A rapid, clean, and highly efficient method for synthesis of dihydropyrano[3,2-
Multicomponent reactions (MCRs) are very important in organic synthesis due to the formation of carbon-carbon and carbon-hetero atom bonds in one pot [
Several methods have been reported for the synthesis of pyrano[3,2-
In recent years, 1,4-diazabicyclo[2.2.2]octane (DABCO) has received considerable attention as an inexpensive, ecofriendly, high reactive, easy to handle, and nontoxic base catalyst for various organic transformations, affording the corresponding products in excellent yields with high selectivity [
When aromatic aldehyde
In our initial study, the reaction of benzaldehyde, malononitrile, and 4-hydroxycoumarin was used as a model reaction to optimize the reaction conditions. First the reaction was conducted in various solvents using DABCO as a catalyst under refluxing conditions and also under solvent-free conditions. As can be seen from Table
DABCO catalyzed synthesis of
Entry | Solvent |
|
Time/h | Yielda/% |
---|---|---|---|---|
1 | EtOH | Reflux | 2 | 85 |
2 | CH2Cl2 | Reflux | 6 | 54 |
3 | CH3CN | Reflux | 4 | 73 |
4 | THF | Reflux | 4 | 62 |
5 | H2O | Reflux | 1.5 | 87 |
6 | — | 100 | 0.5 | 94 |
7 | — | 60 | 2 | 65 |
8 | — | 80 | 1 | 76 |
9 | — | 120 | 0.5 | 92 |
10b | — | 100 | 2 | 65 |
11c | — | 100 | 0.5 | 95 |
b1 mol% of catalyst was used.
c10 mol% of catalyst was used.
Under the optimized reaction conditions, a series of dihydropyrano[3,2-
Synthesis of 2-Amino-4-aryl-3-cyano-5-o
Entry | Ar | Product | Time/min | Yield/% | m.p./°C Found (reported) |
---|---|---|---|---|---|
1 | C6H5 |
|
30 | 94 | 256-257 (256–258) [ |
2 | 4-O2N C6H4 |
|
30 | 96 | 259–261 (258–260) [ |
3 | 3-O2N C6H4 |
|
30 | 93 | 261–263 (262–264) [ |
4 | 4-ClC6H4 |
|
30 | 92 | 264–267 (263–265) [ |
5 | 4-BrC6H4 |
|
30 | 91 | 247–250 (249–251) [ |
6 | 4-CH3OC6H4 |
|
30 | 89 | 241–244 (240–242) [ |
7 | 4-CH3C6H4 |
|
30 | 87 | 252–254 (250–252) [ |
8 | 2,4-Cl2C6H3 |
|
30 | 90 | 256–258 (257–259) [ |
9 |
|
|
30 | 97 | 251–254 (252-253) [ |
10 |
|
|
30 | 96 | 226–230 (228) [ |
In summary, a new clean and efficient protocol for the synthesis of pyrano[3,2-
All chemicals were purchased from Merck and Sigma-Aldrich as “synthesis grade” and used without further purification. Melting points were determined in open glass capillaries and are uncorrected. 1H NMR spectra were obtained at 400 MHz with a Bruker (AVANCE) spectrometer using DMSO-d6 as solvent and TMS as an internal standard. Elemental analysis was performed using Carlo Erba-1108 analyzer.
Aromatic aldehyde
All the compounds were characterized by spectroscopic and physical data which were found to be identical to those described in the literature.
White Solid, Yield: 94%; m.p.256-257°C (256–258°C) [
Pale Yellow Solid, Yield: 96%; m.p. 259–261°C (258–260°C) [
White Solid, Yield: 93%; m.p. 261–263°C (262–264°C) [
White Solid, Yield: 92%; m.p. 264–267°C (263–265°C) [
White Solid, Yield: 91%; m.p. 247–250°C (249–251°C) [
White Solid, Yield: 89%; m.p. 241–244°C (240–242°C) [
White Solid, Yield: 87%; m.p. 252–254°C (250–252°C) [
White Solid, Yield: 90%; m.p. 256–258°C (257–259°C) [
Brown Solid, Yield: 97%; m.p. 251–254°C (252-253°C) [
White Solid, Yield: 96%; m.p. 226–230°C (228°C) [
The authors thank the director of SAIF, Punjab University, Chandigarh, for NMR spectral data.