Lewis acid mediated control of allylic epoxide opening in carbocyclization and halide addition pathways

Various novel carbocyclization processes were observed to occur in Lewis acid mediated cyclizations of an allylic epoxide substrate with a tethered enol(ate) function as nucleophile. Both cation-olefin polycyclization pathways and SN-prime macrocyclization processes were observed to occur in the presence of different Lewis acid additives. Lewis acid additives were also observed to direct the stereochemistry of allylic epoxide opening by SN-prime addition of halide ions. This provided a route to the corresponding E- or Z-allylic halides, which served as substrates in an alternative, successful approach to the terpestacin/fusaproliferin ring system by a subsequent alkylative macrocyclization reaction.