Tetrabutylammonium Acetate: Green and Efficient Synthesis of Dihydropyrano [3, 2-C] Quinolones from 1-Methylquinoline-2, 4(1H, 3H)-Diones

An efficient one-pot synthesis of dihydropyrano[3,2-c]quinolones 4a-p by three-component reaction of N-methylquinoline-2,4-dione (1) with malononitrile (3a) or ethylcyanoacetate (3b) and benzaldehydes 2a-h in water in the presence of TBA acetate has been described. The above synthesis was also tried alternatively by the reaction of 1 with 2a-h in refluxing water using TBA acetate for 30 min and yielded 5. Compound 5 on reaction with 3a or 3b did not yield the target compound 4. This was approached alternatively by the reaction of 2a-h with 3a or 3b that gave benzylidine derivatives 6a-h which on further reaction with 1 gave the title compound 4a-p. The methodology described here has the advantages of environment friendliness, higher yields, shorter cost, low reaction times and convenient operation.