Study On The Synthesis Of Some Spiro-pyrimidinetetrones Under Microwave Irradiation

During the last few years, microwave irradiation as efficient thermal energy source is becoming a standard technique in various fields of chemistry. Especially, the application in organic chemistry developed very fast. The catalytic mechanism and characteristic of the microwave irradiation to organic reactions and the recent progress in the research and application of the microware technique in organic synthesis are reviewed. Synthesis of compounds which normally require long reflux periods can be achieved conveniently and very rapidly in microware oven. The benefit of microwave irradiation includes reduction of reaction time, high yields, cleaner reaction products and easier workup than classical heating methods as reported in literature. The use of microwave energy to activate organic reactions has been taking a new dimension very recently. It has been used for a great variety of organic reaction as esterification and saponification, sulfonation, oxidation, hydrolysis, olefin addition, replacement, condensation, alkylation, rearrangement, Diels-Alder reaction, Reformatsky reaction, Knovenagel reaction, Perkin reaction, Deckmann reaction, Witting reaction, Bischler-Napieraski reaction, Protection and deprotection, concerted reaction, cyclization and ring-opening, etherification, etc..In our attempt towards a non-traditional approach to the experimental set up of organic reactions, the concept of "Microwave-Induced Organic Reaction Enhancement"(MORE) Chemistry has been utilized for rapid and efficient synthesis of 1,5-diaryl-1,4-pentadien-3-one by the condensation of acetone and seven aromatic aldehydes in the presence of sodium hydroxide under microwave irradiation using ethanol as energy transfer medium. The results obtained demonstrate the versatility of the process as considerable reaction rate enhancement has been observed bringing down the reaction time form hours to minutes. The products obtained have improved yields with respect to conventional methods. The formation of cannizzaro product of aromatic aldehydes and self-condensed product of acetone were negligibe. These compounds are important intermediates in the synthesis of various natural products.Since the publication of Fischer and Von Mering on the hypnotic properties of diethylbarbituric acid literally thousands of barbituric acid derivatives have been prepared and their hypnotic value tested. The application of the barbituric acid on pharmaceutical synthesis is well known. Some derivatives of barbituric acid haveimportant physiological activity and can be used for sedative, narcotic, soporific, antitumor, antibiotic etc.. In this paper, a new method was described for the synthesis of barbituric acid which involves the reaction between malonate and urea under microware irradiation in a domestic microwave oven for a certain period of time. The reaction proceeds efficiently in excellent yields with minutes time. The scope of this reaction can be extended by the preparation of spirobarbiturates-a class of compounds known for their interesting physiological activity.The Michael reaction is one of the most efficient methods for effecting carbon-carbon bond formation and has wide synthetic application. The Michael addition of l,5-diaryl-1,4-pentadien-3-one to barbituric acid can be carried out in present of triethanolamine as catalyst and ethanol with dioxane as solvent under microwave irradition. The authenticity of the end products was established by their melting points, elemental analysis and spectral data(IR, 1HNMR). The present investigation thus provides a very simple, low energy consumption, efficient methodology for above reaction types. This also shows high potential of microwave technology in organic synthesis.