Palladium-Catalyzed Intramolecular Hydroamination of Allenes Coupled to Aerobic Alcohol Oxidation

摘要

The direct addition of a nitrogenChydrogen bond across an unsaturated carbonCcarbon bond (hydroamination) is a powerful strategy to generate nitrogenCcarbon bonds and an effective way to synthesize biologically active nitrogen-containing heterocycles.[1] The development of catalyst systems for this type of transformation has been extensively studied. Although lanthanides[2] and Group IV transition metals[3] are among the most reactive catalyst systems, the synthetic utility of these protocols is compromised by the poor functional group compatibility and excessive air and moisture sensitivity. In contrast, late transition metals have been shown to have better tolerance. For instance, some late transition metals catalyze the addition of amines to vinylarenes;[ 4] the catalysis of the addition of amides and sulfonamides to alkenes, allenes, and dienes[5, 6] has also been reported recently. Most late-transition-metal-catalyzed hydroaminations require the use of phosphine ligands, and, hence, are not compatible with aerobic reaction conditions owing to rapid degradation of phosphine ligands. On the other hand, nitrogen-containing ligands, which are generally stable under oxidative reaction conditions,[7] have rarely been used in hydroamination reactions.[8] Herein, we report the first PdII-catalyzed intramolecular hydroamination of allenes under a dioxygen atmosphere, in which bathocuproine[9] is used as the ligand.