An expedient general synthesis of pyrrolo[3,2-e]indazoles: domino Sonogashira/Cacchi coupling-heteroannulation reactions (original) (raw)
A one-pot Sonogashira coupling-heteroannulation of 4-iodo-1-phenylsulfonyl-5-trifluoroacetamidoindazole with terminal acetylenes using bis(triphenylphosphine)palladium(II) dichloride as the catalyst, cuprous iodide as the co-catalyst and triethylamine as the base in DMF furnished, after N(3)-deprotection, 7-H/substituted 3,6-dihydropyrrolo[3,2-e]indazoles in high yields. This is the first general synthesis of pyrrolo[3,2-e]indazoles. Uncatalyzed hydrodesilylation was observed during reaction with trimethylsilylacetylene, leading to the 7unsubstituted parent pyrrolo[3,2-e]indazole.
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