Pyrazoles, synthesis from oximes

Synthesis of some pyrazole derivatives from amidoximes was reviewed by Karbonits and Horvath. It has been shown that acrylophenone or methacrylophenone oximes (110) on treatment with BuONO in the presence of pyridine and copper(II) sulfate, and with subsequent interaction with dilute NaOH and acidification, gives 3(5)-phenyl-1-hydroxypyrazole 2-oxide or 4-methyl-3(5)-phenyl-l-hydroxypyrazole 2-oxide (111), respectively (equation 47) ... 

The creation of the N—N bond as the last step of the ring synthesis is common in indazoles and very rare in pyrazoles. In indazoles this method is well known (type B synthesis (67HC(22)l), for example, the dehydration of oximes (570) with acetic anhydride yields 1-acetylindazoles (571), and in basic medium the indazole 1-oxides (573) are formed from the nitro derivatives (572). 

The concept of the use of dilithio reagents for the preparation of heterocyclic systems has been extended to the synthesis of 2-isoxazolin--5-ones10 by carboxylation of a dilithio oxime, followed by eyolin-zation, and the synthesis of pyrazoles from dilithiophenylhydrazones and trilithiothiohydrazones.11 12... 

The nitrosation of oximes can also serve to produce N-hydroxy-N-nitrosamines (Scheme 3.9). The acidified nitrite procedure can be applied to oximes derived from terpenes [132] and hydroxyguanidine [133] for the synthesis of N-hydroxy-N-nitrosamines. However, some a, 5-uri saturated oximes were converted into pyrazole-1,2-dioxides [134]. The alkyl nitrites under basic conditions have produced interesting results. Quinone dioximes yielded only monodiazeniumdiolates [135], while simple aliphatic oximes gave products resulting from addition to the imine double bond... 

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