PhI(OCOCF3)2-Mediated Construction of a 2-Spiropseudoindoxyl Skeleton via Cascade Annulation of 2-Sulfonamido-N-phenylpropiolamide Derivatives.

A cascade annulation of 2-sulfonamido-N-phenylpropiolamide derivatives leading to the construction of the 2-spiropseudoindoxyl skeleton was realized under mild conditions with phenyliodine(III) bis(trifluoroacetate) (PIFA) as the sole oxidant. This metal-free spirocyclization process is suggested to encompass a sequential C(sp2)-C(sp) and C(sp2)-N bond formation with the concomitant introduction of a carbonyl oxygen.