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Synthesis of 1H-Indol-3-ylpyrazole Derivatives from 1,3,5-Triketones and Arylhydrazines: One-Pot Construction of Pyrazole and Indole Rings

  • Kim, Sung Hwan (Department of Chemistry and Institute of Basic Science, Chonnam National University) ;
  • Lee, Sangku (Immune Modulator Research Center, KRIBB) ;
  • Kim, Se Hee (Department of Chemistry and Institute of Basic Science, Chonnam National University) ;
  • Kim, Ko Hoon (Department of Chemistry and Institute of Basic Science, Chonnam National University) ;
  • Kim, Jae Nyoung (Department of Chemistry and Institute of Basic Science, Chonnam National University)
  • Received : 2013.07.03
  • Accepted : 2013.08.30
  • Published : 2013.11.20
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Abstract

The reaction of 1,3,5-triketones and arylhydrazines provided indolylpyrazole derivatives in a one-pot reaction in good to moderate yields. Both the pyrazole and indole rings were constructed simultaneously with phenylhydrazine, $RCOCH_2CO$- moiety for the pyrazole and the remaining -$CH_2COR$ part for the indole ring.

Keywords

Introduction

The synthesis of indolylpyrazole derivatives has been examined extensively due to their potential biological activities.1-3 The synthesis was carried out most frequently via the transition metal-catalyzed coupling reaction between indoles and pyrazoles.2 However, this approach required one preactivated reaction partner such as bromopyrazole or bromoindole.2 Other method involving the use of 4-pyranones as starting materials has also been reported.3

 

Results and Discussion

During our recent studies on the synthesis of 2,3-dihydro- 4H-pyran-4-ones from 1,5-dicarbonyl compounds,4 we presumed that the 1,3,5-triketone moiety of 1,5-diphenyl-1,3,5- pentanetrione (1a) could be used for the simultaneous construction of both pyrazole and indole rings in the reaction with phenylhydrazine, PhCOCH2CO- moiety for the pyrazole and the remaining -CH2COPh part for the indole ring, as shown in Scheme 1.

Thus, we examined the reaction of 1a and phenylhydrazine hydrochloride (2a, 5.0 equiv) in ODCB (130 ℃, 5 h). To our delight, a desired 5-(indol-3-yl)pyrazole derivative 4a was obtained in moderate yield (50%)5 along with 3-(indol- 3-yl)pyrazole 5a (17%). The combined yield of 4a/5a decreased when the reaction was performed with lesser amount of 2a. Compounds 4a and 5a could be formed via the formation of regioisomeric pyrazoles 3a/3a' and a subsequent Fischer indole synthesis process. The typical mechanism for the formation of indole ring is also shown in Scheme 1. However, we could not separate the corresponding intermediates 3a and 3a'.6

Scheme 1

In order to confirm the structure of 4a and 5a unequivocally, we carried out the synthesis of these compounds from 2-phenylindole (6) although the synthesis required threesteps, as shown in Scheme 2. The formylation of 6 was carried out with POCl3 and DMF to produce 7 in good yield (86%) according to the known method.7 Aldol condensation of 7 with acetophenone afforded α,𝛽-enone 9 in good yield (68%).8 The reaction of this enone 9 and phenylhydrazine in ODCB (130 ℃, 6 h) produced 4a in moderate yield (48%), presumably via an aerobic oxidation of the intermediate pyrazoline derivative. Similarly, 3-acetylindole 8 was prepared by the acetylation of 6 with POCl3 and DMA.7 A sequential aldol reaction with benzaldehyde to make 10,8 and the following reaction with phenylhydrazine afforded 5a in 55% yield.

Scheme 2

Encouraged by the successful result we synthesized various indolylpyrazoles 4b-e, 5b, and 5c, as shown in Table 1. The reaction of 1a and 4-chlorophenylhydrazine hydrochloride (2b) afforded 4b (49%) and 5b (19%), as shown in entry 2. Similarly, the reaction with 4-methoxyphenylhydrazine hydrochloride (2c) gave 4c (52%) and 5c (22%) in good combined yields (entry 3). The reactions with 2,4,6-heptanetrione (1b) also afforded the corresponding products 4d and 4e in moderate yields (entries 4 and 5). However, isolation of the corresponding minor products 5d and 5e failed in these cases, although the formations of these compounds were observed on TLC at the right position in a small amount. Similarly, the reaction of 1,5-di(2-pyridyl)-1,3,5-pentanetrione (1c) and 2a (entry 6) afforded 4f in good yield (64%).9

Table 1.aConditions: triketone (0.5 mmol), ArNHNH2HCl (5.0 equiv), ODCB, 130 ℃, 3-5 h. b1b is 2,4,6-heptanetrione. cFailed to isolate. d1c is 1,5- di(2-pyridyl)-1,3,5-pentanetrione.

In order to make N-unsubstituted indolylpyrazole 12, we examined a sequential synthesis of pyrazole 11 and a subsequent construction of indole ring, as shown in Scheme 3. Pyrazole 11 could be prepared by the reaction of 1a and hydrazine hydrate in good yield (72%).10 The following synthesis of indole ring was performed with phenylhydrazine hydrochloride (2a), and indolylpyrazole 12 was obtained in good yield (81%).

As a next entry, we examined the synthesis of pyrimidylindole derivative 14,11 as shown in Scheme 4. The reaction of 1a and guanidine carbonate produced 2-aminopyrimidine derivative 13 in the presence of a catalytic amount of p- TsOH in ODCB in moderate yield (46%). In the reaction, a retro-aldol type side reaction lowered the yield of 13.1213 With this compound 13 in our hand, the reaction with 2a was carried out in refluxing ODCB. However, pyrimidylindole 14 was not formed at all. Instead, indolylpyrazole 4a was formed in moderate yield (57%). The plausible reaction mechanism is proposed in Scheme 4. The intermediate IV, a corresponding hydrazone of 13, could be converted to a spiro intermediate V. The ring-opening of V to VI and a following 1,5-H shift would generate VII. Addition of 2a to VII and subsequent elimination of guanidine would produce I (vide supra, Scheme 1). As a last, the hydrazone I was converted to indolylpyrazole 4a.14

Scheme 3

Scheme 4

In summary, we disclosed an efficient synthesis of indolylpyrazole derivatives from 1,3,5-triketones and arylhydrazines by simultaneous construction of both pyrazole and indole rings.

 

Experimental Section

Typical Procedure for the Synthesis of 4a and 5a. A mixture of 1a (133 mg, 0.5 mmol) and 2a (362 mg, 2.5 mmol) in ODCB (2.5 mL) was heated to 130 ℃ for 5 h. After the usual extractive workup and column chromatographic purification process (hexanes/CH2Cl2/EtOAc, 15:5:1) compound 4a5 was obtained as a pale yellow solid (103 mg, 50%) along with 5a (35 mg, 17%). Other compounds were synthesized similarly, and the spectroscopic data of 4a-f, 5ac, 11,10a 12,5 and 13 are as follows.

Compound 4a:5 50%; pale yellow solid, mp 192-193 ℃; IR (KBr) 3412, 1597, 1499, 1456, 1362 cm−1; 1H NMR (CDCl3, 300 MHz) 𝛿 6.94-7.00 (m, 6H), 7.02-7.07 (m, 2H), 7.12-7.21 (m, 4H), 7.23-7.29 (m, 1H), 7.31-7.36 (m, 1H), 7.38-7.46 (m, 3H), 7.61 (d, J = 7.5 Hz, 1H), 7.97 (d, J = 6.9 Hz, 2H), 8.33 (br s, 1H); 13C NMR (CDCl3, 75 MHz) 𝛿 103.27, 106.37, 111.00, 119.54, 120.86, 122.98, 124.03, 125.78, 126.42, 127.13, 127.85, 127.92, 128.11, 128.59, 128.64, 128.75, 131.65, 133.13, 135.74, 136.48, 137.71, 139.80, 151.97; ESIMS m/z 412 (M++H). Anal. Calcd for C29H21N3: C, 84.64; H, 5.14; N, 10.21. Found: C, 84.47; H, 5.33; N, 10.04.

Compound 5a: 17%; pale yellow solid, mp 116-117 ℃; IR (KBr) 3416, 1595, 1499, 1456, 1360 cm−1; 1H NMR (CDCl3, 300 MHz) 𝛿 6.29 (s, 1H), 7.10-7.38 (m, 16H), 7.62 (d, J = 7.8 Hz, 2H), 8.20 (br s, 1H), 8.20-8.23 (m, 1H); 13C NMR (CDCl3, 75 MHz) 𝛿 106.91, 107.72, 110.58, 120.64, 121.63, 122.68, 124.93, 126.83, 128.01, 128.13, 128.23, 128.32, 128.55, 128.69, 128.77, 128.93, 130.84, 132.96, 135.86, 135.90, 140.28, 142.91, 147.61; ESIMS m/z 412 (M++H). Anal. Calcd for C29H21N3: C, 84.64; H, 5.14; N, 10.21. Found: C, 84.78; H, 5.42; N, 10.13.

Compound 4b: 49%; yellow solid, mp 211-212 ℃; IR (KBr) 3412, 1595, 1493, 1460, 1362 cm−1; 1H NMR (CDCl3, 300 MHz) 𝛿 6.74 (d, J = 9.0 Hz, 2H), 6.85 (d, J = 9.0 Hz, 2H), 6.91-6.94 (m, 2H), 6.96 (s, 1H), 7.10-7.21 (m, 4H), 7.27 (d, J = 8.4 Hz, 1H), 7.32-7.37 (m, 1H), 7.40-7.46 (m, 2H), 7.58 (d, J = 1.8 Hz, 1H), 7.94 (d, J = 6.9 Hz, 2H), 8.61 (br s, 1H); 13C NMR (CDCl3, 75 MHz) 𝛿 102.43, 106.50, 112.25, 118.79, 123.50, 125.29, 125.84, 126.83, 127.14, 128.19, 128.28, 128.36, 128.69, 128.75, 129.63, 131.10, 132.29, 132.58, 134.10, 137.20, 137.90, 137.91, 152.35; ESIMS m/z 481 (M++H), 483 (M++H+2) and 485 (M++H+4). Anal. Calcd for C29H19Cl2N3: C, 72.51; H, 3.99; N, 8.75. Found: C, 72.75; H, 4.11; N, 8.84.

Compound 5b: 19%; yellow solid, mp 120-121 ℃; IR (KBr) 3418, 1566, 1495, 1464, 1356 cm−1; 1H NMR (CDCl3, 300 MHz) 𝛿 6.32 (s, 1H), 7.13-7.24 (m, 5H), 7.28-7.33 (m, 6H), 7.37-7.41 (m, 3H), 7.58-7.61 (m, 2H), 8.21 (d, J = 2.1 Hz, 1H), 8.43 (br s, 1H); 13C NMR (CDCl3, 75 MHz) 𝛿 105.96, 107.88, 111.79, 120.73, 123.02, 126.05, 126.34, 128.48, 128.55, 128.62, 128.65, 128.72, 128.76, 128.83, 128.98, 130.15, 132.22, 132.75, 134.23, 137.46, 138.33, 143.40, 147.37; ESIMS m/z 481 (M++H), 483 (M++H+2) and 485 (M++H+4).

Compound 4c: 52%; yellow solid, mp 237-239 ℃; IR (KBr) 3393, 1595, 1510, 1485, 1462, 1248 cm−1; 1H NMR (CDCl3+DMSO-d6, 300 MHz) d 3.67 (s, 3H), 3.79 (s, 3H), 6.51 (d, J = 9.0 Hz, 2H), 6.85 (dd, J = 8.7 and 2.1 Hz, 1H), 6.89 (s, 1H), 6.92 (d, J = 9.0 Hz, 2H), 6.94 (d, J = 2.1 Hz, 1H), 7.18 (app s, 5H), 7.30-7.35 (m, 2H), 7.41-7.45 (m, 2H), 7.96 (d, J = 7.2 Hz, 2H), 10.28 (br s, 1H); 13C NMR (CDCl3 +DMSO-d6, 75 MHz) 𝛿 55.09, 55.48, 100.11, 102.19, 105.49, 111.99, 112.64, 113.09, 125.01, 125.37, 127.08, 127.24, 127.45, 128.06, 128.34, 128.92, 130.98, 131.97, 133.20, 137.01, 138.09, 151.21, 154.37, 157.66 (one carbon is overlapped); ESIMS m/z 472 (M++H). Anal. Calcd for C31H25N3O2: C, 78.96; H, 5.34; N, 8.91. Found: C, 79.15; H, 5.39; N, 8.74.

Compound 5c: 22%; yellow solid, mp 198-200 ℃; IR (KBr) 3408, 1597, 1614, 1454, 1248 cm−1; 1H NMR (CDCl3, 300 MHz) 𝛿 3.79 (s, 3H), 3.87 (s, 3H), 6.33 (s, 1H), 6.83 (d, J = 9.0 Hz, 2H), 6.87 (dd, J = 8.7 and 2.4 Hz, 1H), 7.18-7.40 (m, 11H), 7.65 (d, J = 7.5 Hz, 2H), 7.77 (d, J = 2.4 Hz, 1H), 8.25 (br s, 1H); 13C NMR (CDCl3, 75 MHz) 𝛿 55.40, 55.92, 103.35, 106.79, 107.08, 111.35, 112.77, 113.86, 126.30, 127.88, 128.07, 128.28, 128.49, 128.67, 128.70, 128.78, 130.84, 131.13, 133.02, 133.65, 136.58, 142.83, 147.35, 154.77, 158.35; ESIMS m/z 472 (M++H).

Compound 4d: 50%; white solid, mp 183-184 ℃; IR (KBr) 3391, 1599, 1501, 1458, 1366 cm−1; 1H NMR (CDCl3, 300 MHz) 𝛿 1.94 (s, 3H), 2.43 (s, 3H), 6.32 (s, 1H), 7.02- 7.07 (m, 1H), 7.09-7.21 (m, 4H), 7.26 (d, J = 7.8 Hz, 1H), 7.28 (d, J = 8.1 Hz, 2H), 7.38 (d, J = 7.8 Hz, 1H), 8.26 (br s, 1H); 13C NMR (CDCl3, 75 MHz) 𝛿 12.21, 13.73, 103.77, 108.94, 110.28, 118.88, 120.15, 121.68, 123.63, 126.26, 127.91, 128.65, 133.65, 135.17, 137.26, 140.64, 149.56; ESIMS m/z 288 (M++H). Anal. Calcd for C19H17N3: C, 79.41; H, 5.96; N, 14.62. Found: C, 79.48; H, 6.19; N, 14.47.

Compound 4e: 52%; white solid, mp 178-179 ℃; IR (KBr) 3410, 1595, 1497, 1464, 1414, 1364 cm−1; 1H NMR (CDCl3, 300 MHz) 𝛿 1.96 (s, 3H), 2.42 (s, 3H), 6.31 (s, 1H), 7.09 (dd, J = 8.7 and 1.8 Hz, 1H), 7.14-7.22 (m, 5H), 7.32 (d, J = 1.8 Hz, 1H), 8.41 (br s, 1H); 13C NMR (CDCl3, 75 MHz) 𝛿 12.27, 13.65, 103.23, 109.42, 111.43, 118.19, 122.13, 124.72, 126.11, 128.85, 128.93, 132.04, 133.52, 135.22, 136.64, 138.96, 150.03; ESIMS m/z 357 (M++H), 359 (M++H+2), 361 (M++H+4). Anal. Calcd for C19H15Cl2N3: C, 64.06; H, 4.24; N, 11.80. Found: C, 64.31; H, 4.15; N, 11.92.

Compound 4f: 64%; pale yellow solid, mp 100-102 ℃; IR (KBr) 3430, 1594, 1494, 1459, 1451 cm−1; 1H NMR (CDCl3, 300 MHz) 𝛿 7.02-7.09 (m, 4H), 7.13 (ddd, J = 8.1, 6.9 and 1.2 Hz, 1H), 7.19-7.30 (m, 5H), 7.31-7.38 (m, 2H), 7.47 (td, J = 7.8 and 1.8 Hz, 1H), 7.54 (d, J = 7.8 Hz, 1H), 7.79 (td, J = 7.8 and 1.8 Hz, 1H), 8.19 (dt, J = 7.8 and 1.2 Hz, 1H), 8.41-8.47 (m, 1H), 8.67-8.73 (m, 1H), 10.16 (br s, 1H); 13C NMR (CDCl3, 75 MHz) 𝛿 104.14, 108.43, 111.42, 119.98, 120.34, 120.77, 121.26, 122.31, 122.72, 123.74, 123.85, 126.99, 128.40, 129.45, 134.32, 135.33, 136.63, 136.64, 137.79, 139.81, 148.85, 149.20, 149.53, 152.15, 152.62; ESIMS m/z 414 (M++H). Anal. Calcd for C27H19N5: C, 78.43; H, 4.63; N, 16.94. Found: C, 78.62; H, 4.89; N, 16.68.

Compound 11:10a 72%; white solid, mp 151-152 ℃; IR (KBr) 3333, 1674, 1578, 1462, 1449, 1339 cm−1; 1H NMR (CDCl3+DMSO−d6, 300 MHz) 𝛿 4.38 (s, 2H), 6.47 (s, 1H), 7.24-7.29 (m, 1H), 7.33-7.39 (m, 2H), 7.43-7.49 (m, 2H), 7.54-7.59 (m, 1H), 7.70 (d, J = 7.2 Hz, 2H), 8.05 (d, J = 7.2 Hz, 2H), 12.45 (br s, 1H); 13C NMR (CDCl3+DMSO−d6, 75 MHz) 𝛿 37.44, 102.40, 125.35, 127.70, 127.72, 128.50, 128.52, 128.57, 131.23, 133.24, 136.16, 196.30 (one carbon is overlapped); ESIMS m/z 263 (M++H).

Compound 12:5 81%; white solid, mp 285-286 ℃; IR (KBr) 3397, 1599, 1489, 1456, 1329 cm−1; 1H NMR (CDCl3 +DMSO-d6, 300 MHz) 𝛿 6.70 (s, 1H), 7.13-7.24 (m, 2H), 7.26-7.43 (m, 7H), 7.54-7.56 (m, 2H), 7.77-7.80 (m, 1H), 7.81 (d, J = 7.2 Hz, 2H), 10.00 (br s, 2H); 13C NMR (CDCl3 +DMSO−d6, 75 MHz) 𝛿 102.01, 103.27, 111.23, 119.55, 120.66, 122.78, 125.55, 127.72, 127.84, 128.21, 128.32, 128.59, 128.85, 132.04, 132.70, 135.67, 135.98, 139.99, 150.60; ESIMS m/z 336 (M++H).

Compound 13: 46%; yellow solid, mp 111-112 ℃; IR (KBr) 3484, 3390, 3319, 1685, 1637, 1602, 1578, 1493, 1449, 1372 cm−1; [keto form] 1H NMR (CDCl3, 300 MHz) 𝛿 4.32 (s, 2H), 5.26 (br s, 2H), 7.04 (s, 1H), 7.40-7.49 (m, 6H), 7.94-7.99 (m, 2H), 8.05 (d, J = 7.2 Hz, 2H); [enol form] 1H NMR (CDCl3, 300 MHz) 𝛿 5.26 (br s, 2H), 6.01 (s, 1H), 6.78 (s, 1H), 7.40-7.49 (m, 5H), 7.55-7.60 (m, 1H), 7.81- 7.86 (m, 2H), 7.94-7.99 (m, 2H), 15.06 (br s, 1H); [keto+ enol form] 13C NMR (CDCl3, 75 MHz) 𝛿 47.90, 93.55, 104.15, 107.84, 125.86, 126.99, 127.12, 128.40, 128.67 (2C), 128.75, 130.10, 130.42, 130.52, 133.48, 136.00, 136.35, 137.15, 137.40, 159.07, 163.36, 164.60, 164.80, 165.16, 165.87, 169.01, 195.82 (one carbon is overlapped); ESIMS m/z 290 (M++H).

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