1.2.3- Benzotriazin-4 -ones thermal decomposition

Thermal decomposition of 3-arylidenamino- (91) and 3-imidoyl-l,2,3-benzotriazin-4-ones (93) in solution gives 2-aryl- (92) and 2,3-diaryl-quinazolin-4( 177)-ones (94) respectively (80JCS(Pl)633,75S187,75S709). In the latter decomposition phenanthridinones (95) are also formed in minor yields. Mechanisms to account for the isolated products were discussed. 3 -Amino-l,2,3-benzotriazin-4-ones (96) in boiling 1-methylnaphthalene yield in all cases... 

Arylideneamino)-l,2,3-benzotriazin-4-ones 1 undergo thermal decomposition on heating in an inert medium (e.g., paraffin oil) to give the isomeric 2-arylquinazolin-4(3//)-ones 2 in preparative yields. 

Smalley and co-workers obtained the pyrido[2,l- i]quinazolin-l l-one 286 through the thermal decomposition of 3-(2-pyridyl)-1,2,3-benzotriazin-4-one (284) in 1-methylnaphthalene. The pyrido[2,l-i]quinazolinone 286 probably arises from the benzazetinone-iminoketene intermediate 285. Photodecomposition of the benzotriazinone 284 in tetrahydrofuran was very slow. Irradiation for 72 hr furnished the pyridoquinazolinone 286 in less than 5% yield along with the unchanged benzotriazinone 284. 

Thermal decomposition of 3-alkenyl-l,2,3-benzotriazin-4(3/f)-ones leads to 3-substituted quinolin-4(3/f)-ones in reasonable yields.314... 

The thermal decomposition of solid l-methyl-l,4-dihydro-l,2,3-benzotriazin-4-one 59 at >120°C in a stream of argon results in ready loss of N2 with ring contraction to the benzazetinone 60 (Equation 6), which was identified by matrix isolation at 15 K (IR C=0 at 1843 cm ). Irradiation of 60 results in photoreversible ring opening to the iminoketene 61, characterized by an IR band at 2125 cm and a UV absorption centered at 420 nm <1989CC1777>. 

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