4-Ethynyl-l,3-dimethylpyrazole

In 1973, the unexpected transformation of 4-chloroethynyl-l,3,5-trimethylpy-razole under the action of sodium amide in liquid ammonia into 5-aminomethyl-4-ethynyl-l,3-dimethylpyrazole in 85% yield was reported (73IZV2166). Within... 

From 4-chloroethynyl-l,3-dimethylpyrazole 80% of 4-ethynyl-5-chloro-l,3-dimethylpyrazole was obtained. There is simultaneous formation of about 10% of 4-ethynyl-l,3-dimethylpyrazole (76IZV2148 77IZV2306) (Scheme 106). 

Cross-coupling of 5-ethynyl-4-chloro-l,3-dimethylpyrazole with 3-iodo-4-chloronitrobenzene was carried out in the presence of (PPh3)2PdCl2, Cul, and EtjN (66%) (96MC98) (Scheme 69). 

Attempts were made to perform heterocyclization with 4-phenylethynyl- and 4-ethynyl-5-aminomethyl-l,3-dimethylpyrazole where, on the one side, a strained six-membered ring can be formed, and, on the other side, the aliphatic amino group is more nucleophilic than the aromatic (Scheme 112). However, all attempts to cyclize the ethynylpyrazole and its phenyl analog failed (86TH1). 

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