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551.
Roland Bischoff 《Tetrahedron letters》2005,46(42):7147-7149
A new approach for the asymmetric synthesis of blastidic acid, the β-amino acid component of the antibiotic, (+)-blasticidin S has been achieved in 11 steps and 30% overall yield. The key transformations involve a one-pot Swern/Wittig reaction sequence to prepare the carbon backbone followed by a stereoselective conjugate addition to introduce the β-amino functionality. 相似文献
552.
Christopher A. Lee 《Tetrahedron letters》2004,45(39):7193-7196
Several dihydroagarofuran esters have been reported to be effective multidrug resistance (MDR) reversing agents for both cancer cells and bacteria. We report a rapid synthesis of the dihydroagarofuran ring system from carvone in a sequence that is highlighted by a sequential conjugate addition/aldol sequence, a ring closing metathesis reaction, and a diastereoselective alkene reduction to provide an axial methyl group. The synthesis allows for differential esterification reactions as required to study the roles of these groups in MDR reversal. 相似文献
553.
Stephen G. Davies Jairton Dupont Robert J.C. Easton Osamu Ichihara Jeffrey M. McKenna Andrew D. Smith José A.A. de Sousa 《Journal of organometallic chemistry》2004,689(24):4184-4209
Conjugate addition of achiral lithium dimethylamide to the chiral iron cinnamoyl complexes (S,E)- and (S,Z)-[(η5-C5H5)Fe(CO)(PPh3)(COCHCHPh)] proceeds with high diastereoselectivity, with this protocol being used to establish unambiguously the absolute configuration of Winterstein’s acid (3-N,N-dimethylamino-3-phenylpropanoic acid) as (R). The highly diastereoselective conjugate addition of lithium N-benzyl-N-trimethylsilylamide to a range of α,β-unsaturated iron acyl complexes, followed by in-situ elaboration of the derived enolate by either alkylation or aldol reactions is also demonstrated, facilitating the stereoselective synthesis of both cis- and trans-β-lactams. This methodology has been used to effect the formal asymmetric syntheses of (±)-olivanic acid and (±)-thienamycin. Addition of chiral lithium amides derived from primary and secondary amines to the iron crotonyl complex [(η5-C5H5)Fe(CO)(PPh3)(COCHCHMe)] indicates that lithium N-α-methylbenzylamide shows low levels of enantiorecognition, while lithium N-3,4-dimethoxybenzyl-N-α-methylbenzylamide and lithium N-benzyl-N-α-methylbenzylamide show high levels of enantiodiscrimination. The high level of observed enantiorecognition was used to facilitate a kinetic resolution of (RS)-[(η5-C5H5)Fe(CO)(PPh3)(COCHCHMe)] with homochiral lithium (R)-N-3,4-dimethoxybenzyl-N-α-methylbenzylamide. Further mechanistic studies show that conjugate additions of (RS)-lithium N-benzyl-N-α-methylbenzylamide to either the (RS)- or homochiral iron crotonyl complex show 2:1 stoicheiometry, while homochiral lithium N-benzyl-N-α-methylbenzylamide shows 1:1 stoicheiometry. 相似文献
554.
Christopher J. Chapman Kelly J. Wadsworth Christopher G. Frost 《Journal of organometallic chemistry》2003,680(1-2):206-211
The enantioselective rhodium-catalysed conjugate addition of aryl boronic acids to dehydroalanine derivatives has been successfully carried out in the presence of C2-symmetric aryl diphosphite ligand (R,R,R-4) to prepare unnatural amino acid esters. The products have been obtained in up to 72% ee and with good isolated yield. 相似文献
555.
Introduction Incellbiology,fluorescenceprobesarewidely used.Organicdyes,mostcommonlyusedinfluores cenceprobes,sufferfromfastphotobleachingandbroad overlappingemissionlinessothattheyarelimitedin theirapplications.Progressinsemiconductornanocrys tals,orquan… 相似文献
556.
J.S. Yadav B.V. Subba Reddy Ashutosh Pratap Singh A.K. Basak 《Tetrahedron letters》2007,48(24):4169-4172
Baylis-Hillman adducts undergo smooth, one-pot oxidative conjugate addition with indoles in the presence of 2-iodoxybenzoic acid (IBX) under neutral conditions to afford a new class of substituted indoles in good yields. 相似文献
557.
Satomi Hirasawa 《Tetrahedron》2007,63(45):10930-10938
We report herein that the conjugate reduction of α,β-unsaturated esters and amides, such as aryl acrylates, pantolactone esters of acrylic acids, diethyl itaconate and N-crotonylcamphorsultam, with tributyltin hydride proceeded in moderate to high yields in the presence of magnesium bromide diethyl etherate. The effect of metal halide enhancing the yields is also described. 相似文献
558.
Markus Weymann Martin Schulz-Kukula Stephan Knauer Horst Kunz 《Monatshefte für Chemie / Chemical Monthly》2002,133(4):571-587
Summary. Using tetra-O-pivaloyl-β-D-galactopyranosylamine as the chiral auxiliary, both trans- and cis-annelated decahydroquinoline alkaloids can be synthesized stereoselectively. This methodology of asymmetric synthesis is
based on the effect that both enantiomers of 2,6-disubstituted piperidin-4-ones are selectively and alternatively accessible
using the auxiliary as the identical stereodifferentiating tool. In addition, the carbohydrate auxiliary controls the stereoselective
protonation of enolates formed by conjugate addition of cuprates to N-galactosyl octahydroquinolin-4-ones. The syntheses of
trans-4a-epi-pumiliotoxin C and cis-4a-epi-perhydro-219A illustrate this concept of asymmetric synthesis of decahydroquinoline alkaloids.
Received September 7, 2001. Accepted October 16, 2001 相似文献
559.
DNA which binds monocationic [60]fullerene (1) and tetracationic porphyrin (TMPyP) was readily fabricated by electrochemical oxidative polymerization of 3.4-ethylenedioxythiophene (EDOT) and the resultant poly(EDOT) composite was deposited on an ITO electrode as a stable thin film. Spectral and CV analyses established that one 1 and one TMPyP are bound per 57 nucleobase units, that is, every three pitches of DNA. Photoirradiation of this 1/TMPyP/DNA-poly(EDOT) film generated a photocurrent in 3.8% quantum yield, which was much higher than those obtained from 1/DNA and TMPyP/DNA systems. One can conclude, therefore that the photoexcited energy of TMPyP is transferred to 1, which is collected by the electron-conducting poly(EDOT) film. The present paper shows that DNA is useful as a scaffold to arrange redox-active couples in a one-dimensional matrix. 相似文献
560.
The conjugate reduction of aryl acrylates performed with tributyltin hydride in the presence of magnesium bromide diethyl etherate in dichloromethane gave the corresponding saturated esters in moderate to high yields. The reduction of α-methylene-γ-benzyloxycarboxylic acid esters proceeded syn-selectively, but α-methylene-β-oxycarboxylic acid esters afforded reductive elimination products under the reaction conditions. 相似文献