A Novel Acid-Catalyzed O-Benzylating Reagent with the Smallest Unit of
Imidate Structure
Kohei Yamada, Hikaru Fujita, and Munetaka Kunishima*
Faculty of Pharmaceutical Sciences, Institute of Medical, Pharmaceutical, and Health Sciences, Kanazawa University,
Kakuma-machi, Kanazawa 920-1192 Japan
[email protected]
Supporting Information
1. General methods
2. Experimental procedure and characterization data for products
3. References
4. HPLC analyses
5. 1H and 13C NMR spectra
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1. General methods
Nuclear magnetic resonance (1H NMR (400 MHz), 13C NMR (100 MHz)) spectra were determined on a JEOL JNM-ECS400
spectrometer. Chemical shifts for 1H NMR are reported as δ values relative to tetramethylsilane as the internal standard and
coupling constants are in hertz (Hz). The following abbreviations are used for spin multiplicity: s = singlet, d = doublet, t =
triplet, m = multiplet, br = broad. Chemical shifts for 13C NMR were reported in ppm relative to the center line of a triplet at
77.0 ppm for deuteriochloroform or to tetramethylsilane as the internal standard for deuteriodimethyl sulfoxide. Infrared (IR)
spectra were recorded on a HORIBA FT-720 FREEXACT-II spectrometer and were reported in wavenumbers (cm-1). Mass
spectra were measured on a Micromass Zq2000 spectrometer (ESI-MS), JMS-SX102A (FAB). Chiral HPLC was performed on
a JASCO LC-2000 series using Daicel CHIRALPAK IB-3. Analytical thin layer chromatography (TLC) was performed on
Merck precoated analytical plates, 0.25 mm thick, silica gel 60 F254. Preparative TLC separations were performed on Merck
analytical plates (0.25 or 0.50 mm thick) precoated with silica gel 60 F254. Flash chromatography separations were performed
on KANTO CHEMICAL Silica Gel 60 N (spherical, neutral, 40-100 mesh) unless otherwise noted. Reagents were commercial
grades and were used without any purification unless otherwise noted. Dehydrated acetonitrile, diethyl ether, toluene, N,Ndimethylformamide, dimethylsulfoxide, toluene, α,α,α-trifluorotoluene, 1,4-dioxane and dichloromethane were purchased from
commercial sources, and 1,2-dimethoxyethane was purchased from commercial sources and distilled over calcium hydride
before use. All reactions sensitive to oxygen or moisture were conducted under a N2 atmosphere.
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2. Experimental procedure and characterization data for products
2,4,6-Tris(benzyloxy)-1,3,5-triazine (TriBOT)1)
To the suspension of powdered sodium hydroxide (125.3 mg, 3.13 mmol) in benzyl alcohol (0.88 mL, 8.5 mmol) was added
cyanuric chloride (172.4 mg, 0.935 mmol) portionwise at 0 °C. After stirred for 30 min, the reaction mixture was heated to
50 °C and stirred for additional 2 hours. Then the reaction mixture was cooled to rt, and a precipitate was filtered off through a
silica pad. Excess benzyl alcohol was evaporated under reduced pressure, and the residue was purified by column
chromatography to afford 2,4,6-tris(benzyloxy)-1,3,5-triazine (301.4 mg, 81%) as a white crystalline solid.
1
H NMR (CDCl3): δ 7.46-7.29 (m, 15H), 5.45 (s, 6H); 13C NMR (CDCl3): δ 173.0, 135.3, 128.5, 128.4, 128.3, 69.9; Anal.
Calcd for C24H21N3O3: C, 72.16; H, 5.30; N, 10.52. Found: C, 72.02; H, 5.33; N, 10.45; HRMS (FAB) Calcd for C24H22N3O3
([M+H]+): 400.1661, Found: 400.1660; IR (KBr): 3053, 3035, 3026, 3005, 2981, 2929, 2891, 1570, 1417, 1346, 1333, 1134,
960, 814, 741, 696; Mp: 106.0-106.6 °C.
General procedure for benzylation of 1a: To a solution of 1a (817 mg, 6.00 mmol), TriBOT (958.7 mg, 0.4 equiv) and MS5A
(750.0 mg, 25 mg/mL) in 1,4-dioxane (30.0 mL, 0.2 M) was added trifluoromethanesulfonic acid (105 µL, 0.2 equiv) at rt. The
reaction mixture was stirred until TLC indicated the reaction was complete (5 hours). The reaction mixture was quenched with
NEt3 (220 µL, 0.5 equiv) and the resulting mixture was filtered through a Celite pad, and the filtrate was evaporated. The
residue was dissolved with EtOAc (20 mL) and washed with sat. NaHCO3 (20 mL), water (20 mL) and brine (20 mL). The
organic layer was dried over MgSO4, filtered, and concentrated under reduced pressure. The residue was purified by column
chromatography (hexane:EtOAc = 19:2) to afford benzyl ether 2a (1.36 g, quant).
O
HN
O
NH
N
H
O
Identification of isocyanuric acid: Partition of crude material between EtOAc and sat. NaHCO3 resulted in a precipitate. The
precipitate was filtered, washed with cold 6 M HCl and cold water. The precipitate was recrystallized from water to give
isocyanuric acid (138.2 mg, 45%) as a white solid.
1
H NMR (DMSO-d6): δ 11.16 (br s, 3H); 13C NMR (DMSO-d6): δ 149.8; Anal. Calcd for C3H3N3O3: C, 27.92; H, 2.34; N,
32.55. Found: C, 27.94; H, 2.32; N, 32.65; LRMS (ESI-MS): 128([M-H]-); IR (KBr): 3116, 3028, 2781, 1778, 1751, 1724,
1473, 1398, 1053, 775, 754, 536.
Benzyl 3-phenylpropyl ether (2a)2)
1
H NMR (CDCl3): δ 7.40-7.14 (m, 10H), 4.50 (s, 2H), 3.49 (t, J = 6.4 Hz, 2H), 2.72 (d, J = 7.6 Hz, 2H), 1.94 (tt, J = 6.4, 7.6
Hz, 2H); 13C NMR (CDCl3): δ 142.0, 138.5, 128.5, 128.3, 128.3, 127.7, 127.5, 125.7, 72.9, 69.5, 32.3, 31.3; LRMS (ESI-MS):
249 ([M+Na]+).
Benzyl (2-(2-methoxyethoxy)ethyl ether (2b)3)
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1
H NMR (CDCl3): δ 7.40-7.20 (m, 5H), 4.57 (s, 2H), 3.70-3.60 (m, 6H), 3.58-3.53 (m, 2H), 3.38 (s, 3H); 13C NMR (CDCl3): δ
138.1, 128.2, 127.6, 127.4, 73.1, 71.8, 70.5, 70.4, 69.3, 58.9; LRMS (ESI-MS): 211 ([M+H]+).
(1R, 2S, 5R)-(–)-O-Benzylmenthol (2c)4)
1
H NMR (CDCl3): δ 7.37-7.23 (m, 5 H), 4.65 (d, J = 11.5 Hz, 1H), 4.40 (d, J = 11.5 Hz, 1H), 3.17 (td, J = 4.2, 10.5 Hz, 1H),
2.37-2.24 (m, 1H), 2.23-2.16 (m, 1H), 1.70-1.58 (m, 2H), 1.33 (m, 2H), 1.03-0.80 (m, 3H), 0.94 (d, J = 6.9 Hz, 3H), 0.90 (d, J
= 6.9 Hz, 3H), 0.71 (d, J = 6.9 Hz, 3H); 13C NMR (CDCl3): δ 139.1, 128.2, 127.8, 127.4, 78.7, 70.4, 48.3, 40.3, 34.5, 31.5,
25.5, 23.2, 22.4, 21.0, 16.0; LRMS (ESI-MS): 247 ([M+H]+).
Benzyl 1-adamantyl ether (2d)5)
1
H NMR (CDCl3): δ 7.38-7.20 (m, 5H), 4.51 (s, 2H), 2.18 (s, 3H), 1.88-1.82 (m, 6H), 1.74-1.55 (m, 6H); 13C NMR (CDCl3): δ
140.1, 128.2, 127.4, 127.0, 72.7, 62.3, 41.7, 36.4, 30.5; LRMS (ESI-MS): 243 ([M+H]+).
Benzyl 1,1-dimethyl-3-phenylpropyl ether (2e)6)
To a mixture of TriBOT (28.0 mg, 0.0701 mmol), 1e (34.0 µL, 0.200 mmol) and MS5A (25.0 mg) in 1,4-dioxane (1.00 mL)
was added trifluoromethanesulfonic acid (6.1 µL, 0.070 mmol) at rt under a N2 atmosphere. After stirred for 15 minutes,
TriBOT (28.0 mg, 0.0701 mmol) was added. After stirred for additional 45 minutes, TriBOT (28.0 mg, 0.0701 mmol) was
added. The reaction mixture was stirred for 10 minutes, then neutralized with solid NaHCO3, filtered through silica gel and
concentrated under reduced pressure. The residue was purified by preparative TLC to afford a clear colorless oil (38.7 mg)
which was determined by 1H NMR analysis to consist of 2e (36.5 mg, 0.144 mmol, 72%) and dibenzyl ether (2.2 mg, 0.111
mmol).
1
H NMR (CDCl3): δ 7.40-7.13 (m, 10H), 4.47 (s, 2H), 2.75-2.69 (m, 2H), 1.91-1.84 (m, 2H), 1.32 (s, 6H); 13C NMR (CDCl3):
δ 142.9, 139.7, 128.3, 128.3, 128.3, 127.3, 127.1, 125.6, 74.9, 63.7, 42.4, 30.4, 25.8; LRMS (ESI-MS): 255 ([M+H]+).
Benzyl α-methylbenzyl ether (2f)7)
To a mixture of TriBOT (63.9 mg, 0.160 mmol), 1f (48.2 µL, 0.400 mmol) and MS5A (50.0 mg) in 1,4-dioxane (2.00 mL) was
added trifluoromethanesulfonic acid (7.0 µL, 0.080 mmol) at rt under a N2 atmosphere. After stirred for 1 hour, TriBOT (32.0
mg, 0.0801 mmol) was added and the reaction mixture was stirred for 40 minutes, then quenched with NEt3 (55.0 µL). The
mixture was filtered through silica gel and concentrated under reduced pressure. The residue was purified by column
chromatography to afford a clear colorless oil (71.1 mg) which was determined by 1H NMR analysis to consist of 2f (68.9 mg,
0.325 mmol, 81%) and dibenzyl ether (2.2 mg, 0.111 mmol).
1
H NMR (CDCl3): δ 7.44-7.22 (m, 10H), 4.50 (q, J = 6.4 Hz, 1H), 4.45 (d, J = 11.9 Hz, 1H), 4.29 (d, J = 11.9 Hz, 1H), 1.48 (d,
J = 6.4 Hz, 3H); 13C NMR (CDCl3): δ 143.6, 138.5, 128.4, 128.3, 127.6, 127.5, 127.4, 126.3, 76.7, 70.2, 24.2; LRMS (ESIMS): 235 ([M+Na]+).
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1-Acetoxy-10-(benzyloxy)decane (2g)
1
H NMR (CDCl3): δ 7.34-7.24 (m, 5H), 4.50 (s, 2H), 4.05 (t, J = 6.8 Hz, 2H), 3.46 (t, J = 6.8 Hz, 2H), 2.05 (s, 3H), 1.62 (tt, J
= 6.8 Hz, 2H), 1.60 (tt, J = 6.8 Hz, 2H), 1.40-1.10 (m, 12H); 13C NMR (CDCl3): δ 171.2, 138.6, 128.3, 127.5, 127.4, 72.8, 70.4,
64.6, 29.7, 29.4, 29.4, 29.4, 29.2, 28.5, 26.1, 25.8, 21.0; HRMS (ESI-MS) Calcd for C19H31O3 ([M+H]+): 307.2273, Found:
307.2275; IR (KBr): 3001, 2931, 2858, 1732, 1454, 1365, 1261, 1097, 1039.
Benzyl (2-(2-chloroethoxy)ethyl ether (2h)8)
1
H NMR (CDCl3): δ 7.38-7.25 (m, 5H), 4.58 (s, 2H), 3.76 (t, J = 6.0 Hz, 2H), 3.72-3.67 (m, 2H), 3.66-3.61 (m, 4H); 13C NMR
(CDCl3): δ 138.1, 128.3, 127.7, 127.6, 73.3, 71.3, 70.7, 69.3, 42.7; LRMS (ESI-MS): 215 ([M+H]+).
Benzyl 2-bromoethyl ether (2i)9)
To a mixture of TriBOT (127.8 mg, 0.320 mmol), 1i (56.5 µL, 0.800 mmol) and MS5A (100.0 mg) in 1,4-dioxane (4.00 mL)
was added trifluoromethanesulfonic acid (14.0 µL, 0.160 mmol) at rt under a N2 atmosphere. After stirred for 1 hour, TriBOT
(63.9 mg, 0.160 mmol) was added. The reaction mixture was stirred for 4 hours, then neutralized with solid NaHCO3, filtered
through silica gel and concentrated under reduced pressure. The residue was purified by column chromatography to afford a
clear colorless oil (168.7 mg, 98%).
1
H NMR (CDCl3): δ 7.40-7.25 (m, 5H), 4.59 (s, 2H), 3.79 (t, J = 6.0 Hz, 2H), 3.49 (t, J = 6.0 Hz, 2H); 13C NMR (CDCl3): δ
137.6, 128.4, 127.8, 127.7, 73.1, 69.9, 30.4; LRMS (ESI-MS): 237 ([M+Na]+).
Methyl (2R)-3-(benzyloxy)-2-methylpropionate (2j)10)
1
H NMR (CDCl3): δ 7.39-7.22 (m, 5H), 4.52 (s, 2H), 3.70 (s, 3H), 3.66 (dd, J = 7.3, 9.2 Hz, 1H), 3.50 (dd, J = 6.0, 9.2 Hz, 1H),
2.85-2.73 (m, 1H), 1.18 (d, J = 7.3 Hz, 3H); 13C NMR (CDCl3): δ 175.3, 138.1, 128.3, 127.5, 127.5, 73.0, 71.9, 51.7, 40.1,
13.9; LRMS (ESI-MS): 209 ([M+H]+).
Ethyl (2S)-(benzyloxy)propanoate (2k)6)
To a mixture of TriBOT (63.9 mg, 0.160 mmol), 1k (45.6 µL, 0.400 mmol) and MS5A (50.0 mg) in 1,4-dioxane (2.00 mL)
was added trifluoromethanesulfonic acid (7.0 µL, 0.080 mmol) at rt under a N2 atmosphere. After stirred for 1 hour, TriBOT
(32.0 mg, 0.0801 mmol) was added. After stirred for additional 5 hours, TriBOT (32.0 mg, 0.0801 mmol) was added. The
reaction mixture was stirred for 1 hour, then quenched with NEt3 (55.0 µL), filtered through silica gel and concentrated under
reduced pressure. The residue was purified by column chromatography to afford 2k (71.8 mg, 86%) as a clear colorless oil.
1
H NMR (CDCl3): δ 7.39-7.25 (m, 5H), 4.70 (d, J = 11.5 Hz, 1H), 4.45 (d, J = 11.5 Hz, 1H), 4.29-4.15 (m, 2H), 4.05 (q, J =
6.9 Hz, 1H), 1.44 (d, J = 6.9 Hz, 3H), 1.29 (t, J = 7.0 Hz, 3H); 13C NMR (CDCl3): δ 173.2, 137.5, 128.3, 127.9, 127.8, 74.0,
71.9, 60.8, 18.6, 14.2; LRMS (ESI-MS): 209 ([M+H]+).
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4-Benzyloxybiphenyl (2l)11)
1
H NMR (CDCl3): δ 7.58-7.27 (m, 12H), 7.08-7.02 (m, 2H), 5.11 (s, 2H); 13C NMR (CDCl3): δ 158.3, 140.7, 136.9, 134.0,
128.7, 128.6, 128.2, 128.0, 127.5, 126.7, 126.7, 115.1, 70.1; LRMS (FAB): 260 ([M]+).
2-(2-(Benzyloxy)ethoxy)ethanamine (2m)12)
To a mixture of TriBOT (127.8 mg, 0.320 mmol), 1m (79.4 µL, 0.800 mmol) and MS5A (100.0 mg) in 1,4-dioxane (4.00 mL)
was added trifluoromethanesulfonic acid (84.3 µL, 0.960 mmol) at rt under a N2 atmosphere. After stirred for 1 hour, TriBOT
(63.9 mg, 0.160 mmol) was added. The reaction mixture was stirred for 4 hours, then neutralized with solid NaHCO3, filtered
through silica gel and concentrated under reduced pressure. The residue was purified by column chromatography using NH
silica gel (Fuji Silysia Chemical) to afford a clear colorless oil (120.8 mg, 77%).
1
H NMR (CDCl3): δ 7.38-7.25 (m, 5H), 4.57 (s, 2H), 3.68-3.60 (m, 4H), 3.52 (t, J = 5.0 Hz, 2H), 2.87 (t, J = 5.0 Hz, 2H), 2.01
(br s, 2H); 13C NMR (CDCl3): δ 138.0, 128.3, 127.7, 127.6, 73.1, 72.4, 70.2, 69.2, 41.3; LRMS (ESI-MS): 196 ([M+H]+).
Methyl 2,3,4,6-tetra-O-benzyl-α-D-glucopyranoside (2n)13)
To a mixture of TriBOT (127.8 mg, 0.320 mmol), 1n (38.8 mg, 0.200 mmol) and MS5A (100.0 mg) in 1,4-dioxane (4.00 mL)
was added trifluoromethanesulfonic acid (14.0 µL, 0.160 mmol) at rt under a N2 atmosphere. After stirred for 1 hour, TriBOT
(63.9 mg, 0.320 mmol) was added. The reaction mixture was stirred for 1 hour, then quenched with 1 M NaOH (0.20 mL). The
mixture was filtered through a celite pad and concentrated under reduced pressure. The residue was purified by column
chromatography to afford 2n (81.8 mg, 74%) as a clear colorless oil.
1
H NMR (CDCl3): δ 7.37-7.22 (m, 18H), 7.15-7.11 (m, 2H), 4.98 (d, J = 11.0 Hz, 1H), 4.83 (d, J = 11.0 Hz, 1H), 4.82 (d, J =
11.0 Hz, 1H), 4.79 (d, J = 12.0 Hz, 1H), 4.66 (d, J = 12.0 Hz, 1H), 4.63 (d, J = 3.6 Hz, 1H), 4.60 (d, J = 12.2 Hz, 1H), 4.47 (d,
J = 12.2 Hz, 1H), 4.47 (d, J = 11.0 Hz, 1H), 3.98 (t, J = 9.6 Hz, 1H), 3.77-3.69 (m, 2H), 3.66-3.59 (m, 2H), 3.58-3.54 (dd, J =
3.5, 9.6 Hz, 1H), 3.37 (s, 3H); 13C NMR (CDCl3): δ 138.7, 138.2, 138.1, 137.8, 128.4, 128.3, 128.3, 128.1, 127.9, 127.8, 127.8,
127.6, 127.6, 127.5, 98.1, 82.1, 79.8, 77.6, 75.7, 75.0, 73.4, 73.3, 70.0, 68.4, 55.1; LRMS (ESI-MS): 577 ([M+Na]+).
Benzylpentamethylbenzene (5)14)
To a mixture of TriBOT (26.6 mg, 0.0666 mmol), pentamethylbenzene (29.7 mg, 0.200 mmol) and MS5A (50.0 mg) in 1,4dioxane (1.00 mL) was added trifluoromethanesulfonic acid (3.5 µL, 0.040 mmol) at rt under a N2 atmosphere. After stirred for
12 hours, the reaction mixture was neutralized with solid NaHCO3, filtered and concentrated under reduced pressure. The
residue was purified by column chromatography to afford 5 (33.2 mg, 70%) as a white solid.
1
H NMR (CDCl3): δ 7.26-7.11 (m, 3H), 7.03 (d, J = 7.2 Hz, 2H), 4.11 (s, 2H), 2.27 (s, 3H), 2.25 (s, 6H), 2.17 (s, 6H); 13C
NMR (CDCl3): δ 140.6, 133.8, 133.1, 132.8, 132.5, 128.3, 127.9, 125.5, 36.1, 17.0, 16.8, 16.8; LRMS (FAB): 238 ([M]+).
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2,4,6-Trimethoxy-1,3,5-triazine (6)
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H NMR (CDCl3): δ 4.03 (s, 9H); 13C NMR (CDCl3): δ 173.5, 55.3; LRMS (ESI-MS): 172 ([M+H]+).
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3. References
1. Srinivas, K.; Sitha, S.; Rao, V. J.; Bhanuprakash, K.; Ravikumar, K. J. Mater. Chem. 2006, 16, 496.
2. Sajiki, H.; Hirota, K. Tetrahedron 1998, 54, 13981.
3. Grobelny, Z.; Stolarzewicz, A.; Maercker, A.; Krompiec, S.; Kasperczyk, J.; Rzepa, J. J. Organomet. Chem. 2004, 689,
1580.
Johnson II, D. C.; Widlanski, T. S. Org. Lett. 2004, 6, 4643.
Poon, K. W. C.; Dudley, G. B. J. Org. Chem. 2006, 71, 3923.
Aoki, H.; Mukaiyama, T. Bull. Chem. Soc. Jpn. 2006, 79, 1255.
Rahaim, R. J.; Maleczka, R. E. Org. Lett. 2011, 13, 584.
Coudert, G.; Mpassi, M.; Guillaumet, G.; Selve, C. Synth. Commun. 1986, 16, 19.
Chellat, M. F.; Proust, N.; Lauer, M. G.; Stambuli, J. P. Org. Lett. 2011, 13, 3246.
White, J. D.; Kawasaki, M. J. Org. Chem. 1992, 57, 5292.
Percec, V.; Golding, G. M.; Smidrkal, J.; Weichold, O. J. Org. Chem. 2004, 69, 3447.
Harjani, J. R.; Liang, C.; Jessop, P. G. J. Org. Chem. 2011, 76, 1683.
Li, T.; Guo, L.; Zhang, Y.; Wang, J.; Zhang, Z.; Li, J.; Zhang, W.; Lin, J.; Zhao, W.; Wang, P. G. Bioorg. Med. Chem.
2011, 19, 2136.
14. Sun, H. -B.; Li, B.; Chen, S.; Li, J.; Hua, R. Tetrahedron 2007, 63, 10185.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
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4. HPLC analyses
Methyl (2R)-3-(benzyloxy)-2-methylpropionate (2j)
conditions
flow: 1.0 mL/min (hexane:EtOH = 99.9:0.1)
detection at 256 nm
panel a. Methyl (2R)-3-(benzyloxy)-2-methylpropionate, retention time: 17.0 min, 100%
panel b. 1: Methyl (2R)-3-(benzyloxy)-2-methylpropionate, retention time: 17.1 min, 50.18%
2: Methyl (2S)-3-(benzyloxy)-2-methylpropionate, retention time: 21.7 min, 49.82%
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Ethyl (2S)-(benzyloxy)propanoate (2k)
conditions
flow: 1.0 mL/min (hexane:2-PrOH = 99.93:0.07)
detection at 256 nm
panel a. Ethyl (2S)-(benzyloxy)propanoate, retention time: 20.4 min, 100%
panel b. 1: Ethyl (2S)-(benzyloxy)propanoate, retention time: 20.8 min, 49.82%
2: Ethyl (2R)-(benzyloxy)propanoate, retention time: 31.3 min, 50.18%
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1
13
5. H and C NMR spectra
2,4,6-Tris(benzyloxy)-1,3,5-triazine (TriBOT)
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Isocyanuric acid
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Benzyl 3-phenylpropyl ether (2a)
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Benzyl (2-(2-methoxyethoxy)ethyl ether (2b)
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(1R, 2S, 5R)-(–)-O-Benzylmenthol (2c)
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S20
Benzyl 1-adamantyl ether (2d)
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Benzyl 1,1-dimethyl-3-phenylpropyl ether (2e)
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Benzyl α-methylbenzyl ether (2f)
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1-Acetoxy-10-(benzyloxy)decane (2g)
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Benzyl (2-(2-chloroethoxy)ethyl ether (2h)
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S30
Benzyl 2-bromoethyl ether (2i)
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Methyl (2R)-3-(benzyloxy)-2-methylpropionate (2j)
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S34
Ethyl (2S)-(benzyloxy)propanoate (2k)
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S36
4-Benzyloxybiphenyl (2l)
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2-(2-(Benzyloxy)ethoxy)ethanamine (2m)
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S40
Methyl 2,3,4,6-tetra-O-benzyl-α-D-glucopyranoside (2n)
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Benzylpentamethylbenzene (5)
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2,4,6-Trimethoxy-1,3,5-triazine (6)
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