Asymmetric Total Synthesis of (-)-Englerin A through Catalytic Diastereo- and Enantioselective Carbonyl Ylide Cycloaddition.

An asymmetric total synthesis of the guaiane sesquiterpene (-)-englerin A, a potent and selective inhibitor of the growth of renal cancer cell lines, was accomplished. The basis of the approach is a highly diastereo- and enantioselective carbonyl ylide cycloaddition with an ethyl vinyl ether dipolarophile under catalysis by dirhodium(II) tetrakis[N-tetrachlorophthaloyl-(S)-tert-leucinate], [Rh2 (S-TCPTTL)4 ], to construct the oxabicyclo[3.2.1]octane framework with concomitant introduction of the oxygen substituent at C9 on the exo-face. Another notable feature of the synthesis is ruthenium tetraoxide-catalyzed chemoselective oxidative conversion of C9 ethyl ether to C9 acetate.