Retro-ene reactions. III. Alkylation of 4,5-dichloro-1-hydroxymethylpyridazin-6-ones: Synthesis of 4,5-dichloro-1-(ω-phthalimido and saccharin-2′-ylalkyl)pyridazin-6-ones

4,5-Dichloro-1-(ω-phthalimido and saccharinyl-2′-ylalkyl)pyridazin-6-ones were synthesized from 4,5-dichloro-1-hydroxymethylpyridazin-6-one and the corresponding N-(ω-haloalkyl)phthalimides and saccharins via a fragmentation of retro-ene type.