N′‐dioxide (−)‐9 has been designed, synthesized and examined as an organocatalyst in the enantioselective ring opening of meso‐epoxides using tetrachlorosilane (SiCl4). The catalyst (−)‐9 is found to exhibit good enantioselectivity for substituted cis‐stilbene epoxides; whereas, the saturated cyclic meso‐epoxides display a moderate enantioselectivity. At −30 °C in chloroform, the catalyst (−)‐9 with 0
Enantioselective Ring Opening of<i>meso</i>-Epoxides with Silicon Tetrachloride Catalyzed by Pyridine<i>N</i>-Oxides Fused with the Bicyclo[3.3.1]nonane Framework
作者:Algirdas Neniškis、Sigitas Stončius
DOI:10.1002/ejoc.201500762
日期:2015.10
chiral Lewis basic organocatalysts that contain pyridine N-oxide moieties fused with the bicyclo[3.3.1]nonane framework is reported. The obtained pyridine N-oxides were employed as catalysts in the enantioselective ring opening of meso-epoxides with silicon tetrachloride. Derivative 1b endowed with two 2,4-diaryl-substituted pyridine N-oxide moieties proved to be a particularly effective catalyst for desymmetrization
Allenes in Asymmetric Catalysis: Asymmetric Ring Opening of <i>meso</i>-Epoxides Catalyzed by Allene-Containing Phosphine Oxides
作者:Xiaotao Pu、Xiangbing Qi、Joseph M. Ready
DOI:10.1021/ja9041127
日期:2009.8.5
Unsymmetrically substituted allenes (1,2-dienes) are inherently chiral and can be prepared in optically pure form. Nonetheless, to date the allene framework has not been incorporated into ligands for asymmetric catalysis. Since allenes project functionality differently than either tetrahedral carbon or chiral biaryls, they may create complementary chiral environments. This study demonstrates that optically
The facile synthesis of chiral 1,2-chlorohydrins via the enantioselective ring-opening of meso-epoxides with silicon tetrachloride in the presence of a chiral phosphine oxide was accomplished. The chiral 1,2-chlorohydrins were also obtained from the corresponding cis-alkenes in one-pot without significant loss in the selectivity, thereby permitting easy access to the 1,2-chlorohydrins from cis-alkenes with good yields and enantioselectivities. (C) 2013 Elsevier Ltd. All rights reserved.
Helical Chiral Pyridine<i>N</i>-Oxides: A New Family of Asymmetric Catalysts