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.