Total Synthesis and Structure Revision of (−)-Siphonodictyal B and Its Biomimetic Conversion into (+)-Liphagal

• DOI: 10.1021/acs.orglett.5b01973
• Publication Date: 2015-08-21T12:36:45Z
• Authors: Adrian W. Markwel...; Kevin K. W. Kuan; Jonathan H. George
• Keywords: Molecular Structure; Terpenes; Sesquiterpenes; 01 natural sciences; Catalysis; Hydroquinones; 0104 chemical sciences

The structure of siphonodictyal B has been reassigned on the basis of the total synthesis of both possible C-8 epimers. The revised structure of siphonodictyal B was converted into liphagal by acid catalyzed rearrangement of a proposed epoxide intermediate. This biomimetic cascade features a succession of four distinct reactions (epoxidation, o-quinone methide formation, ring expansion, and benzofuran formation) that occur in a one-pot operation under mild conditions. During these studies we also isolated a surprisingly stable o-quinone methide that supports our mechanistic proposal for liphagal biosynthesis.