|
Mini-Reviews
in Organic Chemistry
ISSN: 1570-193X
Mini-Reviews
in Organic Chemistry
Volume 3, Number 4, November 2006
Contents
Recent Applications of Niobium Catalysts in Organic
Synthesis Pp. 271-280
Carlos Kleber Z. Andrade and Rafael O. Rocha
[Abstract]
Dimolybdenum Tetraacetate as an Auxiliary Chromophore
in Absolute Configuration Determination of Amino Acids from
their Circular Dichroism Spectra – Foundations and Developments
Pp. 281-290
Jadwiga Frelek, Marcin Górecki, Agata Suszczyñska,
Enikõ Forró and Zsuzsa Majer
[Abstract]
Stereoselective Synthesis of Cyclopropanols
Pp. 291-314
P. Garcia, D. Diez, A. B. Antón, N. M. Garrido,
I. S. Marcos, P. Basabe and J. G. Urones
[Abstract]
Synthesis of Guanidines in Solution Pp.
315-331
T. Suhs and B. König
[Abstract]
Azolium Cyclophanes Pp. 333-354
Murray V. Baker and David H. Brown
[Abstract]
1,3-Alternate, the Smart Conformation of Calix[4]arenes
Pp. 355-384
Lassaad Baklouti, Jack Harrowfield, Buncha Pulpoka and
Jacques Vicens
[Abstract]
Abstracts
[Back to top]
Recent Applications of Niobium Catalysts
in Organic Synthesis
Carlos Kleber Z. Andrade and Rafael O. Rocha
Niobium catalysts generally possess a good Lewis acidity and
have received increased attention in recent years. The applications
of niobium pentachloride as Lewis acid in organic synthesis
have been recently reviewed. Since then, there has been an
increasing number of examples on the use of niobium catalysts
in organic reactions such as Biginelli reactions, Friedel-Crafts
acylation and Sakurai-Hosomi reactions of acetals, Knoevenagel
condensation, acetylation of alcohols and phenols, among others.
Also, chiral niobium complexes have been reported to give
high enantiomeric excesses in asymmetric Mannich-type reactions.
In this review, recent applications of these versatile reagents
in organic synthesis, including our own results, will be disclosed.
[Back to top]
Dimolybdenum Tetraacetate as an Auxiliary Chromophore
in Absolute Configuration Determination of Amino Acids from
their Circular Dichroism Spectra – Foundations and Developments
Jadwiga Frelek, Marcin Górecki, Agata Suszczyñska,
Enikõ Forró and Zsuzsa Majer
A straightforward and versatile method for the determination
of the absolute configuration of amino acids is presented.
The proposed method involves the in situ formation
of chiral complexes of optically active amino acids with the
achiral dimolybdenum tetraacetate [Mo2(OAc)4]
acting as an auxiliary chromophore. Optically active amino
acids in reaction with [Mo2(OAc)4] in
DMSO exchange in situ its acetate ligand to form
chiral Mo-complexes. These complexes display several CD bands
in the spectral range from 600 to 250 nm. The resulting CD
spectra are suitable for the assignment of absolute configuration,
since the observed sign of Cotton effects arising within the
d−d
absorption bands of the metal core depends solely upon the
chirality of the amino acid ligands. It is shown that two
Cotton effects at around 300 nm and 400 nm are especially
useful for the correlation between their sign and the stereostructure
of amino acids by means of the hexadecant rule. The present
study demonstrates that the hexadecant rule can be extended
to differently N-protected amino acids. The dimolybdenum
method can also be applied for determination of the absolute
configuration of cyclic β-amino
acids representing precursors of peptidomimetics.
[Back to top]
Stereoselective Synthesis of Cyclopropanols
P. Garcia, D. Diez, A. B. Antón, N. M. Garrido,
I. S. Marcos, P. Basabe and J. G. Urones
Cyclopropanols have found an increasing number of uses as
synthetic intermediates and as functional groups in the design
of enzyme inhibitors. This mini-review will discuss some of
the most recent and successful methodologies for the synthesis
of these entities, focusing mainly on the stereoselective
transformations. The new procedure developed in our group
for the preparation of cyclopropanols in chiral form is also
reviewed.
[Back to top]
Synthesis of Guanidines in Solution
T. Suhs and B. König
The guanidinium group is a typical functional group in molecules
with physiological or biological activity. Its geometry and
physiochemical properties are of importance for molecular
recognition processes. We discuss in this review modern synthetic
methods for the introduction of the guanidinium group and
focus our survey on examples from natural product synthesis
and drug synthesis. The presented methods are sufficiently
mild and selective to allow guanidylation of more complex
structures.
[Back to top]
Azolium Cyclophanes
Murray V. Baker and David H. Brown
This review covers the synthesis, conformational analysis,
mass spectrometry, and reactivity and supramolecular chemistry
of azolium cyclophanes. Included is a comprehensive coverage
of the structural diversity of azolium cyclophanes. Aspects
of reactivity examined include anion binding, carbene formation
and metal coordination chemistry and H/D exchange.
[Back to top]
1,3-Alternate, the Smart Conformation of Calix[4]arenes
Lassaad Baklouti, Jack Harrowfield, Buncha Pulpoka and
Jacques Vicens
The syntheses and fascinating properties of calix[4]arene
derivatives in the 1,3-alternate conformation are reviewed.
Particular attention is given to the supramolecular chemistry
and applications in nanochemistry of such calixarenes.
|
