A method for the catalytic C-H activation of hydrazone compounds followed by intramolecular amination is described. It requires the use of a catalytic amount of Pd(OAc)2 in the presence of Cu(OAc)2 and AgOCOCF3, which efficiently effects the cyclization to afford variously substituted indazoles. The reactions proceed under relatively mild conditions and thus tolerate a variety of functional groups, including alkoxycarbonyl and cyano groups and halogen atoms.
The efficient method for the preparation of 3-substituted indazoles was developed using the palladium catalyzed intramolecular amination reaction of 2-bromophenyl hydrazone derivatives. Good functional group compatibility was observed under mild reaction conditions and various 3-substituted indazoles were obtained in moderate to excellent yield.
Alkaloids U 0600Synthesis of 3-Substituted Indazoles and Benzoisoxazoles via Pd-Catalyzed Cyclization Reactions: Application to the Synthesis of Nigellicine. -Palladium-catalyzed intramolecular carbon-nitrogen and carbon-oxygen bond formation under very mild conditions allows the synthesis of title compounds (V) and (XIII). Derivative (Va) is converted into the natural product nigellicine (X). -(INAMOTO*, K.; KATSUNO, M.; YOSHINO, T.; ARAI, Y.; HIROYA, K.; SAKAMOTO, T.; Tetrahedron 63 (2007) 12, 2695-2711; Grad. Sch. Pharm. Sci., Tohoku Univ., Aoba, Sendai 980, Japan; Eng.) -Kieslich 28-178
A New Route to 3-Aryl/Alkylindazoles. -The reaction proceeds under very mild conditions and allows the presence of various functional groups in the aryl rings. An aliphatic analogue (XIV) is also prepared. -(INAMOTO*, K.; SAITO, T.; KATSUNO, M.; SAKAMOTO, T.; HIROYA, K.; Org. Lett. 9 (2007) 15, 2931-2934; Grad. Sch. Pharm. Sci., Tohoku Univ., Aoba, Sendai 980, Japan; Eng.) -R. Steudel 47-124
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