Stereoselective synthesis of highly congested tetralin-fused spirooxindoles with hydroxy group: Pseudo oxygen atom induced hydride shift/cyclization process

Expeditious entry into carbocyclic and heterocyclic spirooxindoles

Spirocyclic frameworks have attracted synthetic practitioners due to their unique three-dimensional assembly, improved metabolic stability, solubility, and increased molecular complexity with regard to planar architectures. A recent surge in the number of spirocyclic oxindoles inhibiting enzymes, moderating unique protein-protein interactions, modulating receptors and transporters is testament to their prevalence. Against this background, the construction of spirocyclic frameworks containing an oxindole moiety as a torsional switch via stereoselective methods is in great demand. Herein we present a summary of the past three years in the progress of metal, organic molecule, nanostructured particle mediated, and even uncatalyzed versions of the highly diastereo- and enantioselective pathways leading to oxindole spirocycles.

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

The direct functionalization of inert C–H bonds is regarded as one of the most powerful strategies to form various chemical bonds and construct complex structures. Although significant advancements have been witnessed in the area of transition metal-catalyzed functionalization of inert C–H bonds, several challenges, such as the utilization and removal of expensive transition metal complexes, limited substrate scope and large-scale capacity, and poor atom economy in removing guiding groups coordinated to the transition metal, cannot fully fulfill the high standard of modern green chemistry nowadays. Over the past decades, due to its inherent advantage compared with a transition metal-catalyzed strategy, the hydride shift activation that applies “tert-amino effect” into the direct functionalization of the common and omnipresent C(sp³)–H bonds adjacent to tert-amines has attracted much attention from the chemists. In particular, the intramolecular [1,5]-hydride shift activation, as the most common hydride shift mode, enables the rapid and effective production of multifunctionally complex frameworks, especially the spiro-tetrahydroquinoline derivatives, which are widely found in biologically active natural products and pharmaceuticals. Although great accomplishments have been achieved in this promising field, rarely an updated review has systematically summarized these important progresses despite scattered reports documented in several reviews. Hence, in this review, we will summarize the significant advances in the cascade [1,5]-hydride shift/intramolecular C(sp³)-H functionalization from the perspective of “tert-amino effect” to build a spiro-tetrahydroquinoline skeleton, and the content is categorized by structure type of final spiro-tetrahydroquinoline products containing various pharmaceutical units. Besides, current limitations as well as future directions in this field are also pointed out. We hope our review could provide a quick look into and offer some inspiration for the research on hydride shift strategy in the future.

Divergent Access to Seven/Five-Membered Rings Based on [1,6]-Hydride Shift/Cyclization Process

We have achieved a divergent access to seven/five-membered rings based on a [1,6]-hydride shift/cyclization process from benzylidenemalonate with an o-alkoxymethyl group. Whereas Yb(OTf)₃ afforded benzoxepines (with a seven-membered ring) selectively, indanes (with a five-membered ring) were the main products when Sc(OTf)₃ was employed.