Pyrazoles A-alkylation

Deprotonation can occur at the -GH of pyrazole A-alkyl groups for example 1-methylpyrazole with -BuLi. Such proton loss is facilitated in cationic azido rings, and the ylides so formed sometimes undergo rearrangement. Thus, quaternized 1,2-benzisoxazoles 796 lose a proton and then rearrange to 1,3-benzoxazines, e.g., 797. Quaternized derivatives of benzofuroxan formed in situ undergo rearrangement to 1-hydroxybenzimidazole A-oxides 798. Reactions of this type are also known for A-alkylazolinones. 

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