Intramolecular Aminolactonization for Synthesis of Furoindolin-2-One.

Propellanes are polycyclic compounds in which tricyclic systems share one carbon-carbon single bond. Propellane frameworks that consist of larger sized rings are found in a variety of natural products. As an approach to the stereoselective synthesis of the propellane framework, one of the efficient methods is forming several rings in a single operation. Lapidilectine B ( 1 ) is composed of a propellane framework and was synthesized through the oxidative cyclization of trisubstituted alkenes. When the alkene with an ester moiety was treated with N -iodosuccinimide (NIS), iodocyclization proceeded to give the cyclic carbamate. On the other hand, when PhI(OAc) 2 was allowed to react in the carboxyl form, a furoindolin-2-one structure corresponding to the A-B-C ring of lapidilectine B ( 1 ) was produced. Furthermore, when Pd(OAc) 2 catalyst was used for cyclization under oxidative conditions, the product yield was improved.