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Current
Organic Chemistry
ISSN: 1385-2728
Current Organic
Chemistry
Volume 10, Number 15, October 2006
Contents
Advances in Asymmetric Synthesis Using Organoselenium
Chemistry
Guest Editor: Pete Silks
Editorial
Pp. 1891
New Developments with Chiral Electrophilic
Selenium Reagents Pp. 1893-1903
Danielle M. Browne and Thomas Wirth
[Abstract]
Asymmetric Synthesis of Chiral Organoselenium
Compounds Pp. 1905-1920
Chengjian Zhu and Yijun Huang
[Abstract]
Enantioselective Synthesis Mediated by Catalytic
Chiral Organoselenium Compounds Pp. 1921-1938
Antonio L. Braga, Diogo S. Lüdtke and Fabrício
Vargas
[Abstract]
Phenylselenoethers as Precursors of Acyclic Free
Radicals. Creating Tertiary and Quaternary Centers Using Free
Radical-Based Intermediates Pp. 1939-1961
Benoit Cardinal-David, Jean-François Brazeau, Ioannis
A. Katsoulis and Yvan Guindon
[Abstract]
Syntheses and Properties of Phosphinoselenoic
Chlorides, Acids, and Their Salts Pp. 1963-1973
Toshiaki Murai and Tsutomu Kimura
[Abstract]
Current Progress in the Acetate/Methyl Ketone
Aldol Reaction Pp. 1975-1992
David B. Kimball and Louis A. “Pete” Silks
III
[Abstract]
Utilization of Nonbonded Interactions Involving
Organoselenium Compounds Pp. 1993-2005
Martyn P. Coles
[Abstract]
Abstracts
[Back to top]
Editorial
Organoselenium chemistry continues to
attract the attention of many researchers. Perhaps the underlying
reason for this is the broad interest in the unique applications
of selenium to inorganic, biological, and organic chemistries.
Inorganic selenium complexes range from metal complexes and
new materials (organic semiconductors) to quantum dots. Since
the discovery of selenium as an essential trace element, the
role of selenium in biological systems has been actively investigated.
There are many selenium- containing proteins that have been
discovered. A large number of these are involved in redox
reactions and the most commonly encountered proteins are glutathione
peroxidase, selenoprotiens and selenophosphate synthetase
2. Incorporation of selenium into proteins can be accomplished
with selenocysteine and selenomethionine. In fact, selenocysteine
is the 21st proteinogenic amino acid. The special
role that selenium plays in many of these biological systems
can be directly linked to its unique chemical and physical
properties. New developments in organoselenium chemistry are
a reflection of the diversity of reactions that are accessible.
Anionic, cationic, and radical behaviors have been well studied
and are usually represented in the initial strategies researchers
use when devising a chemical transformation. Other reactions,
such as rearrangements and eliminations, are frequently employed.
The recent discovery of non-bonded interactions of the divalent
selenium atom with heteroatoms has been instrumental in the
development of novel chemistry in which this interaction plays
a critical role in the outcome of the reaction. Many of these
processes are attractive because of the ease of selenium introduction,
access to multiple oxidation states, and ease of removal at
the end of the sequence, giving rise to predictable chemo,
regio, and stereoselectivity. Logical extensions of many of
these novel chemistries have led to the development of asymmetric
methods which, in many cases, have provided chemical manifolds
to gain access to chiral compounds with excellent enantiomeric
excesses.
This issue of Current Organic Chemistry presents
specific examples of new advances in asymmetric methods that
employ selenium as a chiral controller unit. The reports authored
by Professor T. Wirth and D. M. Browne (New Developments with
Chiral Electophilic Selenium Regents), Professor C. Zhu and
Y. Huang (Asymmetric Synthesis of Chiral Organoselenium Compounds),
Professor A. L. Braga, D. S. L üdtke, and F. Vargas (Enantioselective
Synthesis Mediated by Catalytic Chiral Organoselenium Compounds),
and Professor Y. Guindon, B. Cardinal-David, J-F. Brazeau,
I. A. Katsoulis (Phenylselenoethers as Precursors of Acylic
Free Radicals. Creating Tertiary and Quaternary Centers Using
Free Radical-Based Intermediates) are excellent examples of
the level of science that is moving this field forward. Professor
T. Murai and T. Kimura present recent advances in the “Syntheses
and Properties of Phosphinoselenoic Chlorides, Acids and Their
Salts.” In this manuscript the synthesis and characterization
of optically active phosphinoselenoic acid derivatives is
described. This important work enables the steric and electronic
tuning of organophosphorus compounds to improve on catalytic
processes. The manuscript by Dr. D. Kimball and L. A. “Pete”
Silks reviews the literature on this segment of aldol reactions
and briefly describes the use of a chiral selenocarbonyl controller
unit to promote such reactions. Finally, the report of Professor
M. P. Cole (“Utilization of Nonbonded Interactions Involving
Organoselenium Compounds”) includes a review of the
literature that pertains to weak interactions involving the
selenium atom. With the advances in methods to directly observe
these weak interactions a general realization has emerged
that, indeed, these interactions can be quantified, physically
described, and more importantly utilized to design molecular
complexes with defined reactivities. The author has assimilated
the most recent developments in this area of organoselenium
chemistry and biochemistry, specifically where the role of
non-bonded interactions have been implicated, studied or used.
This manuscript describes a physical basis for these types
of interactions, links a number of areas of science to a common
theme, and clearly demonstrates that these interactions are
more prevalent than once ever imagined.
Louis A. "Pete" Silks
Biotechnology, Spectroscopy, and Isotope Chemistry group
Los Alamos National Laboratory
Bioscience Division, MS; E529
Los Alamos, NM 87544
[Back to top]
New Developments with Chiral Electrophilic Selenium
Reagents
Danielle M. Browne and Thomas Wirth
This review describes the development of enantiomerically
pure selenium reagents as electrophiles in stereoselective
synthesis. It outlines the addition of selenium electrophiles
to alkenes, which can be used as part of key reactions in
various transformations. Different nucleophiles can be employed
in the addition reactions including oxygen, nitrogen and carbon
nucleophiles. Furthermore, it has been shown that selenocyclisations
can been performed using similar nucleophiles for the formation
of different heterocycles. It has been established that the
structure of the selenium electrophile, its counterion and
the solvent all influence the course of these reactions. Most
transformations use stoichiometric amounts of selenium containing
reagents. Recently, selenenylation - deselenenylation reactions
were discovered where only catalytic amounts of reagents are
necessary.
[Back to top]
Asymmetric Synthesis of Chiral Organoselenium Compounds
Chengjian Zhu and Yijun Huang
Chiral organoselenium compounds can be attained from
three types of asymmetric synthesis. Chiral substrate-controlled
methods, chiral auxiliary-controlled methods, and chiral catalyst-controlled
methods toward optically active organoselenium derivatives
were illustrated. The strategy and classification of methods
underlying all asymmetric synthesis therefore involve enantiomerically
pure compounds to influence the stereochemical outcome of
the reactions. In this review, the advances in asymmetric
synthesis of some important classes of chiral organoselenium
compounds were described.
[Back to top]
Enantioselective Synthesis Mediated by Catalytic Chiral
Organoselenium Compounds
Antonio L. Braga, Diogo S. Lüdtke and Fabrício
Vargas
Selenium-based methods have developed rapidly over
the past few years and certain features of chiral selenium-containing
compounds make these reagents particularly valuable for efficient
stereoselective reactions.
Recent advances in stereoselective transformations involving
one-pot selenenylation-deselenylation sequences, which occur
using only catalytic amounts of the optically active diselenides
in the synthesis of valuable building blocks will be summarized.
Additionally, recent results of catalytic reactions using
chiral selenides and diselenides such as the enantioselective
copper catalyzed conjugate addition of organometallic reagents
to enones, diorganozinc addition to aldehydes, palladium-catalyzed
enantioselective allylic alkylation, among other topics will
also be addressed.
[Back to top]
Phenylselenoethers as Precursors of Acyclic Free Radicals.
Creating Tertiary and Quaternary Centers Using Free Radical-Based
Intermediates
Benoit Cardinal-David, Jean-François Brazeau,
Ioannis A. Katsoulis and Yvan Guindon
In the last two decades, enantioselective and diastereoselective
free radical-based processes have started to emerge as viable
methods to create stereogenic centers. To this end, chemists
have taken advantage of the homolytic carbon-selenium bond
cleavage as an efficient way to generate carbon-centered radicals.
The reactivity of the radicals generated from β-hydroxy
(or alkoxy) α-phenylseleno
(or α-halo)
esters in hydrogen transfer or allylation reactions will be
reviewed.
The minimization of the allylic-1,3 strain and the intramolecular
dipole-dipole effect in the transition states are at the origin
of the diastereoselectivities noted in these reactions (acyclic
stereocontrol). The predominance of the anti isomer,
in the hydrogen transfer reactions, has been shown to be enhanced
by taking advantage of the exocyclic effect. Lewis acids were
successfully used to create temporary cycles α
to the carbon-centered radical in order to induce the latter
effect.
Reversing the sense of the diastereoselectivity could be efficiently
achieved using bidendate Lewis acids through the endocyclic
effect. The synthesis of stereogenic quaternary centers using
free radical-based allylation is described. The development
of tandem reactions combining the Mukaiyama and the hydrogen
transfer reactions, with various Lewis acids, led to the synthesis
of propionates and polypropionate motifs. The use of novel
phenylselenoenoxysilanes in the Mukaiyama reaction is described.
[Back to top]
Syntheses and Properties of Phosphinoselenoic Chlorides,
Acids, and Their Salts
Toshiaki Murai and Tsutomu Kimura
The synthetic methods for phosphinoselenoic chlorides,
acids, and alkali metal and ammonium salts are overviewed.
The addition of elemental selenium to trivalent chlorophosphines
readily took place to give phosphinoselenoic chlorides. P-Chiral
chlorides were efficiently prepared by the one-pot reaction
of dichlorophenylphosphine or phosphorus trichloride with
elemental selenium and Grignard reagents. The amination of
the chlorides with optically active amines led to optically
active phosphinoselenoic amides, which were applied to asymmetric
synthesis as optically active ligands. The reaction of the
chlorides with carbon nucleophiles occurred both at the phosphorus
and selenium atoms, and the selectivity depended on the carbon
nucleophiles used and the substituents at the phosphorus atom
of the chlorides. The chlorides were used as key precursors
leading to a variety of phosphinoselenoic, -selenothioic,
-diselenoic acids and their alkali metal and ammonium salts.
Finally, the stereochemical outcome at the phosphorus atom
in the synthesis and substitution reaction of optically active
P-chiral phosphinoselenoic chlorides is shown.
[Back to top]
Current Progress in the Acetate/Methyl Ketone Aldol
Reaction
David B. Kimball and Louis A. “Pete”
Silks III
The aldol reaction of acetate and methyl ketone-based
donors with aldehyde acceptors is reviewed. Emphasis is placed
on major advances reported in the last 10-15 years. Several
methods for inducing chirality at the newly formed stereogenic
center are discussed, including popular alternate methods
for equivalent syntheses. Different methods for stereospecific
synthesis are compared in terms of yield, selectivity, ease
of synthesis, and applicability to both small molecule and
large macrolide production.
[Back to top]
Utilization of Nonbonded Interactions Involving Organoselenium
Compounds
Martyn P. Coles
Nonbonded interactions involving selenium have been
recognized for many years and are known to involve a number
of groups and atoms that form close contacts to the chalcogen
atom. With substantial improvements in high field NMR spectroscopy
and single crystal X-ray diffraction, enabling such techniques
to become ever more accessible, further understanding of the
role that these interactions play in the chemistry of selenium
has been gained in recent years. Given the well documented
use of organoselenium compounds in organic chemistry and the
recognition that certain enzymatic pathways utilize selenium
within the active centre, the design of new systems that incorporate
a group able to form nonbonded interactions of the type Se•••Y
forms an important field of research, with particular interest
in how this affects the chemistry associated with the resultant
selenium reagent.
This article aims to bring together some of the more recent
developments in the area of organoselenium chemistry, specifically
where the role of nonbonded interactions have been implicated
in affecting the outcome of the observed reactivity.
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