Tether-controlled cycloadditions for the asymmetric synthesis of decalins:Increased selectivity in acetonitrile solvent

The beneficial influence of cis-isopropylidene acetal tether control groups , to facilitate the asymmetric synthesis of substituted decalins by intramo lecular Diels-Alder reactions, is described. Compared to trans-acetonides, these cases proceed under milder conditions to afford the cis-fused adducts from an endo transition state. An unusual acetonitrile solvent effect exer ts a dramatic influence on the diastereoselectivity. This strategy leads to the chiral nonracemic bicyclo[4.4.0]decane core of diverse natural product s.