Thiones, Dimroth rearrangement

Heating of a solution of 5-ethyl-3-phenyl-l,3,4-thiadiazol-2(377)-imine 85 in aq. NaOH to 80°C for 5h gave the 5-ethyl-2,3-dihydro-2-phenyl-l/7-l,2,4-triazole-3-thione 86 via Dimroth rearrangement (Scheme 7) <2002HCA1883>. Nucleophilic attack of the hydroxide on the electrophilic C-5 resulted in ring opening and, after rotation around the C(2)-N(3) bond and subsequent recyclization, triazole thione 86 formed. 

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>. 

A reversible Dimroth rearrangement is observed between 1,4-dihydro-7if-w-triazolo[4,5-f>]pyridine-7-thione (655) and 4-amino[l,2,3]thiadiazolo[4,5-c]pyridine (657) on heating... 

A modification of the dihydropyrimidone MCR was performed by applying isothiocyanates 107 as the fourth component, which resulted in the formation of 2-aminothiazines 108 which upon microwave heating could rearrange (Dimroth rearrangement) to dihydropyrimidine-2-thiones 109 [87]. 

Amino-l,3-thiazoline-2-thiones undergo Dimroth rearrangement to give imidazole-2,5-dithiols in a reaction which does not appear to have... 

The Dimroth rearrangement of iminoquinazolinones and thiones has been known for some time (see Armarego, p. 335), and more recently Brown and co-workers have examined the rates of rearrangement of iminoquin-azolines which lack an oxo or thio group in the pyrimidine ring. 2-Imino-3-methyl-2,3-dihydroquinazolines (93) (prepared by direct methylation of... 

When 4//-l,3-benzothiazine-4-thiones react with propargylamine imidazoles form in 53-72% yields by way of an amidine intermediate <87LA103>. Oxidation of the dehydration product of creatine gives creatone (205) with concurrent Dimroth rearrangement (Scheme 138) <82BCJ1912, 87BCJ4115>. 

The cyclocondensation of alkylidenemalononitriles (182) and thiobenzamides in acetic acid solution containing perchloric acid affords 6-imino-l,3-thiazines (183). Dimroth rearrangement of these products in the presence of a base yields pyrimidine-4(3f/)-thiones (184) (Scheme 34) <88PS55>. 

Whereas there appear to be no general synthetic routes to 2//-l,3,5-thiadiazines, the 2-thiones and the 2,4-dione derivatives are accessible by Dimroth rearrangement of l,3,5-oxadiazine-2-thiones (see Section 6.18.11.2) and by base-catalyzed cyclization of A -acyl-A -thioacylureas (see Section... 

Thiones such as 1,2,3-triazolopyridinethione 69 underwent Dimroth rearrangement to form the corresponding amino-l,2,3-thiadiazolopyridine 70 in the presence of refluxing isopropanol.The authors noted that triazole... 

Irradiation of 2-methyl-4-phenyl-substituted benzaldehyde thiosemicarbazones (171) leads to the corresponding A -l,2,4-triazohne-5-thione derivatives (173) through the formation of stable 1,2,4-tria-zoHdine-5-thione derivatives (172) (Scheme 27). Irradiation of N-acylthiourea (174) in the presence of triethylamine gives thiourea (175) and benzothiazoles (176) via an electron-transfer mechanism. A photochemicaUy induced Dimroth rearrangement has been reported in the l,2-thiazolino[5.4-d]-l,2-thiazoline-3,6-dithione (177) and yields the 3ff,6ff-l,2-dithiolo[4.3-c]-l,2-dithiole (178). ... 

Sukumaran and Rajasakharan [89IJC(B)642] reported that reaction of o-aminocarbonitriles 48 and powdered sodium hydroxide in DMF with alkyl or aryl isothiocyanates gave directly 3-alkyl- or 3-aryl-4-iminothieno [2,3-d]pyrimidine-2-thiones 77a. By altering these reaction conditions slightly, the same authors claimed to isolate thioureas 79a, which were cyclized in boiling pyridine to 4-phenyl- or 4-arylthieno[2,3-d]pyrimidine-2(lH)-thiones 78a via Dimroth-type rearrangement of intermediate 4-... 

The Dimroth-type rearrangements are sensitive to both solvent and electronic effects. Electron-withdrawing substituents on the pyridine nucleus (—HNC=S or—NC=SH —NCNH2) facilitate the rearrangement, while the solvent effect is based on empirical observations. For example, 5-amino-l,4-dihydro-7//-[l,2,3]triazolo[4,5-6]pyridine-7-thione 3-riboside (258) is converted in DMF... 

The products of nucleophilic attack on 4-alkoxy-6-amino-l,3,5-thiadiazine-2-thiones (81) depend on the nature of the attacking nucleophile. Primary amines bring about amino-dealkoxylation, whereas on hydrolysis, initial attack at C-4 is accompanied by ring opening to give an 7V-(alkoxy-carbonyl)thiourea. In contrast, in the presence of ethanolic sodium hydroxide an ANRORC process (Dimroth-type rearrangement) takes place to yield 6-ethoxy-l,3,5-triazine-2,4(177,37/)-dithione (82) <92NKK1450>. ... 

The acid-sensitive 4-alkylamino-6-aryl-l,3,5-oxadiazine-2-thiones (235) undergo a rapid Dimroth-type rearrangement in boiling acetic acid to the isomeric l,3,5-thiadiazin-2-ones (236) (Scheme 40) <86zci32, 89LA93i>. 

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