N-Heterocyclic Carbene Catalyzed Ring Expansion of Formylcyclopropanes: Synthesis of 3,4-Dihydro-α-pyrone Derivatives
摘要:
N-Heterocyclic carbene catalyzed ring expansion of readily accessible 2-acyl-l-formylcyclopropanes was developed. With 5 mol % of triazoliurn salt 5 and 30 mol % of DBU, ring expansion of various 2-acyl-l-formylcyclopropanes led to 3,4-dihydro-alpha-pyrones in good to excellent yields.
Tetrazolic Acid Functionalized Dihydroindol: Rational Design of a Highly Selective Cyclopropanation Organocatalyst
摘要:
Herein we wish to report our development of an improved catalyst (S)-(-)-indoline-2-yl-1H-tetrazole (1) for the enantioselective organocatalyzed cyclopropanation of alpha,beta-unsaturated aldehydes with sulfur ylides. The new organocatalyst readily facilitates the enantioselective organocatalytic cyclopropanation, providing cyclized product in excellent diastereoselectivities ranging from 96% to 98% along with enantioselectivities exceeding 99% enantiomeric excess for all reacted alpha,beta-unsaturated aldehydes. The new catalyst provides the best results so far reported for intermolecular enantioselective organocatalyzed cyclopropanation.
Organocatalytic asymmetric cyclopropanation of α,β-unsaturated aldehydes with arsonium ylides
作者:Yun-Hui Zhao、Gang Zhao、Wei-Guo Cao
DOI:10.1016/j.tetasy.2007.10.007
日期:2007.10
A novel organocatalytic asymmetric cyclopropanation of alpha,beta-unsaturated aldehydes with arsonium ylides using diphenylprolinol silylether as a catalyst is described. A variety of chiral cyclopropyl aldehydes are obtained in moderate to good yields with up to 99:1 dr (diastereomeric ratio) and 99% ee under simple and mild reaction conditions. (c) 2007 Elsevier Ltd. All rights reserved.