No abstract

A series of unusual fused heterocyclic compound derivatives, consisting of a pyridine and a imidazole or pyrimidine core, with a bridgehead nitrogen, were successfully synthesized by a microwave-assisted, three-component domino reaction of aldehydes, enaminones, and malononnitrile. In this one-pot reaction, up to five new bonds were formed accompanied by generating the lactam group. This method has the advantages of short synthetic route, operational simplicity, increased safety for small-scale high-speed synthesis, and minimal environment impact.

Benzo [4,5]imidazo[1,2-a]pyrimidine derivatives were synthesized via the three-component reaction of aldehyde, -dicarbonyl compound and 2-aminobenzimidazole in water under microwave irradiation and without catalyst conditions. The new protocol has the advantages of higher yield, lower cost, reduced environment impact, wider scope and convenient procedure.

S y n t h e s i s o f P y r i d o [ 2 , 3 -d ] p y r i m i d i n e D e r i v a t i v e s u n d e r M i c r o w a v e I r r a d i a t i o nAbstract: A facile and selective synthesis of poly-substituted pyrido [2,3-d]pyrimidines is accomplished via microwave-assisted multicomponent reactions controlled by the nature of solvent. In addition, a possible mechanism accounting for the reaction is proposed.Selectivity is a key issue to be controlled in organic synthesis. In particular, chemoselectivity is synthetically useful because it gives one of several products selectively from the same substrate without the need to separate the product(s) from the product mixture. It continues to be developed as organic synthesis strives for ever-increasing levels of efficiency. As a result, many studies have focused on the chemoselectivity of reactions. 1 In recent years, many reports have dealt with the control of chemoselectivity reactions with metal catalysts, 1a-e while solvent-dependent chemoselective reactions have been researched in relatively few papers. 1g-i Therefore, the development of highly solvent-dependent chemoselective reactions remains a challenge.Pyrido[2,3-d]pyrimidine and its derivatives are useful as antitumor, 2 antibacterial, 3 anti-inflammatory, 4 and antifungal agents. 5 In particular, the pyrido[2,3-d]pyrimidin-7-one template has been identified previously as a privileged structure for the inhibition of ATP-dependent kinases, and good potency against Cdks has been reported for representative examples. 6-8 Obtaining selectivity for individual Cdk enzymes, particularly Cdk4, has been challenging. Many extensive investigations of the structureactivity relationships for pyrido[2,3-d]pyrimidin-7-one inhibition of Cdk4 have been initiated. Therefore, to obtain the new potential inhibitors of Cdk4, the synthesis of pyrido[2,3-d]pyrimidin-7-one should be of great significance. For the preparation of these molecules large efforts have been directed toward the synthetic manipulation of pyrido[2,3-d]pyrimidine derivatives. As a result, a number of reports have appeared in the literature 9 that generally require long reaction times and complex synthetic pathways. Thus, new routes for the synthesis of these molecules have attracted considerable attention in the search for a rapid entry to these heterocycles.In the context of our interest in the design and development of useful tactics and strategies for the synthesis of heterocyclic compounds, 10 herein, we wish to report a new microwave-assisted chemoselective reaction controlled by the nature of solvents for the synthesis of pyrido[2,3-d]pyrimidine derivatives using aldehydes 1, 2,6-diaminopyrimidin-4(3H)-one (2), and 4-hydroxy-2H-chromen-2-one (3) (Scheme 1). To the best of our knowledge to date, the solvent-dependent chemoselective synthesis of pyrido[2,3-d]pyrimidine derivatives has not yet been reported.Choosing an appropriate solvent is of crucial importance not only for successful microwave-promoted (MW) synScheme 1