Indoles spiro pyrrolidin

The isolation and synthesis of indole alkaloids containing a non-rearranged monoterpenoid unit have been reviewed <03NPR216>, as has the synthesis of spiro[pyrrolidine-3,3 -oxindoles] as building blocks for oxindole alkaloids <03EJ02209>. 

An asymmetric one-pot sequential Mannich/hydroamination sequence involves a three-catalyst system a chiral organocatalyst, BF3 and a gold complex. It converts an indole-imine into privileged spiro[pyrrolidin-3,2 -oxindole] structures in up to 91/97% yield/ee. 

In order to improve the nucleophilicity of the lactam, we decided to pre-form the potassium salt of pyrrolidin-2-one III-69 [172]. Unfortunately, no alkylated product was detected in the reaction of III-69 with N-Boc indole III-67 in DMF (Scheme 4.42) [173]. When the reaction was carried of using toluene as the solvent, only spiro[cyclopropane-l,3 -indole] (III-66) was detected. Futhermore, spiro[cyclopropane-l,3 -indole] (III-66) was the only product observed in the reaction of the potassium salt III-69 with 3-(2-bromoethyl)-l//-indole in toluene. 

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