ipso-Annulation represents an attractive approach to synthesize a variety of spirocyclic compounds having a quaternary carbon center. Furthermore, these compounds also serve as a handy synthon for the construction of various complex molecules. This review presents various useful approaches for the intramolecular ipso-cyclization to afford a wide range of spirocyclohexadienones. In addition, the utility of spirocyclic compounds towards the synthesis of complex molecules is also included.
A novel methodology for the synthesis
of 5-selenyl/sulfenyl nicotinates
involving copper-catalyzed organochalcogenyl aza-annulation
of enynyl azide with diorganyl-dichalcogenides has been described.
This method offers difunctionalization of alkynes via regioselective
intramolecular chalcogenoamination in one pot to provide substituted
5-chalcogenyl nicotinates in good to excellent yields. The resulting
nicotinates provide access to their oxides, sulfones, and acid derivatives.
An unprecedented copper-catalyzed aminative aza-annulation of enynyl azide using commercially available N-fluorobenzenesulfonimide (NFSI) as an amination reagent is described. The reaction proceeds via regioselective inter-/intramolecular diamination, incorporating one nitrogen from the NFSI and the other from the azide, to provide amino-substituted nicotinate derivatives in a single step with moderate to high yield. This method represents an efficient way to access diverse aminonicotinates through direct C-N bond-coupling processes.
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