Oxidation of polyfunctional threo-(1S,2S)-2-amino-1,3-propanediol derivatives with a 717 anion-exchange resin-supported bromine has been investigated. The result showed that oxidized products were in close relationship with the substituents at nitrogen in the starting materials. Its primary and secondary amine derivatives were oxidized in the presence of Na(2)HPO(4) to give essentially a substituted chiral oxazoline or C(3)-O acylated product in high yield, while oxidation of its N,N-dimethyl derivative mainly gave a chiral N-methyl oxidation-formylation product. This selective oxidation was first observed in 2-amino-1,3-propanediol chemistry. 相似文献
The selective cycloboronation of enantiopure 1,1,4,4-tetrasubstituted butanetetraols was investigated, and a general preparation of chiral cyclic boron-containing bifunctional Lewis acids was discovered. Compounds (2R,3R)- or (2S,3S)-1,1,4,4-tetrasubstituted butanetetraols were reacted with ArB(OH)2 at reflux in toluene, or THF, or under solvent-free condition to furnish tricoordinated, chiral bicyclo[4.4.0]diboronic esters in high yield via selective 1,3-cycloboronation. Structural characterization and properties of the novel chiral boron compounds are also reported. 相似文献
Asymmetric catalytic activity of the chiral spiroborate esters 1 – 9 with a O3BN framework (see Fig. 1) toward borane reduction of prochiral ketones was examined. In the presence of 0.1 equiv. of a chiral spiroborate ester, prochiral ketones were reduced by 0.6 equiv. of borane in THF to give (R)‐secondary alcohols in up to 92% ee and 98% isolated yields (Scheme 1). The stereoselectivity of the reductions depends on the constituents of the chiral spiroborate ester (Table 2) and the structure of the prochiral ketones (Table 1). The configuration of the products is independent of the chirality of the diol‐derived parts of the catalysts. A mechanism for the catalytic behavior of the chiral spiroborate esters (R,S)‐ 2 and (S,S)‐ 2 during the reduction is also suggested. 相似文献
Multi‐micelle aggregation (MMA) mechanism is widely acknowledged to explicate large spherical micelles self‐assembly, but the process of MMA during self‐assembly is hard to observe. Herein, a novel kind of strong, regular microspheres fabricated from self‐assembly of amphiphilic anthracene‐functionalized β‐cyclodextrin (CD‐AN) via Cu(I)‐catalyzed azide‐alkyne click reactions is reported. The obtained CD‐AN amphiphiles can self‐assemble in water from primary core–shell micelles to secondary aggregates with the diameter changing from several tens nm to around 600–700 nm via MMA process according to the images of scanning electron microscopy, transmission electron microscopy, and atomic force microscopy as well as the dynamic light scattering measurements, followed by further crosslinking through photo‐dimerization of anthracene. What merits special attention is that such photo‐crosslinked self‐assemblies are able to disaggregate reversibly into primary nanoparticles when changing the solution conditions, which is benefited from the designed regular structure of CD‐AN and the rigid ranging of anthracene during assembly, thus confirming the process of MMA.