HFIP-mediated three-component imidization of electron-rich arenes with in situ formed spiroindolenines for facile construction of 2-arylspiroindolenines

Abstract

The three-component reaction of o-aminobenzaldehydes with 5-hydroxyindole and electron-rich arenes has been achieved through HFIP-mediated cascade hydride transfer/dearomative cyclization/CDC-type imidization at room temperature under air.

Merging dearomatization with redox-neutral C(sp3)–H functionalization via hydride transfer/cyclization: recent advances and perspectives

“…Inspired by the above-mentioned Sc(OTf) 3 -catalyzed continuous transformation, in 2021, our group designed and achieved a HFIP-mediated, three-component reaction with readily available 5-hydroxyindole 26 , o -aminobenzaldehydes 27 , and electron-rich arenes 28 as starting materials (Scheme 7). 14 An array of 2,3,3′-polyfunctionalized indolenines 29 were straightforwardly provided in good yields with excellent diastereoselectivities (up to >20 : 1 dr), and the diastereoselectivity contrasted sharply with that in previous hydride transfer-involved indole dearomatization reactions. As shown in Scheme 7, HFIP served as the hydrogen bond donor and acceptor template and played the crucial role in the whole process.…”

“…9 Recently, a conceptually new hydride transfer-involved dearomatization, which combines two hot research fields of dearomatization and direct C(sp 3 )-H functionalization in a single reaction, has drawn much attention from chemists. [10][11][12][13][14][15][16][17][18][19] This "two-birds-with-one-stone" strat- egy opens a powerful avenue to not only streamline the synthesis of previously challenging target molecules but also prepare unreported structurally novel skeletons. In the past few years, with an ever-growing understanding of this rising area, our group have dedicated and made contributions to the hydride transfer-involved dearomatization reactions.…”

1,6-Hydride Transfer-Enabled [6 + 1] Annulation to Access Polycyclic 3,4-Fused Azepinoindoles

“…The hydride transfer (HT) reaction, involving the formation of two or more bonds in one step, is a powerful tool in synthetic organic chemistry . Recent efforts by us and other groups have led to the unveiling of the high synthetic potential of this strategy. − In particular, the sequential 1,5-HT/cyclization process provided distinctive synthetic capability for the rapid construction of complex polycyclic azepinoindole frameworks, such as 1,2-fused azepinoindoles and 2,3-fused azepinoindoles (Scheme b). Nevertheless, the HT reaction to access indole-3,4-fused azepines remains undeveloped.…”

Hydride Transfer-Initiated Cross-Dehydrogenative Coupling Reaction to Access Nine-Membered Rings

“…Featuring redox-neutral and atom-economic properties, the hydride transfer (HT) reaction has turned out to be one of the most robust tools for the assembly of heterocycles . With the assistance of this versatile protocol, various spiro- and fused-heterocycles have been efficiently constructed. − However, this strategy has been long restricted to the indispensable necessity of the transition metal catalysts and high temperatures. Moreover, it has been mainly exploited for the synthesis of five- or six-membered rings and seldom employed to achieve medium-sized heterocyclic rings, especially nine-membered rings. , To address these formidable challenges, our group has focused on the development of organocatalytic hydride transfer reactions to assemble medium-sized heterocyclic rings and a series of medium-sized heterocycles have been synthesized in an efficient manner .…”