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Scheme 4. The reduction of diazenyl group and formation of amino benzopyrane 9.
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24. General procedure for the synthesis of substituted benzaldehydes 3a–d: To a
syn, and exo-Z-syn.7h The 1H NMR study showed that the reaction
product is mainly of its cis-isomeric form even though the two
pathways (a and b) are possible (Scheme 2). Allyl moiety based
substrates required higher temperature compared to the one con-
taining prenyl moiety. These observations are well supported by
the fact that the HOMO–LUMO gap30 for diene and dienophile
interaction is relatively less in the case of prenyl moiety. Therefore,
it is assumed that the interaction of prenyl dienophile is more
favorable.7f
As part of our preliminary studies, we could isolate the amino-
chromene 9 by reducing 7n (Scheme 4). The formation of this novel
product 9 has been confirmed by spectroscopic data.31
In summary, we have described a one pot synthesis of novel
chromeno[40,30:4,5]pyrano[2,3-c]pyrazoles, by TBA-HS mediated
DKHDA reaction. The advantages of this methodology are the easy
work-up procedure, high stereoselectivity and isolation of the
product in high yield with excellent purity. Furthermore, TBA-HS
is a nontoxic, noncorrosive, commercially available, and inexpen-
sive catalyst.
stirred solution of
2 (0.01 mol) with anhydrous potassium carbonate
(0.015 mol) in DMF (25 ml), a solution of allyl bromide (0.015 mol) or prenyl
bromide (0.015 mol) in DMF (5 ml), was added drop-wise. The reaction
mixture was stirred at room temperature till the completion of the reaction as
confirmed by the TLC (10–12 h). The resulting mass was then poured into 100 g
of ice with constant stirring. The solid residue was filtered, washed with cold
water (3 ꢀ 10 ml), and dried at room temperature. The products 3a–d were
obtained quantitatively with an excellent purity.
25. Sarma, K.; Basu Baul, T. S.; Basaiawmoit, W. L.; Saran, R. Spectrochim. Acta A
1993, 49, 1027.
26. General procedure for the synthesis of benzopyran-annulated pyrano[2,3-
c]pyrazoles (7a–p): A mixture of aldehydes 3a–d (2 mmol), pyrazolones 4a-d
(2 mmol) and catalyst TBA-HS (25 mol %) was stirred under refluxing xylene
(when R = H) or acetonitrile (when R = CH3) for a specified time shown in
Table 2. After complete conversion, as indicated by the TLC, the mixture was
cooled and subjected to reduced pressure to remove solvent. The residue 7a–p
were washed with an appropriate solvent such as xylene or acetonitrile to
remove any residual starting material and dried in vacuo. The products were
obtained in 68–88% yields. Analytically pure sample was obtained by
preparative TLC using ethyl acetate/hexane (3:7) as an eluent.
27. Spectroscopic data of some selected compounds: Compound 7a:Yellow solid, mp
190–192 °C; IR (KBr): mmax (cmꢁ1) 2957, 2927, 1490, 1467, 1241, 1092, 1026,
831, 758; 1H NMR (400 MHz, CDCl3): d 1.58 (s, 3H, 5-CH3 ax), 1.60 (s, 3H, 5-CH3
eq), 2.43 (s, 4H, 1-CH3), 2.60 (m, 1H, 5a-H), 4.18 (t, J = 10.4 Hz, 1H, 6-H ax), 4.33
(d, J = 4.8 Hz, 1H, 11b-H), 4.47 (m, 2H, 5-H), 4.66 (dd, J = 8.0 Hz, J = 2.4 Hz, 1H,
6-H eq), 6.99 (d, J = 8.8 Hz 1H, 8-H), 7.22–7.87 (m, 11H, Ar–H); 13C NMR
(100 MHz, CDCl3): d 14.41, 29.51, 30.12, 66.20, 68.52, 99.48, 118.11, 120.29,
122.76, 123.63, 125.15, 125.66, 126.01, 129.55, 129.86, 131.34, 138.65, 145.11,
146.49, 146.77, 148.09, 149.24, 149.95, 152.40, 152.81; ESI-MS: m/z: 423.1
(M+H)+; Compound 7d: Yellow solid, mp 187–189 °C; IR (KBr): mmax
(cmꢁ1) = 3080, 3000, 2900, 1600, 1250, 1090, 850, 780, 675; 1H NMR
(400 MHz, CDCl3): d 1.60 (s, 3H, 5-CH3 ax), 1.62 (s, 3H, 5-CH3 eq), 2.26 (br s,
4H, 1-CH3 and 5a-H), 4.09 (t, J = 11.0 Hz, 1H, 6a-H), 4.30 (d, J = 4.0 Hz, 1H, 11b-
H), 4.54 (dd, J = 8.4 Hz, J = 3.2 Hz, 1H, 6H eq), 6.96 (d, J = 8.4 Hz, 1H, 8-H), 7.25–
8.07 (m, 11H, Ar–H); 13C NMR (100 MHz, CDCl3): d 15.01, 25.46, 26.26, 30.35,
38.08, 63.60, 81.76, 94.85, 117.37, 118.46, 120.57, 120.97, 122.62, 123.98,
125.87, 126.78, 128.10, 129.07, 130.06, 130.48, 131.49, 134.75, 146.13, 148.02,
152.96, 156.45; ESI-MS: m/z: 487.1 (M+H)+; Compound 7h: Yellow solid, mp
210–213 °C; IR (KBr): mmax (cmꢁ1) = 2924, 1489, 1446, 1249, 1094, 1031, 877,
759; 1H NMR (400 MHz, CDCl3): d 2.74 (m, 1H, 5a-H), 4.32 (t, J = 11.4 Hz, 1H, 6-
H ax), 4.55 (m, 2H, 5-H), 4.62 (dd, J = 7.2 Hz, J = 3.6 Hz, 1H, 6-H eq), 4.74 (d, 1H,
J = 4.8 Hz, 11b-H), 6.90 (d, J = 8.4 Hz, 1H, 8-H), 7.25–8.02 (m, 15H, Ar–H); 13C
NMR (100 MHz, CDCl3): d 30.67, 30.95, 66.62, 67.88, 98.28, 117.45, 120.95,
121.44, 123.81, 123.90, 124.01, 125.63, 126.12, 127.17, 128.21, 128.89, 128.94,
129.10, 130.21, 134.40, 136.10, 138.48, 147.22, 148.79, 149.72, 150.87, 154.75;
Acknowledgments
We sincerely express our thanks to the Head, Department of
Chemistry, S.P. University for providing necessary research facili-
ties. Two of us (S.B.T. and R.A.P.) are grateful to the UGC, New Delhi
for research fellowships under the UGC scheme of RFSMS. We also
acknowledge the help rendered by the Vaibhav Analytical Labora-
tories, Ahmadabad and Nutan Dye Chem, Surat.
Supplementary data
Supplementary data associated with this article can be found, in
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