Dearomative (4 + 3) Cycloaddition Reactions of 3-Alkenylindoles and 3-Alkenylpyrroles to Afford Cyclohepta[b]indoles and Cyclohepta[b]pyrroles

Abstract

The dearomative (4 + 3) cycloaddition reactions of 3-alkenylindoles with in situ-generated oxyallyl cations furnish cyclohepta­[b]­indoles, functionality-rich frameworks found in many bioactive compounds, including all pentacyclic ambiguine alkaloids. The analogous reactions between oxyallyl cations and 3-alkenylpyrroles afford cyclohepta­[b]­pyrroles. The cycloadducts are generally formed in good to high yields and diastereoselectivities and can be readily transformed into useful derivatives. Additionally, we report preliminary investigations into the enantioselective catalysis of the dearomative (4 + 3) cycloaddition using imidodiphosphorimidate catalysts.

Dearomative pyrrole (3+2) reaction with geminal bromonitroalkane: synthesis of 2,3-dihydropyrroles

“…2,3-Dihydropyrroles are important intermediates to prepare pyrrolidines, the backbone of which is a privileged structure in numerous pharmaceutically relevant compounds. 1 In recent years, dearomative transformations of pyrroles to prepare functionalized 2,3-dihydropyrroles, like hydrogenation, 2 borylation, 3 [4+3] annulation 4 and cycloadditions, 5 were reported. Cyclopropanation of 1-carboalkoxypyrrole was firstly reported by Fowler, 6 and intensively studied by Reiser since 1994, and the enantioenriched cyclopropane-fused 2,3-dihydropyrroles were converted into valuable derivatives (Scheme 1a).…”

In(OTf)3-catalyzed formal (4 + 3) cycloaddition reactions of 3-benzylideneindoline-2-thiones with 2-indolylmethanols

“…In 2018, Sun disclosed an Rh( ii )-catalyzed asymmetric dearomative (4 + 3) cycloaddition of vinylindoles with vinyldiazoacetates. 9 Subsequently, the (4 + 3) annulation reactions with 2-indolylmethanols, 10 oxyallyl cations 11 and aziridines 12 were realized by Yan, Rawal and Punniyamurthy respectively. Indolylmethanols can also function as the four-carbon component in (4 + 3) cycloaddition reaction.…”

Synthesis of Cyclohepta[b]indoles and Furo[3,4-b]carbazoles from Indoles, Tertiary Propargylic Alcohols, and Activated Alkynes

“…This has triggered the invention of novel methodologies, which involve pericyclic reactions from indoles. Notably, most synthetic strategies for the construction of cyclohepta­[ b ]­indoles from indoles required substrates prefunctionalized on either the C2 or C3 position . Until now, only a few examples for the synthesis of cyclohepta­[ b ]­indoles from 2,3-unsubstituted indoles have been reported.…”