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.
Catalytic asymmetric C3-indolylation of N-protected spiro-epoxyoxindoles has been developed for the access of 3-(3-indolyl)-oxindole methanols with excellent enantioselectivity (ee up to > 99%). The widespread substrate scope and easily accessible Co(III)-salen over 1,1'-Spirobiindane-7,7'-diol phosphoric acid prove our condition to be more beneficial than the chiral Brønsted acid-catalyzed reaction. Further, kinetic resolution of spiro-epoxides is achieved in high enantiomeric excess under certain conditions. The detailed mechanistic study endorses that the feedback inhibition played a key role which restricts the dynamic kinetic resolution process. Besides it also revealed the S N 2' mechanism for the Co(III)-salen catalysed C3-indolylation of spiro-epoxyoxindoles.
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