Catalyst-free, one-pot strategy to access 3-substituted-5-amino-1,2,4-thiadiazoles in water

Sodium Carbonate-Promoted Formation of 5-Amino-1,2,4-thiadiazoles and 5-Amino-1,2,4-selenadiazoles with Elemental Sulfur and Selenium

“…On the basis of the control experiments and previous reports, ,,,, a proposed mechanism for the formation of 3-substituted 5-amino-1,2,4-thiadiazoles and 5-amino-1,2,4-selenadiazoles is outlined in Scheme . In the presence of a base, isocyanide 2 reacts with sulfur powder or selenium powder to give isothiocyanate A or isoselenate C . , For the synthesis of 1,2,4-thiadiazole, a lone pair of electrons on the nitrogen of N -hydroxybenzimidamide attacks the electrophilic carbon of the isothiocyanate to give intermediate B ; subsequent deprotonation from intermediate B , followed by intramolecular cyclization to form the S–N bond, gives the 3-substituted 5-amino-1,2,4-thiadiazole 3 . However, a radical mechanism is suggested for the synthesis of 5-amino-1,2,4-selenadiazoles.…”

“…In the presence of a base, isocyanide 2 reacts with sulfur powder or selenium powder to give isothiocyanate A 16 or isoselenate C. 13a,17 For the synthesis of 1,2,4-thiadiazole, a lone pair of electrons on the nitrogen of N-hydroxybenzimidamide attacks the electrophilic carbon of the isothiocyanate to give intermediate B; subsequent deprotonation from intermediate B, followed by intramolecular cyclization to form the S−N bond, gives the 3- substituted 5-amino-1,2,4-thiadiazole 3. 18 However, a radical mechanism is suggested for the synthesis of 5-amino-1,2,4-Table 3. Substrate Scope of 5-Amino-1,2,4 then dehydrated in the presence of the action of base or a peroxide anion, to give product 4.…”