摘要:
The In and Zn-mediated allylation of substituted pyrazol-4-yl derived (R)-N-tert-butanesulfinyl imines proceeds with high diastereoselectivity depending on the conditions and additives (up to 99.4% de). Thus, the synthesized diastereomeric homoallylsulfinamides were isolated and characterized as pure diastereomers, which were then converted into the corresponding pyrazol-4-yl-derived N-Boc-homoallylamines via consecutive treatment with HCl and Boc(2)O. The latter were then subjected to a sequence of reactions: cyclobromocarbamation with NBS and enolateisocyanate rearrangement with tBuOK to give novel enantiomerically pure (S)-6-(pyrazol-4-yl)-piperidine-2,4-diones in 88-96% yield. The absolute configurations of the allylation products were assigned by X-ray single crystal analysis of the intermediate bromomethylurethanes. (C) 2014 Elsevier Ltd. All rights reserved.