An efficient condensation of 4-oxo-4 H -benzopyran-3-carbaldehydes with 3-methyl-1-phenyl-1 H -pyrazol-5 (4 H )-one

An efficient synthesis of 3-methyl-4-[(4-oxo-4 H -chromen-3-yl) methylene]-1-pheny-1 H - pyrazol-5-(4 H )-ones 3a-m in solid-state by grinding without solvent at room temperature.


Introduction
Environmental concern in research and industry are increasing with the increasing pressure to reduce the amount of pollutants produced, including organic solvents whose recoveries mandated by ever more strict laws.Hence the challenge for sustainable environments calls for the use of clean procedures, which can avoid the use of harmful solvents.We are interested in seeking new processes involving solvent-free reactions, for these methods many advantages such as reduced pollution, low cost, and simplicity in processing.3][4] Most article have appeared reporting solid-state reactions by grinding such as, Grignard reaction, 5 Reformatsky reaction, 6 Aldol condensation, 7 Dickhmann condensation, 8 phenol coupling reaction, 9 reduction reaction 10 and others. 11Most of these reactions are carried out at room temperature, absolutely solvent-free and use only a mortar and pestle.In addition too economical and environmentally friendly, these procedures are efficient as well.Therefore, we focus on developing the novel procedure involving a solid-state reaction performed by grinding.
Compound having chromone moiety are synthetically versatile molecules with a reactive carbonyl group.They have considerable significance for their biological activities 12 and for their reactivity towards nucleophiles, which allow the synthesis of a wide variety of heterocycles.The condensation reaction of active methylene group with aldehydes function of 3-formyl chromone is studied by different workers. 13these condensations require acid or base catalyst and prolonged heating period and the product are obtained in low yields.Keeping in view of these observations and in continuation of our work on 3-formyl chromone, 14 herein we wish to report a mild and highly efficient method for the synthesis of 3-methyl-4-[(4-oxo-4H-chromen-3-yl)-methylene]-1-phenyl-1H-pyrazol-5 (4H)-ones by grinding in mortar and pestle in excellent yield.
In this communication, we have developed a newer root for the condensation of various 4oxo-4H-benzopyran-3-carbaldehyde 1a-m with active methylene compound such as 3-methyl-1phenyl-1H-pyrazol-5 (4H)-ones 2 ground in mortar and pestle at room temperature.The substrate 4-oxo-4H-benzopyran-3-carbaldehyde has three active sites; the unsaturated carbonyl group i.e. the pyrone ring, a carbon-carbon double bond and a formyl group.Of these, the formyl group has the highest reactivity towards active methylene compounds.

Results and Discussion
In order to verify the role of grinding, we have examined the model reaction of 1a-m and 2 stirred and left standing at room temperature for overnight, reaction remained incomplete.To keep this method simple, economical and efficient, we have used a glass mortar and pestle to repeat this experiment under the same conditions.Surprisingly, the reaction completes within 2 minutes and the color of the ground substance changed (yellow to red color).It leads to the almost quantitative formation of the Knoevenagel product 3a-m.
Isolation of the product is achieved by quenching in water, followed by filtration and drying.This process is fairly general, facial, efficient and is devoid of any side products.The process is environmentally benign and experimental process is very simple.

Experimental Section
General procedures.All products are known compounds and their physical data, IR, 1 H NMR spectra were essentially identical with those of authentic samples.Melting pints were obtained on a melting point apparatus with capillary tubes and are uncorrected.IR spectra were recorded on Perkin-Elmer FT Spectrophotometer in KBr disc. 1 H NMR spectra were recorded on Varian 300 MHz spectrophotometer in CDCl3 as a solvent and TMS as an internal standard.Melting point and other data were recorded in table 1

Table 1 .
. Reaction All the products were characterized by IR, 1 H NMR, spectra and by comparison of their physical cheristeristics with those of the authentic compounds.
a bYield of isolated product.