Further Studies on Total Synthesis of Sarain A. Efforts Toward Annulation of the Macrocyclic Rings

Studies have been conducted on testing strategies for annulation of the two macrocyclic rings onto the central tricyclic nucleus of sarain A (1). In particular, methodology has been developed for introduction into the core of C-3‘ and C-3 substituents, which are necessary for construction of the “eastern” and “western” macrocyclic rings of 1, respectively. Formation of the western ring has been successfully addressed via a ring-closing olefin metathesis strategy utilizing the Grubbs ruthenium catalyst. With this macrocyclization approach, a key intermediate lactam has been prepared which will be utilized in a total synthesis of the natural product.