DDQ (2,3-dichloro-5,6-dicyano-1,4-benzoquinone) is one of the most frequently used reagents to perform several organic transformations such as dehydrogenation or oxidation of allylic and benzylic alcohols. DDQ also has been used for the deprotection of several protecting groups from alcohols such as allyl, p-methoxybenzyl (PMB), and dimethoxy benzyl (DMB) groups. Recently, we reported the synthesis of polysubstituted pyrazoles and oxidation of the pyrazoles into indazoles by DDQ oxidation. During the oxidation of pyrazole 1a with DDQ, we observed an interesting regioselective formation of 2a (58%) by the moisture in the reaction medium (Scheme 1). In the reaction we could not find other regioisomeric alcohol derivatives. Intrigued by the selective formation of 2a we intended to examine the selective oxidation of pyrazole derivatives with DDQ. In order to increase the yields of oxygenated products we used carboxylic acids and wish to report herein the results. For the mechanism of DDQ oxidations, initial rate determining hydride abstraction by DDQ from the substrate to form the carbocation intermediate is generally accepted. Following proton transfer from the carbocation leading to hydroquinone formation is a rapid process. Thus, dehydrogenation is dependent upon the degree of stabilization of the incipient carbocation and is enhanced by the presence of functionality capable of stabilizing the transition state. The carbon atom of the carbocation (I) is positioned at the α-position of an enamine-like moiety of pyrazole ring, while the carbon atom of the carbocation (II) is positioned nearby the electron-withdrawing imine functionality (Scheme 1). In addition, carbocation (I) can be stabilized further by the resonance effect of the phenyl group at the 3-position of pyrazole ring. Thus, when we consider the resonance stabilization effects, selective formation of carbocation (I) and 2a, as a result, could be easily understood. In order to examine the generality of this selectivity we examined the oxidation of pyrazoles 1a-d with DDQ in the presence of carboxylic acid as the carbocation quencher. As expected pyrazole 1a was transformed into 2b (62%) with acetic acid (Scheme 1 and entry 1 in Table 1). We did not detect nor isolate the other possible regioisomer. This was true for most of the other cases as shown in Table 1 (entries 2-5) irrespective of the kinds of carboxylic acids. However, when we carried out the reaction with 1d, we obtained 2g' as the major product instead of 2g (entry 6). The two compounds 2g and 2g' were very difficult to separate and we determined the ratios (2g/2g' = 1 : 4) based on H NMR spectrum of the mixtures (see, Experimental section). With propionic acid and 1d, we obtained a mixtures of 2h and 2h' in a ratio of 1 : 12 (entry 7). Fortunately, the major isomer 2h' could be isolated in pure state after determination of the ratios in this case. The results can be easily explained when