Stereoselective Synthesis of Highly-Congested Tetralin-Fused Spirooxindoles with Hydroxyl Group: Net Oxygen Atom Induced Hydride Shift/cyclization Process.

Abstract A highly stereoselective synthesis of tetralin-fused spirooxindoles with two contiguous stereogenic centers was developed. In the present reaction, not only the [1,5]-hydride shift/cyclization process, but also the replacement of nitrogen atom by oxygen atom occurred smoothly to give target compounds with hydroxy group in good chemical yields with good to excellent diastereoselectivities (up to d.r. = >20:1). Investigation of the reaction mechanism suggested that this “atom replacement” event occurred via the iminium cation intermediates.