Application of Organolithium and Related Reagents in Synthesis; Part 26.~1 Synthetic Strategies Based on Directed ortho-Metalation: Synthesis of 4-Methyl-2H-phthalazin-1-ones

摘要

The synthesis of 3-hydroxy-3-methylisoindolin-1-ones 10, masked ortho-acetylated derivatives of anilides, via metalation (BuLi) of the benzanilides 1 and subsequent reaction of the generated bis-lithiated anilides 2 with acetylating agents such as acetic anhydride or ethyl acetate were studied. The 3-hydroxy-3-methylisoindolin-1-ones 10 thus obtained are very sensitive towards dehydration process, which caused their conversion into enamides 11. Conversion of 3-hydroxy-3-methylisoindolin-1-ones 10 or enamides 11 into the corresponding 4-methyl-2H-phthalazin-1-ones 13 by treatment with hydrazine, as a way of regioselctive transformation of the benzoic acids, is also described.