Indoles Pummerer rearrangement

The total synthesis of (+)-deethylibophyllidine was accomplished by J. Bonjoch and co-workers, who applied a regioselective Fischer indole synthesis as one of the key steps to obtain octahydropyrrolo[3,2-c]carbazoles. The indole formation was followed by a tandem Pummerer rearrangement-thionium ion cyclization to generate the quaternary spiro stereocenter. 

Bonjoch, J., Catena, J., Vails, N. Total Synthesis of ( )-Deethylibophyllidine Studies of a Fischer Indolization Route and a Successful Approach via a Pummerer Rearrangement/Thionium Ion-Mediated Indole Cyclization. J. Org. Chem. 1996, 61, 7106-7115. 

Indole synthesis. This Michael acceptor reacts with o-lithio-N-Boc-aniline. The product undergoes a sila-Pummerer rearrangement to induce ring closure. Indoles are obtained on elimination of the [PhSH] element. 

During these explorations, the Pummerer rearrangement of sulfoxide 235 was found to undergo cyclization only to the indole nitrogen to yield thioaminal 236. Protection of the indole nitrogen also did not lead to any... 

A Pummerer rearrangement cyclization was next achieved hy treating indole 242 with trifluoroacetic anhydride in dichloromethane. The indole-nine product was then reduced with sodium cyanoborohydride and desulfurized with Raney nickel to furnish lactam 243. It is interesting to note that in contrast to the Pummerer cychzation of the acetamide 242, which undergoes cyclization to the indole 3-position as shown, photocyclization of... 

The synthesis of 1-substituted carbazole sulfides formed by an unusual Pummerer rearrangement has been reported. The acyloxy group is displaced by an internal nucleophile, in this case, the indole 84. Tautormerisation followed by the addition of a nucleophile then regenerated the indole and resulted in sulphides 87a-d. A range of nucleophiles can be employed, giving good yields and moderate diastereoselectivity. 

Phenylsulfinyl)indole 187 bearing a pendant nucleophile at C3 undergoes a Pummerer-like rearrangement upon treatment with Tf20 to furnish 3,3-spirocyclic-2-(phenylthio)indolenine 188 in high yield (Equation 85)... 

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