2-Aminopyrazoles, methylation with diazomethane

Adembri et al. (72JHC1219) (Scheme 15) demonstrated the existence of a tautomeric mixture of 2-aminopyrazol-3-ones 47a-c/2-aminopyrazoles 48a-c in diethyl ether by methylation with diazomethane. The products were 2-amino-1-methylpyrazol-3-one 49a-c and 2-amino-3-methoxypyrazole 50a-c, respectively. 

Since 1,3-dipolar cycloadditions of diazomethane are HOMO (diazomethane)-LUMO (dipolarophile) controlled, enamines and ynamines with their high LUMO energies do not react (79JA3647). However, introduction of carbonyl functions into diazomethane makes the reaction feasible in these cases. Thus methyl diazoacetate and 1-diethylaminopropyne furnished the aminopyrazole (620) in high yield. 

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See also in sourсe #XX -- [ ]

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