Synthesis of the FGHI Ring System of Azaspiracid

Synthesis of the ABCD Ring System of Azaspiracid

“…[3] Here we report the synthesis of the ABCD ring framework of azaspiracid (1) by a special strategy requiring a hydrogen bonding auxiliary group to establish the proper configuration of one of the spirocenters (C13). According to our previously articulated retrosynthetic analysis, [3] azaspiracid (1) is disconnected by rupturing the C25 À C26 bond leading to the ABCD and FGHI domains 2 and 3 as shown in Scheme 1. Considering that neither the absolute stereochemistry of 1 nor the relative stereochemistry of the two domains of this compound are known, we decided arbitrarily to develop routes to these systems which could be adaptable to either enantiomer.…”