Enantioselective Total Synthesis of Hyperforin and Pyrohyperforin
Yunpeng Ji, Benke Hong, Ivan Franzoni, Mengyang Wang, Weiqiang Guan, Hongli Jia, Houhua Li
Abstract
Abstract Capitalizing on the late‐stage diversification of an essential 1,3‐diene intermediate, we describe herein a 9‐step enantioselective total synthesis of (+)‐hyperforin and (+)‐pyrohyperforin, starting from commercially available allylacetone. Our convergent synthesis features a series of critical reactions: 1) an enantioselective deconjugative α‐alkylation of α,β‐unsaturated acid using chiral lithium amides as noncovalent stereodirecting auxiliaries; 2) a HfCl 4 ‐mediated carbonyl α‐ tert ‐alkylation to forge the intricate bicyclo[3.3.1]nonane framework; 3) an abiotic cascade pyran formation; and 4) a selective 1,4‐semihydrogenation of polyenes. During the course of our synthesis, we also identified a 1,2‐cyclopropanediol overbred intermediate which was responsible for the 1,3‐diene precursor formation through a controlled fragmentation.