Phthalazinium-1-olates

Deprotonation of 7-hydroxypyrido[2,l-a]phthalazinium perchlorate with NEt3 in ethanol gave pyrido[2,l-a]phthalazinium-7-olate (20) (92CB929). 4-Hydroxy-2-phenyl and 2-hydroxy-4-phenylpyrido[l,2-6]pyridazinium perchlorates with aqueous KOH afforded 73 and 75 (90JHC1673). 

N-methyl 78 and 7-methoxy derivatives 79, whereas dimethyl sulfate and tri-methyloxonium tetrafluoroborate gave only the 7-methoxy derivative 79 (92CB929). Although the 11-methoxy derivative 77 could be rearranged to the A-methyl derivative 43 by heating in a mixture of toluene and DMF for 17 h in the presence of a small amount of pyrido[l,2-h]cinnolinium-ll-olate (17, R = H), no isomerization to the A-methyl derivative 78 occurred when the 7-methoxy compound 79 was heated in the presence of pyrido[2,l-a] phthalazinium-7-olate (20) (92CB929). 

Examples of phthalazinium-l-olates (196) were first prepared in 1926 by Rowe" and co-workers using the sequence shown in Scheme 8. Subsequent... 

Like isoconjugate mesomeric betaines, which have been discussed in preceding sections, phthalazinium-l-olates (196) give 1,3-dipolar adducts with acetylenes. Thermally induced isomerization reactions of these adducts (255) make them of special interest. The A-methyl derivative and diphenyl-... 

Phthalazinium-l-olates (196) are stable, yellow or colorless crystalline compounds that undergo an interesting variety of reactions. Reduction of aryl derivatives with zinc and dilute hydrochloric acid gives phthalimidines (210) whereas reduction with alkaline sodium hyposulfite gives 3-aryl-3,4-dihydro-1 (2f/)-phthalazinones (2H). 3-Methylphthal-... 

Phthalazine 4-Hydroxy-l-methyl-E9a, 751 (2-Acetyl-benzoesaure/ N2H4), 756 (l,2-H2-Der./Oxid.) Phthalazinium-l-olate 3-Methyl-E9a, 785 (OT -+ O or N-Methylamino-phthalimid/ NaBH4)... 

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