Acid–base reactions of adamantanethione S-methylide and its spiro-1,3,4-thiadiazoline precursor

The spiro-1,3,4-thiadiazoline 1 loses N2 at 45°C, and, as recently reported, the short-lived adamantanethione S-methylide (2) is an active 1,3-dipole. Interception of 2 by acids HX consists of CH2-protonation and ion recombination. Even 1 acts as HX vs 2 and—after electrocyclic ring opening of the anion (13 →15)—affords the dithioacetal C22H32N2S2 (14). The Δ3-thiadiazoline 1 is converted by base or acid catalysis to the Δ2-tautomer 21. Amidrazones (25, 26) are formed from 1 and sec-amines. The mechanisms are discussed and the structures elucidated.