Structural characterization and synthesis of 7-thia-1,5-diazatricyclo[7.4.1.05,14]tetradec-9(14)-ene-6,8-dithione

Contrasting Reactivity of CS2 with Cyclic vs. Acyclic Amidines

“…We find that the reaction proceeds readily at room temperature. The molecular structure we obtained of 1 (Figure S35) was in good agreement with that produced by Vlasse and co‐workers 24. Structures that feature a cyclic carbamic carboxylic trithioanhydride ring are known (Scheme ), but the synthesis of 1 is the only example where the use of CS 2 affords the cyclic carbamic carboxylic trithioanhydride without additional reagents and occurs readily at room temperature.…”

“…We also observed the red oil after the synthesis of 1 and 3 . The IR spectrum of the red oil recovered after the synthesis of 3 has similar wavenumbers, including a very weak band at 2622 cm –1 , as that of the isolated red oil reported by Vlasse and co‐workers 24. The IR spectrum following the addition of hydrogen sulfide to 2 also exhibited a very weak band at 2622 cm –1 , which agrees with a band for hydrosulfide salts 30,31…”

“…Path A, in which that adduct undergoes an internal rotation and an intramolecular nucleophilic attack by an anionic sulfur atom, is analogous to a mechanism proposed by Barton and co‐workers for the reaction of guanidines with CS 2 47. Path B, in which that same anionic sulfur reacts with a second CS 2 molecule, is an elaboration of Vlasse's mechanism24 for the reaction of DBU with CS 2 . We propose a third mechanism, path C, in which the zwitterionic adduct is deprotonated (by another amidine) at the acidic methylene α to the central amidine carbon.…”

“…While DBU does not react with CO 2 in dry conditions, it does react with CS 2 , and in a manner that involves activation of the acidic methylene C‐H α to the amidine carbon. Vlasse and co‐workers24 in 1986 refluxed a solution of DBU in CS 2 for 6 h and then removed the CS 2 by distillation, leaving behind an orange viscous material from which a cyclic carbamic carboxylic trithioanhydride, 1 , was precipitated (Scheme ). They also found that the DBU hydrogen sulfide salt was formed as a byproduct.…”

“…Upon the formation of a carbamic carboxylic trithioanhydride, one equivalent of dihydrogen sulfide is evolved by this route; the amidinium hydrogen sulfide is formed as a byproduct. The amidinium hydrogen sulfide salt that forms during the synthesis of 1 was described by Vlasse and co‐workers as a red oil;24 treatment of the red oil with potassium hydroxide removes the hydrogen sulfide. We also observed the red oil after the synthesis of 1 and 3 .…”