MW-Assisted Three-Component Reactions

SCHEME 11,1 Mannich multicomponent reaction for the synthesis of spirocyclic compounds. 

This novel approach was applied to the synthesis of a series of novel spiro[indoline-3,5 -pyrimidin]-2-one and spiro[indene-2,5 -pyrimidin]-l(3//)-one derivatives 11 in an aqueous medium (Table 11.1). In this developed procedure, six molecules of reactants are involved, and six new covalent bonds are generated, making the reaction highly atom economic and affording final products in good to excellent yields (68-94%) and in short reaction times (20- 5min). The recovery and reusability of the catalyst were also investigated in one model reaction, and the results showed no loss of catalytic activity even after five cycles. 

MW-assisted organic transformations have gained considerable popularity, particularly in the past decade, for its ability to accelerate diverse synthetic reactions, thus becoming a powerful tool in synthetic chemistry [14], MW heating is advantageous over conventional heating because it can decrease the reaction time [15], inaease the yield of the final products, provide better selectivity, and simplify the workup of the reaction, in most cases without the use of catalysts. 

TABLE 11.1 Synthesis of spiroheterocycles via the one-pot Mannich reaction of ketone, amine, and formaldehyde 

MW has been used in the multicomponent syntheses of privileged structures by MCRs (Fig. 11.2). Pyridine nucleus 

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