Spectrométrie de Masse de Pyrazoline‐5‐Ones N₁ Substituées. 1. 5‐AlkoXypyrazoles et 3‐Pyrazoline‐5‐Ones A Structures Fixes

Abstract

S U M M A R Y . T h e m a s s s p e c t r a o f f i x e d p y r a z o l i n -5 -o n e s ( 5 -a l k o x y p y r a z o l e s a n d 3 -p y r az o l i n -5 -o n e s ) a r e r e p o r t e d a n d d i s c u s s e d . M a s s s p e c t r o m e t r y a l l o w s c h a r a c t e r iz a t i o n of t h e s e t w o i s o m e r i c s t r u c t u r e s .

An Improved Preparation of 3-Alkoxypyrazoles

“…As shown in Scheme 3, a similar yield in- crease was also observed when reacting 1.05 equivalents of methylhydrazine monohydrochloride with isopropyl acetoacetate (9c) as the corresponding 5-isopropoxy-1,3dimethyl-1H-pyrazole (11) was obtained in 69% yield instead of the previously reported 30%. 13 The regioselectivity of this reaction, which corresponds to the reported examples, 7,13 was determined by 13 C-1 H long distance correlations.…”

“…This result was obtained by reacting hydrazine with 1 in the presence of two equivalents of hydrochloride acid in boiling alcohol; 6 remarkably few reports followed these early studies. [7][8][9][10][11][12][13][14][15][16] This is quite surprising as O-protected pyrazoles, such as compound 4, could be starting materials for many syntheses aimed at selective reactions either on N1 or C4. Another possible synthesis of 3-alkoxypyrazoles is by the alkylation of the corresponding pyrazol-3-ones.…”