Alkoxyalkylation of Electron-Rich Aromatic Compounds

Alkoxyalkylation and hydroxyalkylation methods utilizing oxo-compound derivatives such as aldehydes, acetals or acetylenes and various alcohols or water are widely used tools in preparative organic chemistry to synthesize bioactive compounds, biosensors, supramolecular compounds and petrochemicals. The syntheses of such molecules of broad relevance are facilitated by acid, base or heterogenous catalysis. However, degradation of the N-analogous Mannich bases are reported to yield alkoxyalkyl derivatives via the retro-Mannich reaction. The mutual derivative of all mentioned species are quinone methides, which are reported to form under both alkoxy- and aminoalkylative conditions and via the degradation of the Mannich-products. The aim of this review is to summarize the alkoxyalkylation (most commonly alkoxymethylation) of electron-rich arenes sorted by the methods of alkoxyalkylation (direct or via retro-Mannich reaction) and the substrate arenes, such as phenolic and derived carbocycles, heterocycles and the widely examined indole derivatives.

Selective C(sp3)-S Bond Cleavage of Thioethers to Build Up Unsymmetrical Disulfides

The selective C(sp3)-S bond cleavage of thioethers was first developed to prepare unsymmetrical disulfides by using electrophilic halogenation reagents. In this strategy, NBS (N-bromosuccinimide) achieves selective furfuryl C(sp3)-S bond cleavage of furfuryl alkylthioethers at room temperature. Meanwhile, NFSI (N-fluorobenzenesulfonimide) enables selective methyl C(sp3)-S bond cleavage of aryl and alkyl methylthioethers at an elevated temperature. Notably, the substrate scope investigation indicates that the order of selectivity of the C-S bond cleavage is furfuryl C(sp3)-S > benzyl C(sp3)-S > alkyl C(sp3)-S > C(sp2)-S bond. Moreover, this practical and operationally simple strategy also provides an important complementary way to access various unsymmetrical disulfides with excellent functional group tolerances and moderate to good yields.

Anti-cancer potential of (1,2-dihydronaphtho[2,1-b]furan-2-yl)methanone derivatives

A series of 1,2-dihydronaphtho[2,1-b]furan derivatives were synthesized by cyclizing 1-(aryl/alkyl(arylthio)methyl)-naphthalen-2-ol and pyridinium bromides in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in very good yield. The synthesized compounds were evaluated for their anti-proliferative potential against human triple negative MDA-MB-468 and MCF-7 breast cancer cells and non-cancerous WI-38 cells (lung fibroblast cell) using MTT experiments. Among 21 synthesized compounds, three compounds (3a, 3b and 3 s) showed promising anti-cancer potential and compound 3b was found to have best anti-proliferative activities based on the results of several biochemical and microscopic experiments.

Dioxygen-triggered oxidative cleavage of the C-S bond towards C-N bond formation

Research on the cleavage of C-C bonds has been well developed. By comparison with this, the activation of C-S bonds remains challenging. Herein, dioxygen-triggered oxidative cleavage of C-S bonds has been achieved, delivering a series of N-containing heterocyclic compounds that are frequently found in pesticides and pharmaceuticals. Additionally, the potential utility of this protocol was further demonstrated by a gram-scale experiment. Mechanistically, dioxygen plays a key role in the cleavage of C-S bonds towards C-N bond formation.

Palladium-catalyzed C–S bond activation and functionalization of 3-sulfenylindoles and related electron-rich heteroarenes

A novel palladium-catalyzed approach for constructing functionalized heteroarenes via C–S bond cleavage and C–C bond formation has been demonstrated.

CuI assisted desulfurative Sonogashira reaction of mercapto N-heterocyclic derivatives with alkynes

A palladium catalyzed Sonogashira reaction of mercapto N-heterocyclic derivatives with terminal alkynes by using CuI as the desulfurative reagent was described in this report.