PHOTOINDUCED MOLECULAR-REARRANGEMENTS - THE PHOTOCHEMISTRY OF 1,2,4-OXADIAZOLES IN THE PRESENCE OF SULFUR NUCLEOPHILES - SYNTHESIS OF 1,2,4-THIADIAZOLES
N. Vivona et al., PHOTOINDUCED MOLECULAR-REARRANGEMENTS - THE PHOTOCHEMISTRY OF 1,2,4-OXADIAZOLES IN THE PRESENCE OF SULFUR NUCLEOPHILES - SYNTHESIS OF 1,2,4-THIADIAZOLES, Tetrahedron, 53(37), 1997, pp. 12629-12636
The photochemistry of some 1,2,4-oxadiazoles in the presence of sulphu
r nucleophiles has been investigated. Irradiation of the 5-amino-3-phe
nyl- and 3,5-dipbenyl-1,2,4-oxadiazole at lambda = 254 nm in methanol
in the presence of sodium hydrogen sulphide or thiols gave a photo-ind
uced 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 thiocarbamate
s, essentially gave 3-phenyl-5-substituted 1,2,4-thiadiazoles, which p
resume an N-S bond formation between the ring-photolytic species and t
he sulphur nucleophile. In turn, irradiation of the same 5-amino-3-phe
nyl-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-t
hiadiazoles were also formed. Some mechanistic considerations are repo
rted and synthetic methodologies leading to 1,2,4-thiadiazoles are emp
hasized. (C) 1997 Elsevier Science Ltd.