Regioselective C-H alkylation of anisoles with olefins by cationic imidazolin-2-iminato scandium(iii) alkyl complexes

A new type of rare-earth alkyl complexes supported by monoanionic imidazolin-2-iminato ligands were synthesised and structurally characterised by X-ray diffraction and NMR analyses. The utility of these imidazolin-2-iminato rare-earth alkyl complexes in organic synthesis was demonstrated by their performance in highly regioselective C-H alkylation of anisoles with olefins. With as low as 0.5 mol% catalyst loading, various anisole derivatives without ortho-substitution or 2-methyl substituted anisoles reacted with several alkenes under mild conditions, producing the corresponding ortho-Csp2-H and benzylic Csp3-H alkylation products in high yield (56 examples, 16-99% yields). Control experiments revealed that rare-earth ions, ancillary imidazolin-2-iminato ligands, and basic ligands were crucial for the above transformations. Based on deuterium-labelling experiments, reaction kinetic studies, and theoretical calculations, a possible catalytic cycle was provided to elucidate the reaction mechanism.

Unbiased C3‐Electrophilic Indoles: Triflic Acid Mediated C3‐Regioselective Hydroarylation of N−H Indoles**

The direct dearomative addition of arenes to the C3 position of unprotected indoles is reported under operationally simple conditions, using triflic acid at room temperature. The present regioselective hydroarylation is a straightforward manner to generate an electrophilic indole at the C3 position from unbiased indoles in sharp contrast to previous strategies. This atom‐economical method delivers biologically relevant 3‐arylindolines and 3,3‐spiroindolines in high yields and regioselectivities from both intra‐ and intermolecular processes. DFT computations suggest the stabilization of cationic or dicationic intermediates with H‐bonded (TfOH)_n clusters.

Synthesis of Tetrahydroindolizino[8,7-b]indole Derivatives in the Presence of Fe(OTf)3 or CF3SO3H through Intramolecular Dearomatization of Indole

We have developed a convenient synthesis of tetrahydroindolizino[8,7-b]indole derivatives via intramolecular dearomatization of indole. Highly functionalized tetrahydroindolizinoindoles can be prepared in the presence of trifluoromethanesulfonic acid in good to excellent yields (up to >99% yield) with novel designed pyrrole-tethered indoles. The same products can also be synthesized through a mild Fe(OTf)₃-catalyzed process in acceptable to good yields (up to 75% yield).

Iron(III) Chloride as a Mild Catalyst for the Dearomatizing Cyclization of N-Acylindoles

A catalytic approach for the preparation of indolines by dearomatizing cyclization is presented. FeCl₃ acts as a catalyst to afford tetracyclic 5a,6-dihydro-12H-indolo[2,1-b][1,3]benzoxazin-12-ones in good yields. The cyclization also proceeds with tosylamides forming C-N bonds in 53% yield.

Synthesis of Aza-Eight-Membered Ring-Fused Indolines Initiated by Zn-Catalyzed C2 Alkylation of Indoles and Subsequent Base-Promoted Ring Expansion

A novel and efficient synthesis of aza-eight-membered ring-fused indolines has been developed. This process is realized by zinc-catalyzed C2 alkylation of indoles and subsequent base-promoted ring expansion of the newly formed six-membered ring with alkynes. Easily accessible starting materials, good functional group tolerance, and high atom economy make this procedure attractive.

Dearomatization Reactions of Indoles to Access 3D Indoline Structures

This Account summarizes our involvement in the development of dearomatization reactions of indoles that has for origin a total synthesis problematic. We present the effort from our group to obtain 3D-indolines scaffold from the umpolung of N-acyl indoles via activation with FeCl3 to the oxidative spirocyclizations of N-EWG indoles and via the use of electrochemistry.

1 Introduction

2 Activation of N-Acyl Indoles with FeCl3

2.1 Hydroarylation of N-Acyl Indoles

2.2 Difunctionalization of N-Acyl Indoles

3 Radical-Mediated Dearomatization of Indoles for the Synthesis of Spirocyclic Indolines

4 Electrochemical Dearomatization of Indoles

4.1 Direct Electrochemical Oxidation of Indoles

4.2 Indirect Electrochemical Oxidation of Indoles

5 Conclusion

Iron-mediated site-selective oxidative C–H/C–H cross-coupling of aryl radicals with quinones: synthesis of β-secretase-1 inhibitor B and related arylated quinones

Phenoxy radicals were converted intoparasite selectiveC-aryl radicals and coupled with quinones, using an inexpensive FeCl₃–K₂S₂O₈system, to obtain several arylated quinones, in good to moderate yields.

Ring-Opening of Indoles: An Unconventional Route for the Transformation of Indoles to 1 H-Pyrazoles Using Lewis Acid

An unusual transformation of indoles to pyrazoles via an aromatic ring-opening strategy has been developed. The salient feature of this strategy involves the C2-N1 bond opening and concomitant cyclization reaction of the C2═C3 bond of the indole moiety with the tosylhydrazone, which proceeds under transition-metal and ligand free conditions. This ring-opening functionalization of indoles provides a wide scope of differently substituted pyrazoles.

Revealing the electrophilicity of N-Ac indoles with FeCl3: a mechanistic study

The puzzling hydroarylation of N-Ac indoles promoted by iron trichloride involves a doubly activated intermediate: as supported by the electron density topology of a crystal, IR monitoring, and DFT calculations.

One-step formation of dihydrofuranoindoline cores promoted by a hypervalent iodine reagent

Treatment of aniline derivatives in the presence of a hypervalent iodine reagent and furan produces dihydrofuranoindoline cores in one step.