A convenient synthesis of 2-amino-5,6,7,8,-tetrahydro-5-oxo-4-aryl-7,7-dimethyl-4H-benzo-[b]- pyran-3-ethylcarboxylates under microwave irradiation

Article abstract of DOI:10.1081/SCC-100105394

A series of 2-amino-5,6,7,8-tetrahydro-5-oxo-4-aryl-7,7-dimethyl-4H-benzo-[b] -pyran-3-ethylcarboxylates were synthesized by reaction of β-cyano-β-carbothoxy styrene and 5,5-dimethyl-1,3-cyclo-hexanedione under microwave irradiation without catalyst and s

Full text of DOI:10.1081/SCC-100105394

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A CONVENIENT SYNTHESIS OF 2-AMINO-5,6,7,8,-
TETRAHYDRO-5-OXO-4-ARYL-7,7-DIMETHYL-4H-
BENZO-[b]-PYRAN-3-ETHYLCARBOXYLATES UNDER
MICROWAVE IRRADIATION
Shujiang Tu a , Hai Wang b , Jianqing Feng b , Ailing Tang b & Juncai Feng c
a Department of Chemistry, Xuzhou Normal, University, Xuzhou, 221009, People's
Republic of China
b Department of Chemistry, Nanjing University, Nanjing, 210093, People's Republic of
China
c Department of Chemistry, Nanjing University, Nanjing, 210093, People's Republic of
China
Published online: 09 Nov 2006.
To cite this article: Shujiang Tu , Hai Wang , Jianqing Feng , Ailing Tang & Juncai Feng (2001) A CONVENIENT SYNTHESIS
OF 2-AMINO-5,6,7,8,-TETRAHYDRO-5-OXO-4-ARYL-7,7-DIMETHYL-4H-BENZO-[b]-PYRAN-3-ETHYLCARBOXYLATES UNDER
MICROWAVE IRRADIATION, Synthetic Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 31:17, 2663-2666, DOI: 10.1081/SCC-100105394
To link to this article: http://dx.doi.org/10.1081/SCC-100105394
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SYNTHETIC COMMUNICATIONS, 31(17), 2663–2666 (2001)
A CONVENIENT SYNTHESIS OF
2-AMINO-5,6,7,8,-TETRAHYDRO-5-OXO-4-
ARYL-7,7-DIMETHYL-4H-BENZO-[b]-
PYRAN-3-ETHYLCARBOXYLATES
UNDER MICROWAVE IRRADIATION
Shujiang Tu,* Hai Wang, Jianqing Feng,
Ailing Tang, and Juncai Feng{
Department of Chemistry, Nanjing University, Nanjing 210093,
People’s Republic of China
ABSTRACT
A series of 2-amino-5,6,7,8-tetrahydro-5-oxo-4-aryl-7,7-dimethyl-
4H-benzo-[b]-pyran-3-ethylcarboxylates were synthesized by
reaction of b-cyano-b-carbothoxy styrene and 5,5-dimethyl-
1,3-cyclo-hexanedione under microwave irradiation without
catalyst and solvent.
Microwave heating and its application in organic synthesis has been
reviewed recently.1 Rate enhancement in many reactions has been reported.2
We have been working on developing new synthetic methods for the pre-
paration of substituted 4H-benzo-[b]-pyrans employing both microwave
irradiation and dry reaction conditions.
*Current address: Department of Chemistry, Xuzhou Normal, University, Xuzhou
221009, People’s Republic of China.
{Corresponding author.
2663
Copyright & 2001 by Marcel Dekker, Inc.
www.dekker.com

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2664
TU ET AL.
The title compound is a useful and versatile building block for the
synthesis of a number of unusual natural products.3 Their conventional
syntheses involve acid as well as base catalyzed condensation of appropriate
active methylene carbonyl compounds and are plagued by prolonged
reaction times, poor yields, and side reactions of the aldehydes. Kamaljit S.
et al. reported4 that 2-amino-5,6,7,8-tetrahydro-5-oxo-4-aryl-7,7-dimethyl-
4H-benzo-[b]-pyran-3-ethylcarboxylates(3) were synthesized from b-cyano-
b-carbethoxy styrene and 1,3-cyclohexanedione in refluxing acetonitrile:
acetic acid (10 : 1). Here we would like to report a convenient synthesis of
these compounds using reaction condition which employ microwave irradia-
tion without catalyst and solvent. The reactions are completed in 4–8 min
with yields of 61–90%.
The results are shown in the Table 1.
EXPERIMENTAL
Melting points were determined in open capillaries and are uncor-
rected. IR spectra were recorded on a Nicolet FI-IR50DX instrument.
1HNMR spectra were measured on a DPX 300 MHz spectrometer using
TMS as internal standard. Elemental analyses were determined by using
Perkin-Elmer 240c elemental analysis. Microwave irradiation was carried
Table 1. Syntheses of Compound 3 Under Microwave Irradiation
Time
(min)
Isolated
Yield (%)
Entry
Ar
3a
3b
3c
3d
3e
3f
C6H5
2-ClC6H4
4-ClC6H4
3,4-OCH2OC6H3
3,4-(OCH3)2C6H3
3-NO2C6H4
4-BrC6H4
4
7
6
8
8
7
6
61
90
74
61
87
81
77
3g

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2665
out with a commercial microwave oven (2450 MHz, 500 W) under atmos-
pheric pressure.
General Procedure
b-Cyano-b-carbethoxy styrene was synthesized from aromatic alde-
hydes and ethyl cyanoacetate with KF-alumina as catalyst refluxing in alco-
hol. Other reagents were used without further purification.
5,5-Dimethyl-1,3-cyclohexanedione (5 mmol) and b-amino-b-carb-
ethoxy styrene (5 mmol) were thoroughly mixed with silica (2 g) in an
agate mortar. The resulting fine power was transferred to a flask (50 mL)
connected with refluxing equipment. After irradiation of several minutes,
the reaction mixture was cooled to room temperature. The crude products
were purified by recrystallization from 95% EtOH or column chromato-
graphy to give (3).
3a: m.p. 146–148ꢀC. IR (KBr, v, cm–1): 3400, 3300, 1700, 1654. 1HNMR
(CDCl3): d 0.98 (s, 3H, CH3), 1.10 (s, 3H, CH3), 1.15 (t, J ¼ 7.11 Hz, 3H,
CH3), 2.18 (m, 2H, CH2), 2.44 (s, 2H, CH2), 4.02 (q, J ¼ 7.01 Hz, 2H, CH2),
4.71 (s, 1H, CH), 6.20 (brs, 2H, NH2), 7.26–7.45 (m, 5H, ArH); Anal. calcd.
(%) for C20H23NO4, C 70.38, H 6.74, N 4.10; found: C 70.16, H 6.88, N
4.03.
3b: m.p. 166–168ꢀC. IR (KBr, v, cm–1): 3400, 3300, 1680, 1654. 1HNMR
(CDCl3): d 0.99 (s, 3H, CH3), 1.08 (s, 3H, CH3), 1.12 (t, J ¼ 7.11 Hz, 3H,
CH3), 2.19 (m, 2H, CH2), 2.41 (s, 2H, CH2), 4.01 (q, J ¼ 7.12 Hz, 2H, CH2),
5.00 (s, 1H, CH), 6.27 (brs, 2H, NH2), 7.04–7.32 (m, 4H, ArH); Anal. calcd.
(%) for C20H22ClNO4, C 63.91, H 5.90, N 3.72; found: C 63.80, H 6.12, N
3.83.
3c: m.p. 149–150ꢀC. IR (KBr, v, cm–1): 3438, 3304, 1680, 1658. 1HNMR
(CDCl3): d 0.98 (s, 3H, CH3), 1.08 (s, 3H, CH3), 1.14 (t, J ¼ 7.11 Hz, 3H,
CH3), 2.14 (m, 2H, CH2), 2.43 (s, 2H, CH2), 4.06 (q, J ¼ 7.11 Hz, 2H, CH2),
4.68 (s, 1H, CH), 6.21 (brs, 2H, NH2), 7.16–7.30 (m, 4H, ArH); Anal. calcd.
(%) for C20H22ClNO4, C 63.91, H 5.90, N 3.72; found: C 63.79, H 6.10, N
3.90.
3d: m.p. 142–144ꢀC. IR (KBr, v, cm–1): 3402, 3300, 1683, 1657. 1HNMR
(CDCl3): d 1.00 (s, 3H, CH3), 1.10 (s, 3H, CH3), 1.17 (t, J ¼ 7.14 Hz, 3H,
CH3), 2.18 (m, 2H, CH2), 2.43 (s, 2H, CH2), 4.08 (q, J ¼ 7.14 Hz, 2H, CH2),
4.64 (s, 1H, CH), 5.93 (s, 2H, OCHO), 6.17 (brs, 2H, NH2), 6.71–6.76 (m,
3H, ArH); Anal. calcd. (%) for C21H23NO6, C 65.44, H 6.01, N 3.63; found:
C 65.32, H 5.92, N 3.78.
3e: m.p. 155–157ꢀC. IR (KBr, v, cm–1): 3448, 3346, 1698, 1662. 1HNMR
(CDCl3): d 0.98 (s, 3H, CH3), 1.09 (s, 3H, CH3), 1.18 (t, J ¼ 7.11 Hz, 3H,

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2666
TU ET AL.
CH3), 2.19 (m, 2H, CH2), 2.41 (s, 2H, CH2), 3.81 (s, 3H, OCH3) 3.85 (s, 3H,
OCH3), 4.05 (q, J ¼ 7.08 Hz, 2H, CH2), 4.65 (s, 1H, CH), 6.21 (brs, 2H,
NH2), 6.70–6.86 (m, 3H, ArH); Anal. calcd. (%) for C22H27NO6, C 65.82, H
6.78, N 3.49; found: C 65.93, H 6.70, N 3.50.
3f: m.p. 172–174ꢀC. IR (KBr, v, cm–1): 3500, 3310, 1698, 1679. 1HNMR
(CDCl3): d 0.98 (s, 3H, CH3), 1.11 (s, 3H, CH3), 1.15 (t, J ¼ 7.11 Hz, 3H,
CH3), 2.18 (m, 2H, CH2), 2.47 (s, 2H, CH2), 4.04 (q, J ¼ 7.14 Hz, 2H, CH2),
4.79 (s, 1H, CH), 6.33 (brs, 2H, NH2), 7.35–8.10 (m, 4H, ArH); Anal. calcd.
(%) for C20H22N2O6, C 62.16, H 5.74, N 7.25; found: C 62.07, H 5.90, N
7.38.
3g: m.p. 160–162ꢀC. IR (KBr, v, cm–1): 3448, 3310, 1684, 1647. 1HNMR
(CDCl3): d 0.99 (s, 3H, CH3), 1.10 (s, 3H, CH3), 1.16 (t, J ¼ 7.11 Hz, 3H,
CH3), 2.18 (m, 2H, CH2), 2.42 (s, 2H, CH2), 4.05 (q, J ¼ 7.13 Hz, 2H, CH2),
4.66 (s, 1H, CH), 6.23 (brs, 2H, NH2), 7.13–7.34 (m, 4H, ArH); Anal. calcd.
(%) for C20H22BrNO4, C 57.15, H 5.27, N 3.33, found: C 57.00, H 5.38, N
3.43.
REFERENCES
1. Abramovitch, R.A. Org. Prep. Proc. Int. 1991, 23, 685.
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Lett. 1986, 27, 4945; (b) Berian, J.; Giboreau, P.; Le Feuver, S.;
Marchand, C. Tetrahedron Lett. 1991, 32, 2363; (c) Chen, S.T.;
Chiou, S.H.; Warg, K.T. J. Chem. Soc., Chem. Commun. 1990, 807;
(d) Sowmya, S.; Balasubramanian, K.K. Synth. Commun. 1994, 24,
2097; (e) Srikrishna, A.; Praveen Kumar, P. Tetrahedron Lett. 1995,
36, 6313.
3. (a) Hatakeyama, S.; Ochi, N.; Numata, H.; Takano, S. J. Chem. Soc.,
Chem. Commun. 1988, 1202; (b) O’Callaghan, C.N.; Mc Marry, T.B.H.
J. Chem. Res(s), 1995, 214 and (M), 1995, 1448.
4. Kamaljit S. Jasbir S.; Harjit S. Tetrahedron 1996, 52(45), 14273.
Received in the USA Novemeber 10, 2000

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