The development of the sequential Corey-Chaykovsky reactions of isatins, spiroepoxy-, or spiroaziridine oxindoles with sulfur ylide has led to the discovery of a unique reaction mode that allows easy and direct one-pot access to a range of spirocyclopropyl oxindoles.
A highly efficient regioselective C3-peroxylation of
spiro-aziridine
and spiro-epoxy oxindoles has been developed with commercially available
70% aqueous tert-butyl hydroperoxide under solvent-free
and metal/catalyst-free conditions. The protocol provides an easy
access of 3-peroxyoxindoles, which undergo acid-mediated rearrangement
to afford unprecedented 2-hydroxy-2-substituted-2H-benzo[b][1,4]oxazin-3(4H)-ones.
The protocol is also equally effective for the ring opening of simple
phenyl aziridine with excellent regio-selectivity.
A simple catalyst-free method was developed for the ring opening of spiroaziridine oxindoles by three different nucleophiles, namely, amines, thiols, and methanol, to produce enantiopure (up to 99%) vicinal diaminooxindoles, β-aminosulfides, and β-amino-3-methoxyoxindole, respectively, in good to excellent yields. In contrast to the spiroepoxides, spiroaziridines are opened regio- and stereospecifically through the pseudobenzylic spirocenter under catalyst-free conditions. Moreover, unlike simple 2-substituted aziridines, these spiroaziridines are opened up with retention in configuration at the C3-spirocenter.
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