DABCO-Catalyzed DMSO-Promoted Sulfurative 1,2-Diamination of Phenylacetylenes with Elemental Sulfur and o-Phenylenediamines: Access to Quinoxaline-2-thiones

Samarium(II) Diiodide-Mediated Deoxygenation of Sulfoxides

Samarium diiodide-mediated deoxygenative activation of sulfoxides by selective S-O cleavage to construct thioethers under mild room temperature conditions has been achieved. A broad variety of sulfoxides, including aryl-aryl, aryl-alkyl, aryl-alkenyl, and alkyl-alkyl sulfoxides, can be readily converted to the corresponding thioethers using the highly chemoselective, operationally simple, and benign SmI2/Et3N reagent system. Extensive studies on the effect of additives indicate that typical samarium(II) iodide additives, such as water, alcohols, HMPA or nickel, have a negative impact on this valuable deoxygenation, while triethylamine promotes the deoxygenation in a versatile manner to afford synthetically useful thioether products.

Novel Catalyst-Free Synthesis of Some 3-Alkylaminoquinoxaline-2(1H)-thiones and 3-Alkyloxyquinoxaline-2(1H)-thiones in Ethanol

Seventeen 3-alkylaminoquinoxaline-2(1H)-thiones and 3-alkyloxyquinoxaline-2(1H)-thiones were prepared by a novel thionation protocol from the readily available quinoxaline-2,3-dione in excellent overall yields. This protocol starts with the chlorination of dione using thionyl chloride to give 2,3-dichloroquinoxaline followed by the reaction with equimolar amounts of N-nucleophiles (primary amines and secondary amines) or O-nucleophiles (phenols and alcohols) to principally afford 2-alkanamino-3-chloroquinoxalines or 2-alkyloxy-3-chloroquinoxalines, respectively. The chloroquinoxalines reacted with the thionation reagent N-cyclohexyl dithiocarbamate cyclohexyl ammonium salt in ethanol under reflux to principally give the corresponding quinoxalin-2-yl cyclohexylcarbamodithioate that finally rearranges in situ to give the corresponding thiones in 76-93% overall yields. Our novel catalyst-free synthesis of some 3-alkylaminoquinoxaline-2(1H)-thiones and 3-alkyloxyquinoxaline-2(1H)-thiones in ethanol protocol has many advantages compared with traditional methods: excellent yields, one-pot reaction, simple experimental procedure, and commercial availability of the required reagents. In addition, this method could be generalized to involve a wide range of amines, phenols, and alcohols, and also during the reaction, we did not notice a bad odor. The structures of synthesized compounds are elucidated via different methods such as 1H NMR, 13C NMR, elemental analysis, and MS.

Divergent Reaction of Alkynes and TsCN: Synthesis of β-Sulfinyl Alkenylsulfones and (E)-Vinyl Sulfones

An efficient and high-selectivity approach for the divergent synthesis of β-sulfinyl alkenylsulfones and (E)-vinyl sulfones from alkynes and TsCN is described. A series of disulfurized products were constructed under mild conditions in the absence of transition metals. This transformation featured excellent regio- and stereoselectivity, good functional group compatibility, and broad substrate scope. The copper(I)-catalyzed sulfonation of alkynes with TsCN that affords (E)-vinyl sulfones in good to excellent yields was also developed.

Sulfur-Promoted Access to 3-Arylquinoxalin-2-ones by Oxidative Coupling of o-Phenylenediamines with Arylacetates

We disclose the synthesis of 3-arylquinoxalin-2-ones from o-phenylenediamines and readily available arylacetates. The method harnesses the selective oxidative property of elemental sulfur in the presence of amine base catalyst and DMSO. The reactions are operationally simple and tolerate a wide range of functional groups.

Sodium sulfide-promoted regiodefined redox condensation of o-nitroanilines with aryl ketones to benzo[a]phenazines and quinoxalines

Inexpensive sodium sulfide trihydrate was found to promote unprecedented 6e-regio-predefined redox condensation of o-nitroanilines with α-tetralones to benzo[a]phenazines. The method was also successfully extended to acetophenones and higher homologs as reducing partners to provide 2-phenylquinoxalines. Compared to traditional approaches toward benzo[a]phenazine and quinoxaline cores starting with o-phenylenediamines, the present strategy could afford these heterocycles with well-defined regiochemistry based on the structure of starting o-nitroanilines.