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

The spiro-1,3,4-thiadiazoline I loses N-2 at 45 degreesC, 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 Delta (3)-thiadiazoline 1 is converted by base or acid catalysis to the Delta (2) -tautomer 21. Amidrazones (25, 26) are formed from 1 and sec-amines. The me chanisms are discussed and the structures elucidated. (C) 2000 Elsevier Sci ence Ltd. All rights reserved.