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A novel category of di(N,N-dimethylbenzylamine)prolinol silyl ether catalyst, which when used in conjunction with an acidic co-catalyst, generates an ammonium salt supported organocatalyst. This catalytic system is shown to be very effective for the Michael reaction of benzyloxyacetaldehyde and various nitroolefins in isopropanol. Excellent enantioselectivities (up to 99%) and diastereoselectivities (syn/anti of 75:25) and short reaction times were obtained. The presence of the bulky OTMS group combined with the presence of two large N,N-dimethylbenzyl ammonium ion groups accounts for the effectiveness of this catalytic system. 相似文献
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Akihiro Koizumi Yukiko Matsuda Ryosuke Haraguchi Shin-ichi Fukuzawa 《Tetrahedron: Asymmetry》2017,28(3):428-432
The silver/ThioClickFerrophos (a chiral ferrocenyl P,S-ligand)-catalyzed Michael additions of 2-oxazoline- and thiazoline-4-carboxylate to nitroalkenes were highly anti-selective and enantioselective and produced the corresponding adducts in high yields. 相似文献
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Lingui Zhu Chuanfa Ni Petr Beier G.K. Surya Prakash George A. Olah 《Journal of fluorine chemistry》2007,128(10):1241-1247
We have successfully achieved nucleophilic (phenylsulfinyl)difluoromethylation of both enolizable and non-enolizable aldehydes and ketones by using difluoromethyl phenyl sulfone (1) as the fluoroalkylating agent. Although the chemical yields of the reactions are good to excellent, the observed diastereoselectivity is poor (dr = 1:1.04-2.03). The present synthetic methodology provides a convenient alternative for the preparation of α-(phenylsulfinyl)difluoromethylated carbinols that were previously synthesized via a two-step procedure. 相似文献
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A simple and effective synthesis of enantiomerically pure 2-(N-aryl-, N-alkyl-aminomethyl)aziridines from (2S)-N-tritylaziridine-2-carboxylic acid methyl ester has been developed. Treating of this key ester with several primary and secondary amines in the presence of AlMe3 provided the corresponding chiral N-trityl-2-carboxamides, and their reduction performed with different reagents resulted in the formation of the expected 2-(aminomethyl)aziridines. The choice of reaction conditions allows to either keep or leave the trityl substituent in the product. Such 2-(aminoalkyl)aziridines have shown very high catalytic efficiency in the asymmetric arylation of aldehydes and in other testing asymmetric reactions. On the other hand, homochiral N-trityl-2-carboxamides are interesting building blocks for the synthesis of various biologically active compounds. 相似文献
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Liquid chromatographic separation of enantiomers was accomplished using a chiral stationary phase (CSP) derived from (S)-biotin on silica gel. In both nonaqueous and aqueous media, this CSP (1) permitted separation of racemic amino acid derivatives based on hydrogen bonding with a urea moiety of the biotin moiety. 相似文献
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Katarzyna Zielińska Katarzyna Szymańska Roman Mazurkiewicz Andrzej Jarzębski 《Tetrahedron: Asymmetry》2017,28(1):146-152
The kinetic resolution of racemic 1-(N-acylamino)alkylphosphonic acids 3 (R3 = OH) and their dimethyl esters 1, as well as 1-(N-acylamino)alkylphosphinic acids 4 (R3 = H or Ph) using penicillin G acylase (PGA) immobilized on three types of mesoporous silicas in both a batch slurry system and in a continuous-flow reactor was studied. The initial hydrolytic deacylation rates in the presence of those catalysts were measured and the relationships between the substrate structure and the enzyme efficiency are discussed. The stereospecific hydrolysis of the N-acyl group of both racemic N-acylated phosphorus analogues of amino acids and their esters catalyzed by the immobilized PGA proved to be a highly effective method for the kinetic resolution of all the investigated compounds, with the stereochemical preference of PGA for (R)-substrates. 相似文献
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