Ring/Ketten‐Tautomerie bei 1.3.4‐Thiadiazolidin‐thionen‐(2) und Δ²‐1.3.4‐Thiadiazolinen

Abstract

Durch NMR-spektroskopische und chemische Untersuchungen wird nachgewiesen, da8 bisher als 1.3.4-Thiadiazolidin-thione-(2) 1 angesehene Verbindungen in Losung mit ihrer ,,Hydrazon-Form" 12 in einem Tautomerie-Gleichgewicht stehen, welches in alkalischem Milieu vollstandig zur ,,Hydrazonsalz-Form" 13 verschoben ist. Umgekehrt konnen bisher als linear aufgefal3te Verbindungen vom Typ 16 auch in Form tautomerer A2-I .3.4-Thiadiazoline 18 vorliegen. Ring1 Chain Tautomerisnz of 1,3,4-Thiadiazolidine-2-thiones and A2-1,3,4-ThiadiazolinesNMR spectroscopic and chemical investigations prove that compounds hitherto considered to be 1,3,4-thiadiazolidine-2-thiones 1 are, in solution, in a tautomeric equilibrium with their "hydrazone form" 12; in alkaline medium, the equilibrium is entirely shifted to the "hydrazone salt form" 13. Conversely, compounds of the type 16 which have so far been considered linear may also be present in the form of tautomeric A2-1,3,4-thiadiazolines 18. Das 1.3.4-Thiadiazolidin-thion-(2)-Ringsystem 1 wurde erstmalig von Busch') beschrieben. Zunachst wurden nur 4-Aryl-substituierte Derivate 2) (R"= H, R"'= Aryl), in neuerer Zeit auch 3.4-Dialkyl-substituierte Vertreter3) (R", R"'= Alkyl) dargestellt. 1966 berichteten Heugebaert und Wil/ems4) uber die Synthese von 1 ( R ' = H, Alkyl; R"'= H) aus Aldehyden oder Ketonen und Dithiocarbazinsauren bzw. aus Aldehyd-oder Ketonhydrazonen und Schwefel kohlenstoff. 1 25)34'

Investigation of the Mechanism of Racemization of Litronesib in Aqueous Solution: Unexpected Base‐Catalyzed Inversion of a Fully Substituted Carbon Chiral Center

“…Insight as to whether pathway ( a ) or ( b ) (Scheme 6) would be preferred can be gained from consideration of the work of others on thiosemicarbazones, which have been found to be in a dynamic equilibrium with 1,3,4‐thiadiazolidines . The work of Uda and Kubota is particularly instructive.…”

“…Insight as to whether pathway (a) or (b) (Scheme 6) would be preferred can be gained from consideration of the work of others on thiosemicarbazones, which have been found to be in a dynamic equilibrium with 1,3,4-thiadiazolidines. [14][15][16][17][18][19][20] The work of Uda and Kubota 12 is particularly instructive. They observed that under neutral conditions the ring-chain equilibrium between acetone thiosemicarbazone and the corresponding 2-amino-1,3,4-thiadiazoline lies essentially completely on the side of the acyclic species.…”

The Reaction of Bu3P-CS2Adduct with Azo Compounds and Aromatic Aldehydes­

“…They have recently gained attention as fungicides, 1 herbicides 2,3 and anticancer agents. [4][5][6] Figure 1 Structure of thiadiazolidine-2-thiones 3-Alkyl-and 3-aryl-1,3,4-thiadiazolidine-2-thiones can be prepared by reacting an aldehyde or ketone with Nalkyldithiocarbazic acid, [7][8][9][10][11][12][13] or by reacting carbon disulfide with hydrazones. 7,8,14,15 3,4-Dialkyl derivatives are synthesized by the reaction of 1,2-dialkylhydrazines with aldehydes and carbon disulfide.…”

Electron deficient heteroaromatic ammonioamidates. Part 25. N-(Quinazolin-3-io)amidates. Part 12. The synthesis of n-(6,7-dimethoxy-2-methylquinazolin-3-io)ethoxythioformamidate and of 2-(3,4-dimethoxyphenyl)-8,9-dimethoxy-5-methyl-10bH-[1,3,4]-thiadiazolo [3,2-c] quinazoline, the ring isomer of N-(6,7-dimethoxy-2-methylquinazolin-3-io)-3,4-dimethoxy(thiobenzamidate)

“…The open-chain forms (7) and the cyclic forms ( 12) may be differentiated on the basis of their n.m.r. spectra.…”

“…Hz, 5'-H),6.92 (s, 5-H),7.07 (dd, J 8.5, 2.0 Hz, 6'-H),70.3d ((2-9, 108.1 (d), 109.1 (d), 109.9 (d), 110.7 (d), 120.8 (d), 2-Acetylamino-4,5-dimethoxybenzaldehyde Ethoxy(thi0-carbony1)hydrazone (6a).-(a) A mixture of compound (5a) (3.13 g, 10 mmol), 40% aqueous ethanol (140 cm3), and Na2S204 (5 1 g, 30 mmol) was stirred at 65-70 "C. After * Unprimed locants refer to the thiadiazoline ring, while primed locants refer to the 5-aryl group. t Unprimed locants refer to the thiadiazoline ring, primed Iocants to the 2-aryl group, and doubly primed locants to the 5-aryl group.…”