Spiro compounds spiroheterocycles

Isatin-3-imines 822 are versatile precursors for the synthesis of spiroheterocycles. They were prepared by grinding together an equimolar mixture of isatin and aromatic or heterocyclic amine. Subsequent treatment with mercaptoacetic acid using inorganic supports such as montmorillonite KSF, alumina, or silica gel in an open vessel upon MWI gave spiro compounds 823 within 5-7 min. The montmorillonite KSF is the best solid support, giving the best yields (92-97%) in the shortest time and easiest work-up (Scheme 156) (030PP401). 

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