23356-96-9Relevant articles and documents
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Gassman,Fentiman
, p. 2388,2390 (1967)
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Asymmetric Synthesis. Metal Complex Mediated Synthesis of Chiral Glycine by Enantioselective Proton Exchange
Dokuzovic, Zdravko,Roberts, Nicholas K.,Sawyer, Jeffery F.,Whelan, John,Bosnich, B.
, p. 2034 - 2039 (1986)
The complex (1+), a species containing a chiral tridentate triamine ligand, (S,S)-proam, and a tridentate ligand incorporating a glycine residue, picgly, has been prepared.The α-protons of the coordinated glycine residue exchange at different rates in basic D2O solutions.The difference in rate was found to be 7.8:1 in favor of the pro-S proton at pD 11.2 at 25 deg C with a NaHCO3/Na2CO3 buffer.It is proposed that the origins of this enantiosection arise from both steric and hydrogen-bonding effects as inferred from the determined crystal structure of the complex.A kinetic analysis of the exchange process shows that the system is essentially that of an asymmetric synthesis (CH2 -> CHD) followed by a reinforced kinetic resolution (CHD -> CD2).As such, the optical purity of the chiral glycine (NH2CHDCO2H) continuously increases with the extent of reaction.This was confirmed.It is suggested that the present kinetic relationships are representative of the majority of asymmetric syntheses involving enantiotopic atoms or groups, and it follows that, for such systems, quoting an enantiomeric excess has meaning only when the extent of reaction is specified.
London Dispersion Interactions Rather than Steric Hindrance Determine the Enantioselectivity of the Corey–Bakshi–Shibata Reduction
Eschmann, Christian,Song, Lijuan,Schreiner, Peter R.
supporting information, p. 4823 - 4832 (2021/02/01)
The well-known Corey–Bakshi–Shibata (CBS) reduction is a powerful method for the asymmetric synthesis of alcohols from prochiral ketones, often featuring high yields and excellent selectivities. While steric repulsion has been regarded as the key director of the observed high enantioselectivity for many years, we show that London dispersion (LD) interactions are at least as important for enantiodiscrimination. We exemplify this through a combination of detailed computational and experimental studies for a series of modified CBS catalysts equipped with dispersion energy donors (DEDs) in the catalysts and the substrates. Our results demonstrate that attractive LD interactions between the catalyst and the substrate, rather than steric repulsion, determine the selectivity. As a key outcome of our study, we were able to improve the catalyst design for some challenging CBS reductions.
Understanding the Alkylation Mechanism of 3-Chloropiperidines – NMR Kinetic Studies and Isolation of Bicyclic Aziridinium Ions
Helbing, Tim,Georg, Mats,St?hr, Fabian,Carraro, Caterina,Becker, Jonathan,Gatto, Barbara,G?ttlich, Richard
, p. 5905 - 5913 (2021/10/29)
The present study describes the kinetic analysis of the 3-chloropiperidine alkylation mechanism. These nitrogen mustard-based compounds are expected to react via a highly electrophilic bicyclic aziridinium ion, which is readily attacked by nucleophiles. Halide abstraction using silver salts with weakly coordinating anions lead to the isolation of these proposed intermediates, whereas their structure was confirmed by single crystal XRD. Kinetic studies of the aziridinium ions also revealed notable reactivity differences of the C5 gem-methylated compounds and their unmethylated counterparts. The observed reactivity trends were also reflected by NMR studies in aqueous solution and DNA alkylation experiments of the related 3-chloropiperidines. Therefore, the underlying Thorpe-Ingold effect might be considered as another option to adjust the alkylation activity of these compounds.
Selective hydrogenation of primary amides and cyclic di-peptides under Ru-catalysis
Subaramanian, Murugan,Sivakumar, Ganesan,Babu, Jessin K.,Balaraman, Ekambaram
supporting information, p. 12411 - 12414 (2020/10/30)
A ruthenium(II)-catalyzed selective hydrogenation of challenging primary amides and cyclic di-peptides to their corresponding primary alcohols and amino alcohols, respectively, is reported. The hydrogenation reaction operates under mild and eco-benign conditions and can be scaled-up.
