Selective ring closure to substituted pyrido[1,2-b]-as-triazinium salt

✍ Scribed by György Hajós; Zsuzsanna Riedl; Eszter Gács-Baitz; Messmer András

• Book ID: 104204108
• Publisher: Elsevier Science
• Year: 1992
• Tongue: French
• Weight: 405 KB
• Volume: 48
• Category: Article
• ISSN: 0040-4020
• DOI: 10.1016/s0040-4020(01)86594-7

✦ Synopsis

Absb~& Reaction of arylglycxal with 1,2-diaminopyridinium salt 1 under acidic conditions afforded 2-arylpyiido[l,2-b]-as-triazinium salt 9 selectively, whereas cyclization of the same dioxo compound with l-amino-2iminopyridine 5 under neutral conditions -due to "umpolung" of the exo nitrogen atom -led exclusively to the 3-aryl isomer 8.

In the course of our extended research on fused 1,2,4-triaxinesl we became interested in the synthesis of the pyrido[ 1,Zb]-as-triaxinium ring system 3. Survey of the pertinent literature showed, interestingly, that fairly little has been published2 in this area. The first synthesis was descriid by Kost et a1.3,4; these authors reported that 1,Zdiaminopyridinium salt 1 when reacted with different cy-dioxo compounds 2 in acidic media afforded the fused pyridotriazinium salt 3 in good yields. These authors claimed, furthermore, that unsymmetrically substituted adioxo compounds (e.g. phenylgiyoxal: 2, R'=Ph; R"= H) gave selectively the Zsubstituted product (3, R'=Ph; R"=H) which was found to be identical with the reaction product obtained from l-amino-24minopyridine 5 and phenacyl bromide.