Solid-State Synthesis of β-Enamino Ketones from Solid 1,3-Dicarbonyl Compounds and Ammonium Salts or Amines

Abstract

A facile amination of solid 1,3-dicarbonyl compounds with ammonium salts or amines in solid state has been achieved by mechanochemical grinding in the presence of KHSO₄ and SiO₂. Most of the reactions proceed smoothly at room temperature under solid-state conditions and give their corresponding β-imino derivatives in high yields. The method has the advantage of simple manipulation and mild conditions.

Key words

enamination - 1,3-dicarbonyl compounds - solid state - mechanochemistry

References and Notes

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32

General Procedure for the Preparation of β-Enamino Ketones
A mixture of the solid 1,3-dicarbonyl compound (5 mmol), amine (or ammonium, 5 mmol), and KHSO₄/SiO₂ (0.136 g, weight ratio 1:1) was ground in a mortar at r.t. for the appropriate time. After completion of the reaction as indicated by TLC, the reaction mixture was extracted with CH₂Cl₂ (2 × 10 mL). The combined organic layers were dried over Na₂SO₄ and concentrated under reduced pressure to give a product with high purity. The solid product could be further purified by recrystallization in PE (Table  [²] , entries 1-15) or in EtOH (Table  [³] , entries 1-12).
3-Amino-1-phenylbut-2-en-1-one (2a)
Mp 138-140 ˚C; lit. [³³a] 144-145 ˚C. ^¹H NMR (500 MHz, CDCl₃): δ = 2.06 (s, 3 H), 5.21 (br, 1 H, NH), 5.74 (s, 1 H), 7.39-7.45 (m, 3 H), 7.87-7.89 (m, 2 H), 10.22 (br, 1 H, NH). ^¹³C NMR (125 MHz, CDCl₃): δ = 22.92, 92.34, 127.10, 128.22, 130.83, 140.20, 162.91, 189.54.
3-Amino-1-(4-methoxyphenyl)but-2-en-1-one (2b) [³³b]
Mp 106-108 ˚C. ^¹H NMR (500 MHz, CDCl₃): δ = 2.04 (s, 3 H), 3.85 (s, 3 H), 5.11 (br, 1 H,NH), 5.70 (s, 1 H), 6.89-6.92 (m, 2 H), 7.85-7.88 (m, 2 H), 10.13 (br, 1 H, NH). ^¹³C NMR (125 MHz, CDCl₃): δ = 22.95, 55.36, 91.88, 113.43, 129.03, 132.90, 161.89, 162.14, 188.65.
3-Amino-1-(4-fluorophenyl)but-2-en-1-one (2c) [³³b]
Mp 106-108 ˚C. ^¹H NMR (500 MHz, CDCl₃): δ = 2.06 (s, 3 H), 5.21 (br, 1 H, NH), 5.67 (s, 1 H), 7.06-7.09 (m, 2 H), 7.87-7.90 (m, 2 H), 10.19 (br, 1 H, NH). ^¹³C NMR (125 MHz, CDCl₃) δ = 22.95 91.99, 115.14 (d, J = 20 Hz), 129.39 (d, J = 9 Hz), 136.40, 136.42 163.30 (d, J = 56 Hz), 165.52, 188.08. Ethyl 2-Amino-4-oxo-4-phenylbut-2-enoate (2d)
Mp 49-51 ˚C; lit. [³³c] 50-51 ˚C. ^¹H NMR (500 MHz, CDCl₃): δ = 1.41 (t, 3 H, J = 7 Hz), 4.38 (q, 2 H, J = 7 Hz), 6.04 (br, 1 H, NH), 6.67 (s, 1 H), 7.46-7.54 (m, 3 H), 7.96-9.98 (m, 2 H), 9.49 (br, 1 H, NH). ^¹³C NMR (125 MHz, CDCl₃): δ = 14.13, 62.70, 93.26, 127.45, 128.44, 131.29, 139.28, 147.49, 163.88, 191.80.
3-Aminocyclohex-2-enone (2e)
Mp 128-130 ˚C; lit. [³³d] 133 ˚C. ^¹H NMR (500 MHz, CDCl₃): δ = 1.97 (m, 2H), 2.29 (t, 2H, J = 6 Hz), 2.35 (t, 2H, J = 6 Hz), 4.67 (br, 2H, NH), 5.26 (s, 1H). ^¹³C NMR (125 MHz, D₂O) δ = 23.89, 30.60, 36.94, 99.56, 177.00, 203.01.
3-Amino-5,5-dimethylcyclohex-2-enone (2f)
Mp 164-166 ˚C; lit. [³³d] 165-167 ˚C. ^¹H NMR (500 MHz, CDCl₃): δ = 1.08 (s, 6 H), 2.16 (s, 2 H), 2.20 (s, 2 H), 4.71 (br, 2 H, NH), 5.25 (s, 1 H). ^¹³C NMR (125 MHz, D₂O) δ = 28.35, 32.88, 42.65, 49.86, 99.27, 163.46, 197.31.
3-Amino-1,3-diphenylprop-2-en-1-one (2g) [³³e]
Mp 78-79 ˚C. ^¹H NMR (500 MHz, CDCl₃) δ = 5.46 (br, 1 H, NH), 6.16 (s, 1 H), 7.42-7.53 (m, 6 H), 7.64-7.65 (m, 2 H), 7.94-7.96 (m, 2 H), 10.43 (br, 1 H, NH). ^¹³C NMR (125 MHz, CDCl₃) δ = 91.93, 126.36, 127.24, 128.32, 129.06, 130.74, 131.06, 137.63, 140.36, 162.88, 190.26.
3-Amino-1-(thiophen-2-yl)but-2-en-1-one (2h)
Mp 168-170 ˚C; lit. [³³b] 168-170 ˚C. ^¹H NMR (500 MHz, CDCl₃): δ = 2.03 (s, 3 H), 5.31 (br, 1 H,NH), 5.60 (s, 1 H), 7.05-7.56 (m, 3 H), 9.91 (br, 1 H, NH). ^¹³C NMR (125 MHz, CDCl₃): δ = 22.73, 92.00, 127.73, 127.87, 130.21, 146.99, 162.82, 182.21.
3-(4-Methoxyphenylamino)-1-phenylbut-2-en-1-one (3a) [³³f]
Mp 100-102 ˚C. ^¹H NMR (500 MHz, CDCl₃): δ = 2.07 (s, 3 H), 3.82 (s, 3 H), 5.86 (s, 1 H), 6.89-6.91 (m, 2 H), 7.10-7.12 (m, 2 H), 7.41-7.46 (m, 3 H), 7.90-7.92 (m, 2 H), 12.92 (br, 1 H, NH). ^¹³C NMR (125 MHz, CDCl₃): δ = 20.27, 55.52, 93.59, 114.37, 126.64, 127.05, 128.28, 130.80, 131.46, 140.16, 157.89, 163.21, 188.47.
3-(4-Chlorophenylamino)-1-phenylbut-2-en-1-one (3b)
Mp 126-128 ˚C; lit. [³³g] 128-129 ˚C. ^¹H NMR (500 MHz, CDCl₃): δ = 2.12 (s, 3 H), 5.91 (s, 1 H), 7.09-7.15 (m, 2 H), 7.31-7.34 (m, 2 H), 7.41-7.48 (m, 3 H), 7.90-7.92 (m, 2 H), 13.07 (br, 1 H, NH). ^¹³C NMR (125 MHz, CDCl₃): δ = 20.30, 94.63, 125.80, 127.01, 128.26, 129.23, 131.02, 131.15, 137.20, 139.71, 161.63, 188.88.
3-(4-Nitrophenylamino)-1-phenylbut-2-en-1-one (3c) [³³h]
Mp 140-142 ˚C. ^¹H NMR (500 MHz, CDCl₃): δ = 2.33 (s,
3 H), 6.04 (s, 1 H), 7.25-7.28 (m, 2 H), 7.44-7.47 (m, 2 H), 7.50-7.52 (m, 1 H), 7.88-7.93 (m, 2 H), 8.21-8.25 (m, 2 H), 13.41 (br, 1 H, NH). ^¹³C NMR (125 MHz, CDCl₃): δ = 21.18, 97.54, 122.26, 125.22, 127.30, 128.50, 131.73, 139.20, 144.13, 145.18, 159.16, 189.99.
1-Phenyl-3-( p -tolylamino)but-2-en-1-one (3d) [³³i]
Mp 114-116 ˚C. ^¹H NMR (500 MHz, CDCl₃): δ = 2.10 (s,
3 H), 2.35 (s, 3 H), 5.87 (s, 1 H), 7.05-7.07 (m, 2 H), 7.15-7.25 (m, 2 H), 7.40-7.46 (m, 3 H), 7.90-7.93 (m, 2 H), 13.03 (br, 1 H, NH). ^¹³C NMR (125 MHz, CDCl₃): δ = 20.38, 20.97, 93.92, 124.85, 127.06, 128.27, 129.76, 130.82, 135.72, 136.02, 140.14, 162.60, 188.48.
1-(4-Methoxyphenyl)-3-(4-methoxyphenylamino)but-2-en-1-one (3e) [³³j]
Mp 142-143 ˚C. ^¹H NMR (500 MHz, CDCl₃): δ = 2.05 (s, 3 H), 3.82 (s, 3 H), 3.86 (s, 3 H), 5.82 (s, 1 H), 6.88-6.94 (m, 4 H), 7.09-7.11 (m, 2 H), 7.89-7.91 (m, 2 H), 12.85 (br, 1 H, NH). ^¹³C NMR (125 MHz, CDCl₃): δ = 20.26, 55.36, 55.49, 93.05, 113.47, 114.31, 126.57, 128.90, 131.67, 132.81, 157.74, 161.87, 162.41, 187.62. 1-(4-Fluorophenyl)-3-(4-methoxyphenylamino)but-2-en-1-one (3f)
Mp 116-118 ˚C. ^¹H NMR (500 MHz, CDCl₃): δ = 2.06 (s, 3 H), 3.82 (s, 3 H), 5.80 (s, 1 H), 6.89-6.91 (m, 2 H), 7.07-7.11 (m, 4 H), 7.90-7.93 (m, 2 H), 12.87 (br, 1 H, NH). ^¹³C NMR (125 MHz, CDCl₃): δ = 20.25, 55.49, 93.15, 114.37, 115.16 (d, J = 21 Hz), 126.63, 129.24 (d, J = 9 Hz), 131.35, 136.36 (d, J = 4 Hz), 157.94, 163.38 (d, J = 22 Hz), 165.47, 186.94. IR (KBr): 3440, 1599, 1543, 1515, 1496, 1462, 1436, 1328, 1251, 1198, 1105, 1031, 855, 779, 520 cm^-¹. MS (EI): m/z (%) = 286 (18), 285 (100) [M⁺], 284 (70), 270 (18), 190 (11), 162 (36), 147 (22), 123 (71), 108 (9), 95 (27). Anal. Calcd for C₁₇H₁₆FNO₂: C, 71.56; H, 5.65; N, 4.91. Found: C, 71.51; H, 5.60; N, 4.87.
Ethyl 2-(4-Nitrophenylamino)-4-oxo-4-phenylbut-2-enoate (3g)
Mp 98-99 ˚C. ^¹H NMR (500 MHz, CDCl₃): δ = 1.22 (t, 3 H, J = 7 Hz), 4.28 (q, 2 H, J = 7 Hz), 6.67 (s, 1 H), 7.04-7.05 (m, 2 H), 7.47-7.51 (m, 2 H), 7.57-7.60 (m, 1 H), 7.97-7.99 (m, 2 H), 8.19-8.21 (m, 2 H), 11.95 (br, 1 H, NH). ^¹³C NMR (125 MHz, CDCl₃): δ = 13.83, 62.79, 101.02, 120.30, 125.09, 127.77, 128.76, 132.95, 138.10, 143.72, 145.72, 146.95, 163.64, 191.94. IR (KBr): 3441, 2981, 1373, 1619, 1585, 1510, 1337, 1281, 1226, 1163, 1108, 1051, 1016, 831, 853, 750, 591, 552, 493 cm^-¹. MS (EI): m/z (%) = 341 (5), 340 (33) [M⁺], 339 (31), 294 (14), 268 (18), 267 (84), 236 (26), 221 (15), 105 (100), 77 (42). Anal. Calcd for C₁₈H₁₆N₂O_5: C, 63.52; H, 4.74; N, 8.23. Found: C, 63.50; H, 4.67; N, 8.14.
3-(4-Nitrophenylamino)cyclohex-2-enone (3h) [³³k]
Mp 176-178 ˚C.^¹H NMR (500 MHz, CDCl₃): δ = 2.07-2.11 (m, 2 H), 2.42 (t, 2 H, J = 7 Hz), 2.56 (t, 2 H, J = 6 Hz), 5.85 (s, 1 H), 6.83 (br, 1 H, NH), 7.26-7.29 (m, 2 H), 8.19-8.21 (m, 2 H). ^¹³C NMR (125 MHz, CDCl₃): δ = 21.65, 29.82, 36.55, 103.13, 121.31, 125.32, 143.35, 144.94, 159.90, 198.94.
3-(4-Methoxyphenylamino)-5,5-dimethylcyclohex-2-enone (3i)
Mp 186-188 ˚C; lit. [³³l] 186-188 ˚C. ^¹H NMR (500 MHz, CDCl₃): δ = 1.05 (s, 6 H), 2.15 (s, 2 H), 2.32 (s, 2 H), 3.78 (s, 3 H), 5.34 (s, 1 H), 6.82 (dd, 2 H, J = 2, 7 Hz), 7.04 (dd, 2 H, J = 2, 7 Hz), 7.28 (s, 1 H).^¹³C NMR (125 MHz, CDCl₃): δ = 28.27, 32.76, 43.02, 50.36, 55.46, 96.96, 114.37, 126.07, 131.14, 157.46, 162.87, 197.61.
3-(2,5-Dichlorophenylamino)-5,5-dimethylcyclohex-2-enone (3j)
Mp 182-184 ˚C. ^¹H NMR (500 MHz, CDCl₃): δ = 1.14 (s, 6 H), 2.26 (s, 2 H), 2.39 (s, 2 H), 5.61 (s, 1 H), 6.12 (br, 1 H), 7.07-7.42 (m, 3 H). ^¹³C NMR (125 MHz, CDCl₃): δ = 28.28, 32.89, 43.74, 50.34, 100.78, 124.56, 125.27, 125.96, 130.79, 133.30, 136.28, 158.05, 198.18. IR (KBr) 3442, 3225, 2953, 2873, 1597, 1537, 1464, 1402, 1364, 1269, 1092, 1048, 925, 893, 827, 743, 519 cm^-¹. MS (EI): m/z (%) = 285 (42), 283 (50), 268 (20), 266 (20), 227 (36), 192 (100), 164 (28). Anal. Calcd for C₁₄H₁₅Cl₂NO: C, 59.17; H, 5.32; N, 4.93. Found: C, 59.09; H, 5.28; N, 4.90.
1,3-Diphenyl-3-( p -tolylamino)prop-2-en-1-one (3k) [³³m]
Mp 120-122 ˚C. ^¹H NMR (500 MHz, CDCl₃): δ = 2.23 (s, 3 H), 6.05 (s, 1 H), 6.68-7.95 (m, 14 H), 12.90 (br, 1 H, NH). ^¹³C NMR (125 MHz, CDCl₃): δ = 20.79, 96.57, 123.21, 127.22, 128.33, 128.38, 128.49, 129.31, 129.55, 131.17, 133.86, 135.94, 136.80, 139.98, 161.74, 189.43.
3-(4-Chlorophenylamino)-1-(thiophen-2-yl)but-2-en-1-one (3l)
Mp 80-82 ˚C. ^¹H NMR (500 MHz, CDCl₃): δ = 2.11 (s, 3 H), 5.78 (s, 1 H), 7.06-7.61 (m, 7 H), 12.71 (br, 1 H, NH). ^¹³C NMR (125 MHz, CDCl₃): δ = 20.31, 94.51, 125.74, 127.89, 128.14, 129.34, 130.66, 131.21, 137.24, 146.56, 161.33, 181.88. IR (KBr): 3441, 3095, 1623, 1562, 1481, 1418, 1373, 1381, 1229, 1093, 1031, 824, 834, 766, 722, 502
cm^-¹. MS (EI): m/z (%) = 279 (25), 278 (39), 277 (67), 276 (84), 244 (87), 111 (100), 83 (8). Anal. Calcd for C₁₄H₁₂ClNOS: C, 60.54; H, 4.35; N, 5.04. Found: C, 60.50; H, 4.31; N, 5.01.