Total synthesis of (+)-alpha-onocerin in four steps via four-component coupling and tetracyclization steps.
A remarkably short (four steps, 31% overall yield) enantioselective synthesis of the structurally unique C2-symmetric tetracyclic triterpene (+)-alpha-onocerin (1) has been developed. The brevity of this mechanism depends on the assembly of four fragments (two molecules of a chiral epoxy ketone and two molecules of vinyllithium) to generate the chiral bis-epoxide 4 in one step, and on the efficient formation of all four carbocyclic rings in one step by cation-olefin tetracyclization. New and general methodology for the conversion of vinyl tert-butyldimethylsilyl ethers to vinyl triflates with retention of E or Z olefinic geometry also was utilized in the synthesis of 1. A short enantioselective synthesis of a non-C2-symmetric diastereomer of 1 is also described which uses the new methodology.
Mi
Yuan
Y
Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
Schreiber
Jürg V
JV
Corey
E J
EJ
D003500:Cyclization; D013237:Stereoisomerism; D014315:Triterpenes / Q000138:chemical synthesis*
D014315:Triterpenes; C409888:alpha-onocerin