Advances in the Synthesis of Benzo‐Fused Spiro Nitrogen Heterocycles: New Approaches and Modification of Old Strategies

The review covers the results of studies published in the literature on the synthesis of spiro‐linked heterocycles of the indole, quinoline, benzoxazine, benzothiazine, indenoquinoxaline, pyridopyrimidine, and acridine series. Possible approaches to the synthesis of spirocycles through a sequence of well‐known Knoevenagel , Michael reactions, deamination cyclization of 1,2‐dicarbonyl, CH‐acid compounds, direct cycloaddition of activated olefins to isatins, 3‐alkylideneindoles, 2‐oxindoles, in situ generated azomethine ylides, indenoquinoxalines are analyzed. Attention is drawn to approaches to the preparation of spiro‐fused compounds using reactions of intra‐ and intermolecular dearomatization of indoles. Recent advances in the synthesis of spiro‐linked benzo heterocycles from derivatives of 2‐olefin substituted anilines are summarized. The examples of the synthesis of spiro‐fused heterocycles by means of metal complexes catalyzed decomposition of diazo compounds are given. Some syntheses of biologically active representatives are shown, as well as the use of transformations of spiroheterocycles in the preparation of other heterocycles.