4-Phenyl-3 -phenylethynylpyrazole

Note that 1,4-substituted butadiynes with diazomethane can form two isomers. Kuznetsov and co-workers have considered this problem in detail and established that diphenyldiacetylene with diazomethane forms, in standard conditions (ether, 0°C, 9 days), only one of the two possible regioisomers 4-phenyl-3(5)-phenylethynylpyrazole (yield 86%) (93ZOB1107). The cyclization of derivatives of phenoxy-2,4-hexadiyn-6-oles with diazomethane leads to only one isomer of alkynylpyrazole (76MI1 77MI1) (Scheme 8). 

In the presenee of silver oxide andBFs-ethereomplex, 4-phenylethynylpyrazole forms only one isomer of the two possible ones, i.e., 2-phenyl-l-(4-pyrazolyl)etha-none in 72% yield (88M253) (Seheme 86). 

At the same time, the hydration of 3(5)-phenyl-5(3)-phenylethynylpyrazole 45 in sulfuric acid in the presence of mercury acetate leads to the formation of two isomeric ketones 46 (yield 44%) and 47 (yield 3%) (68LA117) (Scheme 88). 

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