Oxyallyl cation promoted dearomative semipinacol rearrangement: a facile stereodivergent synthesis of spiro-indolines with contiguous quaternary centers

[1+5] Cyclization of Indoline-Derived Azadienes with 1,3,5-Triazinanes: An Efficient Protocol for the Synthesis of Indoline-Spiro-Hexahydropyrimidines

An unprecedented formal [1+5] cyclization of indoline-derived azadienes with 1,3,5-triazinanes has been realized, providing a facile access to biologically important indoline-spiro-hexahydropyrimidines with good to excellent yields (up to 99 % yield). Different from previous reports, this is the first study that indoline-derived azadienes could participate in cyclizations as one-atom synthons. This methodology is also distinguished by not involving any additive or catalyst, readily available starting materials, wide range of substrate applicability, operational simplicity and simultaneously reassembling two C-N and two C-C bonds in one-step reaction.

Chiral Brønsted Acid-Catalyzed Intramolecular Asymmetric Dearomatization Reaction of Indoles with Cyclobutanones via Cascade Friedel-Crafts/Semipinacol Rearrangement

The highly efficient synthesis of chiral indolines fused with an azabicyclo[2.2.1]heptanone moiety is achieved by an asymmetric dearomatization reaction of indoles with cyclobutanones. A new chiral imidodiphosphorimidate (IDPi) catalyst is synthesized and exhibits extraordinary activity in promoting a cascade Friedel-Crafts/semipinacol rearrangement. Target molecules are prepared in good yields (up to 95%) with excellent enantioselectivity (up to 98% ee) with operational convenience. Combined experimental and computational studies provide detailed mechanistic insights into the energy landscape and origin of the stereochemical induction of the reaction.

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.

Synthesis of spirocyclic oxazole derivatives from 2-arylidene cycloalkanones and α-halohydroxamates

Herein we disclose a facile route to spirocyclic oxazole derivatives via [3 + 2] cycloaddition reactions between 2-arylidene cycloalkanones and azaoxyallyl cations that formed in situ from α-halohydroxamates in the presence of base. This methodology was shown to lead to an efficient formation of a series of functionalized spirocyclic oxazole derivatives in good to excellent yields.

An NHC-Catalyzed [3+2] Cyclization of β-Disubstituted Enals with Benzoyl Cyanides

The NHC-catalyzed asymmetric [3+2] cyclization of benzoyl cyanides to homoenolate generated in-situ from enals was reported. This methodology leads to the efficient construction of a series of chiral cyclic compounds...