Hydride Transfer Initiated Redox-Neutral Cascade Cyclizations of Aurones: Facile Access to [6,5] Spirocycles

Abstract

Reported herein is the hydride transfer initiated redox-neutral cascade cyclizations of aurones, providing a variety of [6,5] spiro-heterocycles in satisfactory yields and good diastereoselectivities.

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

“…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.…”

“…Later, Xiao's group pre-prepared an array of aurones 64 as o-QM analogues to initiate the redox-neutral cascade cyclizations for the assembly of [5,6] spiroheterocycles 65 (Scheme 13). 18 Under the catalysis of Sc(OTf ) 3 , the propensity of aromatization of aurones served as a driving force to trigger intramolecular [1,5]-hydride transfer, providing the rearomatic iminium ion intermediates 67. Subsequently, the Mannichtype dearomative spirocyclization occurred to furnish [5,6] spiroheterocycles 65.…”

The Cascade [1,5]-Hydride Shift/Intramolecular C(sp3)–H Activation: A Powerful Approach to the Construction of Spiro-Tetrahydroquinoline Skeleton

“…Soon after, an efficient access to tetrahydroquinoline spiro-heterocycles via the hydride shift cyclizations of aurones 94 was developed by Xiao’s group ( Scheme 10 ) ( Duan et al, 2020a ). With low loading of Sc(OTf) 3 in 2 mol%, a series of biologically important spiro-heterocycles were achieved with good yield (up to 95%) and good diastereoselectivities (up to >20:1 dr) under mild conditions.…”

Cascade dearomative [4 + 2] cycloaddition of indoles with in situ generated ortho-quinone methides: practical access to divergent indoline-fused polycycles

“…As a central theme of research in our group, we have realized a series of strategies for constructing complex spiro and fused scaffolds via the rationally designed o -QMs. 10 Quite recently, a cascade hydride transfer/dearomative cyclization was developed in our group for one-step construction of structurally diverse polycyclic amines in high yields. 11 The in situ generated o -QM acted as a novel hydride initiator to induce the whole cascade reaction.…”