共查询到20条相似文献,搜索用时 22 毫秒
1.
Jew SS Jeong BS Lee JH Yoo MS Lee YJ Park BS Kim MG Park HG 《The Journal of organic chemistry》2003,68(11):4514-4516
Systematic investigations to develop an efficient enantioselective synthetic method for alpha-alkyl-alanine by catalytic phase-transfer alkylation were performed. The alkylation of 2-naphthyl aldimine tert-butyl ester, 1E, with RbOH and O(9)-allyl-N-2',3',4'-trifluorobenzylhydrocinchonidinium bromide, 6, at -35 degrees C showed the highest enantioselectivities, up to 96% ee. 相似文献
2.
Lee J Lee YI Kang MJ Lee YJ Jeong BS Lee JH Kim MJ Choi JY Ku JM Park HG Jew SS 《The Journal of organic chemistry》2005,70(10):4158-4161
[reaction: see text] An enantioselective synthetic method for alpha-alkylserines by the phase-transfer catalytic alkylation of 2-phenyl-2-oxazoline-4-carbonylcamphorsultam (4a) was developed. The phase-transfer catalytic alpha-alkylation of 4a using P2-Et at -78 degrees C gave alpha-alkylation (75 to approximately 99%, 90 to approximately 97% de), which could be easily hydrolyzed to alpha-alkylserines. 相似文献
3.
[reaction: see text] A highly enantioselective synthetic method for (R)-alpha-alkylserines was developed by the phase-transfer catalytic alkylation of o-biphenyl-2-oxazoline-4-carboxylic acid tert-butyl ester (4i) using cinchona-derived phase-transfer catalyst N(1)-(9-anthracenylmethyl)-O(9)-allyl-dihydrocinchonidinium bromide (up to 96% ee). 相似文献
4.
Despite phase transfer catalysis (PTC) is an important and useful method in organic synthesis, asymmetric synthesis using chiral phase-transfer catalyst has not been well documented and limited number of chiral phase-transfer catalyst have been developed[1].In 1989,O'Donnell published his pioneering work in the asymmetric synthesis of α-amino acids by enantioselective alkylation of a prochiral protected glycine derivative using chiral phase-transfer catalyst[2]. Since then, several groups reported their improvements on enantioselectivity and applicability on this useful synthetic reaction[3,4]. However, almost all of the chiral phase-transfer catalysts reported so far are the derivatives of cinchona[5]. In this presentation, we wish to describe the design and synthesis of a new type of chiral phase-transfer catalyst based on the camphor and its application in asymmetric alkylation of tert-bntyl glycinate-benzophenone Schiff base. 相似文献
5.
A new efficient enantioselective synthetic method of (+)-isonitramine is reported. (+)-Isonitramine was obtained in 12 steps (98% ee and 43% overall yield) from δ-valerolactam via enantioselective phase-transfer catalytic alkylation, Dieckman condensation, and diastereoselective reduction as key steps. 相似文献
6.
Shirakawa S Liu K Ito H Maruoka K 《Chemical communications (Cambridge, England)》2011,47(5):1515-1517
Efficient catalytic asymmetric synthesis of 1,1-disubstituted tetrahydro-β-carbolines has been achieved via asymmetric alkylation of 1-cyanotetrahydro-β-carbolines using a binaphthyl-modified N-spiro-type chiral phase-transfer catalyst. This is a valuable example of hitherto difficult highly enantioselective alkylations at α-carbon of the cyano group under phase-transfer conditions. 相似文献
7.
[structure: see text] Various N-benzylcinchonidinium salts were prepared to study electronic factors in the catalytic enantioselective phase-transfer alkylation of glycine anion equivalent. An ortho-fluoro substituent on the benzyl group in the quaternary ammonium salt dramatically increased the enantioselectivity in the alkylation. O(9)-Allyl-N-2',3',4'-trifluorobenzylhydrocinchonidinium bromide (27), which gave the highest enantioselectivity of the catalysts studied, was used to prepare 12 alpha-alkylated amino acid derivatives in 94 approximately >99% ee. 相似文献
8.
Tomoaki Inukai Prof. Dr. Taichi Kano Prof. Dr. Keiji Maruoka 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(6):2231-2234
A highly enantioselective synthesis of δ-lactams having a chiral quaternary carbon center at the α-position has been developed through an asymmetric alkylation of 3-arylpiperidin-2-ones under phase-transfer conditions. In this transformation, a 2,2-diarylvinyl group on the δ-lactam nitrogen atom plays a crucial role as a novel protecting group and an achiral auxiliary for improving both yield and enantioselectivity of the reaction. 相似文献
9.
The first enantioselective synthesis of (+)-hygrine (1) is reported. 1 was obtained in 12 steps with 29% overall yield and 97% ee via asymmetric phase-transfer catalytic alkylation and ring-closing metathesis as key steps. The absolute configuration of (+)-hygrine could be directly confirmed as R. 相似文献
10.
Dae Hyun Kim Jin Kyu Im Dae Won Kim Hyunjoo Lee Honggan Kim Hoon Sik Kim Minserk Cheong Deb Kumar Mukherjee 《Transition Metal Chemistry》2010,35(8):949-957
The asymmetric C-alkylation of benzophenone Schiff base glycine esters has been achieved using a palladium(II) chiral complex as a phase-transfer
catalyst. The aromatic moiety around the metal center and various physicochemical parameters were investigated to study their
effect on the asymmetric alkylation reaction under phase-transfer conditions. Moderate enantioselectivity(30–40%) was achieved
under room temperature conditions, which is a significant improvement compared to no enantioselectivity with a chiral palladium-salen
complex reported earlier. Computer simulation studies indicate that coordination of the metal center with Z-enolate forming
a square planar complex provides a favorable steric environment where the α-carbon atom of the enolate is available for enantioselective
alkylation. 相似文献
11.
We reported efficient enantioselective synthetic methodologies for (R)-alpha-alkylcysteines and (S)-alpha-alkylcysteines. The phase-transfer catalytic alkylation of 2-phenyl-2-thiazoline-4-carboxylic acid tert-butyl ester and 2-o-biphenyl-2-thiazoline-4-carboxylic acid tert-butyl ester, in the presence of chiral catalysts (1 or 2), gave the corresponding alkylated products, which could be hydrolyzed to provide (R)-alpha-alkylcysteines (67->99% ee) and (S)-alpha-alkylcysteines (66-88% ee), respectively. 相似文献
12.
Shannon R. Fix-Stenzel Xiaolei Zhang Pintipa Grongsaard Steven M. Hannick Robert H. Stoffel 《Tetrahedron letters》2009,50(28):4081-2250
A scalable and enantioselective synthesis of a potent S1P1 agonist containing two stereogenic centers on a cyclopentane ring is described. Control of the absolute chirality of an amino alcohol precursor, generated via a robust phase-transfer catalyzed alkylation protocol, allows for substrate directed hydrogenation to install the second stereogenic center providing access to gram-quantities of compound 2. 相似文献
13.
Barry LygoBenjamin I. Andrews 《Tetrahedron letters》2003,44(24):4499-4502
In this paper we report the development of a highly enantioselective method for the synthesis of aroylalanines. The approach described employs a protected 2-amino-4-bromopent-4-enoic acid, generated via the asymmetric phase-transfer catalyzed alkylation of a glycine imine, as a key intermediate. Suzuki coupling with an aryl boronic acid followed by ozonolysis of the resulting styrene provides efficient access to the aroylalanine derivatives. The utility of this methodology is illustrated by the synthesis of l-kynurenine along with several aroylalanine inhibitors of the kynurenine pathway. 相似文献
14.
Qinghua Shi Mi-Jeong Kim Kyoungyim Lee Maosheng Cheng Hyeung-geun Park Sang-sup Jew 《Tetrahedron letters》2008,49(8):1380-1383
Merrifield resin supported cinchona ammonium salts bearing 2′-fluorobenzene, 2′-cyanobenzene and 2′-N-oxypyridine groups were prepared and applied to the phase-transfer catalytic alkylation of N-(diphenylmethylene)glycine tert-butyl ester for the enantioselective synthesis of α-amino acids (76-96% ee). 相似文献
15.
Enantioselective synthesis of (-)-cis-clavicipitic acid 总被引:1,自引:0,他引:1
An enantioselective synthetic method for (-)-cis-clavicipitic acid (1) was reported. 1 was obtained in 10 steps (99% ee and 20% overall yield) from 1H-indole-3-carboxylic acid methyl ester (9) via asymmetric phase-transfer catalytic alkylation and diastereoselective Pd(II)-catalyzed intramolecular aminocyclization as key steps. 相似文献
16.
《Tetrahedron》2019,75(27):3667-3696
This review focuses on the introduction and early development, in solution, of phase-transfer catalyzed (PTC) reactions to afford racemic or enantioenriched natural and unnatural amino acids. To form monosubstituted amino acids alkylation reactions are performed on the benzophenone Schiff base of glycine. For α,α-disubstituted amino acids the activated intermediate is an aldimine derivative of the monosubstituted amino acid. Enantioenriched products are produced by organocatalysis using derivatives of Cinchona alkaloids as the phase-transfer catalyst. Selectivity for monoalkylatation and lack of product racemization depend on the acidities of the glycine imines, and dialkylated products are formed from aldimine esters of monoalkyl amino acids. The racemic and catalytic enantioselective reactions of a cationic glycine equivalent with organoboranes, organometallics and malonate anion are discussed as are other reactions of these versatile Schiff bases derivatives. 相似文献
17.
Park HG Kim MJ Park MK Jung HJ Lee J Choi SH Lee YJ Jeong BS Lee JH Yoo MS Ku JM Jew SS 《The Journal of organic chemistry》2005,70(5):1904-1906
A new Merrifield-resin-derived glycinimine tert-butyl ester (9) was prepared and applied to the enantioselective synthesis of non-natural alpha-amino acids. High enantioselectivities (86 to >99% ee) were accomplished by employing the aldimine linker under phase-transfer alkylation conditions, using 50% aqueous CsOH in toluene/chloroform (7:3) at 0 degrees C in the presence of N-(9-anthracenylmethyl)-O(9)-allylcinchonidium bromide (10 mol %). 相似文献
18.
Hong S Lee J Kim M Park Y Park C Kim MH Jew SS Park HG 《Journal of the American Chemical Society》2011,133(13):4924-4929
A novel enantioselective synthetic method for the construction of a quaternary carbon center from malonates via phase-transfer catalytic (PTC) alkylation has been developed. The asymmetric α-alkylation of diphenylmethyl tert-butyl α-alkylmalonates with alkylating agents under phase-transfer catalysis conditions (aq 50% KOH, toluene, 0 °C) in the presence of (S,S)-3,4,5-trifluorophenyl-NAS bromide (8) as PTC catalyst afforded the corresponding α,α-dialkylmalonates in high chemical (up to 99%) and optical yields (up to 97% ee) which could be readily converted to versatile chiral intermediates. Notably, the direct double α-alkylations of diphenylmethyl tert-butyl malonate also provided the corresponding α,α-dialkylmalonates without loss of enantioselectivity. The synthetic potential of this method has been demonstrated by the preparation of α,α-dialkylamino acid and oxindole systems. 相似文献
19.
20.
Zhenfu Han 《Tetrahedron letters》2005,46(49):8555-8558
A highly active phase-transfer catalyst was conveniently prepared from the known, easily available (S)-4,5,6,4′,5′,6′-hexamethoxybiphenyldicarboxylic acid. This catalyst exhibited the high catalytic performance (0.01-1 mol %) in the asymmetric alkylation of N-(diphenylmethylene)glycine tert-butyl ester and N-(p-chlorophenylmethylene)alanine tert-butyl ester compared to the existing chiral phase-transfer catalysts, thereby allowing to realize a general and useful procedure for highly practical enantioselective synthesis of structurally diverse natural and unnatural α-alkyl-α-amino acids as well as α,α-dialkyl-α-amino acids. 相似文献