Pd^II触媒を用いる分子内不斉転写反応の立体化学と合成的応用

抄録

Oxypalladation is an attractive reaction to introduce an oxygen functionality to alkene. This review focuses on the recent development of stereocontrolled THP and THF ring formations by intramolecular oxypalladation reaction. Chiral THP and THF rings are constructed by Pd^II-catalyzed O-C bond forming reaction with 1,3-chirality transfer of chiral allylic alcohol. Examples of the stereoselective synthesis of these rings from chiral allylic alcohols are described. The origin of stereoselectivity of the chirality transfer is discussed and we propose that the reaction proceeds in the following sequences, i) formation of Pd^II-π-complex by syn-coordination of Pd^II-catalyst directed by chiral hydroxy group, ii) hydroxyl ligand exchange with nucleophilic hydroxyl group, iii) syn-oxypalladation, and iv) syn-elimination of the resulted σ-Pd-complex with the adjacent hydroxyl group.
THP and THF rings are often found in the core structure of many natural products and these natural products exhibit often a diverse range of biological activities. Some examples for the total synthesis of natural products achieved in our laboratory are described, in which Pd^II-catalyzed THP and DHP ring formations are demonstrated for the synthesis of (−)-diospongins, (−)-aspergillide B, (−)-laulimalide, and (−)-apicularen A.