Two intramolecular cyclization approaches for the formation of C(2)-C(3) cyclopentannelated indole architectures (4) using indolidene/indolidenium chemistry is presented. A cyclization cascade initiated by the irradiation of allenyl azide 1 is presumed to go through an indolidene intermediate (3a), which is trapped by a pendant alkenyl sulfide nucleophile. A Lewis acid-mediated cationic cyclization results from the reaction of a putative indolidenium cation (3b) and a tethered alkenyl sulfide nucleophile. In both cases, regiochemical and stereochemical issues arise and our efforts to favor the desired isomer 4 are discussed.

Intramolecular [3 + 2] cyclocondensations of alkenes with indolidenes and indolidenium cations

249th National Meeting (2015)

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