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 are of potential interest as chiral building blocks.
A bicyclo[3.1.1]heptano[4,3-c]pyrazole derived chiral auxiliary for dipolar cycloadditions / G. Molteni, P. Del Buttero. - In: TETRAHEDRON-ASYMMETRY. - ISSN 0957-4166. - 16:11(2005), pp. 1983-1987. [10.1016/j.tetasy.2005.04.014]
A bicyclo[3.1.1]heptano[4,3-c]pyrazole derived chiral auxiliary for dipolar cycloadditions
G. Molteni;
2005
Abstract
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 are of potential interest as chiral building blocks.
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