Synthesis of Spiro 3,3'-Cyclopropyl Oxindoles Via N-Bromosuccinimide-Mediated Ring-Closing and Contraction Cascade

POCl3/Sulfoxide-Promoted Synthesis of Indolizino[8,7-b]indoles

A mild chlorocyclization of pyrrole-tethered indoles has been realized using POCl3 as the chlorine source and tetramethylene sulfoxide as the promoter. A variety of chlorinated indolizino[8,7-b]indole derivatives have been constructed efficiently under this reaction system in moderate to good yields (19 examples, up to 93% yield).

Electrochemical bromocyclization enables 3,5-diversification of heterocyclic indolines

Electrophilic bromocyclization reactions are widely used as key steps in the synthesis of diverse functionalized tetrahydrofuroindolines and hexahydropyrroloindolines. However, the direct dibromination variants of these reactions for the synthesis of 3,5-dibromoindolines remain undeveloped. Here, we report a protonic-acid-promoted electrooxidative protocol for the dearomative C3,C5-dibromocyclizations of tryptophol and tryptamine derivatives. This electrosynthetic approach, which enables direct selective construction of heterocyclic 3a,5a-dibromoindolines with inexpensive, non-hazardous NaBr as both the electrolyte and Br source, provides a convenient, practical method for the late-stage 3,5-diversification of heterocyclic indolines.

NBS-induced intramolecular annulation reactions for the divergent synthesis of fused- and spirocyclic indolines

An NBS-induced intramolecular annulation of 3-(1H-indol-3-yl)-N-alkoxypropanamide is described. The reactions proceed well and quickly under mild conditions with the help of a base. It was found that C2-substituents on the indole ring in 3-(1H-indol-3-yl)-N-alkoxypropanamide have a great influence upon the reaction. By using C2-methyl- and C2-phenyl-3-(1H-indol-3-yl)-N-alkoxypropanamide as templates, practical protocols for the divergent synthesis of fused- and spirocyclic indoline compounds were studied and established.

Asymmetric Synthesis of Spiro-3,3'-cyclopropyl Oxindoles via Vinylogous Michael Initiated Ring Closure Reaction

A novel organocatalytic cascade approach for the synthesis of spiro-cyclopropyl oxindole derivatives has been developed. The methodology is based on asymmetric vinylogous Michael addition of 4-nitroisoxazole derivatives to N-Boc isatylidene malonates followed by intramolecular alkylation. Its remarkable stereocontrol, wide substrate scope, and scalability highlight this new developed strategy. Moreover, this work represents the first example of vinylogous Michael initiated ring closure (MIRC) reaction for the synthesis of chiral 3,3'-cyclopropyl oxindole.