Nov 22, 1999 - 1.3.4-Trisubstituted pyrazoles synthesized by the reaction of ... pyrazole derivatives (Scheme I) due to its close association with various ...
Indian Jo urnal of Chemistry Vol. 408, Aug ust 2001 , pp. 717-718
Note
Microwave assisted synthesis of novel pyrazoles Mazaahir Kidwai"*, Rupak Kumar Aryal b & Preeti Misra' "Department of C he mi stry , University of Delhi, Delhi 110 007, India bDe partment o f Chemistry, Kathmandu University, Nepal
Received 22 No vember 1999; 22 Janllary 2001 1.3.4-Trisubstituted pyrazoles sy nthesized by the reacti o n of 2-methyl-2-phenylpropanoy l hydrazide with substituted acetopheno ne foll owed by Vilsme ier Haack reage nt (POC liDMF) under mi crowave irradiation (MWI ) and by conventional methods are desc ribed. The reaction rate is enhanced tremendo usly under mi crowave irradi ati o n as co mpared to conventional method with improved yields.
Recently much interest of the use of domestic microwave oven for the synthesis of heterocyclic compounds has been shown and that is due to substantial reduction in reaction time and better yields of the products ' "". Thi s led us to synthesize the pyrazole derivatives (Scheme I) due to its close 5s association with various biological activities - . Results and Discussion 2-Methy l-2-phenyl propanoyl hydrazide 3 was prepared from 2-methyl-2-phenyl propanoic acid 1 by esterification and followed by reaction with hydrazine hydrate9 . Hydrazide 3 on reaction with substituted acetophenone afforded corresponding hydrazones Sa-e which on reaction with POCl}/OMF under MWI as well as conventional method yielded the corresponding pyrazoles 'o . The disappearance of peak at 8 3.13.3 of - N=C(CH 3), the appearance of -CHO signal at 8 9.6-9.8 and pyrazole ring protons S-CH at 8 8.5-8.6 I in ' H NMR and band absorbed at 1705 cm- due to CO- of aldehyde in IR spectra confirms the formation of 6a-e. The significance of our approach using MWI is that in classical approach cyclocondensation of hydrazone required 3-5 hr with constant heating at JOO- I20°C whi le the same reaction was completed in 45-120 secs when carried out under microwaves with improved yie ld .
6a-e
R = H. 4-NH2' 2-0H. 4-0CH). 4-Br
Scheme J.
Experimental Section Melting points were taken on an Electrothermal melting point apparatus and are uncorrected. IR spectra were recorded on 1710 Perkin-Elmer FTIR spectrophotometer using KBr di sc and proton NMR were recorded on FT NMR Hitachi R-600 using TMS as internal standard. The purity of compounds were checked on TLC plate of Merck. Synthesis of 2-methyl-2-phenyl propanoyl hydrazones Sa-e. An equimolar solution of hydrazide 3 in ethanol and 2 drops of gl. acetic acid and (substituted) acetophenone 4a-e were taken in a round
INDIAN 1. CHEM., SEC B, AUGUST 2001
718
Table I - The characterization data of compounds 5a-e and 6a-e Compd*
R
m.p. (0C)
Method A Yield (% )1 Time (hr)
Sa
H
108
74/5
5b
4-NH2
202
78/5
5c
2-0H
160
79/6
5d
4-0CH 3
221
74/5 .5
5e
4-Br
172
76/6
6a
H
11 2
54/4.2
69/80
6b
4-NH 2
124
63/3 .2
71180
6c
2-0H
88
66/3
82/40
6d
4-0CH 3
165
56/3
741120
6e
4-Br
102
58/4
76/60
Method B Yield (% )1 Time (sec)
IH NMR (CDCI 3)
2.30 (5, 6H, (CH 3hC), 3.10 (5, 3H, N=C-CH 3), 7.5-7.9 (m, 10H, Ar- H), 9.80 (brs, I H, NH) 2.30 (5, 6H, (CH 3hC), 3.30 (5, 3H, N=CCH 3), 5.1 (brs, 2H, NH 2), 6.7-7 .8 (m, 9H, Ar- H). 9.8 (brs, IH, NH ) 2.35 (5, 6H, (CH)hC). 3.20 (5, 3H, N=C-CH 3). 4.8 (brs. I H, OH), 7.5-8.0 (m. 9H, Ar-H). 9.8 (brs, lH, NH) 2.30 (5, 6H , (CH 3hc). 3.20 (5. 3H. N=C-CH 3). 3.80 (5. 3H, OCH) , 7.5-7.95 (m. 9H, Ar- H), 9.7 (brs. IH, NH ) 2.30 (5. 6H. (CH 3hC), 3.1 (5. 3H. N=C- CH3). 7.5-7 .9 (m. 9H, Ar-H), 9.80 (brs, I H, NH) 2.35 (5, 6H, (CH 3hC), 7.5-8.0 (m, 10H , Ar-H), 9.60 (5, IH, CHO) 2.30 (5, 6H, (CH 3hC), 6.6-7.8 (m, 9H . Ar-H). 8.5 (5, I H. 5-CH), 9.7 (5, I H. CHO) 2.30 (5, 6H, (CH)2C), 4.8 (brs, I H, OH ), 7. 5-8.0 (m, 9H. Ar-H), 8.6 (5. I H. 5-CH). 9.8 (5. I H. CHO) 2.30 (5, 6H, (CH 3h c). 3.75 (5. 3H, OCH) , 7.5-8 .0 (m, 9H, Ar- H), 8.5 (5. I H. 5-CH). 9.75 (5. I H, CHO) 2.30 (5. 6H. (CH 3hC). 7.5-8.0 (m. 9H . Ar-H ). 8.5 (5. I H, 5-CH), 9.80 (5, I H, CHO)
*All the new compounds showed satisfac tory C H N ana lysis with variations ±0.04%
bottom flask and refluxed for 3-5 hr. The solid that separated on cooling was filtered off and washed with cold ethano l. Finall y it was recrystallized from chloroform/acetone/ethanol. The physical and spectral data of compounds are given in Table I. Synthesis of 1-(2-methyl-2-phenyl propanoyl)-4formyl-3-(substituted) phenyl pyrazoles 6a-e. Method A (conventional). The hydrazone Sa-e (0.004 mole) was added in mixture of VilsmeierHaack reagent (prepared by dropwi se addition of 1.2 mL POCh in ice cooled 10 mL DM F) and refluxed for 3-4 hr. After completio n of reaction the mixture was poured into ice cold water followed by neutralization using sodium bicarbonate. The precipitate was filtered off and recry stallised using DMF/EtOH to give 6a-e. Method B (MWI). The hydrazone Sa-e (0.004 mole) was added in mixture of Vilsmeier-Haack reagent in an open Erlenmeyer flask and irradiated in
microwave oven for 45-120 sec. After co mpletion of the reaction, product was worked-up as described in method A. References I Caddick S. Tetrahedrol/ . 5 1. 1995, 10403. 2 Kidwai M & Kumar P, J Chem Res (S). 1996. 254. 3 Kidwai M. Goel Y & Kohli S, J II/dial/ Chem Soc. 34B. 1995. 734. 4 Kidwai M, Kumar P & Kohli S. J Chem Res (S). 1997,24. 5 Rao 1 S, Sreenivasulu B & Mogil aiah K, II/ diall J Chem. 1995,734. 6 Bhardwaj S D & Jolly Y S, Orie11l J Chem, 12, 1996. 185. 7 Ikeda M, Muraya ma K. Nobuhara Y. Yamada T & Okabe S. Ch em Pharm BIIII, 44, 1996, 1700. 8 Bourrain S. Collins E, Nedurelil J G, Rowley M. Lesson P D. Patel S, Emms F, Marwood R, Chapman K L, Fletcher A E & Schowell G A, Bioorg Med Ch em. 6. 1998. 1731 . 9 Vogel' s Textbook of Practical Organic Chemistry, Fifth Edn. 1989, p. 695, 807. 10 Kira M A, Nofal Z M & Gadalla K Z. Tetrah edroll Lett. 48 , 1970, 42 15.
