Construction of contiguous quaternary carbon centers enabled by dearomatization of phenols with 3-bromooxindoles

A transition metal-free and oxidation-free dearomatization of phenols through conjugate addition to in situ generated indol-2-one from 3-bromooxindole is detailed in this report. This methodology offers an effective approach for the synthesis of a range of 3-substituted oxindoles containing contiguous quaternary carbon centers (CQCCs) with yields of up to 99%. The reaction is characterized by mild conditions, exceptional efficiency, environmental compatibility, favorable functional group tolerance, and scalability to large-scale production.

α-Halocarbonyls as a Valuable Functionalized Tertiary Alkyl Source

This review introduces the synthetic organic chemical value of α-bromocarbonyl compounds with tertiary carbons. This α-bromocarbonyl compound with a tertiary carbon has been used primarily only as a radical initiator in atom transfer radical polymerization (ATRP) reactions. However, with the recent development of photo-radical reactions (around 2010), research on the use of α-bromocarbonyl compounds as tertiary alkyl radical precursors became popular (around 2012). As more examples were reported, α-bromocarbonyl compounds were studied not only as radicals but also for their applications in organometallic and ionic reactions. That is, α-bromocarbonyl compounds act as nucleophiles as well as electrophiles. The carbonyl group of α-bromocarbonyl compounds is also attractive because it allows the skeleton to be converted after the reaction, and it is being applied to total synthesis. In our survey until 2022, α-bromocarbonyl compounds can be used to perform a full range of reactions necessary for organic synthesis, including multi-component reactions, cross-coupling, substitution, cyclization, rearrangement, stereospecific reactions, asymmetric reactions. α-Bromocarbonyl compounds have created a new trend in tertiary alkylation, which until then had limited reaction patterns in organic synthesis. This review focuses on how α-bromocarbonyl compounds can be used in synthetic organic chemistry.

Visible-Light-Induced Dearomative Annulation of Indoles toward Stereoselective Formation of Fused- and Spiro Indolines

Dearomatization approaches are attractive for their abilities to transform simple, planar arenes into complex, three-dimensional architectures. In particular, visible-light driven dearomatization strategies are significant because of their mild, green, and sustainable nature, enabling the fabrication of new chemical bonds via an electron transfer or energy transfer process. Indole compounds, being potentially bioactive and readily accessible, can be employed efficiently as building blocks for constructing diverse annulated frameworks under photocatalysis. Highly stereoselective radical cascade reactions of appropriate indole systems can provide complex cyclic scaffolds bearing multiple stereocenters. In fact, the past few years have witnessed the renaissance of dearomative cycloadditions of indoles via visible-light-induced photocatalysis. The present review highlights recent advances (2019-mid 2024) in visible-light-driven dearomative annulation of indoles leading to formation of polycyclic indolines, including angularly fused and spiro indolines. Most of the reactions described in this review are simple, providing quick access to the desired products. Additionally, characteristic reaction mechanisms are offered to provide an understand of how indole scaffolds show distinctive reactivity under photocatalytic conditions.

Catalytic Asymmetric Reverse Prenylation of Indol-2-one Enabled a Synthesis of (-)-Debromoflustramine A

A catalytic asymmetric nucleophilic reverse prenylation of indol-2-ones in situ generated from 3-bromooxindoles with prenyltributylstannane promoted by Ni(II)/chiral N,N'-dioxide was developed. This reaction provides facile access to C3 reverse-prenylated oxindoles in good to excellent enantioselectivities, which enabled the asymmetric synthesis of debromoflustramine A in five steps.

Copper-catalyzed cascade reaction of tryptamines with diazo compounds to access hexahydropyrroloindoline derivatives

A Cu-catalyzed cyclopropanation/ring-opening/iminium cyclization of tryptamine derivatives with donor–acceptor diazo compounds is developed to furnish pyrroloindolines, creating three consecutive stereogenic centers.