Microwave-Assisted Solvent-Free Synthesis of Enol Carbamates

Abstract

An efficient and simple method for the synthesis of enol carbamates by irradiation with microwaves under solvent-free ­conditions has been developed. The method has been applied to substituted acetophenones, cyclic aryl ketones and α-aryl ketones. Its main advantages are short reaction times, good conversions ­except for nitro acetophenones, and the environmentally friendly nature of the process. For α-aryl ketones the reaction shows regio­selectivity to afford conjugated products.

solvent-free - microwave - enol carbamates

References and Notes

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2 Bambury RE, and Seelye DE. inventors; Eur. Patent, EP  0396364.  ; Chem. Abstr. 1991, 114, 254062

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19

It has been described that 1-phenylvinyl N,N-diisopropyl-carbamate was obtained in 73% yield; however, we have never been able to get yields higher than 50%, even with longer reaction times or higher temperatures.

20 Varma RS. Green Chem.  1999,  1:  43 

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32

Longer reaction times did not improve the yield significantly.

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34

General Procedure for the Synthesis of 1-Arylalkenyl N , N- Diisopropylcarbamates 2; Synthesis of 1-Phenyl-vinyl N , N -Diisopropylcarbamate (2a): A stirred mixture of acetophenone (1a) (120 mg, 1 mmol), N,N-diisopropyl-carbamoyl chloride (163 mg, 1.5 mmol) and 2,4,6-collidine (121 mg, 1.5 mmol) was irradiated in an open vessel with microwaves in a monomode oven (Discover CEM, 50 W and temperature control set at 150 °C measured with an IR sensor) for 60 min. The crude was dissolved in CH₂Cl₂ (30 mL) and washed with 10% aq HCl (2 × 20 mL), dried (Na₂SO₄) and evaporated to give 1-phenylvinyl N,N-diiso-propylcarbamate (2a). Further purification by distillation (160 °C, 1 mm Hg) gave 155 mg (63%) of 2a; mp 61-63 °C (hexane), lit.¹³ mp 60-62 °C.

35

Enol carbamates and parent ketones show very similar R _f values, making it very difficult to separate them by chromatography. When purification by distillation is not possible, a very easy way to remove the starting material is to reduce it to the corresponding alcohol with sodium borohydride followed by column chromatography. This very method must also have been used in previously described literature procedures as we confirmed in our laboratory.

36

Data of previously undescribed compounds:
1-(4-Methoxyphenyl)vinyl N , N -Diisopropylcarbamate (2b): Oil. ¹H NMR (300 MHz, CDCl₃): δ = 1.28-1.32 [m, 12 H, 2 × CH(CH ₃)₂], 3.80 (s, 3 H, OMe), 3.99-4.03 [m, 2 H, 2 × CH(CH₃)₂], 4.87 (d, J = 1.8 Hz, 1 H, C=CH₂), 5.28 (d, J = 1.8 Hz, 1 H, C=CH₂), 6.87 (d, J = 8.8 Hz, 2 H, ArH), 7.41 (d, J = 8.8 Hz, 2 H, ArH). ¹³C NMR (75 MHz, CDCl₃): δ = 20.7, 21.8, 46.4, 46.8, 55.5, 99.7, 114.0, 126.5, 128.4, 153.5, 153.7, 160.1. MS (EI): m/z (%) = 278 (9) [M⁺ + 1], 277 (22) [M⁺], 135 (45), 128 (100). IR (KBr, film): 1713, 1512, 1252, 1041, 837 cm^-1. Anal. Calcd for C₁₆H₂₃NO₃: C, 69.29; H, 8.36; N, 5.05. Found: C, 68.95; H, 8.76; N, 4.72.
1-(4-Benzyloxyphenyl)vinyl N , N -Diisopropylcarbamate (2c): mp 94-95 °C (hexane). ¹H NMR (300 MHz, CDCl₃): δ = 1.24-1.33 [m, 12 H, 2 × CH(CH ₃)₂], 4.02 [br s, 2 H, 2 × CH(CH₃)₂], 4.90 (d, J = 1.8 Hz, 1 H, C=CH₂), 5.07 (s, 2 H, OCH ₂Ph), 5.30 (d, J = 1.8 Hz, 1 H, C=CH₂), 6.93 (d, J = 8.8 Hz, 2 H, ArH), 7.32-7.42 (m, 7 H, ArH). ¹³C NMR (75 MHz, CDCl₃): δ = 20.7, 20.8, 46.4, 46.9, 70.3, 99.8, 115.0, 126.6, 127.7, 128.2, 128.6, 128.8, 137.1, 153.5, 153.7, 159.4. MS (EI): m/z (%) = 353 (50) [M⁺], 128 (100). IR (KBr, film): 1705, 1246, 1215, 1011, 841 cm^-1. Anal. Calcd for C₂₂H₂₇NO₃: C, 74.76; H, 7.70; N, 3.96. Found: C, 75.12; H, 8.07; N, 3.91.
1-(4-Isopropoxyphenyl)vinyl N , N -Diisopropylcarbamate (2d): Oil. ¹H NMR (300 MHz, CDCl₃): δ = 1.29-1.33 [m, 18 H, 3 × CH(CH ₃)₂], 4.01 [sept, J = 6.8 Hz, 2 H, 2 × CH(CH₃)₂], 4.54 [sept, J = 6.0 Hz, 1 H, CH(CH₃)₂], 4.86 (d, J = 2.2 Hz, 1 H, C=CH₂), 5.27 (d, J = 1.8 Hz, 1 H, C=CH₂), 6.8 (d, J = 8.8 Hz, 2 H, ArH), 7.39 (d, J = 8.8 Hz, 2 H, ArH). ¹³C NMR (75 MHz, CDCl₃): δ = 20.7, 21.8, 22.2, 46.3, 46.8, 70.1, 99.5, 115.7, 115.9, 126.5, 153.6, 153.7, 158.5. MS (EI): m/z (%) = 305 (8) [M⁺], 128 (100), 86 (36). IR (KBr, film): 2975, 1712, 1509, 1248 cm^-1. Anal. Calcd for C₁₈H₂₇NO₃: C, 70.79; H, 8.91; N, 4.59. Found: C, 71.07; H, 8.94; N, 4.76.
1-(4-{[(Diisopropylamino)carbonyl]oxy}phenyl)vinyl N , N -Diisopropylcarbamate (2e): mp 59-61 °C. ¹H NMR (300 MHz, CDCl₃): δ = 1.30 [m, 24 H, 4 × CH(CH ₃)₂], 4.00 [hept, J = 6.6 Hz, 4 H, 4 × CH(CH₃)₂], 4.95 (d, J = 2.2 Hz, 1 H, CH=CH ₂), 5.33 (d, J = 2.2 Hz, 1 H, CH=CH ₂), 7.10 (d, J = 8.8 Hz, 2 H, ArH), 7.46 (d, J = 8.8 Hz, 2 H, ArH). ¹³C NMR (75 MHz, CDCl₃): δ = 20.7, 21.6, 21.8, 46.4, 46.8, 101.2, 121.9, 126.2, 132.6, 151.9, 153.2, 153.5, 153.8. MS (EI): m/z (%) = 390 (4) [M⁺], 128 (100), 86 (44). IR (KBr, film): 1715, 1315, 1258, 1214, 1154 cm^-1. Anal. Calcd for C₂₂H₃₄N₂O₄: C, 67.66; H, 8.78; N, 7.17. Found: C, 67.36; H, 8.89; N, 7.05.
1-(4-Fluorophenyl)vinyl N , N -Diisopropylcarbamate (2f): Oil. ¹H NMR (300 MHz, CDCl₃): δ = 1.25-1.33 [m, 12 H, 2 × CH(CH ₃)₂], 4.00 [sept, J = 6.6 Hz, 2 H, 2 × CH(CH₃)₂], 4.96 (d, J = 2.2 Hz, 1 H, C=CH ₂), 5.33 (d, J = 2.2 Hz, 1 H, C=CH ₂), 7.02 (t, J = 8.8 Hz, 2 H, ArH), 7.44 (dd, J = 5.3, 9.0 Hz, 2 H, ArH). ¹³C NMR (75 MHz, CDCl₃): δ = 20.7, 21.8, 47.0, 101.4, 115.6 (d, ² J _CF = 22 Hz), 127.0, 131.9, 152.9, 153.5, 163.1 (d, ¹ J _CF = 248 Hz). MS (EI): m/z (%) = 265 (5) [M⁺], 128 (68), 86 (100). IR (KBr, film): 2968, 1712, 1510, 1259, 1214, 1043 cm^-1. Anal. Calcd for C₁₅H₂₀FNO₂: C, 67.90; H, 7.60; N, 5.28. Found: C, 68.07; H, 7.47; N, 5.19.
1-(4-Nitrophenyl)vinyl N , N -Diisopropylcarbamate (2g): mp 83-86 °C. ¹H NMR (300 MHz, CDCl₃): δ = 1.26-1.35 [m, 12 H, 2 × CH(CH ₃)₂], 4.01 [sept, J = 6.6 Hz, 2 H, 2 × CH(CH₃)₂], 5.19 (d, J = 2.2 Hz, 1 H, C=CH₂), 5.56 (d, J = 2.2 Hz, 1 H, C=CH₂), 7.60 (d, J = 9.2 Hz, 2 H, ArH), 8.20 (d, J = 8.8 Hz, 2 H, ArH). ¹³C NMR (75 MHz, CDCl₃): δ = 20.6, 21.8, 46.6, 47.1, 105.5, 124.1, 125.9, 142.0, 147.9, 151.9, 153.1. MS (EI): m/z (%) = 292 (1) [M⁺], 165 (28), 128 (94), 86 (100). IR (KBr, film): 2971, 1709, 1519, 1345, 1262 cm^-1. Anal. Calcd for C₁₅H₂₀N₂O₄: C, 61.63; H, 6.90; N, 9.58. Found: C, 61.34; H, 6.41; N, 9.62.
1-(3-Benzyloxyphenyl)vinyl Diisopropylcarbamate (2h): Oil. ¹H NMR (300 MHz, CDCl₃): δ = 1.29-1.34 [m, 12 H, 2 × CH(CH ₃)₂], 4.03 [sept, J = 6.8 Hz, 2 H, 2 × CH(CH₃)₂], 5.00 (d, J = 1.8 Hz, 1 H, C=CH ₂), 5.07 (s, 2 H, OCH ₂Ph), 5.40 (d, J = 1.8 Hz, 1 H, C=CH ₂), 6.93 (br d, J = 7.9 Hz, 1 H, ArH), 7.10 (m, 2 H, ArH), 7.26 (t, J = 7.9 Hz, 1 H, ArH), 7.30-7.45 (m, 5 H, ArH). ¹³C NMR (75 MHz, CDCl₃): δ = 20.7, 21.8, 46.5, 46.9, 70.3, 101.9, 111.8, 115.5, 118.0, 127.7, 128.2, 128.8, 129.7, 137.1, 137.2, 153.5, 159.1. MS (EI): m/z (%) = 353 (2) [M⁺], 128 (100), 91 (30). IR (KBr, film): 2969, 1712, 1431, 1264, 1042 cm^-1. Anal. Calcd for C₂₂H₂₇NO₃: C, 74.76; H, 7.70; N, 3.96. Found: C, 74.38; H, 7.24; N, 3.38.
1-(3-{[(Diisopropylamino)carbonyl]oxy}phenyl)vinyl N , N -Diisopropylcarbamate (2i): mp 74-77 °C. ¹H NMR (300 MHz, CDCl₃): δ = 1.29 [m, 24 H, 4 × CH(CH ₃)₂], 4.00 [br s, 4 H, 4 × CH(CH₃)₂], 5.00 (d, J = 1.8 Hz, 1 H, CH=CH ₂), 5.41 (d, J = 2.2 Hz, 1 H, CH=CH ₂), 7.08 (dt, J = 2.2, 7.0 Hz, 1 H, ArH), 7.20 (m, 1 H, ArH), 7.28-7.34 (m, 2 H, ArH). ¹³C NMR (75 MHz, CDCl₃): δ = 20.7, 21.7, 46.6, 102.2, 118.7, 121.7, 122.3, 129.4, 137.1, 151.7, 153.0. MS (EI): m/z (%) = 390 (18) [M⁺], 128 (100). IR (KBr, film): 1712, 1427, 1257, 1198, 1153 cm^-1. Anal. Calcd for C₂₂H₃₄N₂O₄: C, 67.66; H, 8.78; N, 7.17. Found: C, 67.57; H, 8.42; N, 7.68.
1-(3-Nitrophenyl)vinyl N , N -Diisopropylcarbamate (2j): mp 85-89 °C. ¹H NMR (300 MHz, CDCl₃): δ = 1.27-1.39 [m, 12 H, 2 × CH(CH ₃)₂], 4.02 [br s, 2 H, 2 × CH(CH₃)₂], 5.17 (d, J = 2.6 Hz, 1 H, C=CH₂), 5.54 (d, J = 2.2 Hz, 1 H, C=CH₂), 7.52 (t, J = 8.1 Hz, 1 H, ArH), 7.81 (ddd, J = 0.8, 1.7, 7.9 Hz, 1 H, ArH), 8.16 (ddd, J = 1.4, 2.2, 8.2 Hz, 1 H, ArH), 8.30 (t, J = 2.0 Hz, 1 H, ArH). ¹³C NMR (75 MHz, CDCl₃): δ = 20.6, 21.7, 46.7, 47.1, 104.1, 120.0, 123.4, 129.7, 130.9, 137.6, 148.7, 151.6, 153.1. MS (EI): m/z (%) = 292 (2) [M⁺], 165 (40), 128 (100), 86 (32). IR (KBr, film): 2975, 1713, 1532, 1350, 1255, 1042 cm^-1. Anal. Calcd for C₁₅H₂₀N₂O₄: C, 61.63; H, 6.90; N, 9.58. Found: C, 61.36; H, 7.15; N, 9.34.
1-(2-Benzyloxyphenyl)vinyl N , N -Diisopropylcarbamate (2k): mp 38-40 °C. ¹H NMR (300 MHz, CDCl₃): δ = 1.25 [d, J = 6.6 Hz, 12 H, 2 × CH(CH ₃)₂], 3.97 [sept, J = 6.6 Hz, 2 H, 2 × CH(CH₃)₂], 5.16 (m, 3 H, C=CH ₂, OCH ₂Ph), 5.60 (d, J = 0.9 Hz, 1 H, C=CH ₂), 6.93-6.98 (m, 2 H, ArH), 7.20-7.46 (m, 7 H, ArH). ¹³C NMR (75 MHz, CDCl₃): δ = 20.7, 21.7, 46.3, 46.7, 70.7, 106.5, 113.2, 121.0, 125.2, 127.5, 128.0, 128.7, 129.6, 137.2, 150.5, 153.8, 156.4. MS (EI): m/z (%) = 353 (40) [M⁺], 128 (100) [Cb], 91 (23). IR (KBr, film): 2969, 1710 (C=O), 1446, 1289, 1240 (CO), 1043, 754 cm^-1. Anal. Calcd for C₂₂H₂₇NO₃: C, 74.76; H, 7.70; N, 3.96. Found: C, 74.76; H, 7.43; N, 3.87.
1-(2-{[(Diisopropylamino)carbonyl]oxy}phenyl)vinyl N , N -Diisopropylcarbamate (2l): Oil. ¹H NMR (300 MHz, CDCl₃): δ = 1.23-1.32 [m, 24 H, 4 × CH(CH ₃)₂], 3.91 [br s, 3 H, 3 × CH(CH₃)₂], 4.18 [br s, 1 H, CH(CH₃)₂], 5.15 (s, 1 H, C=CH ₂), 5.18 (s, 1 H, CH=CH ₂), 7.09 (d, J = 7.9 Hz, 1 H, ArH), 7.16 (t, J = 7.5 Hz, 1 H, ArH), 7.29 (t, J = 7.7 Hz, 1 H, ArH), 7.42 (d, J = 7.9 Hz, 1 H, ArH). ¹³C NMR (75 MHz, CDCl₃): δ = 20.7, 21.7, 46.7, 46.9, 105.4, 123.6, 125.1, 129.3, 129.4, 129.6, 149.0, 149.8, 153.4, 153.5. MS (EI): m/z (%) = 391 (5) [M⁺ + 1], 390 (1) [M⁺], 128 (100), 86 (81). IR (KBr, film): 2970, 1715, 1316, 1207, 1042 cm^-1. Anal. Calcd for C₂₂H₃₄N₂O₄: C, 67.66; H, 8.78; N, 7.17. Found: C, 67.22; H, 9.21; N, 6.95.
1-(3,4-Dimethoxyphenyl)vinyl N , N -Diisopropyl-carbamate (2m): Oil. ¹H NMR (300 MHz, CDCl₃): δ = 1.26-1.32 [m, 12 H, 2 × CH(CH ₃)₂], 3.86 (s, 6 H, 2 × OMe), 4.01 [sept, J = 6.6 Hz, 2 H, 2 × CH(CH₃)₂], 4.89 (d, J = 1.8 Hz, 1 H, C=CH₂), 5.28 (d, J = 1.8 Hz, 1 H, C=CH₂), 6.81 (d, J = 8.4 Hz, 1 H, ArH), 6.98 (d, J = 1.8 Hz, 1 H, ArH), 7.04 (dd, J = 2.2, 8.3 Hz, 1 H, ArH). ¹³C NMR (75 MHz, CDCl₃): δ = 20.7, 21.8, 46.4, 46.8, 55.9, 56.1, 100.0, 108.4, 111.2, 118.0, 128.6, 148.9, 149.7, 153.4, 153.5. MS (EI): m/z (%) = 307 (7) [M⁺], 180 (13), 128 (100), 86 (65). IR (KBr, film): 1712, 1516, 1265, 1221, 1143 cm^-1. Anal. Calcd for C₁₇H₂₅NO₄: C, 66.43; H, 8.20; N, 4.56. Found: C, 66.41; H, 7.79; N, 4.63.
1-(4-Benzyloxy-3-methoxyphenyl)vinyl N , N -Diiso-propylcarbamate (2n): mp 75-77 °C. ¹H NMR (300 MHz, CDCl₃): δ = 1.26-1.33 [m, 12 H, 2 × CH(CH ₃)₂], 3.89 (s, 3 H, OMe), 4.02 [m, 2 H, 2 × CH(CH₃)₂], 4.90 (d, J = 1.8 Hz, 1 H, C=CH ₂), 5.16 (s, 2 H, OCH ₂Ph), 5.30 (d, J = 2.2 Hz, 1 H, C=CH₂), 6.84 (d, J = 8.4 Hz, 1 H, ArH), 6.98-7.03 (m, 2 H, ArH), 7.25-7.44 (m, 5 H, ArH). ¹³C NMR (75 MHz, CDCl₃): δ = 20.8, 21.8, 46.4, 46.9, 56.1, 71.2, 100.2, 109.0, 113.9, 117.9, 127.4, 128.1, 128.8, 129.1, 137.2, 148.9, 149.6, 153.4, 153.6. MS (EI): m/z (%) = 383 (5) [M⁺], 128 (100), 91 (94), 86 (66). IR (KBr, film): 1712, 1520, 1272, 1222, 1147, 1020 cm^-1. Anal. Calcd for C₂₃H₂₉NO₄: C, 72.04; H, 7.62; N, 3.65. Found: C, 71.95; H, 7.93; N, 3.60.
1-(4-{[(Diisopropylamino)carbonyl]oxy}-3-methoxy-phenyl)vinyl N , N -Diisopropylcarbamate (2o): Oil. ¹H NMR (300 MHz, CDCl₃): δ = 1.30 [m, 24 H, 4 × CH(CH ₃)₂], 3.80 (s, 3 H, OMe), 4.00 [sept, J = 6.4 Hz, 4 H, 4 × CH(CH₃)₂], 4.96 (s, 1 H, CH=CH ₂), 5.32 (s, 1 H, CH=CH ₂), 7.03-7.05 (m, 3 H, ArH). ¹³C NMR (75 MHz, CDCl₃): δ = 20.3, 20.7, 21.6, 46.8, 56.0, 101.3, 109.6, 117.8, 123.4, 133.8, 135.3, 141.3, 151.7, 153.3. MS (EI): m/z (%) = 420 (2) [M⁺], 293 (1), 128 (100), 86 (44). IR (KBr, film): 1716, 1316, 1281, 1267, 1204, 1154, 1126 cm^-1. Anal. Calcd for C₂₃H₃₆N₂O₅: C, 65.69; H, 8.63; N, 6.66. Found: C, 65.63; H, 8.74; N, 6.54.
1-(2-Naphthyl)vinyl N , N -Diisopropylcarbamate (2p): mp 58-59 °C. ¹H NMR (300 MHz, CDCl₃): δ = 1.26-1.40 [m, 12 H, 2 × CH(CH ₃)₂], 4.07 [m, 2 H, 2 × CH(CH₃)₂], 5.09 (d, J = 2.0 Hz, 1 H, C=CH₂), 5.55 (d, J = 2.0 Hz, 1 H, C=CH₂), 7.44-7.48 (m, 2 H, ArH), 7.63 (dd, J = 1.8, 8.8 Hz, 1 H, ArH), 7.79-7.82 (m, 3 H, ArH), 7.90 (d, J = 1.7 Hz, 1 H, ArH). ¹³C NMR (75 MHz, CDCl₃): δ = 20.7, 21.8, 46.5, 46.9, 102.1, 123.2, 124.3, 126.5, 126.6, 127.8, 128.4, 128.7, 133.0, 133.4, 133.6, 153.6, 153.7. MS (EI): m/z (%) = 298 (11) [M⁺ + 1], 297 (42) [M⁺], 170 (39), 128 (90), 86 (100). IR (KBr, film): 2968, 1707 (C=O), 1645, 1429, 1323, 1265, 1041, 864, 760 cm^-1. Anal. Calcd for C₁₉H₂₃NO₂: C, 76.73; H, 7.80; N, 4.71. Found: C, 77.11; H, 7.47; N, 5.13.
1 H -Inden-3-yl N , N -Diisopropylcarbamate (2q):³³ Oil. ¹H NMR (300 MHz, CDCl₃): δ = 1.31 [d, J = 7.0 Hz, 12 H, 2 × CH(CH ₃)₂], 3.62 (s, 2 H, CH₂), 3.90 [br s, 1 H, CH(CH₃)₂], 4.11 [br s, 1 H, CH(CH₃)₂], 6.53 (s, 1 H, CHCH₂), 7.12 (td, J = 1.8, 7.0 Hz, 1 H, ArH), 7.20-7.29 (m, 2 H, ArH), 7.32 (d, J = 7.2, 1 H, ArH). ¹³C NMR (75 MHz, CDCl₃): δ = 20.7, 21.8, 38.3, 46.4, 47.1, 113.3, 120.7, 123.5, 124.0, 126.8, 137.6, 143.7, 152.8, 156.8. MS (EI): m/z (%) = 260 (2) [M⁺ + 1], 132 (54), 128 (84), 86 (100). IR (KBr, film): 2970, 1711, 1606, 1272, 1132, 748, 715 cm^-1.
2 H -Chromen-4-yl N , N-Diisopropylcarbamate (2s): mp 74.1-77.4 °C (hexane). ¹H NMR (300 MHz, CDCl₃): δ = 1.30-1.32 [m, 12 H, 2 × CH(CH ₃)₂], 4.02 [sept, J = 6.8 Hz, 2 H, 2 × CH(CH₃)₂], 4.96 (d, J = 3.5 Hz, 2 H, CH₂O), 5.49 (t, J = 3.7 Hz, 1 H, C=CHCH₂), 6.79 (dd, J = 0.9, 8.0 Hz, 1 H, ArH), 6.87 (td, J = 0.9, 7.5 Hz, 1 H, ArH), 7.06 (dd, J = 1.6, 7.7 Hz, 1 H, ArH), 7.13 (td, J = 1.6, 7.9 Hz, 1 H, ArH). ¹³C NMR (75 MHz, CDCl₃): δ = 20.7, 21.7, 46.7, 47.0, 65.7, 108.0, 116.1, 120.5, 121.3, 121.9, 130.0, 143.4, 152.9, 155.4. MS (EI): m/z (%) = 276 (4) [M⁺ + 1], 275 (19) [M⁺], 147 (69), 128 (83), 86 (100). IR (KBr, film): 2970, 1716 (C=O), 1306, 1207, 755 cm^-1. Anal. Calcd for C₁₆H₂₁NO₃: C, 69.79; H, 7.69; N, 5.09. Found: C, 69.89; H, 8.05; N, 5.06.
1-(4-Methoxyphenyl)prop-1-en-2-yl N , N -Diisopropyl-carbamate (2t); mixture of E- and Z-isomers (2:1): oil. ¹H NMR (300 MHz, CDCl₃): δ = 1.22-1.26 [m, 12 H, 2 × CH(CH ₃)₂], 2.04 (d, J = 0.9 Hz, 3 H, Me, E-isomer), 2.09 (d, J = 0.9 Hz, 3 H, Me, Z-isomer), 3.73 (s, 3 H, OMe, E-isomer), 3.75 (s, 3 H, OMe, Z-isomer), 3.85-4.00 [m, 2 H, 2 × CH(CH₃)₂], 5.83 (s, 1 H, C=CH, E-isomer), 6.19 (s, 1 H, C=CH, Z-isomer), 6.77 (d, J = 8.8 Hz, 2 H, ArH, E-isomer), 6.83 (d, J = 8.8 Hz, 2 H, ArH, Z-isomer), 7.18 (d, J = 8.4 Hz, 2 H, ArH, Z-isomer), 7.26 (d, J = 8.8 Hz, 2 H, ArH, E-isomer). ¹³C NMR (75 MHz, CDCl₃): δ = 17.7, 20.8, 21.1, 21.7, 46.6, 55.3, 113.7, 113.9, 115.7, 117.7, 127.9, 128.2, 129.5, 130.1, 145.2, 147.2, 152.7, 154.1, 158.5. MS (EI): m/z (%) = 292 (6) [M⁺ + 1], 291 (16) [M⁺], 164 (27), 163 (23), 135 (29), 128 (90), 121 (43), 86 (100). IR (KBr, film): 2970, 1707, 1512, 1252, 1041, 837, 757 cm^-1. Anal. Calcd for C₁₇H₂₅NO₃: C, 70.07; H, 8.65; N, 4.81. Found: C, 70.55; H, 8.74; N, 4.79.