Pummerer rearrangement, interrupted

Scheme 20.2S describes the work published by Kawasaki s group where they used a combination of dimethylsulfoxide and trifluoroacetic anhydride as source of trifluoroacetylated sulfonium ion 109 which reacted with 108 generating the new sulfonium salt 110 that underwent the loss of the sulfur-containing moiety promoted by nucleophilic attack. The nucleophile could be an alcohol, thiol, amine or organometallic species, or even another heterocyclic substrate. In cases where the nucleophile was a sulfoxide, the reaction led to an overall CH2 oxidation (Scheme 20.2S). Kawasaki s results suggest that this transformation, based on an interrupted Pummerer rearrangement, could be applied in the synthesis of biologically active tetrahydrocarbazoles and analogues fFigure 20.2T...

Scheme 20.29 Applications of interrupted Pummerer reaction - r3.31-sigmatropic rearrangement sequence.

Scheme 20.29 exemplifies four different approaches to carry out an interrupted Pummerer reaction [3,3]-sigmatropic rearrangement sequence. Oshima s work use phenol 138 as nucleophile generating the optimal intermediate 140 for the sigmatropic rearrangement the formed product 141 can rearrange to afford... 

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