Progress toward the asymmetric de novo synthesis of lanostanes: A counter biomimetic cucurbitane-to-lanostane type transformation

Progress Toward the Asymmetric De Novo Synthesis of Limonoids

“…The synthetic pathway of interest here is distinct from those based on biomimetic polyolefin-type cyclization reactions (cationic or radical in nature), instead being inspired by previous studies in our laboratory that have revealed the strategic value of a late-stage oxidative rearrangement to transpose a quaternary center from the “steroidal” C9 position to C10. For example, as illustrated in Figure A, the tetracyclic phenols 4 and 6 have been smoothly and stereosepecifically converted to rearranged pregnane ( 5 ) and norlanostane ( 7 ) products by exposure to PIDA [PhI(OAc) 2 ] in HFIP (hexafluoroisopropanol) . Notably, these oxidative transformations are thought to proceed by way of the indicated cationic intermediates C and D , both of which have the potential to be terminated by the loss of a proton.…”