Highly Efficient Oxidative Dimerization of Thioamides to 3,5-Disubstituted 1,2,4-Thiadiazoles Mediated by DDQ

Building 1,2,4‐Thiadiazole: Ten Years of Progress

“…In 2012, Cheng and colleagues described the synthesis of a set of 3,5‐disubstituted 1,2,4‐thiadiazoles through highly efficient oxidative dimerization of arylthioamides 32 mediated by 2,3‐dichloro‐5,6‐dicyanobenzoquinone (DDQ; Scheme ) . Under optimal conditions, the reactions took place in dichloroethane at room temperature to form the products in good to excellent yields (88–99 %).…”

Transition-metal-free visible light-promoted photoredox oxidative dehydrogenative cyclization: expeditious approach to 1,2,4-thiadiazoles

“…The traditional method for the synthesis of 3,5-disubstituted 1,2,4-thiadiazoles relies on the oxidative dimerization reaction of thioamides using various oxidants (Scheme 1, a). [16][17][18][19][20][21][22][23] Recently, alternative methods were developed through intramolecular oxidative dehydrogenative cyclization by employing transition-metal or stoichiometric amount of oxidants such as hypervalent iodine (III), I2, or O2 (Scheme 1, b). [24][25][26][27][28][29][30][31] Most recently, an elegant protocol has been published via the electro-oxidative intramolecular dehydrogenative N-S bond formation of imidoyl thioureas (Scheme 1, c).…”

Simple and Green Procedures for the Synthesis of 3,5‐Bis(alkylthio)‐1,2,4‐thiadiazoles via Oxidative Dimerization of Dithiocarbamates

“…Among these methods, the oxidative dimerization technique has been extensively investigated in recent years. Although there are many reports in recent years for the synthesis of 3,5‐dialkyl/diaryl‐ and 3,5‐bis(arylamino)‐1,2,4‐thiadiazole derivatives using various oxidants such as IBX/TEAB, N ‐benzyl‐DABCO tribromide/DMSO, TCT/DMSO in PEG, DDQ/DCE, eosin Y/light, O 2 /I 2 /H 2 SO 4 , and many others, [13c][20] there is only few reports for the synthesis of 3,5‐bis(alkyl/arylthio)‐1,2,4‐thiadiazoles in literature starting from 1,2,4‐thiadiazolidine‐3,5‐dithione (Scheme a), metal thiocyanates (Scheme b), or cyanamide (Scheme c) . Recently, we have shown that by oxidative dimerization of S ‐alkyl dithiocarbamates in the presence of hypervalent iodine (H 5 IO 6 ), it is also possible to prepare the corresponding 3,5‐bis(alkylthio)‐1,2,4‐thiadiazoles in high to excellent yields (Scheme d) .…”