Photochemistry of some heterocyclic systems

Abstract

Whereas 2H-benztriazoles are photochemically stable, 1 H-benztriazoles yield biradicals after splitting ofT nitrogen. These biradicals attack aromatic substratessuch as anisole, toluene, fluorobenzene or benzonitrile preferentially in the o-and p-positions with formation of the corresponding o-amino biphenyls (cf. schemes 2-5). With a deficiency of aromatic substrate, attack at the o-

A Review on the Photochemistry of 2H-Azirines

“…4,5 As explained subsequently, the react i o n of the 2H-azirines i s characterized by a photochemical cleavage of the C(2), C(3)-bond and formation of highly r e a c t i v e d i p o l a r intermediates of the benzonitrilio-methanides 2 type.…”

Photochemical and thermal reactions of some heterocycles containing C=N-O or N=C-O group

“…1. ~rve a is the uv spectrum of (11) and Cürve b that after irradiation with light of '!68 -272nm for a short time where only-17% of (11) has been converted to intermediate (A) having .max at 266nm, and curve c-that after heating of b at 80°, It is äpparent that curve c is a summatTon of curve a and d, the-latter being due to (12) These changes show the exsistence of Tntermediate (A) which 1s thermal!Y converted to (11:). Fig.…”

“…While irradiation of-rll) at -78° or -196° gives no 1,3-oxazepine (12), the yields of (12) increase as the temperature is raised. The evidence substantiates thar-a thermal process intervenes in the path from (11) to (17) and from C.!..Z) to (g_) .…”

“…14 ) • However, on prolonged photolysis of (11) . using light of >290 nm, the yields of (12) decrease and 3-phenyl-2-oxa-4-aii'bicyclo[3.2.0]heptadiene (13) and two ärdehydes (15) and (16) In order to identify the precursor leading to (12) , th.e change of the uv spectrum of (11) is monitored, as shown in Fig. 1.…”

“…Upon heating at 40-50° or irradiation with light of 300nm, (17) produces 2-phenyl-1,3-oxazepine (12) in excellent yields. Although another-example of the thermal transformation of Z-azirinylacrolein into 1,3-oxazepine was also discovered re~ently by Le ~oux (ref.…”