Regioselectivity of Larock Heteroannulation: A Contribution from Electronic Properties of Diarylacetylenes

Quantitative analysis of steric effects on the regioselectivity of the Larock heteroannulation reaction

Alkylphenylacetylene derivatives were synthesized and used as reactants in the Larock heteroannulation reaction to investigate the steric influence on regioselectivity. Large alkyl groups preferentially yielded 2-alkyl-3-phenylindole products, while smaller alkyl groups provided 3-alkyl-2-phenylindole as major products. The logarithm of regioisomeric product ratios exhibited good correlations with various steric parameters. Notably, the Charton values provided the best correlation when excluding the cyclopropyl group. In addition, the Boltzmann-weighted Sterimol parameter (wSterimol) was utilized to generate a good predictive model, indicating the B₁ wSterimol as the significant regiochemical determining parameter with no obvious deviation for the cyclopropyl group. Relative atomic distances within the DFT-optimized transition state structures revealed good correlations with the logarithm of regioisomeric ratios. Furthermore, the cyclopropyl adsorption complex indicated electronic contribution, explaining the peculiar behavior of this substituent in the experimental observation.

Design, development and applications of copper-catalyzed regioselective (4 + 2) annulations between diaryliodonium salts and alkynes

Diaryliodonium salts have been extensively applied in organic synthesis as aryl cation equivalents. However, in the electrophilic reactions with alkenes or alkynes, only the electrophilic carbon of the diaryliodonium salts was involved while the other part of the aryl ring was not utilized. Herein, a reaction pattern of diaryliodonium was reported as oxa-1,4-dipoles to undergo (4 + 2) cycloaddition reactions with alkynes. Broad spectrum of the two reaction partners could be utilized in this protocol, enabling an operationally simple, high yielding, and regioselective synthetic approach to isocoumarins. Particularly, good to excellent regioselectivities were achieved for the sterically unbiased unsymmetrical diaryl acetylenes, which was challenging for other transition metal-catalyzed processes. The reaction could be scaled up with the ideal 1:1 stoichiometry and the isocoumarin type natural products Oospolactone and Thunberginol A could be obtained in one or three steps through this methodology.

Biphasic dose-dependent G0/G1 and G2/M cell cycle arrest by synthetic 2,3-arylpyridylindole derivatives in A549 lung cancer cells

A collection of 2,3-arylpyridylindole derivatives were synthesized via the Larock heteroannulation and evaluated for their in vitro cytotoxic activity against A549 human lung cancer cells. Two derivatives expressed good cytotoxicity with IC 50 values of 1.18±0.25 μM and 0.87±0.10 μM and inhibited tubulin polymerization in vitro , with molecular docking studies suggesting the binding modes of the compounds in the colchicine binding site. Both derivatives have biphasic cell cycle arrest effects depending on their concentrations. At a lower concentration (0.5 μM), the two compounds induced G0/G1 cell cycle arrest by activating the JNK/p53/p21 pathway. At a higher concentration (2.0 μM), the two derivatives arrested the cell cycle at the G2/M phase via Akt signaling and inhibition of tubulin polymerization. Additional cytotoxic mechanisms of the two compounds involved the decreased expression of Bcl-2 and Mcl-1 antiapoptotic proteins through inhibition of the STAT3 and Akt signaling pathways.

Dissecting the Electronic Contribution to the Regioselectivity of the Larock Heteroannulation Reaction in the Oxidative Addition and Carbopalladation Steps

Substituted 2-iodoaniline derivatives were prepared and utilized as reactants, along with asymmetric diarylacetylenes, to synthesize a series of 6-substituted-2,3-diarylindole derivatives via the Larock heteroannulation reaction. Electron-donating substituents on the 2-iodoaniline derivatives retarded the reaction, while electron-withdrawing substituents provided a complete conversion to the indole products. In addition, the electronic properties of the substituted 2-iodoaniline reactants displayed no influence toward regioselectivity. On the contrary, the electronic effect from unsymmetrical diarylacetylenes significantly influenced the regiochemical outcome of the reaction. Density functional theory calculations of the oxidative addition and carbopalladation steps revealed the electronic influences of the substituted 2-iodoaniline derivatives toward the overall rate of the reaction. In contrast, the electronic properties of the asymmetric diarylacetylene remained the critical product-determining factor of regioselectivity.

Synthesis of indoles from aroyloxycarbamates with alkynes via decarboxylation/cyclization

Palladium-catalyzed decarboxylation/cyclization of aroyloxycarbamates with alkynes to construct C–N bonds.

On the regiochemical differences between Pd-catalyzed heterocyclization–allylation and –arylation reactions of alkynylbenzamides: preparation of 4-allyl-isochromen-1-imines and computational study

The divergent regioselectivity of allylation and arylation of 2-alkynylbenzamides under Pd(0)-catalyzed conditions is studied with the aid of DFT calculations.

A synthetic 2,3-diarylindole induces cell death via apoptosis and autophagy in A549 lung cancer cells

A series of 2,3-diarylindoles were synthesized via the Larock heteroannulation, and evaluated for their anticancer activity against A549 lung cancer cells. The most potent compound, PCNT13 with IC50=5.17 μM, caused the induction of two modes of programmed cell death, apoptosis and autophagy.

Intramolecular addition of diarylmethanols to imines promoted by KOt-Bu/DMF: a new synthetic approach to indole derivatives

KOt-Bu/DMF promoted intramolecular addition of diarylmethanols to imines was developed.