Green Protocols for the Synthesis of 3,3′-spirooxindoles - 2016- mid 2019

Spirooxindoles, particularly 3,3'-spirooxindoles constitute a privileged structural scaffold owing to the intensive biological activities which they possess. Because of this over the last twenty years, a large number of methods were devised for their synthesis and some of these molecules have entered pre-clinical trials. Of late, methods for spirooxindole synthesis using green protocols have developed rapidly. Reactions based on multicomponent strategies using non-catalytic / biocatalytic pathways and those done in aqueous media have been largely employed for the synthesis of 3,3'-spirooxindoles. This review focusses on the synthesis of 3,3'-spirooxindoles via green protocols and covers the literature from 2016 onwards (2016 - mid 2019); a review on the same topic has appeared in 2016. The green methods discussed here include reactions done in aqueous media, multicomponent strategies, alternate solvents and photocatalysis.