A bicyclo[3.1.1]heptano[4,3-c]pyrazole derived chiral auxiliary for dipolar cycloadditions
作者:Giorgio Molteni、Paola Del Buttero
DOI:10.1016/j.tetasy.2005.04.014
日期:2005.6
Starting form naturally occurring (S)-cis-verbenol 1 and (1R)-(-)-myrtenol 2, we synthesised enantiopure bicyclo[3.1.1]heptano[4.3-c]pyrazole derivatives 7 and 8 via a stereoselective nitrilimine cycloaddition as the key step. The effectiveness of the above skeleton as a new chiral auxiliary was evaluated towards the 1,3-dipolar cycloadditions of nitrile oxides and nitrilimines. Basic hydrolysis of the major cycloadducts gave enantiopure 5-carboxy-4,5-dihydroisoxazole (S)-(+)-19 and 5-carboxy-4,5-dihydropyrazole (S)-(+)-20, respectively, which Lire of potential interest as chiral building blocks. (c) 2005 Elsevier Ltd. All rights reserved.