Elemental Chalcogen (Se, S) in PEG-400 to the Synthesis of Seleno- and Thioflavones from 2-Chlorophenyl Ethynyl Ketone and Nucleophilic Species of Chalcogen

Abstract

An alternative green method was developed for the synthesis of thio- and selenoflavones by the ring closure of 2-chlorophenyl ethynyl ketone with NaHY (Y = S, Se). These nucleophilic chalcogen species were generated in situ using NaBH4 to reduce the elemental chalcogen in the presence of polyethylene glycol-400 (PEG-400). The efficiency of this reaction is strongly dependent on the PEG-400 solvent, acting like a crown ether, complexing with the sodium atom of NaHY species, making the chalcogen nucleophile more active. The synthetic protocol proceeded efficiently at 100 °C under argon, using a range of 2-chlorophenyl ethynyl ketone containing alkyl, aryl, or vinyl groups and the sulfur and selenium chalcogen. By this efficient and simple approach, 18 chalcogenoflavones were obtained in good to excellent yields after 2 h.

Rongalite in PEG-400 as a general and reusable system for the synthesis of 2,5-disubstituted chalcogenophenes

“…Likewise, PEG-400 is a non-toxic, biodegradable and inexpensive solvent that have been successfully applied in several organic transformations 39 and in organochalcogen chemistry, 40 which was recently identified as a suitable green reaction media for reducing elemental chalcogens into their nucleophilic species. 41 Additionally, attractive recycling protocols are known for this thermally stable solvent. 39,40 Until now, this has been an unexplored area in the synthesis of chalcogenophenes by sustainable chemical methods.…”

Synthesis of Fluoromethylated Chromones and Their Heteroatom Analogues via Sodium Fluoromethanesulfinate-Enabled Direct Fluoromethylation

“…Substrates 1w–y , YCF 2 SO 2 Na (Y = H and F), and TBHP were commercially purchased and used directly. Enamines 1a–y are known compounds , except compounds 1e , 1r , and 1s .…”

Selenate—An internal chemical shift standard for aqueous 77Se NMR spectroscopy

“…Despite the long-standing use of this technique, a reliable and robust chemical shift standard is still an unmet need, as seen in a systematic error between separately reported 77 Se chemical shifts in the literature. [12] In the 77 Se NMR literature, chemical shift data are referenced to a relatively large number of compounds(seleninyl chloride, [13] dimethyl selenide, [14,15] selenophene, [16][17][18][19] diphenyl diselenide, [20][21][22][23][24] 4,4 0dimethyldiphenyl diselenide, [25] selenium oxide, [26] sodium selenite, [27] selenous acid). [13,[28][29][30][31] In addition, indication of the measurement parameters (concentration, ionic strength, temperature) is rather the exception than the case.…”