Sn-Catalyzed Criegee-Type Rearrangement of Peroxyoxindoles Enabled by Catalytic Dual Activation of Esters and Peroxides

We
report here the Sn-catalyzed mild protocol for ring expansion
of peroxyoxindoles to afford the series of substituted-2H-benzo­[b]­[1,4]­oxazin-3­(4H)-one
derivatives. In this protocol, we showed the in situ conversion of tert-butyl peroxy compounds into peresters with the aid
of external esters, which then underwent the ring-expansion process,
and the incipient carbocation was trapped with the alcohol residue
generated from the esters. The reaction is also demonstrated in a
continuous flow process to afford the rearranged product in 22 min
of residence time.