Selective N-functionalization of Arylhydrazines with Primary Alcohols and Acids under PPh3/DDQ System

We present a PPh3/DDQ-mediated regiospecific selective N-functionalization of arylhydrazines with primary benzylic alcohols and aryl carboxylic acids for the synthesis of N1-benzyl arylhydrazines and N2-acyl arylhydrazines, respectively. This metal- and base-free approach features very short reaction times (about 10 min), broad substrate scope, good functional group tolerance, and mild reaction conditions. Furthermore, N1-benzlated products have also been successfully applied to the concise synthesis of N-substituted indoles and anticancer drug MDM2 inhibitor.

Asymmetric Divergent Total Syntheses of (+)-Decursivine and (+)- Serotobenine via Intramolecular Fischer Indole Synthesis

A new asymmetric synthetic route to (+)-decursivine and (+)-serotobenine is formulated. The key developments are the de novo construction of the crucial eight-membered 3,4-fused tricyclic indole ring engaged by the intramolecular Fischer indole synthesis and the stereocontrolled assembly of the dihydrobenzofuran subunit mediated by the asymmetric intramolecular Rh-carbenoid C-H insertion. BF₃-mediated selective C15 epimerization followed by removal of the amine masking groups completed the target natural compounds' asymmetric and divergent total syntheses.

An acid-promoted pseudocine substitution manifold of γ-aminocyclopentenone enables divergent access to polycyclic indole derivatives

We demonstrated γ-aminocyclopentenones to be a suitable surrogate for reactive cyclopentadienone via a pseudocine-substitution manifold. This approach enabled its orchestrated annulation with "tailored" bis-nucleophiles and to furnish complex β,γ-annulated cyclopentanoids or indole-based polycyclic architectures. This strategy represents a generalized means for direct, regioselective and stereoselective β,γ-functionalization of monosubstituted or unsubstituted aminocyclopentenones.

Palladium-catalysed annulative allylic alkylation for the synthesis of benzannulated heteroarenes

A conceptually novel intramolecular allylic alkylation strategy is developed for the synthesis of carbazoles and dibenzothiophenes.

Access to Polycyclic Azepino[5,4,3-cd]indoles via a Gold-Catalyzed Post-Ugi Dearomatization Cascade

The development of a rapid and diverse access to complex natural product-like 3,4-fused indole scaffolds has always attracted considerable attention from synthetic and medicinal communities. We herein disclose a modular and straightforward protocol to prepare the densely substituted polycyclic azepino[5,4,3-cd]indole scaffolds. This synthetic process involves an Ugi four-component reaction from easily available starting materials and a gold-catalyzed post-Ugi domino dearomatization/Michael addition sequence, enabling facile access to the highly functionalized azepino[5,4,3-cd]indole core with excellent chemo-, regio-, and diastereoselectivity.

Synthesis of 3,4-Fused Tricyclic Indoles through Cascade Carbopalladation and C-H Amination: Development and Total Synthesis of Rucaparib

3,4-Fused tricyclic indole scaffolds are ubiquitous in bioactive natural products and pharmaceuticals. A new protocol for the synthesis of 3,4-fused tricyclic indoles has been developed through cascade carbopalladation and C-H amination with N,N-di-tert-butyldiaziridinone. The protocol allows access to a range of 3,4-fused tricyclic indoles, including those containing various linkers and fused with medium-sized rings. Rucaparib can be synthesized via this reaction, providing an advantageous synthetic method for the FDA-approved cancer medicine.

New Synthetic Routes to (+)-Uleine and (-)-Tubifolidine: General Approach to 2-Azabicyclo[3.3.1]nonane Indole Alkaloids

Novel asymmetric synthetic routes to (+)-uleine and (-)-tubifolidine are reported herein. The regioselective formation of enol triflates from 2-azabicyclo[3.3.1]nonane ketones followed by indolizations of the resultant ene-hydrazides allowed the efficient construction of key indole intermediates, facilitating the total synthesis of the target natural alkaloids.

Synthesis of 4,7-Difunctionalized Indoles via Imino Exchange and Sulfinyl Migration

A process that rapidly assembles 4,7-difunctionalized indoles from 2-alkynycyclohexadienimines, sulfinamides, and nucleophiles (amines or alcohols) was developed. The process involves imino exchange, cascade cyclization/1,4-nucleophilic addition/aromatization, and 1,3-migration of the sulfinyl group. The 7-sulfinyl group is easy to convert into the sulfonyl or the thioether group through a simple oxidation and reduction reaction.

Comparing the fragmentation reactions of protonated cyclic indolyl α-amino esters in quadrupole/orbitrap and quadrupole time-of-flight mass spectrometers

RATIONALE

The comparative study of higher-energy collisional dissociation (HCD) and collision-induced dissociation (CID) mechanisms for protonated cyclic indolyl α-amino esters in quadrupole/orbitrap (Q/Orbitrap) and quadrupole time-of-flight (QTOF) mass spectrometers, respectively, is helpful to study the structures and properties of biologically active indole derivatives using tandem mass spectrometry (MS/MS) technology.

METHODS

HCD and CID experiments were carried out using electrospray ionization Q/Orbitrap MS and QTOFMS in positive ion mode, respectively. Only the labile hydrogens were exchanged with deuterium in hydrogen/deuterium exchange (HDX) experiments and only the aromatic indole C-H hydrogens were substituted with deuterium in regiospecific hydrogen-deuterium labeling experiments. Theoretical calculations were carried out using the density functional theory (DFT) method at the B3LYP level with the 6-311G(d,p) basis set in the Gaussian 03 package of programs.

RESULTS

In Q/Orbitrap MS/MS, when the added proton on the N⁸ position of protonated cyclic indolyl α-amino esters migrated in a stepwise fashion to the C³ position via two sequential 1,4-H shifts, an ion-neutral complex INC₁ of [protonated cyclic N-sulfonyl ketimino esters/indoles] was formed by a charge-directed heterolytic cleavage of the C³ -C¹⁰ bond, while an ion-neutral complex INC₃ of [cyclic N-sulfonyl ketimino esters/protonated indoles] was formed when another labile hydrogen on the N⁸ position successively migrated to the C⁴ position. Direct decomposition of INC₁ and INC₃ resulted in protonated cyclic N-sulfonyl ketimino esters and protonated indoles, respectively, while proton transfer led to protonated indoles and protonated cyclic N-sulfonyl ketimino esters. The HDX reaction with residual water in the HCD cell was also observed. In QTOF-MS/MS, protonated cyclic N-sulfonyl ketimino esters and protonated indoles resulted from direct decomposition of INC₁ and INC₃ , respectively, rather than proton transfer.

CONCLUSIONS

Due to the specific construction of the Q/Orbitrap and QTOF mass spectrometers, different fragmentation mechanisms medicated by ion-neutral complexes of protonated cyclic indolyl α-amino esters were proposed. This study is desirable for qualitative and quantitive investigation of indole derivatives using MS/MS technology.

Catalytic Asymmetric Reactions of 4-Substituted Indoles with Nitroethene: A Direct Entry to Ergot Alkaloid Structures

A domino Friedel-Crafts/nitro-Michael reaction between 4-substituted indoles and nitroethene is presented. The reaction is catalyzed by BINOL-derived phosphoric acid catalysts, and delivers the corresponding 3,4-ring-fused indoles with very good results in terms of yields and diastereo- and enantioselectivities. The tricyclic benzo[cd]indole products bear a nitro group at the right position to serve as precursors of ergot alkaloids, as demonstrated by the formal synthesis of 6,7-secoagroclavine from one of the adducts. DFT calculations suggest that the outcome of the reaction stems from the preferential evolution of a key nitronic acid intermediate through a nucleophilic addition pathway, rather than to the expected "quenching" through protonation.

Intramolecular dearomatizing [3 + 2] annulation of α-imino carbenoids with aryl rings furnishing 3,4-fused indole skeletons

The rhodium-catalyzed dearomatizing [3 + 2] annulation reaction of 4-(3-arylpropyl)-1,2,3-triazoles is described. It provides a straightforward synthetic pathway from simple 5-aryl-1-alkynes leading to tricyclic 3,4-fused dihydroindoles via the corresponding 1,2,3-triazoles.

Rhodium-catalyzed intramolecular annulation via C–H activation leading to fused tricyclic indole scaffolds

A new method for the synthesis of fused tricyclic indoles via a rhodium catalyzed intramolecular C–H activation reaction is described.

Rhodium(iii)-catalyzed intramolecular amidoarylation and hydroarylation of alkyne via C–H activation: switchable synthesis of 3,4-fused tricyclic indoles and chromans

An intramolecular amidoarylation and hydroarylation of alkyne via rhodium(iii)-catalyzed C–H activation was developed for the switchable synthesis of 3,4-fused indoles and chromans.