PHOTOINDUCED MOLECULAR-REARRANGEMENTS - THE PHOTOCHEMISTRY OF SOME 1,2,4-OXADIAZOLES IN THE PRESENCE OF NITROGEN NUCLEOPHILES - FORMATION OF 1,2,4-TRIAZOLES, INDAZOLES, AND BENZIMIDAZOLES
S. Buscemi et al., PHOTOINDUCED MOLECULAR-REARRANGEMENTS - THE PHOTOCHEMISTRY OF SOME 1,2,4-OXADIAZOLES IN THE PRESENCE OF NITROGEN NUCLEOPHILES - FORMATION OF 1,2,4-TRIAZOLES, INDAZOLES, AND BENZIMIDAZOLES, Journal of organic chemistry, 61(24), 1996, pp. 8397-8401
The photochemistry of some 3,5-disubstituted 1,2,4-oxadiazoles in the
presence of nitrogen nucleophiles [external, such as added amines or h
ydrazines, or internal, such as an o-aminophenyl moiety at C(3) of the
oxadiazole ring] has been investigated. In the irradiation of 5-amino
-(or 5-N-substituted amino) 3-phenyl-1,2,4-oxadiazoles in the presence
of aliphatic primary amines (or ammonia), photolytic species arising
from heterolytic cleavage of the ring O-N bond capture the nucleophili
c reagent to give open-chain intermediates, which develop into 1,2,4-t
riazolin-5-ones. Similarly, irradiations of 3,5-diphenyl-, 3-methoxy-5
-phenyl-, and 5-methyl-3-phenyl-1,2,4-oxadiazoles gave 1,2,4-triazoles
. In the same context, irradiations of representative substrates in th
e presence of hydrazines have been also investigated. In the irradiati
on of 3-(o-aminophenyl)-5-methyl-, 3-[o-(methylamino)phenyl]-5-methyl-
, and 3-(o-aminophenyl)-5-phenyl-1,2,4-oxadiazoles, concomitant format
ion of indazoles and benzimidazoles, presumably arising from a common
photolytic species, has been observed. Some mechanistic aspects have b
een considered, and possible applications in synthesis have been point
ed out.