Mono, di, tri and tetra spiro heterocyclic compounds: Recent advances

Isatins and its C-3 functionalized derivatives occupy a conspicuous place in organic synthesis and medicinal chemistry. N-substituted isatins, and isatins with different substituents on a phenyl ring have been employed in two, three or four-component reactions leading to the formation of five and six membered spiro-heterocyclic frameworks bearing a 2-oxindole moiety. The development of diastereo and enantioselective methodologies containing two to four stereocenters for the synthesis of spiro-fused cyclic frameworks is the area of current interest. In this review, we presented several recent syntheses of isatin-based spiroheterocycles in different media indicator of significant interest in the area and a lot more interesting chemistry is anticipated. In the mentioned reactions, some cases need heat to accelerate them and some others are microwave assisted reactions. In some cases biological evaluation also has been mentioned. We hope this review will lead the researchers or organic chemists to a strong interest for the isatin based organic synthesis of biologically active compounds.