Diastereoselective Temporary Silicon-Tethered Ring-Closing-Metathesis Reactions with Prochiral Alcohols: A New Approach to Long-Range Asymmetric Induction

Evans et al have shown that long range asymmetric induction is possible via the temporary silicon tethered ring closing metathesis reaction.  Typically in examples of the type shown

ratios of (1):(2) are 20:1 or better depending on the nature of R (nPr, c-Hex, iBu, PhCH₂, Ph(CH₂)₂, BnOCH₂, BnO₂CH₂), with ratios of >99:1 being observed in some cases (R = 2-naphthyl, Ph).With larger rings the d.r. is not only lower but also reversed with homologues of (2) (prepared from RCH(OH)(CH₂)_nCH=CH₂, n = 1-4) being preferred to homologues of (1) . (Angew. Chem. Internat. Ed. , 2003, 42, 1734-1737).