90418-03-4Relevant articles and documents
Photochemistry of phenyl-substituted 1,2,4-thiadiazoles. 15N-labeling studies
Pavlik, James W.,Changtong, Chuchawin,Vikki
, p. 4855 - 4861 (2003)
Irradiation of 5-phenyl-1,2,4-thiadiazole (6) resulted in the formation of benzonitrile (5), 3-phenyl-1,2,4-thiadiazole (4), phenyl- and diphenyl-1,3,5-triazines (7 and 8), and a trace quantity of diphenyl-1,2,4-thiadiazole (9). The formation of 4, 5, 7, and 8 can be explained in terms of photoinduced electrocyclic ring closure resulting in the formation of an intermediate 4-phenyl-1,3-diaza-5-thiabicyclo[2.1.0]pentene. 15N-labeling experiments revealed that sulfur can undergo sigmatropic shifts around all four sides of the diazetine ring. Thus, irradiation of 6-4-15N led to the formation of 6-2-15N and an equimolar mixture of 4-2-15N and 4-4-15N. The thiabicyclo[2.1.0]pentene intermediate is also suggested to undergo sulfur elimination resulting in the formation of phenyldiazacyclobutadiene, which can undergo complete fragmentation to benzonitrile or [4+2] cycloaddition leading to unstable tricyclic adducts, the suggested precursors of the 1,3,5-triazine products 7 and 8. The observed 15N distribution in 7 and 8 is consistent with this mechanism. Irradiation of 4 led only to the formation of 5. 15N-labeling experiments show that 4 does not undergo electrocyclic ring closure but reacts exclusively by photofragmentation of the thiadiazole ring.
Photoinduced molecular rearrangements. The photochemistry of 1,2,4-oxadiazoles in the presence of sulphur nucleophiles. Synthesis of 1,2,4-thiadiazoles
Vivona, Nicolo,Buscemi, Silvestre,Asta, Stefano,Caronna, Tullio
, p. 12629 - 12636 (2007/10/03)
The photochemistry of some 1,2,4-oxadiazoles in the presence of sulphur nucleophiles has been investigated. Irradiation of the 5-amino-3-phenyl- and 3,5-diphenyl-1,2,4-oxadiazole at λ = 254 nm in methanol in the presence of sodium hydrogen sulphide or thiols gave a photo-induced redox reaction at the ring O-N bond, leading to the corresponding N-substituted benzamidines. By contrast, irradiation of the 5-amino-3-phenyl-1,2,4-oxadiazole in the presence of thioureas or thiocarbamates, essentially gave 3-phenyl-5-substituted 1,2,4-thiadiazoles, which presume an N-S bond formation between the ring-photolytic species and the sulphur nucleophile. In turn, irradiation of the same 5-amino-3-phenyl-1,2,4-oxadiazole in the presence of thioamides again afforded the redox reaction; in addition, amounts of 3-phenyl-5-substituted-1,2,4-thiadiazoles were also formed. Some mechanistic considerations are reported and synthetic methodologies leading to 1,2,4-thiadiazoles are emphasized.
