1.2.5- Thiadiazines

Thiadiazine insecticides are derivatives of thiadiazine. Buprofezin is the only current member of this group. It is an insecticide with persistent larvicidal activity against sucking insects such as mealybugs, rice planthoppers, scales, and whiteflies in rice, potatoes, citrus, cotton, and vegetables. Its oral LD50 in rats is 2198 mg/kg. 

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Thioazadienes 90, formed in situ by the reaction of trimethylsilylimines and isothiocyanates, underwent cycloaddition reactions with nitriles bearing electron-withdrawing groups, to afford 1,3,5-thiadiazines [94] in excellent yield (Equation 2.26). 

Triaryl-4H-l,3,5-thiadiazine reagieren in Benzol bei 20° mit Triethylamin als Katalysator in Ausbeuten > 80% zu 2,4,5-Triaryl-imidazolen, wobei aus dem Substituenten in 4-Stel-lung des 4H-1,3,5-Thiadiazins der Rest in 2-Position des Imidazols entsteht442. 

Thiadiazines (535) are obtained by the cycloaddition of thioaryl isocyanates (R CSNCO) with imines R2R3C = NR4. 

Only one kind of six-membered ring system containing two nitrogens and one sulfur has been prepared from thiourea-type starting materials, namely 1,3,5-thiadiazines. The first report of this sort of preparation is that of Fromm and Weller,65 who in 1908 found that the thiourea... 

A very useful preparation of 1,3,5-thiadiazine type rings involves the report of Goerdeler and Ludke167 that 154 undergoes reaction with phenyl isocyanate to give 162 (X = Ph, Y = 0) and with carbodi-imides to give 162 (X = R, Y = NR ). Other compounds 163 may be prepared by treatment of 154 with benzaldehyde imines,167 a process which was also recently utilized by Kristian et al.3oa... 

Less useful preparations of 1,3,5-thiadiazines in which they are formed as components of mixtures include that of Chase and Walker.262 They isolated a thiadiazine as a product of the reaction of thiourea, bromine, and p-chlorophenylacetonitrile in acetone. The function of the nitrile, which was not incorporated into the product, is not apparent. The product of a similar reaction, without the nitrile, was assigned a dithiazine structure by Baumann.304 Oliver and Stokes202 also reported that a 1,3,5-thiadiazine is formed among the myriad of identified products of the 15-month air oxidation of l,l,5,5-tetramethyl-2,4-dithiobiuret. 

The 8ir-electron anions derived from 1,3,5-oxadiazines (30) (75AG(E)581) are unstable and readily ring contract to give imidazolones (141 Scheme 9). The related anions from 1,3,5-thiadiazines (100 Scheme 1) also ring contract to give imidazoles in high yield... 

The heating of 4-o-tolyl-l,3-dithia-2,5-diazolium hexafluoroarsenate 154 with a small excess of o-tolylcyanide 155 in liquid S02 leads to 1,2,4-dithiazolium hexafluoroarsenate 6 in low yield (Equation 24) <1996AXC2148>. The decomposition of the known pesticide, 3,5-dirncthyltctrahydro-2//-1,3,5-thiadiazine-2-thione 156 (DTTT), in water and in salt solutions was studied in detail. 4-Methyl-5-methylimino-l,2,4-dithiazolidine-3-thione 157 and 2,4-dimethyl-l,2,4-thiadiazolidine-3,5-dithione 158 were isolated by HPLC and identified among the noncyclic decomposition products (Equation 25) <1996MI503>. 

The desilylation of 3,5-diaryl-1,2,4-thiadiazolium salts 740 with CsF results in ring expansion to afford substituted 2/7-1,3,5-thiadiazines 741 in moderate yield (Scheme 319) <1999J(P1)1709, CHEC-III(9.09.10.2)514>. 

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