Chemoselective esterification of α-hydroxyacids catalyzed by salicylaldehyde through induced intramolecularity
作者:Shiue-Shien Weng、Hsin-Chun Li、Teng-Mao Yang
DOI:10.1039/c2ra23068b
日期:——
direct and chemoselective esterification of α-hydroxyacids was developed using a reversible covalent-binding strategy. By taking advantage of acetal chemistry, simple aldehydes can be used to efficientlycatalyze the esterification of α-hydroxy carboxylic acids in the presence of β-hydroxyacid moieties or other carboxylic acids in amounts equal to or in excess of the alcohols. A diverse array of α-aryl
Synthesis of an Ammonium Ionophore and Its Application in a Planar Ion-Selective Electrode
作者:John S. Benco、Hubert A. Nienaber、W. Grant McGimpsey
DOI:10.1021/ac0257851
日期:2003.1.1
and possessed high selectivity for ammonium ion over lithium and the divalent cations, calcium and magnesium (log K(POT)NH4+(j) = -7.3, -4.4, and -7.1 for lithium, calcium, and magnesiumions, respectively). The same membrane also exhibited sodium and potassiumselectivity that was comparable to that reported for nonactin (log K(POT)NH4+(j) = -2.1 and -0.6 for sodium and potassium, respectively, compared
A compound represented by the following general formula (I):
[R
1
to R
5
represent hydrogen atom, an alkyl group, or a trialkylsilyl group, X represents —NH—CO—, —CO—NH—, —N(COR
6
)—CO—, —CO—N(COR
7
)— (R
6
and R
7
represent a lower alkoxy group, or a carboxy-substituted phenyl group) etc.; and Z represents —Y—CH(R
12
)—COOH, —CHO, —CH═CH—COOH, or —COOR
13
(Y represents a single bond, —CH
2
—, —CH(OH)—, —CO—, —CO—NH—, or —CO—NH—CH
2
—CO—NH—, R
12
represents hydrogen atom or a lower alkyl group, and R
13
represents hydrogen atom, —CH(R
14
)—COOH(R
14
represents hydrogen atom, a lower alkyl group, or hydroxy group), —[CH
2
CH
2
—O]
n
—CH
2
—CH
2
—OH, —CH
2
—O—[CH
2
CH
2
—O]
m
—CH
2
—OH, or —[CH(CH
3
)—CO—O]
p
—CH(CH
3
)—COOH (m, n and p represent an integer of 1 to 100))], a salt thereof or an ester thereof, which has a property of being converted into a retinoid after absorption in vivo.
(R)- and (S)-α-hydroxy esters 5 are interconverted via their triflates 6 in high chemical as well as optical yields by reaction with dimethylformamide. The same triflates are efficiently converted into N-hydroxy-α-amino acid derivatives 7 of highopticalpurity.
environmentally benign character of iron mean that it is an ideal alternative to precious metals in catalysis. Recent growth in the number of iron-catalysed reactions reported reflects an increasing demand for sustainable chemistry. Only a limited number of chiral iron catalysts have been reported and these have, in general, proven less enantioselective than other transition-metal catalysts, thus limiting their