Cyclohexenone carboxylates. A versatile source for fused isoxazoles and pyrazoles

Article abstract of DOI:10.1081/SCC-100104462

The 6-carbethoxy-3,5-diarylcyclohex-2-enone (1) was subjected to condensation and 1,3-dipolar cycloaddition reactions to get fused isoxazole and pyrazole derivatives.

Full text of DOI:10.1081/SCC-100104462

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CYCLOHEXENONE CARBOXYLATES. A VERSATILE
SOURCE FOR FUSED ISOXAZOLES AND PYRAZOLES
V. Padmavathi a , K. Sharmila a , A. Balaiah a , A. Somasekhar Reddy a & D. Bhaskar
Reddy b
a Department of Chemistry , Sri Venkateswara University , Tirupati, 517 502, India
b Department of Chemistry , Sri Venkateswara University , Tirupati, 517 502, India
Published online: 09 Nov 2006.
To cite this article: V. Padmavathi , K. Sharmila , A. Balaiah , A. Somasekhar Reddy & D. Bhaskar Reddy (2001)
CYCLOHEXENONE CARBOXYLATES. A VERSATILE SOURCE FOR FUSED ISOXAZOLES AND PYRAZOLES, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry, 31:14, 2119-2126,
DOI: 10.1081/SCC-100104462
To link to this article: http://dx.doi.org/10.1081/SCC-100104462
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SYNTHETIC COMMUNICATIONS, 31(14), 2119–2126 (2001)
CYCLOHEXENONE CARBOXYLATES.
A VERSATILE SOURCE FOR FUSED
ISOXAZOLES AND PYRAZOLES
V. Padmavathi, K. Sharmila, A. Balaiah,
A. Somasekhar Reddy, and D. Bhaskar Reddy*
Department of Chemistry, Sri Venkateswara University,
Tirupati – 517 502, India
ABSTRACT
The 6-carbethoxy-3,5-diarylcyclohex-2-enone (1) was sub-
jected to condensation and 1,3-dipolar cycloaddition reac-
tions to get fused isoxazole and pyrazole derivatives.
In our earlier communications, we reported the synthesis and stereo-
chemistry of various fused and spiro isoxazolines and pyrazolines prepared
by 1,3 -dipolar cycloaddition of nitrile oxides and nitrile imines to activated
olefins.1–4 In continuation of this work, we now describe the use of 6-carb-
ethoxy-3,5-diarylcyclohex-2-enone 1 an intermediate with three versatile
functional groups i.e., ketone, olefin and ester, for the syntheses of various
fused isoxazole and pyrazole derivatives.
6-Carbethoxy-3,5-diarylcyclohex-2-enone (1) was prepared by the
Knoevenagel reaction of ethyl acetoacetate and 1,3-diary1-2-propen-1-one.
The compound 1 on treatment with hydroxylamine hydrochloride/hydrazine
hydrate/phenylhydrazine in ethanol in presence of 10% NaOH afforded the
* Corresponding author.
2119
Copyright & 2001 by Marcel Dekker, Inc.
www.dekker.com

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PADMAVATHI ET AL.
corresponding isoxazolinones (2a–c), pyrazolinones (3a–c) and 2-phenyl
pyrazolinones (4a–c) (Scheme 1).
Scheme 1.
Further, the 1,3-cycloaddition of phenyl nitrile oxide or phenyl nitrile
imine to the activated double bond in compound 1 led to the formation
of tetrahydrobenzoisoxazolines (5) and tetrahydrobenzopyrazolines (6)
(Scheme 2). In fact, the reagents were generated from araldoximes and
araldehyde phenylhydrazones, respectively, in the presence of chloramine-T
(CAT). As discussed in the literature this reaction process involves a one-
step concerted ring closure mechanism,6 which governs the regiochemistry
of the cycloaddition (NMR, singlet at 2.44–2.55 ppm (C-9)).
The compound 1 on hydrolysis followed by decarboxylation gave
3,5-diarylcyclohex-2-enone (7).5 Cycloaddition with nitrile oxide or imine, as

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CYCLOHEXENONE CARBOXYLATES
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Scheme 2.
described above, gave tetrahydrobenzoisoxazolines (8) and tetrahydro-
benzopyrazolines (9) (Scheme 2).
Compound 7 on reduction with H2/Pd at 40 psi5 gave ketone 10 which
was derivatized to 3,5-diary1-1-morpholino-3,4,5,6-tetrahydrobenzene (11)
with morpholine. On treatment with phenyl nitrile oxide and nitrile imine
the respective isoxazole (12a–c) and pyrazole derivatives (13a–c) were

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PADMAVATHI ET AL.
obtained (Scheme 2). This was contrary to the previous reaction, where the
products were isoxazolines (8) and pyrazolines (9).
In conclusion the different functionalities in 6-carbethoxy-3,5-diaryl-
cyclohex-2-enone 1 can be used advantageously in the preparation of vari-
ous isoxazole and pyrazole derivatives.
EXPERIMENTAL
Melting points were determined in open capillaries on Tempo Mel-
Temp apparatus and are uncorrected. The yield of the compounds given are
after purification. The purity of the compounds was checked by thin layer
chromatography [Silica gel-G(60–120 mesh, BDH), pet.ether (40–60ꢀC);
ethyl acetate (3:1) as eluents].
The IR spectra were recorded on a Perkin-Elmer grating Infra-
red spectrophotometer (ꢀmax in cmꢁ1) model 337 in KBr pellets. The
1H NMR spectra were recorded in CDCl3/DMSO-d6 at 90 and 200 MHz
on Bruker spectrospin and Varian EM-360 spectrometers with TMS as
an internal standard (chemical shifts in d ppm). Microanalyses were per-
formed by microanalytical laboratory, University of Pune, Pune, India.
The 6-carbethoxy-3,5-diarylcyclohex-2-enone (1a–c), 3,5-diarylcyclohex-2-
enone (7a–c), 3-5-diarylcyclohexanone (10a–c) were prepared according to
the literature procedures.5
5,7-Diaryl-6,7,8-trihydrobenzo[3,4,-d]isoxazolin-1-one (2a–c)/5,7-
diaryl-2,6,7,8-tetrahydrobenzo[3,4,-d]pyrazolin-1-one(3a–c)/5,7-
diaryl-2-phenyl-6,7,8-trihydrobenzo[3,4,-d]pyrazolin-1-one (4a–c)
GeneralProcedure : A mixture of 1 (0.005 mol), hydroxylamine hydro-
chloride/hydrazine hydrate/phenylhydrazine (0.005 mol), 10% NaOH sol-
ution (5 mL) and methanol (30 mL) was refluxed on a water bath for
3 hrs. Then the content was cooled and poured onto crushed ice. The sepa-
rated solid was filtered, washed with aqueous methanol (1:1) and recrystal-
lized from aqueous alcohol. 2a: m.p. 139–141ꢀC, Yield 65%; IR (KBr): 1610
(C ¼ C), 1710 (C ¼ O); 1H NMR (CDCl3): 2.01–2.23 (m, 2H, C6-Ha
&
C8-H), 2.30–2.52 (dd, 1H, J ¼ 4.0 & 15.4 Hz, C6-Hb), 2.99–3.17 (m, 1H,
C7-H), 5.34 (s, 1H, C4-H); Anal. Calcd. for C19H15NO2: C, 78.87; H,
5.25; N, 4.84; Found: C, 78.72; H, 5.39; N, 4.67. 2b: m.p. 179–180ꢀC,
Yield 63%; IR (KBr); 1607 (C ¼ C), 1714 (C ¼ O); Anal. Calcd. for
C20H17NO3: C, 75.21; H, 5.36; N, 4.36; Found: C, 75.32; H, 5.45; N,
4.47. 2c: m.p. 150–151ꢀC, Yield 65%; IR (KBr): 1605 (C ¼ C), 1709

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(C ¼ O), Anal. Calcd. for C19H13Cl2NO2: C, 63.70; H, 3.65; N, 3.91; Found:
C, 63.55; H, 3.53; N, 4.01. 3a: m.p. 158–160ꢀC, Yield 61%; IR (KBr); 1614
1
(C ¼ C), 1698 (C ¼ O), 3410 (NH); H NMR (CDCl3): 2.15–2.36 (m, 2H,
C6-Ha & C8-H), 2.32–2.99 (dd, 1H, J ¼ 3.5 & 14.8 Hz, C6-Hb), 3.10–3.30 (m,
1H, C7-H), 5.22 (s, 1H, C4-H), 6.73 (s, 1H, NH); Anal. Calcd. for C19H16N2O:
C, 79.14; H, 5.59; N, 9.71; Found: C, 79.02; H, 5.70; N, 9.85. 3b: 177–178ꢀC,
Yield 63%; IR (KBr): 1615 (C ¼ C), 1720 (C ¼ O), 3395 (NH); Anal. Calcd.
for C20H18N2O2: C, 75.45; H, 5.69; N, 8.79; Found: C, 75.56; H, 5.56; N,
8.68. 3c: m.p. 98–100ꢀC, Yield 60%; IR (KBr): 1605 (C ¼ C), 1709, (C ¼ O),
3405 (NH); Anal. Calcd. for C19H14Cl2N2O: C, 63.88; H, 3.95: N, 7.84;
Found: C, 64.03; H, 3.84; N, 7.71. 4a: m.p. 118–120ꢀC, Yield 60%; IR
1
(KBr): 1615 (C ¼ C), 1720 (C ¼ O), H NMR (CDCl3): 2.38–2.64 (m, 2H,
C6-Ha & C8-H), 2.60–2.90 (dd, 1H, J ¼ 3.5 & 17.0 Hz-C6-Hb), 3.15–3.52 (m,
1H, C7-H), 5.65 (s, 1H, C4-H); Anal. Calcd. for C25H20N2O: C, 82.39; H,
5.53; N, 7.68; Found: C, 82.26; H, 5.41; N, 7.57. 4b: m.p. 127–128ꢀC, Yield
65%; IR (KBr): 1609 (C ¼ C), 1720 (C ¼ O); Anal. Calcd. for C26H22N2O2:
C, 78.96; H, 5.73; N, 7.17; Found: C, 79.16; H, 5.64; N, 7.10. 4c: m.p.
138–139ꢀC, Yield 63%; IR (KBr) : 1615 (C ¼ C), 1720 (C ¼ O). Anal.
Calcd. for C25H18Cl2N2O: C, 75.46; H, 4.55; N, 7.04; Found: C, 75.33; H,
4.43; N, 7.17.
6,8-Diaryl-5-carbethoxy-4-oxo-3-phenyl-5,6,7,9-tetrahydrobenzo-
[3,4,-d ] isoxazoline (5a–c)
GeneralProcedure : A solution of benzaldoxime (0.60 g, 0.005 mol) in
ethanol (20 mL) was heated to 30–40ꢀC. To this, chloramine-T (CAT)
(1.40 g, 0.005 mol) was added and the contents were heated to reflux. The
solvent was removed under vacuo. The residue obtained was extracted with
ether and washed with 1 N NaOH, brine and dried (an. Na2SO4). When the
solvent was removed under reduced pressure, nitrile oxide was obtained.4
This was added to 1a/b/c (0.005 mol) in ether (25 mL) and the mixture was
stirred for 30 min. and kept aside for another 1 hr. Evaporation of the
solvent gave 5a–c which were purified by filtration through a column of
silica gel [silica gel (BDH), 60–120 mesh:ethyl acetate:hexane; 1:3]. 5a:
m.p. 144–145ꢀC, Yield 72%; IR (KBr): 1690 (C ¼ O) 1715 (C ¼ O of
1
ester), 1316 (C-O); H NMR (CDCl3): 0.92 (t, 3H, CO2CH2CH3), 2.00 (d,
2H, C7-H) 2.44 (s, 1H, C9-H), 2.80 (d, 1H, C5-H), 3.68 (q, 2H,
CO2CH2CH3), 3.84–4.00 (m, 1H, C6-H); Anal. Calcd. for C28H25NO4: C,
76.50; H, 5.73; N, 3.18; Found: C, 76.63; H, 5.60; N, 3.06. 5b: m.p.
144–145ꢀC, Yield 70%; IR (KBr): 1688 (C ¼ O), 1710 (C ¼ O of ester),
1315 (C-O); Anal. Calcd. for C29H27NO5: C, 74.16; H, 5.79; N, 2.98;

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PADMAVATHI ET AL.
Found: C, 74.07; H, 5.90; N, 2.85. 5c: m.p. 127–129ꢀC, Yield 67%; IR
(KBr): 1692 (C ¼ O), 1715 (C ¼ O of ester) 1310 (C-O). Anal. Calcd. for
C28H23Cl2NO4: C, 66.15; H, 4.55; N, 2.75; Found: C, 66.29; H, 4.42; N,
2.62.
6,8-Diaryl-5-carbethoxy-4-oxo-1,3-diphenyl-5,6,7,9-
tetrahydrobenzo[3,4,-d ]pyrazoline (6a–c)
GeneralProcedure : A mixture of benzaldehyde phenylhydrazone
(0.98 g, 0.005 mol) and CAT (1.54 g, 0.0055 mol) was dissolved in ethanol
(20 mL) and swirled on water bath for 15–20 min. The solvent was removed
under vacuo (4–5 mm/Hg) and the residue obtained was extracted with ether
washed with 1 N NaOH, brine and dried (an. Na2SO4). Evaporation of the
solvent gave nitrile imine.4 To this 1a/b/c (0.005 mol) in ethanol (10 mL) was
added and the contents were refluxed for another 1 hr. Then it was cooled
and poured onto crushed ice. The solid separated was filtered and recrys-
tallized from aqueous ethanol (1:1). 6a: m.p. 109–110ꢀC, Yield 61%; IR
1
(KBr): 1698 (C ¼ O), 1715 (C ¼ O of ester); H NMR (CDCl3): 0.98 (t,
3H, CO2CH2CH3), 2.15 (d, 2H, C7-H), 2.56 (d, 1H, C5-H), 2.55 (s, 1H,
C9-H), 3.80 (q, 2H, CO2CH2CH3), 3.95–4.25 (m, 1 H, C6-H); Anal. Calcd.
for C34H30N2O3: C, 79.35; H, 5.87; N, 5.44; Found: C, 79.47; H, 5.66; N,
5.32. 6b: m.p. 120–121ꢀC, Yield 60%; IR (KBr): 1690 (C ¼ O), 1722 (C ¼ O
of ester); Anal. Calcd. for C35H32N2O4: C, 77.18; H, 5.92; N, 5.14; Found:
C, 77.07; H, 5.81; N, 5.24. 6c: m.p. 127–128ꢀC, Yield 65%; IR (KBr): 1684
(C ¼ O), 1715 (C ¼ O of ester). Anal. Calcd. for C34H28Cl2N2O3: C, 69.98;
H, 4.83; N, 4.80; Found: C, 69.85; H, 4.74; N, 4.90.
6,8-Diaryl-4-oxo-3-phenyl-5,6,7,9-tetrahydrobenzo[3,4,-d]isoxazoline
(8a–c)/6,8-diaryl-4-oxo-1,3-diphenyl-5,6,7,9-tetrahydrobenzo-
[3,4,-d]pyrazoline (9a–c)
GeneralProcedure : The compounds 8/9a–c were prepared by the reac-
tion of nitrile oxide and nitrile imine with 7a/b/c as described for 5 and 6.
The compounds were purified by recrystallization from aqueous ethanol
(1:1). 8a: m.p. 187–188ꢀC, Yield 64%; IR (KBr): 1695 (C ¼ O), 1312
1
(C-O); H NMR (CDCl3): 2.10 (d, 2H, C7-H), 2.56 (s, 1H, C9-H), 2.84 (d,
2H, C5-H), 3.45–3.80 (m, 1H, C6-H); Anal. Calcd. for C25H21NO2: C, 81.71;
H, 5.76; N, 3.81; Found: C, 81.58; H, 5.64; N, 3.90. 8b: m.p. 198–200ꢀC,
Yield 62%; IR (KBr): 1690 (C ¼ O), 1298 (C-O); Anal. Calcd. for
C26H23NO3: C, 78.56; H, 5.83; N, 3.52; Found: C, 78.43; H, 5.74; N,

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3.63. 8c: m.p. 164–165ꢀC, Yield 66%; IR (KBr): 1698 (C ¼ O), 1309
(C-O); Anal. Calcd. for C25H19Cl2NO2: C, 74.26; H, 4.73; N, 3.46;
Found: C, 74.40; H, 4.82; N, 3.35. 9a: 92–94ꢀC; Yield 60%; IR (KBr): 1698
1
(C ¼ O) H NMR (CDCl3): 2.15 (d, 2H, C7-H), 2.62 (s, 1H, C9-H), 2.89 (d,
2H, C5-H), 3.05–3.45 (m, 1H, C6-H); Anal. Calcd. for C31H26N2O: C, 84.13;
H, 5.92; N, 6.32; Found: C, 84.00; H, 5.80; N, 6.23. 9b: m.p. 95–97ꢀC, Yield
63%; IR (KBr): 1705 (C ¼ O); Anal. Calcd. for C32H28N2O2: C, 81.32; H,
5.97; N, 5.92; Found: C, 81.42; H, 6.06; N, 5.78. 9c: m.p. 105–106ꢀC, Yield
66%; IR (KBr): 1700 (C ¼ O). Anal. Calcd. for C31H24Cl2N2O: C, 72.80; H,
4.72; N, 5.47; Found: C, 72.94; H, 4.82; N, 5.39.
3,5-Diaryl-1-morpholino-3,4,5,6-tetrahydrobenzene (11a–c)
GeneralProcedure : A mixture of 10a/b/c (0.01 mol), morpholine
(2 mL, 0.018 mol), a catalytic amount of p-toluene sulfonic acid and dry
benzene (30 mL) was taken in a round bottomed flask equipped with
Dean-Stark apparatus and refluxed until the water separation was seized.
The contents were cooled, extracted with benzene and washed with sat.
NaHCO3 solution and water. Evaporation of solvent in vacuo gave a
semi-solid which was purified by filtration through column of silica gel
chromatography [silica gel (BDH), 60–120 mesh; ethyl acetate:hexane,
1:2]. 11a: m.p. 111–112ꢀC, Yield 68%; 11b: m.p. 127–128ꢀC; Yield 65%;
11c: m.p. 115–116ꢀC; Yield 65%.
4,6-Diaryl-3-phenyl-4,5,6,7-tetrahydrobenzo[3,4,-d]isoxazole (12a–c)
GeneralProcedure : A solution of 11a/b/c (0.005 mol), benzaldoxime
(0.005 mol) and a catalytic amount of CAT in ethanol (25 mL) was refluxed
for 4 hrs. The reaction mixture was extracted with ether, washed with dil.
NaOH, brine, water and dried (an. Na2SO4). Evaporation of the solvent
gave oily substance which contains amine and isoxazole, (12). Pure 12 was
separated by column chromatography [silica gel (BDH), 60–120 mesh; ethyl
acetate:hexane, 1:3]. 12a: m.p. 98–99ꢀC, Yield 68%; IR (KBr): 1613 (C ¼ C),
1332 (C-O); 1H NMR (CDCl3): 2.30–2.55 (m, 2H, C5-H), 2.70 (d, 2H,
C7-H), 3.80–3.88 (m, 1H, C6-H), 4.03 (t, 1H, C4-H); Anal. Calcd. for
C25H21NO: C, 85.43; H, 6.16; N, 3.98; Found: C, 85.56; H, 6.29; N, 3.89.
12b: m.p. 111–112ꢀC, Yield 64%; IR (KBr): 1615 (C ¼ C), 1348 (C-O); Anal.
Calcd. for C26H23NO2: C, 81.8; H, 6.07; N, 3.68; Found: C, 81.65; H, 6.16;
N, 3.80. 12c: m.p. 86–87ꢀC, Yield 65%; IR (KBr): 1611 (C ¼ C), 1320 (C-O).
Anal. Calcd. for C25H19Cl2NO: C, 71.30; H, 4.54; N, 3.32; Found:
C, 71.42; H, 4.64; N, 3.23.

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PADMAVATHI ET AL.
4,6-Diaryl-1,3-diphenyl-4,5,6,7-tetrahydrobenzo[3,4,-d]
pyrazole(13a–c)
GeneralProcedure : The compounds 13a–c were obtained by the reac-
tion of 11a/b/c with benzaldehyde phenylhydrazone following the above
described procedure. The compounds were purified by column chromato-
graphy [silica gel (BDH), 60–120 mesh; ethyl acetate:hexane, 1:3]. 13a: m.p.
120–121ꢀC, Yield 63%; IR (KBr): 1613 (C ¼ C); 1H NMR (CDCl3):
2.12–2.38 (m, 2H, C5-H), 2.85 (d, 2H, C7-H), 3.72–3.81 (m, 1H,C6-H);
4.05 (t, 1H, C4-H); Anal. Calcd. for C31H26N2: C, 87.29; H, 6.14; N, 6.56;
Found: C, 87.18; H, 6.24; N, 6.44. 13b: m.p. 112–113ꢀC, Yield 65%; IR
(KBr): 1620, (C ¼ C); Anal. Calcd. for C32H28N2O: C, 84.17; H, 6.18; N,
6.13; Found: C, 84.30; H, 6.09; N, 6.26. 13c: m.p. 118–119ꢀC, Yield 64%; IR
(KBr): 1619 (C ¼ C). Anal. Calcd. for C31H24Cl2N2: C, 75.15; H, 4.88; N,
5.65; Found: C, 75.01; H, 5.03; N, 5.55.
ACKNOWLEDGMENT
One of the authors (ASSR) is grateful to CSIR, New Delhi for the
award of Senior Research Fellowship.
REFERENCES
1. Padmavathi, V.; Bhaskar Reddy, A.V.; Sumathi, R. P.; Padmaja, A. and
Bhaskar Reddy, D. Indian J. Chem. 1998, 37B, 1286.
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Reddy, D. Heterocycl. Commun. 1998, 4, 163.
3. Bhaskar Reddy, D.; Somasekhar Reddy, A. and Padmavathi, V.
J. Chem. Research(s), 1998, 784.
4. Padmavathi, V.; Sumathi, R.P.; Chandrasekhar Babu, N. and Bhaskar
Reddy, D. J. Chem. Research(s) 1999, 610.
5. Balasubramanian, M. and D’souza, A. Tetrahedron 1968, 24, 5399.
6. Caramella, P. and Grunanger, P. in ‘‘1,3-Dipolar Cycloaddition
Chemistry’’, Padva, A. (Ed.) John Wiley and Sons, 1984, Vol. 1,
Chapter 3, pp. 291; Huisgen, R.; Grashey, R. and Sauer, J. in
‘‘Chemistry of Alkenes’’, Patai, S. (Ed.), Interscience, New York, 1964,
pp. 806 ff.
Received in the USA October 11, 2000

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