Accessing highly functionalized cyclopentanoids via a cascade palladation approach: unprecedented benzylic C-H activation towards cyclopentenoindanes.

A Pd-catalyzed synthesis of 3,4,5-trisubstituted cyclopentenes from diazabicyclic olefins and o-iodobenzoates has been developed. The hitherto unknown cascade process involves three stages: carbopalladation, oxypalladation and a Tsuji-Trost reaction. We have also developed a facile route involving a novel benzylic C-H activation towards cyclopentenoindane moieties.

One-Pot MCR-Oxidation Approach toward Indole-Fused Heteroacenes.

A straightforward synthetic route toward indole-fused heteroacenes was developed. The strategy is composed of a one-pot process starting with a multicomponent reaction of cyclohexanone, primary amine and N-tosyl-3-nitroindole followed by an oxidation step. The one-pot approach was found to be general, affording both symmetric and nonsymmetric indolo[3,2-b]indoles in good yields. The strategy was also utilized for accessing 5-ring fused benzo[g]indolo[3,2-b]indole. We could extend the methodology for the synthesis of benzothieno[3,2-b]indoles starting from 3-nitrobenzothiophene. The importance of the developed method was exemplified by performing the reaction sequence on gram scale and also by the synthetic transformations of indolo[3,2-b]indoles. In addition, the change in photophysical properties with extension of conjugation of the synthesized heteroacenes was studied.

Heteroannulation of 3-Nitroindoles and 3-Nitrobenzo[b]thiophenes: A Multicomponent Approach toward Pyrrole-Fused Heterocycles.

A simple, efficient, and general multicomponent reaction involving an enolizable ketone, a primary amine, and an N-protected 3-nitroindole was developed for the synthesis of a range of functionalized pyrrolo[3,2-b]indoles. The methodology was efficaciously utilized for the "pyrroloindoliztion" of natural products, the pyrrolization of 3-nitrobenzo[b]thiophene, and the gram-scale synthesis of pyrroloindole. Furthermore, a "one-pot" approach for accessing indolo[3,2-b]indoles was realized.

Pd-Catalyzed oxidative annulation of enamides with diazabicyclic olefins: rapid access to cyclopentene fused 2-pyrrolines.

An efficient stereoselective route for the synthesis of cyclopentene fused 2-pyrrolines has been established via a Pd-catalyzed C-H activation/oxidative coupling of aryl enamides with diazabicyclic olefins. The proposed two-stage mechanism was successfully proven by isolating the intermediate trans-disubstituted cyclopentene.

Lewis Acid Catalyzed Regioselective Hydroheteroarylation of Pentafulvenes.

A diverse approach toward the catalytic regioselective nucleophilic addition of nitrogen heterocycles to Lewis acid activated pentafulvenes has been established. The developed protocol introduces pentafulvenes as nonsymmetrical alkenes for the hydroheteroarylation reaction, providing alkylidenecyclopentenylation at the C-3 position of indoles and the C-2 position of pyrrole.

Trapping the Lewis acid generated transient species from pentafulvene derived diazanorbornenes with ortho-functionalized aryl iodides and aliphatic alcohols.

Herein we describe our efforts on the Lewis acid catalyzed stereoselective ring-opening of pentafulvene derived diazabicyclic olefins using various ortho-functionalized aryl iodides such as 2-iodoanilines, 2-iodophenols and 2-iodobenzene thiols to access trans-1,2 disubstituted alkylidenecyclopentenes. The scope of the reaction was also explored with a range of easily available aromatic and aliphatic alcohols. Furthermore, the palladium catalyzed intramolecular Heck cyclization of trans-1,2 disubstituted alkylidenecyclopentenes would provide an easy approach for the synthesis of highly functionalized spiropentacyclic frameworks consisting of a cyclopentene fused to an indoline/benzothiophene and pyrazolidine.