The objective was to synthesize the bioactive heterocyclic cores via one-pot multicomponent reactions. The book starts with a general introductory section which includes the effectiveness of multicomponent reaction and heterocyclic compounds. In chapter one mono- and di-heteroatom containing heterocyclic compounds like xanthene, dihydropyridopyrimidine have been synthesized from beta-naphthol via multicomponent reaction. The acyclic amidoalkylnaphthol has also been synthesized from the same beta-naphthol. In chapter two, the applications of beta-oxodithioester for synthesis of heterocycles via Biginelli and Hantzsch type reactions has been described. A direct approach to the aminosubstituted pyrazole from beta-oxodithioester has also been described in this chapter. The chapter three i.e., the final one deals with the applications of beta-oxoketene-N,S-arylaminoacetal for the synthesis of chromene and pyranochromene ring via one-pot multicomponent reaction. All the synthesized compounds have been characterized on the basis of their satisfactory elemental analyses, spectral (IR, 1H NMR, 13C NMR, and mass) studies and in some cases single crystal X-ray analysis also.