Dimroth rearrangement “thiadiazole-triazole”: synthesis and exploration of 3-sulfanyl-1,2,4-triazolium salts as NHC-proligands

• Published in: Russian chemical bulletin Vol. 71; no. 5; pp. 993 - 1008
• Main Authors: Pasyukov, D. V., Chernenko, A. Yu, Lavrentev, I. V., Baydikova, V. A., Minyaev, M. E., Starovoytova, O. A., Chernyshev, V. M.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.05.2022; Springer Nature B.V
• Subjects: Alkylation; Chemistry; Chemistry and Materials Science; Chemistry/Food Science; Dimethyl acetals; Dimethylformamide; Full Article; Heating; Inorganic Chemistry; Organic Chemistry; Thiadiazoles; Thiosemicarbazides; 1,3,4-thiadiazole; palladium; Pd-PEPPSI; Dimroth rearrangement; 1,2,4-triazole; N-heterocyclic carbenes
• ISSN: 1066-5285; 1573-9171
• DOI: 10.1007/s11172-022-3501-7

The reaction of 1,4-disubstituted thiosemicarbazides with N,N -dimethylformamide dimethyl acetal afforded 1,4-disubstituted 1,2,4-triazolium-3-thiolates. Heating of the thiosemicarbazides with trimethyl orthoformate in the presence of Me 3 SiCl yielded 5-RNH-substituted 1,3,4-thiadiazolium salts and, in some cases, 1,4-disubstituted 3-sulfanyl-1,2,4-triazolium salts as by-products. It was found that the obtained heterocycles are capable of reversible interconversions depending on the medium acidity and the structure of substituent R. Aminothiadiazolium salts in the presence of bases underwent rearrangement into triazolium thiolates, except for the case when R = 2,6-diisopropylphenyl. Triazolium thiolates and sulfanyltriazolium salts were converted into aminothiadiazolium salts upon heating in an acidic medium. S-Alkylation of triazolium thiolates gave stable 3-alkylsulfanyl-1,2,4-triazolium salts, which can be used as NHC-proligands. Direct palladation of alkylsulfanyl triazolium salts was used to obtain the PEPPSI type Pd/NHC complexes.