Synthesis of Medium-Ring Nitrogen Heterocycles via Palladium-Catalyzed Heteroannulation of 1,2-Dienes.
Seven-, eight-, and nine-membered-ring nitrogen heterocycles are readily prepared by the palladium-catalyzed heteroannulation of a variety of 1,2-dienes by a range of tosylamide- and amine-containing aryl and vinylic halides. The ease of ring formation is seven > eight > nine, and better results are obtained using aryl halides, rather than vinylic halides, and tosylamide functionality, rather than amine functionality. The reaction is suggested to proceed by the formation and addition of an aryl or vinylic palladium compound to the allene to generate a pi-allylpalladium intermediate, which subsequently undergoes nucleophilic displacement of palladium at the less hindered end of the pi-allyl system.
Larock
Richard C.
RC
Department of Chemistry, Iowa State University, Ames, Iowa 50011.
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Pace
Paola
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