Switchable Synthesis of 4,5-Functionalized 1,2,3-Thiadiazoles and 1,2,3-Triazoles from 2‑Cyanothioacetamides under Diazo Group Transfer Conditions

High yield solvent-base-controlled,
transition metal-free synthesis
of 4,5-functionalized 1,2,3-thiadiazoles and 1,2,3-triazoles from
2-cyanothioacetamides and sulfonyl azides is described. Under diazo
transfer conditions in the presence of a base in an aprotic solvent
2-cyanothioacetamides operating as C–C–S building blocks
produce 5-amino-4-cyano-1,2,3-thiadiazoles exclusively. The use of
alkoxide/alcohol system completely switches the reaction course due
to the change of one of the reaction centers in the 2-cyanothioacetamide
(C–C–N building block) resulting in the formation of
5-sulfonamido-1,2,3-triazole-4-carbothioamide sodium salts as the
only products. The latter serve as good precursors for 5-amino-1,2,3-thiadiazole-4-carboximidamides,
the products of Cornforth-type rearrangement occurring in neutral
protic medium or under acid conditions. According to DFT calculations
(B3LYP/6-311+G­(d,p)) the rearrangement proceeds via intermediate formation
of a diazo compound, and can be catalyzed by acids via the protonation
of oxygen atom of the sulfonamide group.