The reaction of 5,5-dimethylcyclohexane-1,3-dione with various heteroarylaldehydes afforded the corresponding heteroaryl substituted xanthene derivatives
In the past few decades, the synthesis of new heterocyclic compounds has been a subject of great interest due to their wide applicability. The importance of multicomponent reactions in organic synthesis has been recognized, and considerable efforts have been focused on the design and development of one-pot procedures for the generation of libraries of heterocyclic compounds [
Xanthene derivatives are very important heterocyclic compounds and have been widely used as dyes [
With our continued interest in the synthesis of heterocyclic systems [
In order to optimize the reaction conditions, the synthesis of compound
Influence of the amounts of DABCO on the synthesis of
Entry | Catalyst | Amount of catalyst | Time (min) | Yieldb (%) |
---|---|---|---|---|
(mmol%) | ||||
1 | None | — | 80 | Trace |
2 | DABCO | 1 | 70 | 67 |
3 | DABCO | 2 | 60 | 74 |
4 | DABCO | 3 | 50 | 82 |
5 | DABCO | 5 | 40 | 89 |
6 | DABCO | 10 | 30 | 96 |
7 | DABCO | 15 | 30 | 96 |
aReaction conditions: 3-methyl thienaldehyde (1 mmol), dimedone (2 mmol) in water (20 mL) under reflux temperature. bIsolated yields.
The synthesized products
In order to extend the range of substrates, we employed a wide range of aldehydes in the presence of 10 mmol% DABCO under similar conditions. It was found that this method is effective with a variety of substituted heteroarylaldehydes independent of the nature of the substituent on the heteroaromatic ring and obtained satisfactory results (Table
Synthesis of heteroaryl substituted xanthenes and its alkylidene derivativesa,b.
Entry | X | R1 | R2 | Time (min) | Product | Yield (%)c | M.P (°C) |
---|---|---|---|---|---|---|---|
1 | O | H | H | 30 |
|
94 | 168-169 |
2 | O | H | CH3 | 30 |
|
92 | 158–160 |
3 | S | H | H | 30 |
|
95 | 142–144 |
4 | S | CH3 | H | 30 |
|
96 | 156-157 |
5 | S | H | CH3 | 30 |
|
94 | 145–147 |
6 | NH | H | H | 30 |
|
87 | 88–90 |
7 | O | H | H | 60 |
|
78 | 212-213 |
8 | O | H | CH3 | 60 |
|
76 | 183–185 |
9 | S | H | H | 60 |
|
81 | 197-198 |
10 | S | CH3 | H | 60 |
|
77 | 170–172 |
11 | S | H | CH3 | 60 |
|
83 | 177–179 |
12 | NH | H | H | 60 |
|
87 | 112–114 |
aReaction conditions: heteroarylaldehyde (1 mmol), dimedone (2 mmol), and DABCO (10 mmol%) in water (20 mL) under reflux temperature. bReaction conditions:
The formation of the products
In summary, we have reported an efficient, simple, convenient, and straightforward practical one-pot procedure for the synthesis of
The chemicals used in the synthesis of the octahydroxanthene-1,8-diones were obtained from the Merck and Aldrich Chemical Co. All chemicals and solvents used for the synthesis were of analytical reagent grade. Reactions were monitored by thin layer chromatography on 0.2 mm silica gel F-252 (Merck) plates. Melting points were determined by open capillary method and were uncorrected. 1H (400 MHz) and 13C (200 MHz) spectra were recorded on Bruker 3000 NMR spectrometer in CDCl3/DMSO-
A mixture of 5-membered, heteroarylaldehyde (1 mmol), 5,5-dimethylcyclohexane-1,3-dione (2 mmol), and DABCO (10 mmol%) in H2O (20 mL) was refluxed for 30 min. The progress of the reaction was monitored by TLC. After completion of the reaction, the mixture was cooled to room temperature, and the solid was filtered off and washed with H2O. The crude product was purified by recrystallization from 95% ethanol.
A mixture of
The authors are thankful to the Director of SAIF, IIT Mumbai, for spectral analysis and Dr. Asutosh K. Pandey, Department of Engineering Chemistry, Oriental University Indore (M.P.), for valuable suggestions.