Acid strength nitroalkanes

Primary nitro compounds, on base addition, can undergo reactions with dipolarophiles to isoxazole derivatives with loss of water (henceforth called condensations ) only if their acid strength is high enough a screening of many primary nitro compounds indicates that condensation occurs when pATa is lower than 7 (see Table 3 in Ref. [63] and Table 2 in Ref [64]), whereas nitroalkanes carmotbe condensed in these conditions. Those compounds will be indicated hereinafter as active nitro compounds, which include compounds of the type X-CH2-NO2, where X is an EWG as in nitroacetic esters or amides, or in a-nitroketones, or nitroacetonitrile, etc. even phenylnitromethane (pXa 6.8) undergoes condensation with dipolarophiles. However, without addition of a base, condensations in most cases are not observed. 

---