Pyrazolo tetrazin-5-ones

The reaction of thietan-3-one 46 with 1,2,4,5-tetrazines 47 gave 4i/-pyrazolo[5,l-c]thiazines 48 via a rare anti-Michael addition <06TL7893>. 

Since 1974 two publications have appeared dealing with the preparation of monocyclic 1,2,3,5-tetrazines (76BCJ1339, 79LA870). Beside these two articles, Ege and his group have published the synthesis of condensed 1,2,3,5-tetrazines such as pyrazolo[5,l-rf]-[l,2,3,5]tetrazin-4-ones (25) and l,2,3,5-tetrazino[5,4-6]indazol-4-ones (26) (79TL4253). 

The reaction of 2-(diphenylmethylene)thietan-3-one with 1,2,4,5-tetrazines in KOH-MeOH-THF gives 4//-pyrazolo[5,l-c]thiazines. This novel condensation reaction proceeds via the intermediacy of an 8-(diphenylmethylene)-2//-l,4,5-thiadiazocin-7(8H)-one, which undergoes a multi-step rearrangement including a rare anti-Michael addition.30... 

Pyrazolo[5,l-d][l,2,3,5]tetrazin-4-ones synthesis, 3, 535 Pyrazolo[ 1,5-d]tetrazole structure, S, 263... 

Derivatives of pyrazolo[l,2-a]benzo[l,2,3,4]tetrazin-5-ones 66 designed as novel alkylating agents have been synthesized and showed antiproliferative activity <05JMC2859>. Reactions of 2-diazoindoles with alkyl or aryl isocyanates afforded derivatives of the new ring system [l,2,3,5]tetrazino[5,4-a]indole 67, some of which showed antiproliferative activity <05BMC295>... 

The pyrazolo[5,l-f,]-l,2,3,5-tetrazin-4(3//)-one 12 is stable in concentrated sulfuric acid at room temperature but gives the triazene 13 when treated with morpholine.36... 

---