Methods for enantioselective synthesis of P-stereogenic compounds from non-optically active substrates are reviewed. Two stategies can be classified according to the substrates and mechanisms of their reactions, which include enantioselective desymmetrisations and chemical resolutions.
The method of oxidation of N-sulfonylimines to N-sulfonyloxaziridines with m-chloroperbenzoic acid catalyzed by ammonium halides was systematically investigated for the first time. Tetraethylammonium halides (Et 4 NI or Et 4 NCl) and tetramethylammonium halides (Me 4 NI, Me 4 NBr or Me 4 NCl) were firstly used to catalyze the oxidation of a series of N-sulfonylimines to the corresponding N-sulfonyloxaziridines in excellent yields. The experimental results showed that the alkyl group of the ammonium had significant influence on the reaction, whereas the halide ions had lesser influence on the reaction. Thus the research has provided a simple procedure for the preparation of oxaziradine with excellent yields.
Methods for the synthesis of α-alkoxycarbonylaminomethylphosphonates are very limited because of the presence of unique methylene group in their structures. Thus the methodology for the synthesis of this kind of compounds is studied. Under the basic conditions of using LiOH, α-sulfonylmethylcarbamates reacted with dialkylphosphonates in the solvent of commercial EtOAc giving the products of α-alkoxycarbonylaminomethylphosphonates which are typically hard to be synthesized in good to moderate yields. This simple protocol runs under very mild conditions, and can be exploited for multigram amounts with good yield too.
In the title compound, {[Nd(NO3)(C6H5NO2)2(H2O)3](ClO4)2·H2O}n, the NdIII atom is nine-coordinated by four O atoms from four pyridinium-4-carboxylate ligands, two O atoms from a chelating nitrate anion and three water molecules in a distorted tricapped trigonal–prismatic coordination geometry. Adjacent Nd atoms are linked by the bidentate pyridinium-4-carboxylate ligands into a chain running along the b axis. The chains are further connected by O—H⋯O and N—H⋯O hydrogen bonds into a three-dimensional network.
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