at days 1, 2, 3, 4, 5, and 6, respectively, when compared to the control group. In addition, compound 4a reduced around 52, 36%, 32%, 27%, 30%, and 29% at days 1, 2, 3, 4, 5, and 6, respectively, when compared to the control group. Besides, inhibitory effect of mycelia growth by compound 3a was more efficient than 4a and 5b. Furthermore, the effect in reducing the colony diameter by compound 3a was superior to

Yield (%)

N H

Se



4g

a Reactions performed using 2-(organylselanyl) ketoximes 3 (1.0 mmol), TsCl (30 mol %) and ZnCl2 (30 mol %) in 2 mL of acetonitrile at reflux temperature under N2 atmosphere for 5 h.

2-bromo-ketoxime 1a at all days. This study demonstrated, for the first time, the antifungal activity of organoselenium derivatives on S. ampelinum. Based on the antifungal activity of 3a, and in order to explore the pharmacological potential of this compound, we decided to evaluate its antioxidant activity by different assays in vitro. To verify the influence of the selenium atom19 in the antioxidant activity, compounds 1a and 5b were used as control. In this context, initially was carried out the 2,2-diphenyl-1picrylhydrazyl (DPPH) assay.20 The preliminary test showed that 3a, which contains selenium, at 500 lM exhibited antioxidant activity, whereas 1a (with bromine) exhibited lower activity. On the other hand, 5b (without selenium) did not show any antioxidant effect. The values of IMax (which represent efficacy of compounds) was 13.90 ± 3.42% for 3a, 4.24 ± 0.65% for 1a and 1.44 ± 0.59% for 5b. The 2,2-azinobis-3-ethyl-benzothiazoline-6-sulfonic acid (ABTS) assay21 showed that 3a, in a concentration equal or superior

B. Waskow et al. / Tetrahedron Letters 57 (2016) 5575–5580

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Figure 1. Inhibition of mycelia growth of S. ampelinum by compounds 1a, 3a, 4a, and 5b. Data are reported as mean ± SD of five independent experiments. (⁄) Denotes p < 0.05 when compared with the respective control for each day; (#) Denotes p < 0.05 when compared with the compounds 1a, 4a, and 5b for each day (two-way ANOVA/NewmanKeuls).

than 5 lM, exhibited antioxidant activity. On the other hand, 1a and 5b had significant effect at the concentration of 50 lM. Compound 3a presented a high potency, with IC50 values of 12.75 ± 2.63 lM and a IMax of 90.18 ± 4.90%. Compounds 1a and 5b did not inhibit 50% of the ABTS radicals and presented a low value of IMax of the 29.21 ± 3.08 and 26.36 ± 3.43%, respectively. The results of ABTS and DPPH assays suggest that the mechanism of the antioxidant activity of 3a is probably based on single electron transfer and the presence of selenium increases the antioxidant effect. To confirm that the antioxidant mechanism of 3a involves single electron transfer, the ferric ion reducing antioxidant power (FRAP) test was performed.22 In this assay 3a showed ability to reduce ions Fe3+ from the concentration of 10 lM, while 1a and 5b had an antioxidant potential at the starting concentration of 50 lM and 100 lM, respectively. These results are in agreement with the ABTS assay. The lipid peroxidation assay was estimated by the measurement of malondialdehyde (MDA) levels, which is the end product of the lipid peroxidation.20 Compounds 1a, 5b, and 3a were effective on linoleic acid peroxidation inhibition induced by Fe-ascorbic acid at a concentration equal or superior than 50, 100 and 50 lM, respectively. According these results, 3a was the most potent, with a IC50 value of 438 ± 67.88 lM and IMax of 51.82 ± 6.06%. Compounds 1a and 5b presented IMax of the 24.69 ± 4.59 and 30.46 ± 15.29% respectively and they did not present IC50. Conclusion In summary, we demonstrated the simple, efficient and selective synthesis of novel (Z)-2-organylselanyl ketoximes. This new class of compounds was synthesized in moderate to good yields by the reaction of aryl or alkyl selenolate, generated in situ, with substituted aryl and alkyl 2-bromo-ketoximes. In order to verify the synthetic application of the synthesized 2-(organylselanyl) ketoximes, the Beckmann rearrangement reaction was performed and gave the corresponding acetamides in good yields. Still, the preliminary biological studies revealed the potential of the synthesized selanyl ketoximes against grapevine anthracnose infection and as promising antioxidant agents.

Acknowledgments The authors are grateful to FAPERGS (11/2026-4), CNPq (442474/2014-8), CAPES and FINEP for the financial support. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.tetlet.2016.10. 078. References and notes 1. (a) Perin, G.; Alves, D.; Jacob, R. G.; Barcellos, A. M.; Soares, L. K.; Lenardão, E. J. ChemistrySelect 2016, 1, 205; (b) Perin, G.; Lenardão, E. J.; Jacob, R. G.; Panatieri, R. B. Chem. Rev. 2009, 109, 1277; (c) Freudendahl, D. M.; Shahzad, S. A.; Wirth, T. Eur. J. Org. Chem. 2009, 1649; (d) Savegnago, L.; Vieira, A.; Seus, N.; Goldani, B. S.; Castro, M. R.; Lenardão, E. J.; Alves, D. Tetrahedron Lett. 2013, 54, 40; (e) Victoria, N. V.; Radatz, C. S.; Sacchini, M.; Jacob, R. G.; Alves, D.; Savegnago, L.; Perin, G.; Motta, A. S.; Lenardão, E. J.; Silva, W. P. Food Control. 2012, 23, 95; (f) Gerzson, M. F. B.; Victoria, F. N.; Radatz, C. S.; Gomes, M. G.; Boeira, S. B.; Jacob, R. G.; Alves, D.; Jesse, C. R.; Savegnago, L. Pharmcol. Biochem. Behav. 2012, 102, 21. 2. (a) Araújo, C. R. M.; Gonsalves, A. A. Rev. Virtual Chim. 2015, 7, 1469; (b) Sayin, U.; Yuksel, H.; Ozmen, A.; Birey, M. Radiat. Phys. Chem. 2010, 79, 1220; (c) Milios, C. J.; Stamatatos, T. C.; Perlepes, S. P. Polyhedron 2006, 25, 134. 3. Gawley, R. E. Org. React. 1988, 35, 1. 4. Ray, R.; Chowdhury, A. D.; Maiti, D.; Lahiri, G. K. Dalton Trans. 2014, 43, 38. 5. Abele, E.; Abele, R.; Golomba, L.; Visnevska, J.; Beresneva, T.; Lukevics, E. Chem. Heteroc. Comp. 2010, 46, 905. 6. Sakurada, K.; Ikegaya, H.; Ohta, H.; Fukushima, H.; Akutsua, T.; Watanabe, K. Toxicol. Lett. 2009, 189, 110. 7. (a) Lone, I. H.; Khan, K. Z.; Fozdar, B. I.; Hussain, F. Steroids 2013, 78, 945; (b) Özyürek, M.; Akpinar, D.; Bener, M.; Türkkan, B.; Güçlü, K.; Apak, R. Chem. Biol. Interact. 2014, 212, 40. 8. Luo, Y.; Song, R.; Li, Y.; Zhang, S.; Liu, Z. J.; Fu, J.; Zhu, H. L. Bioorg. Med. Chem. Lett. 2012, 22, 3039. 9. Yamazaki, K.; Terauchi, H.; Iida, D.; Fukumoto, H.; Suzuki, S.; Kagaya, T.; Aoki, M.; Koyana, K.; Seiki, T.; Takase, K.; Watanabe, M.; Arai, T.; Tsukahara, K.; Nagakawa, J. Bioorg. Med. Chem. Lett. 2012, 22, 6126. 10. (a) Abele, E.; Abele, R.; Lukevics, E. Chem. Heteroc. Comp. 2009, 45, 1420; (b) Masaki, M.; Fukui, K.; Ohta, M. J. Org. Chem. 1967, 32, 3564. 11. (a) Saikia, L.; Baruah, J. M.; Thakur, A. J. Org. Med. Chem. Lett. 2011, 1, 1; (b) Touaux, B.; Texier-Boullet, F.; Hamelin, J. Heteroat. Chem. 1998, 9, 351. 12. Li, J.-T.; Li, X.-L.; Li, T.-S. Ultrason. Sonochem. 2006, 13, 200. 13. Ganguly, N. C.; Mondal, P. Synthesis 2010, 3705. 14. Batmani, H.; Setamdideh, D. Orient. J. Chem. 2014, 30, 699.

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