Enantioselective Synthesis of Caprolactam and Enone Precursors to the Heterocyclic DEFG Ring System of Zoanthenol.

The enantioselective synthesis of both caprolactam and enone synthons for the DEFG ring system of zoanthenol are described. The evolution of this synthetic approach proceeds first through a synthesis using the chiral pool as a starting point. Challenges in protecting group strategy led to the modification of this approach beginning with (±)-glycidol. Ultimately, an efficient approach was developed by employing an asymmetric hetero-Diels-Alder reaction. The caprolactam building block can be converted by an interesting selective Grignard addition to the corresponding enone synthon. Addition of a model alkyne provides support for the late-stage addition of a hindered alkyne into the caprolactam building block.