Unsymmetrically Functionalized 5,5 -Diaryl- and 5,6,5 -Triaryl-2,2':6',2 -Terpyridines

Unsymmetrically functionalized 5,5''-diaryl- and 5,6,5''-triaryl- 2,2':6',2''-terpyridines, an efficient synthetic route and photophysical properties

Alexey P. Krinochkin,a Dmitry S. Kopchuk,a,b Albert F. Khasanova, Nikolay V. Chepchugov,a

Igor S. Kovalev,a Sougata Santra,a Grigory V. Zyryanov,a,b1 Adinath Majee,c

Vladimir L. Rusinov,a,b and Oleg N. Chupakhina,b

a Ural Federal University, 19, Mira St., 620002 Yekaterinburg, Russian Federation b Postovsky Institute of Organic Synthesis of RAS (Ural Division), 22/20, S. Kovalevskoy/Akademicheskaya St.,

620990 Yekaterinburg, Russian Federation c Department of Chemistry, Visva-Bharati (A Central University), Santiniketan 731235, India

Supplementary information

Ar Ar' O N N Ar O N N + HN N Br NH2 8 9 or Ar' N Ar N O N NH2 N N + N 7

Ar' OH 6 Ar' 5 Ar' N N R N R' N N N 10-12 13, 14 R = COOMe (10), CH2Br (11), CHBr2 (12) R' = Me (13), COOMe (14)

1 Corresponding author. Tel.: +7-343-375-4501; fax: +7-343-374-0458; e-mail: [email protected] Scheme S1. The retrosynthetic analysis for the synthesis of unsymmetrically functionalized 5,5''-diaryl- and 5,6,5''-triaryl-2,2':6',2''-terpyridines by “1,2,4-triaizine” methodology

Experimental Section

General

Unless otherwise mentioned, all common reagents and solvents were used from commercial suppliers without further purification. Melting points were measured on the instrument Boetius. 1H and 13C NMR spectra were recorded with Bruker DRX-400 spectrometer using Me4Si as an internal standard. Mass-spectra were recorded on MicrOTOF-Q II (Bruker Daltonics), electrospray as a method of ionization. Microanalyses (C, H, N) were performed using a Perkin–Elmer 2400 elemental analyzer. UV–Vis. spectra were recorded on a Lambda 45 spectrophotometer (Perkin Elmer). Luminescence spectra were recorded on a Horiba Fluoromax- 4 Spectrofluorometer. Hydrazones of isonitrosoacetophenones,1 (6-methylpyridin-2-yl)-5,6-diphenyl-1,2,4- triazine 13b,2 6’-methyl-5-phenyl-2,2’-bipyridine 15a,3 6’-bromomethyl-5-phenyl-2,2’- bipyridine 11a3 were synthesized as reported previously. 6’-Methyl-5,6-diphenyl-2,2’-bipyridine (15b). The triazine 13b (3.31 g, 10.2 mmol) was suspended in o-xylene (45 ml), 2,5-norbornadiene (3.63 ml, 35.71 mmol) was added and the resulting mixture was refluxed for 9 hrs. The additional portion of 2.5-norbornadiene (1.815 ml, 18.36 mmol) was added and the mixture was refluxed for additional 9 hrs. The solvent was evaporated under reduced pressure, and the residue was purified by column chromatography using DCM and ethylacetate (10:1) as eluent. The analytical sample was obtained by the recrystallization from methanol. Yield 2.49 g (76%). M.p. 129-131 ºC. NMR 1Н, δ, ppm

3 (DMSO-d6): 2.61 (3Н, s, Ме), 7.16-7.33 (9Н, m, Ph, H-5’), 7.40 (2Н, m, Ph), 7.75 (1Н, dd, J = 7.8, 7.8 Hz, Н-4’), 7.87 (1Н, d, 3J = 7.8 Hz, Н-3), 8.31 (1Н, d, 3J = 7.8 Hz, Н-3’), 8.45 (1Н, d, 3J = 7.8 Hz, Н-4). ESI-MS, m/z: found 323.15 [M+H]+, required 323.15. Found, %: С 85.77, Н

5.70, N 8.81. С23Н18N2. Required, %: С 85.68, Н 5.63, N 8.69. General method for the synthesis of mono- and dibromomethylbipyridines 11, 12

The methylbipyridine 15b (1 g, 3.1 mmol) was dissolved in dry CCl4 (60 ml), N- bromosuccinimide (550 mg, 3.1 mmol) and the catalytic amount of benzoyl peroxide were added, and the resulting mixture was refluxed for 8 hrs. The precipitate formed was filtered off, and the mother liquid was evaporated under reduced pressure. The residue was separated by column chromatography using the mixture of DCM and ethylacetate (200:1) as eluent. The obtained products were used for the next step without an additional purification. 6’-Bromomethyl-5,6-diphenyl-2,2’-bipyridine (11b). Rf 0.45. Yield 650 mg (52%).

1 M.p. 177-179 ºC. NMR Н, δ, ppm (DMSO-d6): 4.73 (2Н, s, СН2Br), 7.18-7.33 (8Н, m, Ph), 7.40 (2Н, m, Ph), 7.75 (1Н, dd, 3J = 7.8 Hz, 4J = 0.7 Hz, Н-5’), 7.92 (2Н, m, Н-3,4’), 8.44 (1Н, dd, 3J = 7.8 Hz, 4J = 0.7 Hz, Н-3’), 8.47 (1Н, d, 3J = 8.0 Hz, Н-4). ESI-MS, m/z: found 401.17 [M+H] +, required 401.17. 6’-Dibromomethyl-5,6-diphenyl-2,2’-bipyridine (12b). Rf 0.7. Yield 300 mg (20%).

1 M.p. 189-191 ºC. NMR Н, δ, ppm (DMSO-d6): 7.19-7.33 (9Н, m, Ph, СНBr2), 7.39 (2Н, m, Ph), 7.78 (1Н, d, 3J = 7.8 Hz, Н-5’), 7.94 (1Н, d, 3J = 8.0 Hz, Н-3), 8.00 (1Н, dd, 3J = 7.8, 7.8 Hz, Н- 4’), 8.48 (1Н, d, 3J = 7.8 Hz, Н-3’), 8.51 (1Н, d, 3J = 8.0 Hz, Н-4). ESI-MS, m/z: found 478.99 [M+H]+, required 478.98. 6’-Dibromomethyl-5-phenyl-2,2’-bipyridine (12a). The methylbipyridine 15a (0.5 g,

2.03 mmol) was dissolved in dry CCl4 (60 ml), N-bromosuccinimide (360 mg, 2.03 mmol) and benzoyl peroxide in catalytic amount were added and the resulting mixture was refluxed for 8 hrs. Then the additional portion of N-bromosuccinimide (360 mg, 2.03 mmol) and benzoyl peroxide in catalytic amount were added and the resulting mixture was refluxed for additional 8 hrs. The precipitate formed was filtered off, the mother liquid was evaporated under reduced pressure. The residue was purified by recrystallization (ethanol). Yield 410 mg (50%). M.p. 149-

1 151 ºC. NMR Н, δ, ppm (СDCl3): 6.77 (1Н, s, СHBr2), 7.40-7.47 (1H, m, Ph), 7.48-7.55 (2Н, m, Ph), 7.66 (2Н, m, Ph), 7.84 (1Н, d, 3J = 7.8 Hz), 7.93 (1Н, dd, 3J = 7.8, 7.8 Hz, H-4’), 8.04 (1Н, dd, 3J = 8.4 Hz, 4J = 2.4 Hz, Н-4), 8.41 (1Н, d, 3J = 7.8 Hz), 8.53 (1Н, d, 3J = 8.4 Hz, Н-3), 8.93 (д, 1Н, 4J = 2.4 Hz, Н-6). ESI-MS, m/z: found 402.94 [M+H]+, required 402.94. General method for the synthesis of acetoxymethylbipyridines 16 The corresponding bromomethyl-substituted bipyridine 11 (1.2 mmol) was dissolved in dry DMF (70 ml), sodium acetate (985 mg, 12 mmol) was added and the resulting mixture was stirred at 130 ºC for 10 h. The solvent was evaporated under reduced pressure. Water (20 ml) was added to the residue, and the reaction mixture was extracted with DCM (3 x 25 ml). The combined extracts were dried over anhydrous sodium sulfate. After the filtration the solvent was removed under reduced pressure, and the products were used in the next step without an additional purification. 6’-Acetoxymethyl-5-phenyl-2,2’-bipyridine (16a). Yield 330 mg (90%). NMR 1Н, δ, ppm (DMSO-d6): 2.17 (3Н, s, Ас), 5.23 (2Н, s, СН2ОАс), 7.37-7.44 (2Н, m, Ph, H-3’), 7.46- 7.53 (2Н, m, Ph), 7.72 (2Н, m, Ph), 7.92 (1Н, dd, 3J = 7.8, 7.8 Hz, Н-4’), 8.12 (1Н, dd, 3J = 8.3, 4J = 2.1 Hz, Н-4), 8.38 (1Н, d, 3J = 7.8 Hz, Н-3’), 8.48 (1Н, d, 3J = 8.3 Hz, Н-3), 8.91 (1Н, d, 4J = 2.1 Hz, Н-6). ESI-MS, m/z: found 381.16 [M+H]+, required 381.16. 6’-Acetoxymethyl-5,6-diphenyl-2,2’-bipyridine (16b). Yield 400 mg (88%). NMR 1Н,

δ, ppm (DMSO-d6): 2.19 (3Н, s, Ас), 5.27 (2Н, s, СН2ОАс), 7.19-7.32 (8Н, m, Ph), 7.40 (2Н, m, Ph), 7.43 (1Н, dd, 3J = 7.5 Hz, Н-5’), 7.89-7.95 (2Н, m, Н-3,4’), 8.42-8.47 (2Н, m, Н-4,3’). ESI- MS, m/z: found 305.13 [M+H]+, required 305.13. General method for the synthesis of hydroxymethylbipyridines 17 The corresponding acetoxymethylbipyridine 16 (1 mmol) was dissolved in methanol (25 ml). The solution of NaOH (200 mg, 5 mmol) in water (10 ml) was added and the resulting mixture was refluxed for 30 min. The methanol was removed under reduced pressure, and the residue was extracted with DCM (3 x 25 ml). The combined extracts were dried over anhydrous sodium sulfate, filtered, and the solvent was removed under reduced pressure. The obtained products were used for the next step without an additional purification. 6’-Hydroxymethyl-5-phenyl-2,2’-bipyridine (17a). Yield 210 mg (80%). NMR 1Н, δ,

3 3 ppm (DMSO-d6): 4.66 (2Н, d, J = 5.5 Hz, СН2ОН), 5.24 (1Н, t, J = 5.5 Hz, ОН), 7.38-7.43 (1Н, m, Ph), 7.46-7.53 (2Н, m, Ph), 7.72 (2Н, m, Ph), 7.88 (1Н, dd, 3J = 7.8, 7.8 Hz, Н-4’), 8.10 (1Н, dd, 3J = 8.3, 4J = 2.1 Hz, Н-4), 8.29 (1Н, d, 3J = 7.8 Hz, Н-3’), 8.49 (1Н, d, 3J = 8.3 Hz, Н- 3), 8.90 (1Н, d, 4J = 2.1 Hz, Н-6). ESI-MS, m/z: found 263.12 [M+H]+, required 263.12. 6’-Hydroxymethyl-5,6-diphenyl-2,2’-bipyridine (17b). Yield 280 mg (82%). NMR 1Н,

3 3 δ, ppm (DMSO-d6): 4.68 (2Н, d, J = 5.7 Hz, СН2ОН), 5.29 (1Н, t, J = 5.7 Hz, ОН), 7.19-7.32 (8Н, m, Ph), 7.40 (2Н, m, Ph), 7.53 (1Н, d, 3J = 7.8 Hz, Н-5’), 7.86-7.92 (2Н, m, Н-3,4’), 8.35 (1Н, d, 3J = 7.8 Hz, Н-3’), 8.44 (1Н, d, 3J = 8.0 Hz, Н-4). ESI-MS, m/z: found 339.15 [M+H]+, required 339.15. General method for the synthesis of bipyridinecarbaldehydes 7 The corresponding hydroxymethylbipyridine 17 (0.8 mmol) was dissolved in 1,2- dichloroethane (25 ml), activated MnO2 (0.7 g, 8 mmol) was added and the resulting mixture was stirred at 50 ºC for 5 hrs. Then precipitate was filtered off, washed with hot ethanol. Mother liquid was removed under reduced pressure, and the product was used in the next step without addition purification. 5-Phenyl-2,2’-bipyridine-6’-carbaldehyde (7a). Yield 145 mg (70%). NMR 1Н, δ, ppm

3 (DMSO-d6): 7.39-7.46 (1Н, m, Ph), 7.47-7.56 (2Н, m, Ph), 7.75 (2Н, m, Ph), 7.97 (1Н, d, J = 7.2 Hz, Н-3’), 8.12-8.23 (2Н, m, Н-4,4’), 8.61 (1Н, d, 3J = 8.0 Hz, Н-3), 8.72 (1Н, d, 3J = 7.2 Hz, Н-5’), 8.97 (1Н, d, 4J = 2.1 Hz, Н-6), 10.11 (1Н, s, СНО). ESI-MS, m/z: found 261.10 [M+H]+, required 261.10. 5,6-Diphenyl-2,2’-bipyridine-6’-carbaldehyde (7b). Yield 215 mg (80%). NMR 1Н, δ,

3 ppm (DMSO-d6): 7.19-7.35 (8Н, m, Ph), 7.42 (2Н, m, Ph), 7.97 (2Н, m, Н-3,3’), 8.15 (1Н, dd, J = 7.8, 7.8 Hz, Н-4’), 8.58 (1Н, d, 3J = 8.0 Hz, Н-4), 8.79 (1Н, d, 3J = 7.8 Hz, Н-5’), 10.13 (1Н, s, СНО). ESI-MS, m/z: found 337.13 [M+H]+, required 337.13. General method for the synthesis of (2,2’-bipyridin-6-yl)-1,2,4-triazines 5 The corresponding aldehyde 7 (0.5 mmol) was dissolved in ethanol (20 ml). Then the solution of the corresponding isonitrosoacetophenone hydrazone (0.5 mmol) in ethanol (20 ml) was added and the resulting mixture was left at room temperature overnight. Then the solvent was removed under reduced pressure, the glacial acetic acid (10 ml) was added, and the resulting mixture was reflux for 2-5 minutes. Then the solvent was removed under reduced pressure, and the residue was triturated with ethanol. The precipitate formed was filtered off, washed with ethanol and dried. The analytical samples were obtained by recrystallization from ethanol. 3-(5’-Phenyl-2,2’-bipyridin-6-yl)-6-tolyl-1,2,4-triazine (5a). Yield 112 mg (56%). M.p.

1 244-246 ºC. NMR Н, δ, ppm (DMSO-d6): 2.48 (3Н, s, Ме), 7.39-7.46 (3Н, m, Tol, Ph), 7.49- 7.55 (2Н, m, Ph), 7.75 (2Н, m, Ph), 8.12-8.24 (m, 4Н, Tol, Н-4,4’ (bipy)), 8.56 (1Н, d, 3J = 7.4 Hz, Н-3 (bipy)), 8.65 (1Н, d, 3J = 7.4 Hz, Н-5 (bipy)), 8.74 (1Н, d, 3J = 8.3 Hz, Н-3’ (bipy)), 8.96 (1Н, d, 4J = 2.1 Hz, Н-6’ (bipy)), 9.48 (1Н, s, H-5). ESI-MS, m/z: found 402.17 [M+H]+, required 402.17. Found, %: С 77.61, Н 4.64, N 17.29. С26Н19N5. Required, %: С 77.79, Н 4.77, N 17.44. 6-(4-Methoxyphenyl)-3-(5’-phenyl-2,2’-bipyridin-6-yl)-1,2,4-triazine (5b). Yield 104

1 mg (50%). M.p. 244-246 ºC. NMR Н, δ, ppm (DMSO-d6): 3.91 (3Н, s, ОМе), 7.14 (2Н, m, 4- methoxyphenyl), 7.39-7.46 (1Н, m, Ph), 7.48-7.56 (2Н, m, Ph), 7.76 (2Н, m, Ph), 8.15 (1Н, dd, 3J = 7.8, 7.8 Hz, Н-4 (bipy)), 8.22 (1Н, dd, 3J = 8.3, 4J = 2.1 Hz, Н-4), 8.29 (2Н, m, 4- methoxyphenyl), 8.55 (1Н, d, 3J = 7.4 Hz, Н-3 (bipy)), 8.64 (1Н, dd, 3J = 7.4 Hz, Н-5 (bipy)), 8.73 (1Н, d, 3J = 8.3 Hz, Н-3’ (bipy)), 8.97 (1Н, d, 4J = 2.1 Hz, Н-6 (bipy)), 9.48 (1Н, s, H-5). ESI-MS, m/z: found 418.17 [M+H]+, required 418.17. Found, %: С 74.68, Н 4.50, N 16.55.

С26Н19N5O. Required, %: С 74.80, Н 4.59, N 16.78. 6-Phenyl-3-(5’,6’-diphenyl-2,2’-bipyridin-6-yl)-1,2,4-triazine (5c). Yield 172 mg

1 (74%). M.p. 174-176 ºC. NMR Н, δ, ppm (DMSO-d6): 7.21-7.34 (8Н, m, Ph), 7.44 (2Н, m, Ph), 7.58-7.67 (3Н, m, Ph (triazine)), 7.99 (1Н, d, 3J = 8.3 Hz, Н-3 (bipy)), 8.17 (1Н, dd, 3J = 7.8, 7.8 Hz, Н-4 (bipy)), 8.33 (2Н, m, Ph (triazine)), 8.60 (1Н, d, 3J = 7.8 Hz, Н-3 (bipy)), 8.70 (1Н, d, 3J = 8.3 Hz, Н-4 (bipy)), 8.73 (1Н, dd, 3J = 7.8 Hz, Н-5 (bipy)), 9.55 (1Н, s, H-5). ESI-MS, m/z:

+ found 464.19 [M+H] , required 464.19. Found, %: С 80.13, Н 4.43, N 14.93. С31Н21N5. Required, %: С 80.32, Н 4.57, N 15.11. General method for the synthesis of (2,2’-bipyridin-6-yl)-6,7-dihydro-5Н- cyclopenta[c]pyridines 1 The mixture of the corresponding 1,2,4-triazine 1 (0.25 mmol) and 1- morpholinocyclopentene (0.2 ml, 1.25 mmol) was heated at 200 ºC under argon atmosphere for 2 hrs. Then the additional portion of 1-morpholinocyclopentene (0.1 ml, 0.625 mmol) was added and the resulting mixture was stirred under the same conditions for 1 h. Then the reaction mixture was cooled to room temperature and triturated with acetonitrile. The precipitate formed was filtered off, washed with acetonitrile and dried. The analytical sample was obtained by recrystallization. 1-(5’-Phenyl-2,2’-bipyridin-6-yl)-4-tolyl-6,7-dihydro-5Н-cyclopenta[c]pyridine (1a).

1 Yield 82 mg (75%). M.p. 189-191 ºC. NMR Н, δ, ppm (DMSO-d6): 2.15 (2Н, m, СН2-6), 2.42

3 3 (3Н, s, Ме), 3.07 (2Н, t, J = 7.3 Hz, СН2-7), 3.69 (2Н, t, J = 7.3 Hz, СН2-5), 7.29 (2Н, m, Tol), 7.39-7.45 (3Н, m, Ph), 7.48-7.55 (2Н, m, Ph), 7.74 (2Н, m, Tol), 8.03 (1Н, dd, 3J = 7.4, 7.4 Hz, Н-4 (bipy)), 8.18 (1Н, dd, 3J = 8.3, 4J = 2.1 Hz, Н-4’ (bipy)), 8.40 (1Н, d, 3J = 7.4 Hz, bipy), 8.44-8.49 (2Н, m, Н-3, bipy), 8.57 (1Н, d, 3J = 8.3 Hz, Н-3’ (bipy)), 8.95 (1Н, d, 4J = 2.1 Hz, Н-

13 6’ (bipy)). NMR С, δ, ppm (CDCl3): 21.2, 25.6, 32.6, 34.2, 120.0, 121.1, 123.0, 127.1, 128.2, 128.5, 129.1, 129.4, 133.8, 135.0, 135.2, 136.4, 137.5, 137.6, 137.8, 139.2, 146.7, 147.6, 150.5, 153.1, 154.8, 155.5, 157.7. ESI-MS, m/z: found 440.21 [M+H]+, required 440.21. Found, %: С

84.88, Н 5.87, N 9.41. С31Н25N3. Required, %: С 84.71, Н 5.73, N 9.56. 4-(4-Methoxyphenyl)-1-(5’-phenyl-2,2’-bipyridin-6-yl)-6,7-dihydro-5Н-

1 cyclopenta[c]pyridine (1b). Yield 89 mg (78%). M.p. 204-206 ºC. NMR Н, δ, ppm (CDCl3):

3 3 2.16 (2Н, m, СН2-6), 3.09 (2Н, t, J = 7.3 Hz, СН2-7), 3.69 (2Н, t, J = 7.3 Hz, СН2-5), 7.04 (2Н, m, 4-methoxyphenyl), 7.41-7.55 (5Н, m, Ph), 7.68 (2Н, m, 4-methoxyphenyl), 7.98 (1Н, dd, 3J = 7.4, 7.4 Hz, Н-4 (bipy)), 8.40 (1Н, dd, 3J = 8.3, 4J = 2.1 Hz, Н-4’ (bipy)), 8.37 (1Н, d, 3J = 7.4 Hz, bipy), 8.48 (1Н, d, 3J = 7.4 Hz, bipy), 8.56 (1Н, s, Н-3), 8.95 (1Н, d, 4J = 2.1 Hz, Н-6’

13 (bipy)). NMR С, δ, ppm (CDCl3): 25.6, 32.7, 34.2, 55.4, 114.2, 119.9, 121.1, 123.0, 127.1, 128.2, 129.1, 129.7, 130.3, 133.5, 135.2, 136.4, 136.5, 137.8, 139.2, 146.5, 147.6, 150.2, 153.0, 154.8, 155.5, 157.7, 159.4. ESI-MS, m/z: found 456.21 [M+H]+, required 456.21. Found, %: С

81.81, Н 5.40, N 8.99. С31Н25N3O. Required, %: С 81.73, Н 5.53, N 9.22. 1-(5’,6’-Diphenyl-2,2’-bipyridin-6-yl)-4-phenyl-6,7-dihydro-5Н-

1 cyclopenta[c]pyridine (1c). Yield 90 mg (72%). M.p. 204-206 ºC. NMR Н, δ, ppm (CDCl3):

3 3 2.17 (2Н, m, СН2-6), 3.10 (2Н, t, J = 7.3 Hz, СН2-7), 3.72 (2Н, t, J = 7.3 Hz, СН2-5), 7.23-7.33 (8Н, m, Ph), 7.39-7.45 (1Н, m, Ph), 7.47-7.55 (6Н, m, Ph), 7.90 (1H, d, 3J = 8.1 Hz, Н-3’ (bipy)), 7.97 (1Н, dd, 3J = 7.4, 7.4 Hz, Н-4 (bipy)), 8.37 (1Н, dd, 3J = 7.4, 4J = 0.8 Hz, bipy), 8.56 (1H, d, 3J = 8.1 Hz, Н-4’ (bipy)), 8.58 (1Н, s, Н-3), 8.62 (1Н, dd, 3J = 7.4, 4J = 0.8 Hz, 13 bipy). NMR С, δ, ppm (DMSO-d6): 24.9, 32.0, 33.8, 99.5, 119.1, 120.0, 122.8, 127.3, 127.7, 127.8, 128.3, 128.4, 128.6, 129.3, 129.7, 133.5, 135.8, 137.3, 137.8, 138.7, 139.4, 139.8, 140.2, 146.3, 149.8, 153.0, 154.2, 154.4, 155.7, 157.3. ESI-MS, m/z: found 502.23 [M+H]+, required

502.23. Found, %: С 86.02, Н 5.28, N 8.11. С36Н27N3. Required, %: С 86.20, Н 5.43, N 8.38. 1H NMR (400 MHz, CDCl ) 3

N N Br

1 H NMR (400 MHz, DMSO-d6)

N N Br

Br N N Br

O O N N

OH N N

N N N N N

1 H NMR (400 MHz, CDCl3)

13 C NMR (100 MHz, DMSO-d6)

OH N N

N N N N N

13 C NMR (100 MHz, CDCl3)

1 H NMR (400 MHz, DMSO-d6) O

N N N N N

1 H NMR (400 MHz, CDCl3) O

13 C NMR (100 MHz, CDCl3) O

N N N References

1. Dey, B. B. J. Chem. Soc. 1914, 105, 1039. 2. Guillet, G. L.; Hyatt, I. F. D.; Hillesheim, P. C.; Abboud, K. A.; Scott, M. J. New J. Chem. 2013, 37, 119. 3. Prokhorov, A. M.; Kozhevnikov, V. N.; Kopchuk, D. S.; Bernard, H.; Le Bris, N.; Tripier, R.; Handel, H.; Kőenig, B.; Kozhevnikov, D. N. Tetrahedron 2011, 67, 597.