alexa Perspectives in Modern Asymmetric Catalysis
ISSN: 2161-0401
Organic Chemistry: Current Research
Like us on:
Make the best use of Scientific Research and information from our 700+ peer reviewed, Open Access Journals that operates with the help of 50,000+ Editorial Board Members and esteemed reviewers and 1000+ Scientific associations in Medical, Clinical, Pharmaceutical, Engineering, Technology and Management Fields.
Meet Inspiring Speakers and Experts at our 3000+ Global Conferenceseries Events with over 600+ Conferences, 1200+ Symposiums and 1200+ Workshops on
Medical, Pharma, Engineering, Science, Technology and Business

Perspectives in Modern Asymmetric Catalysis

Angela Patti*
National Research Council of Italy – Institute of Biomolecular Chemistry, Via Paolo Gaifami, 18 – 95126 Catania, Italy
Corresponding Author : Angela Patti
National Research Council of Italy
Institute of Biomolecular Chemistry
Via Paolo Gaifami, 18 – 95126 Catania, Italy
E-mail:
[email protected]
Received November 26, 2012; Accepted November 27, 2012; Published November 30, 2012
Citation: Patti A (2012) Perspectives in Modern Asymmetric Catalysis. Organic Chem Curr Res 1:e117. doi:10.4172/2161-0401.1000e117
Copyright: © 2012 Patti A. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Visit for more related articles at Organic Chemistry: Current Research

Editorial
Asymmetric catalysis is nowadays a fundamental methodology for the preparation of chiral compounds whose demands is continuously growing in different fields of chemistry. Since the pioneering works in mid-60’s of Knowles and Noyori on the asymmetric hydrogenation of olefins and ketones promoted by ruthenium/chiral diphoshine complexes, a wide portfolio of reactions have been developed in their enantioselective version thanks to the identification of the most suitable metal-chiral ligand combinations. With the aid of mechanistic studies, an impressive number of ligands with different coordinating groups and large structural diversity have been synthesized and high levels of stereocontrol achieved by careful tuning of their steric and electronic properties. However, in still limited cases high productivity, broad substrate scope, functional group tolerance and cost of the catalyst have fulfilled the requirements for industrial applications so that the search for new and more efficient catalytic systems remains an active topic in the field.
In the last decade organocatalysis, in which small organic molecules act as catalytically active species, has explosively grown in view of its operational simplicity, the possibility to functionalize carbonyl compounds without any substrate pre-activation and the identification of different activation modes as a basis for rational design of more active catalysts and discovery of novel reactivity. Initially perceived as a complementary approach to the traditional transition-metal based asymmetric catalysis, organocatalysis is today steadily moving as a real discipline toward its mature stage.
In the “sustainable development” era the scientific community is faced with the need to reduce the costs, the toxicity and the amount of waste related with chemical synthesis, but reconsideration of the existing productive processes often proved to be not sufficient to meet the goal so that innovative synthetic strategies and conceptual breakthroughs are greatly expected. Although asymmetric catalysis is a “green” methodology by itself, in accordance with 9th principle of green chemistry, further improvements are possible and extensive search for non-toxic metals and reaction media, more recyclable catalysts and solvents as well as more efficient reactor technology has opened new opportunities in setting effective solutions.
As selected examples, the fast expansion of stereoselective reactions promoted by complexes with the abundant, safe and economical iron metal and greater availability of Cu- and Ir-catalysts provide not only promising alternatives to precious noble metals but have also enlarged the range of applications to include new substrates and nucleophiles. The grafting of active ligands on magnetic nanoparticles or polymers with switchable solubility to give easily recoverable and recyclable catalysts and the use of water as biocompatible solvent in “on water” protocols with unsoluble catalysts and reagents are other interesting approaches likely to increase in the future.
In a long term vision, the added value of “green chemistry” can be recognized in the emerging of new general concepts with potentially high impact on the blossoming of a modern way to thinking and planning organic synthesis.
Taking inspiration from nature in which complex molecules from simple precursors are formed by means of coupled action of different enzymes, multicatalysis is attracting burgeoning attention as a powerful synthetic paradigm for the construction of multiple sterogenic centers through consecutive reactions in a single flask. Obvious advantages in the absence of derivatization steps, the reduction of waste generation related with purification of intermediates and the simplification of product isolation for the predominance of single stereoisomers make multicatalytic processes very effective for high atom economy and lowered environmental factor.
In this context, several cascade sequences promoted by secondary amines, able to react via enamine or iminium intermediate, or by multicatalytic systems, in which distinct organocatalysts work with different activation modes, have been recently developed and their number is expected to quickly increase. The synthesis of tetrasubstituted cyclohex-1-ene carbaldehydes from a multicomponent reaction of aldehydes, α, β-unsaturated aldehydes and β-nitrostyrenes in the presence of the sole prolinol Jorgensøn’s catalyst through a Michael/Michael/aldol sequence is a seminal example of the application of the strategy, that was successfully extended to the preparation of other carbocyclic structures with up to four new stereogenic carbons by using the same catalyst in combination with chiral thioureas or N-heterocyclic carbenes. In the same way, the orthogonal reactivity of proline/Mac Millan’s imidazolinone binary system gives a versatile platform for double functionalization of the ethylenic bond of enals with a broad range of both nucleophiles and electrophiles also allowing the access to all diastereomers by choosing the suitable combination of catalysts configurations.
In a different approach, transition metal complex-organocatalyst hybrids could enable the access to challenging molecular frameworks through unprecendented transformations not possible using a single catalyst alone. The specific activation of alkynes or allenes by gold (I)- catalysts to give a variety of stereoselective cyclization reactions, in some cases also with formation of C-heteroatom bonds, in the presence of an organocatalyst as source of stereocontrol and the enantioselective allylation of α-branched aldehydes to create an all-carbon quaternary stereogenic center by using a Pd/BINOL-derived phosphoric acid system are outstanding examples in this relatively young area.
The high enantioselectivity displayed by BINOL-derived phosphoric acids, alone or in conjunction with transition metal complexes, has been associated with their Brønsted acid character that leads to the formation of chiral anions able to exert stereocontrol by means of strong ion-pairing with cationic intermediates generated in the reactions. For the large occurrence of cationic specie in many chemical transformations this mode of chirality transfer, categorized as asymmetric counterion directed catalysis, could provide a highly general strategy to achieve stereoselectivity. Beyond Brønsted acids based on the 1,1’-binaphtyl privileged scaffold, other systems in which simple anions as halides or carboxylates are rendered chiral by hydrogen bonds with enantiopure thiourea catalysts begin to appear in literature.
The renewed interest in ion-pairing, previously mainly focused on chiral ammonium quaternary salts used in phase-transfer catalysis, also opens new possibility in the design of novel supramolecular catalysts deriving from self-assembly of a chiral amine and a chiral acid, each one with its own organocatalytic activation potential, driven by electrostatic attraction. Cooperative effects could be delivered in wellordered transition states in which all the reaction partners are held in close proximity by ionic bonds, ultimately resulting in improved reactivity and stereoselectivity.
Although the avoidance of possible interferences between multiple catalysts and/or regents is often a difficult task, in some instances resolved using sophisticated site-isolation techniques, multicatalysis offers great opportunities for substantial advances in the synthesis of stereogenically complex structures. Combinatorial libraries of supramolecular catalysts, built on the basis of different non-covalent interactions also including ion-pairing, can contribute to the identification of active and versatile catalysts with unexpected molecular frameworks and simplified synthesis with respect to the covalent analogues. Asymmetric catalysis will surely continue to be an exciting research field and it will play its part in addressing the demands of green chemistry with the development of novel concepts, new chemical reactivity and more sustainable processes.
Select your language of interest to view the total content in your interested language
Post your comment

Share This Article

Relevant Topics

Article Usage

  • Total views: 11748
  • [From(publication date):
    December-2012 - Oct 23, 2017]
  • Breakdown by view type
  • HTML page views : 7982
  • PDF downloads :3766
 

Post your comment

captcha   Reload  Can't read the image? click here to refresh

Peer Reviewed Journals
 
Make the best use of Scientific Research and information from our 700 + peer reviewed, Open Access Journals
International Conferences 2017-18
 
Meet Inspiring Speakers and Experts at our 3000+ Global Annual Meetings

Contact Us

Agri, Food, Aqua and Veterinary Science Journals

Dr. Krish

[email protected]

1-702-714-7001 Extn: 9040

Clinical and Biochemistry Journals

Datta A

[email protected]

1-702-714-7001Extn: 9037

Business & Management Journals

Ronald

[email protected]

1-702-714-7001Extn: 9042

Chemical Engineering and Chemistry Journals

Gabriel Shaw

[email protected]

1-702-714-7001 Extn: 9040

Earth & Environmental Sciences

Katie Wilson

[email protected]

1-702-714-7001Extn: 9042

Engineering Journals

James Franklin

[email protected]

1-702-714-7001Extn: 9042

General Science and Health care Journals

Andrea Jason

[email protected]

1-702-714-7001Extn: 9043

Genetics and Molecular Biology Journals

Anna Melissa

[email protected]

1-702-714-7001 Extn: 9006

Immunology & Microbiology Journals

David Gorantl

[email protected]

1-702-714-7001Extn: 9014

Informatics Journals

Stephanie Skinner

omics[email protected]

1-702-714-7001Extn: 9039

Material Sciences Journals

Rachle Green

[email protected]

1-702-714-7001Extn: 9039

Mathematics and Physics Journals

Jim Willison

[email protected]

1-702-714-7001 Extn: 9042

Medical Journals

Nimmi Anna

[email protected]

1-702-714-7001 Extn: 9038

Neuroscience & Psychology Journals

Nathan T

[email protected]

1-702-714-7001Extn: 9041

Pharmaceutical Sciences Journals

John Behannon

[email protected]

1-702-714-7001Extn: 9007

Social & Political Science Journals

Steve Harry

[email protected]

1-702-714-7001 Extn: 9042

 
© 2008-2017 OMICS International - Open Access Publisher. Best viewed in Mozilla Firefox | Google Chrome | Above IE 7.0 version
adwords