Using l-Alkyl-2-halogenoformylbenzenes as Substrates

This type of cyclocondensation affords a 3,4-dihydro-l(27/)-phthalazinone as illustrated in the reaction of 2-bromomethyl-5-nitrobenzoyl chloride (37) with A, A -diacetylhydrazine to give 2,3-diacetyl-7-nitro-3,4-dihydro-l(277)-phthalazi-none (38, R = Ac) [(—HNAc)2, NaH, dioxane, 85°C, 1 h then substrate/ 15°C — 85°C, 1 h 37%] and thence 7-nitro-3,4-dihydro-l(27/)-phthalazinone (38, R = H) (lOM HCl, 20°C, 5h -50%)/  

Such substrates are usually phthalaldehydes. These give aromatic phthalazines with hydrazine but (partially reduced) phthalazinols with substituted hydrazines, as illustrated in the following examples. 

5-Dimethoxyphthalaldehyde (39, Q = R=OMe) gave 6,7-dimethoxyphthala-zine (40, Q = R = OMe) (substrate, EtOH, warm H2NNH2 H2OJ, dropwise then reflux, 5 h 93%).  

Phthalaldehyde (39, Q = R = H) gave 2-phenyl-1,2-dihydro-1-phthalazinol (41) (PhNHNH2 HCl, H2O, reflux, 2h 96%) and thence frtiMj-2,2 -diphenyl-l,l -bi(l,2-dihydrophthalazin-l-ylidene) (42) (AcOH, MeCN, reflux, 2h good yield ) analogs were made similarly and the structure of trarti-2,2 -di-p-bromophenyl-1,1 -bi( 1,2-dihydrophthalazin-1 -ylidene) was 

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