3.2. O-Allylation of 4-Hydroxy-1H-pyrazoles (Scheme 1)

General procedure: To a solution of 4-formyl-1H-1-tritylprazole (8a) (94.6 mg, 0.28 mmol) in CH₂Cl₂ (6 mL) was added 70% mCPBA (131.8 mg, 0.53 mmol) at 0 °C, with stirring. After 5 h, saturated NaHCO₃ aq (10 mL) was added to quench the reaction mixture. The mixture was extracted with CH₂Cl₂ 3 times. Combined organic layer was dried over MgSO₄, filtered, and condensed under reduced pressure to give a crude formate. To an acetone solution of the crude formate (6 mL), 20% NaOH aq (4 mL) was added, then the mixture was heated under reflux for 1 h, then crotyl bromide (48 µL, 0.42 mmol) was added to the cooled mixture. After stirring for 3 h, saturated NH₄Cl aq was added to the reaction mixture to quench, the mixture was condensed under reduced pressure, extracted with CH₂Cl₂ for 3 times. The combined CH₂Cl₂ layer was dried over MgSO₄, filtered, and condensed under reduced pressure to give a crude residue, which was purified with flash column chromatography (EtOAc:Hexane = 1:10) to give 4-(2-butenyl)oxy-1H-1-tritylpyrazole (1e) (54.5 mg, 51%).

4-(2-butenyl)oxy-1H-1-tritylpyrazole (1e): white powder; melting point (m.p.) 84–87 °C; IR (KBr) v_max 1571 (C=C), 1490 (C=C), 1445 (C=C) cm⁻¹; ¹H-NMR (400 MHz, CDCl₃): δ 1.63 (0.5 H, dd, J = 6.5, 1.0 Hz, (Z)-CH₃CH=CH-), 1.71 (2.5 H, dd, J = 6.4, 1.0 Hz, (E)-CH₃CH=CH-), 4.26 (1.7 H, br d, J = 6.4 Hz, (E)-CH=CHCH₂O-), 4.41 (0.3 H, dd, J = 6.4 Hz, (Z)-CH=CHCH₂O-), 5.31–5.63 (1H, m, -CH=CH-), 5.63–5.78 (1H, m, -CH=CH-), 7.01 (0.83H, d, J = 0.8 Hz, pyrazole-H), 7.03 (0.17H, d, J = 0.8 Hz, pyrazole-H), 7.10–7.20 (6H, m, Tr-H), 7.22–7.38 (9 H, m, Tr-H), 7.40 (0.83H, d, J = 0.6 Hz, pyrazole-H), 7.41 (0.17H, d, J = 0.7 Hz, pyrazole-H); ¹³C-NMR (100 MHz, CDCl₃): δ (13.2), 17.7, 53.4, (67.0), 72.2, 78.5, (81.9), (118.2), 118.3, (125.4), 126.0, 127.2, 128.1, (128.8), 130.0, 130.7, 130.9, 143.1, 144.1, 146.8; High Resolution Electron Impact Mass Spectrum (HREIMS) m/z calcd. for C₂₆H₂₄N₂O [M⁺] 380.1189, found 380.1185.

4-(3-Methyl-2-butenyl)oxy-1H-1-tritylpyrazole (1f): Colorless crystals (CH₂Cl₂); m.p. 60–70 °C; IR (KBr) v_max 1576 (C=C), 1492 (C=C), 1445 (C=C) cm⁻¹; ¹H-NMR (600 MHz, CDCl₃): δ 1.63 (3H, d, J = 0.6 Hz, =CMeMe), 1.74 (3H, d, J = 0.9 Hz, =CMeMe), 4.33 (2H, dt, J = 7.0 Hz, OCH₂CH=), 5.40 (1H, tqq, J = 7.0, 0.9, 0.6 Hz, -OCH₂CH=C(CH₃)₂), 7.00 (1H, d, J = 0.9 Hz, pyrazole-H), 7.14–7.17 (6H, m, Tr-H), 7.26–7.31 (9 H, m, Tr-H), 7.40 (1H, d, J = 0.9 Hz, pyrazole-H); ¹³C-NMR (125 MHz, CDCl₃): δ 18.1, 25.7, 68.1, 78.5, 118.2, 119.7, 127.6, 127.9, 128.2, 130.1, 138.4, 143.2, 144.2; HREIMS m/z calcd. for C₂₈H₂₆N₂O [M⁺] 394.2045, found 394.2047.

(E/Z)-4-(3-Phenyl-2-propenyl)oxy-1H-1-tritylpyrazoles (1g): Colorless needles (CH₂Cl₂); m.p. 115–120 °C; IR (KBr) v_max 1565 (C=C), 1445 (C=C) cm⁻¹; ¹H-NMR (400 MHz, CDCl₃): δ 4.50 (1.8H, dd, J = 6.1, 1.2 Hz, -OCH₂CH=), 4.86 (0.2H, dd, J = 6.5, 1.2 Hz, -OCH₂CH=), 6.31 (1H, dt, J = 16.0, 6.1 Hz, -CH₂CH=CH-), 6.62 (1H, d, J = 16.0 Hz, -CH=CHPh), 7.05 (1H, d, J = 0.5 Hz, pyrazole-H), 7.10–7.19 (8H, m, Tr-H, Ph-H), 7.22–7.40 (12H, m, Tr-H, Ph-H), 7.44 (1H, d, J = 0.5 Hz, pyrazole-H); ¹³C-NMR (100 MHz, CDCl₃): δ 29.7, 72.3, 78.7, 118.7, 124.3, 126.6, 127.6, 127.9, 128.3, 128.6, 130.1, 136.3, 143.1, 144.0; HREIMS m/z calcd. for C₃₁H₂₆N₂O [M⁺] 442.2045, found 442.2046.

(E/Z)-1-Benzyl-4-(2-butenyl)oxy-1H-pyrazoles (1h): Oil; IR (film) v_max 1575 (C=C), 1496 (C=C) cm⁻¹; ¹H-NMR (400 MHz, CDCl₃): δ 1.66 (0.5 H, dd, J = 5.8, 0.5 Hz, (Z)-CH₃CH=CH-), 1.70 (2.5H, dd, J = 6.5, 0.6 Hz, (E)-CH₃CH=CH-), 4.28 (1.7 H, dd, J = 6.2, 1.0 Hz, (E)-OCH₂CH=CH-), 4.42 (0.3 H, dd, J = 6.2, 0.6 Hz, (Z)-OCH₂CH=CH-), 5.18 (2 H, s, ArCH₂Ph), 5.60–5.72 (1H, m, -CH=CH-), 5.72–5.84 (1H, m, -CH=CH-), 7.01 (0.83 H, s, pyrazole-H), 7.03 (0.17 H, s, pyrazole-H), 7.17 (2H, dd, J = 6.9, 1.1 Hz, Ph-H), 7.20–7.40 (6 H, m, Ph-H, pyrazole-H); ¹³C-NMR (100 MHz, CDCl₃): δ (13.3), 17.8, (49.7), 56.6, (67.2), 72.4, (114.96), 150.02, (125.5), 126.0, (126.9), 127.5, 127.6, (128.0), (128.3), 128.5, 128.7, (128.88), (128,.92), (129.0), 131.0, 136.7, (143.5), 145.6; HREIMS m/z calcd. for C₁₄H₁₆N₂O [M⁺] 228.1263, found 228.1263.

1-Benzyl-4-(3-methyl-2-butenyl)oxy-1H-pyrazoles (1i): Oil; IR (film) v_max 1574 (C=C), 1496 (C=C), 1455 (C=C) cm⁻¹; ¹H-NMR (400 MHz, CDCl₃): δ 1.67 (3H, s, =CMeMe), 1.74 (3H, s, =CMeMe), 4.34 (2H, d, J = 6.9 Hz, -OCH₂CH=), 5.18 (2H, s, ArCH₂Ph), 5.42 (1H, m, -CH₂CH=CMe₂), 7.01 (1H, s, pyrazole-H), 7.18 (2H, d, J = 7.3 Hz, Ph-H), 7.24–7.34 (4 H, m, Ph-H, pyrazole-H); ¹³C-NMR (100 MHz, CDCl₃): δ 18.1, 25.7, 56.6, 68.2, 114.9, 119.6, 127.50, 127.54, 128.0, 128.7, 136.7, 138.6, 145.8; HREIMS m/z calcd. for C₁₅H₁₈N₂O [M⁺] 242.1419, found 242.1420.

(E/Z)-1-Benzyl-4-(3-phenyl(2-propenyl))oxy-1H-pyrazoles (1j): white powder; m.p. 68–71 °C; IR (KBr) v_max 1565 (C=C), 1490 (C=C), 1445 (C=C) cm⁻¹; ¹H-NMR (400 MHz, CDCl₃): δ 4.50 (1.9H, dd, J = 7.1, 1.4 Hz, -OCH₂CH=), 4.58 (0.1H, dd, J = 5.8, 1.4 Hz, -OCH₂CH=), 5.17 (1.9H, s, ArCH₂Ph), 5.21 (0.1H, s, ArCH₂Ph), 6.31 (1H, dt, J = 16.0, 5.9 Hz, -CH₂CH=CH-), 6.63 (1H, d, J = 16.0 Hz, -CH=CHPh), 7.04 (1H, s, pyrazole-H), 7.13–7.36 (11H, m, Ph-H, pyrazole-H); ¹³C-NMR (100 MHz, CDCl₃): δ 56.7, 72.4, 115.3, 124.3, 126.6, 127.5, 127.7, 127.95, 128.0, 128.6, 128.8, 133.4, 136.3, 136.6, 145.6; HREIMS m/z calcd. for C₁₉H₁₈N₂O [M⁺] 290.1419, found 290.1418.