Wykorzystanie kompleksów palladu w syntezie związków heterocyklicznych

Heterocyclic compounds focus an attention for many reasons. Many of them are biologically active compounds, natural products, drugs, synthetic materials and practically useful chemicals [1-5]. Therefore, organic chemists have been making extensive efforts to produce these heterocyclic compounds by developing new and efficient synthetic transformations. Among a variety of new synthetic transformations, transition-metal-catalyzed reactions are very attractive methodologies for synthesis of heterocyclic compounds, since they permit to construct complicated molecules directly from readily accessible starting materials under mild conditions. For this purpose palladium is one of the most widely used transition metals mainly due to the mild reaction conditions used, high yields, a tolerance of a large variety of functional groups, and high regio-, stereo- and enantioselectivity observed [6]. Pd^0-catalyzed allylic alkylations and Pd^II-catalyzed oxidative cyclization of hydroksy(amino)alkene(alkyne)nucleophiles in the intermolecular mode have been particularly notable in this area due to their ability to elicit control in the aforementioned areas, often under very mild conditions. Pd^0-catalyzed intra- or intermolecular heteroannulation through allylic alkylation, the so-called Tsuji-Trost reaction, generally employs allylic acetates [9-14], carbonates [15-29] or vinyl epoxides [30-34] bearing a hydroxy or an amino group as the substrates. Allylsilanes have also been used as precursors of the ?3-allyl intermediates, starting from PdCl2 and CuCl2, affording the corresponding THF and THP derivatives in quite good yields [38-40]. The PdII-catalyzed cyclization of alkenyl alcohols has led to cyclic enols by ?-hydride elimination, or to oxygen heterocycles bearing a vinyl group through a ?-hydroxy elimination, if the alkenol possesses an allyl alcohol moiety. Using this methodology a large variety of oxygen- or nitrogen-containing heterocycles have been obtained even in an asymmetric fashion [51-95].