Natural product total synthesis: (-)-frondosin B, (-)-amathaspiramide F, guanacastepene A, and rhazinilam and the synthesis and reactivity of novel boron-ammonia complexes

The synthesis of four natural products was undertaken. The total syntheses of (-)-frondosin B, the enantiomer of naturally-occurring (+)-frondosin B, and (-)-amathaspiramide F were completed. In the first synthesis, a palladium catalyzed cyclization onto a benzofuran furnished the tetracyclic ring structure of the molecule. The previously proposed absolute configuration of the natural product was also reassigned through our synthesis. In the second synthesis, a highly diastereoselective conjugate addition onto a nitro olefin provided the carbon framework. Significant progress was also made toward the synthesis of guanacastepene A, in which a key electrochemical oxidation was used to form the central seven-membered ring and establish the entire carbon skeleton. The palladium catalyzed cyclization described for the synthesis of frondosin B was examined, finally, in order to determine its efficacy in a total synthesis of rhazinilam.; A new class of triaryl boranes that strongly bind ammonia was explored as well. The study of the unique chemistry of these complexes culminated in an X-ray crystal structure of a lithiated methoxymethoxybenzene species.