1,2,6-Thiadiazine 1-Oxides: Unsaturated Three-Dimensional S,N-Heterocycles from Sulfonimidamides

Desymmetrization of Cyclic Sulfonimidamides by Asymmetric Allylation

Herein we report the first transition metal-catalyzed approach to the enantioenriched synthesis of cyclic sulfonimidamides relying on commercially available palladium catalysts and ligands. High-throughput experimentation (HTE) was employed to identify the optimal catalyst system and solvent. The method is applied to a variety of saturated and unsaturated rings and exhibits the highest selectivity for 2-substituted allyl electrophiles. The products are further elaborated to complex, tricyclic scaffolds. DFT experiments presented herein highlight the key ligand substrate interactions leading to the high levels of enantioselectivity.

Evaluation of Chiral Organosulfur Compounds on Their Activity against the Malaria Parasite Plasmodium falciparum

Malaria is one of the deadliest tropical diseases, especially causing havoc in children under the age of five in Africa. Although the disease is treatable, the rapid development of drug resistant parasites against frontline drugs requires the search for novel antimalarials. In this study, we tested a series of organosulfur compounds from our internal library for their antiplasmodial effect against Plasmodium falciparum asexual and sexual blood stages. Some active compounds were also obtained in enantiomerically pure form and tested individually against asexual blood stages of the parasite to compare their activity. Out of the 23 tested compounds, 7 compounds (1, 2, 5, 9, 15, 16, and 17) exhibited high antimalarial activity, with IC₅₀ values in the range from 2.2 ± 0.64 to 5.2 ± 1.95 µM, while the other compounds showed moderate to very low activity. The most active compounds also exhibited high activity against the chloroquine-resistant strain, reduced gametocyte development and were not toxic to non-infected red blood cells and Hela cells, as well as the hematopoietic HEL cell line at concentrations below 50 µM. To determine if the enantiomers of the active compounds display different antimalarial activity, enantiomers of two of the active compounds were separated and their antimalarial activity compared. The results show a higher activity of the (-) enantiomers as compared to their (+) counterparts. Our combined data indicate that organosulfur compounds could be exploited as antimalarial drugs and enantiomers of the active compounds may represent a good starting point for the design of novel drugs to target malaria.

Copper-Catalyzed, Aerobic Synthesis of NH-Sulfonimidamides from Primary Sulfinamides and Secondary Amines

NH-Sulfonimidamides are prepared by copper-catalyzed coupling of primary sulfinamides with secondary amines. Neither a ligand nor an additive is needed, and air is the terminal oxidant. The reactions occur at room temperature, show good functional group tolerance, and lead to products in good yields. A sulfanenitrile is proposed as an intermediate in this oxidative amination.

Organocatalytic Oxidative C-H Amination of Aldehyde Hydrazones with Azoles at Ambient Temperature

An efficient, metal-free, and direct oxidative amination of aldehyde-derived hydrazones with azoles has been developed using 2,3-dichloro-5,6-dicyano-1,4-benzoquinone as an organocatalyst at ambient temperature. This protocol provides a wide range of aminated hydrazone derivatives in a step and atom economical fashion. The reaction possibly follows a radical mechanism.

Synthesis of trifluoromethyl-substituted 1,2,6-thiadiazine 1-oxides from sulfonimidamides under mechanochemical conditions

TBS-protected or NH-sulfonimidamides react with β-alkoxyvinyl trifluoromethylketones under solvent-free mechanochemical conditions to give 3-trifluoromethyl-substituted three-dimensional 1,2,6-thiadiazine 1-oxides. C4-Functionalized products can be obtained by starting from cyclic enones and brominations of the initially formed heterocycles. The stability of the products was investigated by varying the pH value and storage under aerobic conditions.

Mechanochemical Synthesis of Organic Dyes and Fluorophores

The syntheses of dyes and fluorophores have significant commercial importance. In recent years, mechanochemistry has emerged as a green and sustainable alternative for the synthesis of conventional dyes, new fluorophores, and also synthetic modification of known dyes for their use as chemosensors. The dyestuffs based on BODIPYs, rhodamine, fluorescein, perylenedimides, coumarins, benzothiazoles, etc. were synthesized or derivatized by grinding or milling. The synopsis aims to pay key attention to their synthesis and the applications as chemosensors will be briefly covered.

2,3-Dihydro-1,2,6-thiadiazine 1-Oxides by Biginelli-Type Reactions with Sulfonimidamides under Mechanochemical Conditions

Biginelli-type multicomponent reactions (MCRs) with NH-free sulfonimidamides provide 2,3-dihydro-1,2,6-thiadiazine 1-oxides in high yields. The couplings are performed in a planetary ball mill under solvent-free mechanochemical conditions. Acetic acid or ytterbium triflate are used as catalysts. A representative product was characterized by X-ray single crystal structure analysis revealing molecular details of the highly functionalized three-dimensional heterocycle. Further product modifications lead to additional structural scaffolds.

A Unified Strategy for Arylsulfur(VI) Fluorides from Aryl Halides: Access to Ar-SOF3 Compounds

A convenient protocol to selectively access various arylsulfur(VI) fluorides from commercially available aryl halides in a divergent fashion is presented. Firstly, a novel sulfenylation reaction with the electrophilic N-(chlorothio)phthalimide (Cl-S-Phth) and arylzinc reagents afforded the corresponding Ar-S-Phth compounds. Subsequently, the S(II) atom was selectively oxidized to distinct fluorinated sulfur(VI) compounds under mild conditions. Slight modifications on the oxidation protocol permit the chemoselective installation of 1, 3, or 4 fluorine atoms at the S(VI) center, affording the corresponding Ar-SO2 F, Ar-SOF3 , and Ar-SF4 Cl. Of notice, this strategy enables the effective introduction of the rare and underexplored -SOF3 moiety into various (hetero)aryl groups. Reactivity studies demonstrate that such elusive Ar-SOF3 can be utilized as a linchpin for the synthesis of highly coveted aryl sulfonimidoyl fluorides (Ar-SO(NR)F).

Mechanochemical Synthesis of 1,2,6-Thiadiazine 1-Oxides from Sulfonimidamides and the Fluorescence Properties of the Products

A solvent-free mechanochemical synthesis for 1,2,6-thiadiazine 1-oxides starting from NH-sulfonimidamides and propargyl ketones has been developed. Lewis acids affect these one-pot aza-Michael-addition/cyclization/dehydration reaction sequences. The photophysical properties of the resulting heterocyclic sulfonimidamide derivatives were characterized.