3 iodopyrazoles, coupling

A similar phenomenon was observed for 3-amino- and5-amino-4-iodopyrazoles. The anomalous reaction in which the products of oxidative coupling of terminal acetylenes (up to 90%) are present along with the products of deiodination (up to 90%) has been described for the first time [99JCS(P1 )3713] and will be considered below in the part related to cross-coupling of 4-iodopyrazoles. 

Amino-4-iodopyrazoles demonstrate the lower reactivity of the iodine atom in halogenopyrazoles. Todopyrazoles 36 and 37 were coupled with p-nitrophenylace-tylene in EtsN in the presence of Pd(PPh3)2Cl2 and Cul at 80°C to give good yields of the A-acetyl 4-alkynylpyrazoles (Scheme 49). 

However, attempts to couple (A-acetyl)-4-iodopyrazole 36 under the same conditions withphenylacetylene,p-methoxyphenylacetylene, andoct-l-yne, once again, were unsuccessful, instead, reductive deiodination to give 5-(iV-acetylamino)-3-methyl-l-ethylpyrazole and homo-coupling of alk-l-yne occurred (Scheme 49). The isomeric 3-(A-acetylamino)pyrazole 37 was somewhat less inclined to deiodination. 

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