Intramolecular palladium(II)-catalyzed 1,2-addition to allenes

Palladium(II)-catalyzed intramolecular 1,2-additions to allenes substituted with an internal nucleophile have been developed. Carboxylic acids, alcoho ls, N-substituted amides, and carbamates were used as internal nucleophiles in the palladium-catalyzed reaction, which afforded lactones, tetrahydropy rans, tetrahydrofurans, pyrrolidines, and oxazolidinones in good isolated y ields. The reactions were performed in the presence of LiBr with Pd(OAc)(2) as the catalyst. Two different reoxidants, p-benzoquinone or Cu(OAc)(2), w ere used, the choice of oxidant being dependent on the substrate. The react ion proceeds through an external nucleophilic attack (Br-) on a (pi -allene )palladium complex to produce a (pi -allyl)palladium intermediate. Subseque nt intramolecular attack by the second internal nucleophile gives the produ ct. The intermediate (pi -allyl)palladium complexes were isolated and chara cterized. The scope and limitation of the reaction were studied together wi th its mechanism and selectivity, under different reaction conditions.