Extending Pummerer Reaction Chemistry. Asymmetric Synthesis of Spirocyclic Oxindoles via Chiral Indole-2-sulfoxides

The conversion of (Ss)-3-(ω-allylsilane and silyl enol ether)indole-2-sulfoxides to spirocyclic indolenines and then to oxindoles proceeds, in
favorable cases, with moderate levels of chirality transfer from sulfur to C(3) of the indole core. A mechanistic model, which features either
an Sn2‘-like additive Pummerer sequence or a tight ion pair generated by an Sn1-like vinylogous Pummerer transform, is proposed to rationalize
the sense of asymmetric induction.