5- Imino-l,2,4-dithiazolidine-3-thiones

Isomerization of 5-imino-l,2,4-dithiazolidine-3-thiones (34) into l,2,4-thiadiazolidine-3,5-di-thiones (51) by a Dimroth rearrangement (see Section 4.13.6.1.1) is a reversible process <91JPR107>. The equilibrium position strongly depends on the nature of substituents. When R = R = Me or Pr the equilibrium position is (34) (51) =1 2, with R = R = Et the ratio is 1 9. When R = Ar, R = Aik, the equilibrium is almost wholly shifted to the right. The forward process is usually accelerated by bases, the reverse by acids. When both substituents are Ar no isomerization occurs <91JPR107>. Isomerization of the 3,5-diimino analogue (52) to a monothione isomer (53), accelerated by pyridine, reaches an equilibrium ratio of (52) (53) =1 9 <89BSB879>. 

Fused 5-imino-l,2,4-dithiazolidine-3-thiones and 3-imines (100) take up nucleophiles on one sulfur atom, releasing the XCS structural unit of the heterocycle (Scheme 15) <85JCS(P1)1007>. Nonfused analogues (101) give up one sulfur atom to the nucleophile, the rest of heterocycle closing to form a 1,3-thiazetidine ring (102) (Scheme 16) <87ZC142>. 

Only a few examples of a nucleophilic attack at the nitrogen atom of 1,2,4-dithiazolidine derivatives are known. 5-Imino-l,2,4-dithiazolidine-3-thione gives tribenzyl-substituted 5-imino-l,2,4-thiadiazolidine-3-thione with an excess of boiling benzylamine <1996CHEC-II(4)453>. l,2,4-Dithiazolidine-3,5-dione 12 forms the potassium salt 11 under the action of KOH in ethanol or KH in MeCN (Scheme 15) <2000SL1622>. 

Disubstituted 5-imino-l,2,4-dithiazolidine-3-thiones (317) with a 5-alkylimino group rearranged when boiled in triethylamine in the presence of ethanol to give 318 (91JPR107) (Scheme 98). 

Cl i,Hi 2N2S, 3-Phenyl-2-phenylimino-l,3-thiazetidine, 44B, 362 Cl Hi2 80283, 4-(6-Methoxy-3-pyridinyl)-5-[(6-methoxy-3-pyridinyl)-imino]-l,2,4-dithiazolidine-3-thione, 46B, 406 Cl nH, 2N11S, 5-Imino-4-phenyl-3-phenylamino-4H-l,2,4-thiadiazoline, 44B, 363... 

The interconvertibility of 1,2,4-dithiazoles and 1,2,4-thiadiazoles has been known for a long time. Examples of such reactions have been encountered in the study of isoperthiocyanic acid (3-imino-l,2,4-dithiazolidine-5-thione) and its analogs (the thiurets , isothiocyanate oxides and sulfides ), and their elucidation has not been as easy matter.1,3 The interpretation of these, and of novel conversions of 1,2,4-dithiazoles to 1,2,4-thiadiazoles has more recently been greatly aided by the application of physical methods, including X-ray analyses. Since the reactions are not all of one kind, it has been expedient to describe them in two separate Sections, among the syntheses of type A and type C, respectively. 

Amino-3Yi 1,2,4 dithiazole-3-thione, 9CI. Isoperthiocyanic acid. 3-Imino l,2,4-dithiazolidine-5-thione. Xanthan hydride [6846-35-1]... 

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