Two different strategies for photoinduced electron transfer (PET) and fluorescence resonance energy transfer (FRET) have been designed and combined into one sensing system. The novel probe NNRhB was developed based on 1,8-naphthalimide and rhodamine moieties, in which two fluorophores are sensitive to the presence of Cr(3+) in different chromium ion concentration regimens. Therefore, the proposed sensing system represents dual-switch states and segmented detection behavior, with the fluorescence emission color spans from green to orange over an increasing Cr(3+) concentration gradient. When excited in the visible region, the initial emission band at 537 nm was enhanced. That was attributed to the suppression of the PET process, which arose from Cr(3+)-coordination with a 1,8-naphthalimide derivative. At a sufficiently high concentration of Cr(3+) (over 9 μM), the spirolactam rhodamine component in NNRhB converted to the opened form as a result of Cr(3+) coordination, which turned the emission color from green to orange via FRET. The fluorescence phenomena of the compound 1 and compound 2 split from compound NNRhB confirm our hypothesis of the spectral response mechanisms. Moreover, compared with a single fluorescent response in compound 1 or compound 2, the dual-switch fluorescent probe NNRhB shows a more sensitive and distinct visual detection ability for Cr(3+) ions. This probe affords a high selectivity and sensitivity to Cr(3+) from 30 nM to 80 μM; the detection limit was 0.14 nM. The results of practical application experiments suggest that the Cr(3+)-selective ligand prepared here may provide an effective strategy for detection of Cr(3+) in environmental and biological applications.

A highly efficient Ir -catalyzed cascade cyclization of indoles and diazoes giving access to unique pentacyclic-fused carbazoles has been developed. This novel strategy expanded the application scope of coupling partners to take diazo compounds as a C2 source, and two new cycles, three new C-C and one new C-N bonds were formed in one-pot.

Fused oxindoles are the core structures of the naturally occurring oxindole alkaloids, and the fused tricyclic structures have distinguished themselves with unique biological activities. Herein, we developed a synthetic strategy for divergent synthesis of diverse types of [3,4]-seven-or six-membered ringfused 3-alkenyl-oxindoles incorporating benzazepine and significant building blocks from propargyl alcohols via the cascade nucleophilic substitution/site-selective hydride transfer/cyclization process unprecedentedly. In addition, a variety of nucleophiles, including H 2 O, were available for controllable construction of a wide range of conjugated alkenes, conjugated ketones, and allyl alcohols encompassing natural products and pharmaceutical motifs with the utilization of 4-amine substituted isatins and widespread terminal alkyne-derived propargyl alcohols. Furthermore, the synthetic utility of the methodology and mechanistic studies also were well presented.

The switchable synthesis of 3-non, 3-mono, 3,3′-disubstituted 3,4-dihydroquinolin-2­(1H)-ones was developed through a redox-neutral hydride-transfer/N-dealkylation/N-acylation strategy from o-aminobenzaldehyde with 4-hydroxycoumarin, and Meldrum’s acid, respectively. The unprecedented strategy for the synthesis of 3,3′-highly functionalized 3,4-dihydroquinolin-2­(1H)-one has been realized with the in situ utilization of the released HCHO via the o-QM involved Michael addition. In addition, the synthetic utility of this protocol has been well illustrated via concise synthesis of CYP11B2 inhibitor.

The aromatization-driven redox-neutral cascade [1,5]-hydride transfer/spirocyclization and cascade [1,5]-hydride transfer/hydrolysis from para-quinone methide in HFIP were developed. These protocols enabled the synthesis of azaspirocyclohexadienones and ortho-benzylated anilines in good to high yields under mild conditions, featuring room temperature, additive-free, and good functional group tolerance.

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Enantioselective [3+2] coupling of cyclic enamides with quinone monoimines was realised using a chiral phosphoric acid as a catalyst. This transformation allowed for the synthesis of highly enantioenriched polycyclic 2,3-dihydrobenzofurans (up to 99.9% ee). The absolute configuration of one product was determined by an X-ray crystal structural analysis. We also found a possible mechanism for this reaction.

The dearomative [5 + 1] annulation of 2-methylindoles with new five-membered synthon was developed through cascade [1,5]-hydride transfer/dearomative cyclization in HFIP for the synthesis of spirochromanes bearing the 2-methylindolenine skeleton.