Construction of Enantioenriched [3.1.0] Bicycles via a Ruthenium-Catalyzed Asymmetric Redox Bicycloisomerization Reaction

Enantiomerically enriched [3.1.0] bicycles containing vicinal quaternary centers were synthesized from [1,6]-enynes using a cyclopentadienylruthenium catalyst containing a tethered chiral sulfoxide. The reaction was complicated by the fact that the substrates contained a racemic propargyl alcohol that could affect the selectivity of the process. Nonetheless, high levels of enantioinduction were observed, despite complications arising from the use of racemic substrates. Mechanistic studies showed that while the utilization of either enantiomer of the propargyl alcohol led to high product enantiomeric ratios when the reaction was conducted in acetone, a significant matched/mismatched effect was observed in tetrahydrofuran.