An effective and
simple solvent-controlled synthesis of thiocyanated
enaminones and 2-aminothiazoles has been demonstrated from enaminones,
potassium thiocyanate, and N-bromosuccinimide. This
process features mild reaction conditions, simple and easy operation,
short reaction time, and high yield and chemoselectivity and thereby
provides an efficient protocol for the divergent synthesis of thiocyanated
enaminones and substituted 2-aminothiazoles controlled by simply varying
the solvent. All reaction components are commercially available or
easily accessible at low cost. The potential utility of these methods
in organic chemistry and medicinal chemistry applications is highlighted.
Carbohydrates are synthetically challenging molecules
with vital
biological roles in all living systems. Selective synthesis and functionalization
of carbohydrates provide tremendous opportunities to improve our understanding
on the biological functions of this fundamentally important class
of molecules. However, selective functionalization of seemingly identical
hydroxyl groups in carbohydrates remains a long-standing challenge
in chemical synthesis. We herein describe a practical and predictable
method for the site-selective and stereoselective alkylation of carbohydrate
hydroxyl groups via Rh(II)-catalyzed insertion of metal carbenoid
intermediates. This represents one of the mildest alkylation methods
for the systematic modification of carbohydrates. Density functional
theory (DFT) calculations suggest that the site selectivity is determined
in the Rh(II)-carbenoid insertion step, which prefers insertion into
hydroxyl groups with an adjacent axial substituent. The subsequent
intramolecular enolate protonation determines the unexpected high
stereoselectivity. The most prevalent trans-1,2-diols
in various pyranoses can be systematically and predictably differentiated
based on the model derived from DFT calculations. We also demonstrated
that the selective O-alkylation method could significantly
improve the efficiency and stereoselectivity of glycosylation reactions.
The alkyl groups introduced to carbohydrates by OH insertion reaction
can serve as functional groups, protecting groups, and directing groups.
We report the total synthesis of a triazole-epothilone analogue 1. The key step to generate the macrocyclic ring and the triazole ring was to apply Cu 2 O nanoparticles (Cu 2 O-
Glycosyl isoquinoline-1-carboxylate was developed as a novel benchtop stable and readily available glycosyl donor. The glycosylation reaction was promoted by the inexpensive Cu(OTf) salt under mild reaction conditions. The copper isoquinoline-1-carboxylate salt was precipitated from the solution and thus rendered a traceless leaving group. Surprisingly, the proton from the acceptor was absorbed by the precipitated metal complex and the reaction mixture remained at neutral pH. The copper-promoted glycosylation was also proven to be completely orthogonal to the gold-promoted glycosylation, and an iterative synthesis of oligosaccharides from benchtop stable anomeric ester building blocks becomes possible under mild reaction conditions.
The collisionally activated dissociation mass spectra of the protonated and alkali metal cationized ions of a triazole-epothilone analogue were studied in a Fourier transform ion cyclotron resonance mass spectrometer. The fragmentation pathway of the protonated ion was characterized by the loss of the unit of C 3 H 4 O 3 . However, another fragmentation pathway with the loss of C 3 H 2 O 2 was identified for the complex ions with Na + , K + , Rb + , and Cs + . The branching ratio of the second pathway increases with the increment of the size of alkali metal ions. Theoretical calculations based on density functional theory (DFT) method show the difference in the binding position of the proton and the metal ions. With the increase of the radii of the metal ions, progressive changes in the macrocycle of the compound are induced, which cause the corresponding change in their fragmentation pathways. It has also been found that the interaction energy between the compound and the metal ion decreases with increase in the size of the latter. This is consistent with the experimental results, which show that cesiated complexes readily eject Cs + when subject to collisions.
Glycosyl isoquinoline‐1‐carboxylate was developed as a novel benchtop stable and readily available glycosyl donor. The glycosylation reaction was promoted by the inexpensive Cu(OTf)2 salt under mild reaction conditions. The copper isoquinoline‐1‐carboxylate salt was precipitated from the solution and thus rendered a traceless leaving group. Surprisingly, the proton from the acceptor was absorbed by the precipitated metal complex and the reaction mixture remained at neutral pH. The copper‐promoted glycosylation was also proven to be completely orthogonal to the gold‐promoted glycosylation, and an iterative synthesis of oligosaccharides from benchtop stable anomeric ester building blocks becomes possible under mild reaction conditions.
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