Hybrid Nanoscale Ligand

A new salen–C₆₀ dyad forms complexes with transition metals, thereby tuning the optical, redox, and catalytic properties
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sp3-Carbon-Based Liquid Crystals

The liquid-crystalline phase of poly(ethylidene acetate) is described and explained by the formation of triple-helix aggregates
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Co-Catalyzed Radical Cycloaddition of [60]Fullerene with Active Dibromides: Selective Synthesis of Carbocycle-Fused Fullerene Monoadducts

Co-Catalyzed Radical Cycloaddition of [60]Fullerene with Active Dibromides: Selective Synthesis of Carbocycle-Fused Fullerene Monoadducts

Shirong Lu, Weili Si, Ming Bao, Yoshinori Yamamoto, and Tienan Jin

WPI-Advanced Institute for Materials Research (WPI-AIMR), Tohoku University, Sendai 980-8577, Japan, and State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116012, China

Org. Lett., Article ASAP

Publication Date (Web): July 23, 2013 (Letter)

DOI: 10.1021/ol401876n

http://pubs.acs.org/doi/abs/10.1021/ol401876n

An efficient and highly selective Co-catalyzed radical cycloaddition of [60]fullerene with active dibromides for the synthesis of three-, five-, six-, and seven-membered carbocycle-fused fullerene monoadducts has been reported. The controlled experiments unambiguously disclosed that the reaction proceeds through the formation of a fullerene monoradical as a key intermediate.

Co-Catalyzed Radical Cycloaddition of [60]Fullerene with Active Dibromides: Selective Synthesis of Carbocycle-Fused Fullerene Monoadducts

Co-Catalyzed Radical Cycloaddition of [60]Fullerene with Active Dibromides: Selective Synthesis of Carbocycle-Fused Fullerene Monoadducts

Shirong Lu, Weili Si, Ming Bao, Yoshinori Yamamoto, and Tienan Jin

WPI-Advanced Institute for Materials Research (WPI-AIMR), Tohoku University, Sendai 980-8577, Japan, and State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116012, China

Org. Lett., Article ASAP

Publication Date (Web): July 23, 2013 (Letter)

DOI: 10.1021/ol401876n

http://pubs.acs.org/doi/abs/10.1021/ol401876n

An efficient and highly selective Co-catalyzed radical cycloaddition of [60]fullerene with active dibromides for the synthesis of three-, five-, six-, and seven-membered carbocycle-fused fullerene monoadducts has been reported. The controlled experiments unambiguously disclosed that the reaction proceeds through the formation of a fullerene monoradical as a key intermediate.

Self-Assembled Wheels

Self-Assembled Wheels

Two different terpyridine ligands self-assemble when mixed with zinc(II) ions to form 2D or 3D spoked wheels
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Fries Rearrangement Mechanism

The Fries rearrangement proceeds through ionic intermediates. The reaction depends on the structure of the substrates and the reaction conditions. 

The scheme depicts the formation of an ortho-acylated phenol from a substituted phenolic ester in the presence of aluminium trihalide catalyst. The photo Fries rearrangement mechanism proceeds through Radical intermediates.




The Fries rearrangement, named for the German chemist Karl Theophil Fries, is a rearrangement reaction of a phenyl ester to a hydroxy aryl ketone by catalysis of Lewis acids.^[1][2][3][4]
It involves migration of an acyl group of phenyl ester to benzene ring. The reaction is ortho and para selective and one of the two products can be favoured by changing reaction conditions, such as temperature and solvent.

Mechanism

Despite many efforts a definitive reaction mechanism for the Fries rearrangement is not available. Evidence for inter- and intramolecular mechanisms have been obtained by so-called cross-experiments with mixed reactants. Reaction progress is not dependent on solvent or substrate. A widely accepted mechanism involves a carbocation intermediate.

In the first reaction step a Lewis acid for instance aluminium chloride AlCl
3 co-ordinates to the carbonyl oxygen atom of the acyl group. This oxygen atom is more electron rich than the phenolic oxygen atom and is the preferred Lewis base. This interaction polarizes the bond between the acyl residue and the phenolic oxygen atom and the aluminium chloride group rearranges to the phenolic oxygen atom. This generates a free acylium carbocation which reacts in a classical electrophilic aromatic substitution with the aromatic ring. The abstracted proton is released as hydrochloric acid where the chlorine is derived from aluminium chloride. The orientation of the substitution reaction is temperature dependent. A low reaction temperature favors para substitution and with high temperatures the ortho product prevails. Formation of the ortho product is also favoured in non-polar solvents; as the solvent polarity increases, the ratio of the para product also increases.^[5]

Scope

Phenols react to esters but do not react to hydroxyarylketones with acylhalogen compounds under Friedel-Crafts acylation reaction conditions and therefore this reaction is of industrial importance for the synthesis of hydroxyarylketones which are important intermediates for several pharmaceutics such as paracetamol and salbutamol. As an alternative to aluminium chloride, other Lewis acids such as boron trifluoride and bismuth triflate or strong protic acids such as hydrogen fluoride and methanesulfonic acid can also be used. In order to avoid the use of these corrosive and environmentally unfriendly catalysts altogether research into alternative heterogeneous catalysts is actively pursued.

Limits

In all instances only esters can be used with stable acyl components that can withstand the harsh conditions of the Fries rearrangement. If the aromatic or the acyl component is heavily substituted then the chemical yield will drop due to steric constraints. Deactivating meta-directing groups on the benzene group will also have an adverse effect as can be expected for a Friedel–Crafts acylation.

Photo-Fries rearrangement

In addition to the ordinary thermal phenyl ester reaction a so-called photochemical Photo-Fries rearrangement exists^[6] that involves a radical reaction mechanism. This reaction is also possible with deactivating substituents on the aromatic group. Because the yields are low this procedure is not used in commercial production. However, photo-Fries rearrangement may occur naturally, for example when a plastic bottle made of polyethylene terephthalate (PET) is exposed to the sun, particular to UV light at a wavelength of about 310 nm, if the plastic has been heated to 40 degrees Celsius or above (as might occur in a car with windows closed on a hot summer day). In this case, photolysis of the ester groups would lead to leaching of phthalate from the plastic.^[7]

Anionic Fries rearrangment

In addition to Lewis acid and photo-catalysed Fries rearrangements, there also exists an anionic Fries rearrangement. In this reaction, the aryl ester undergoes ortho-metallation with a strong base, which then rearranges in a nucleophilic attack mechanism.

1.  Fries, K. ; Finck, G. (1908). "Über Homologe des Cumaranons und ihre Abkömmlinge". Chemische Berichte 41 (3): 4271–4284. doi:10.1002/cber.190804103146.
2.  Fries, K.; Pfaffendorf, W. (1910). "Über ein Kondensationsprodukt des Cumaranons und seine Umwandlung in Oxindirubin". Chemische Berichte 43 (1): 212–219. doi:10.1002/cber.19100430131.
3.  March, J. Advanced Organic Chemistry, 3rd Ed.; John Wiley & Sons: Chichester, 1985; S. 499ff.
4.  Blatt, A. H. Org. React. 1942, 1.
5.  Kürti, László; Czakó, Barbara (2005). Strategic Applications of Named Reactions in Organic Synthesis: Background and Detailed Mechanisms. Elsevier Academic Press. p. 181. ISBN 0123694833.
6.  Bellus, D. Advances in Photochemistry; John Wiley & Sons: Chichester, 1971; Vol. 8, 109–159.
7.  Norma Searle, "Environmental effects on polymeric materials," pp. 313–358, in Plastics and the Environment, edited by Anthony Andrade, Wiley, 2003.

 

Quindine catalyzed synthesis of spirooxindoles through sequential Michael-Henry reactions.

A novel organocatalytic strategy for the synthesis of highly substituted spirocyclopentaneoxindoles was developed employing simple nitrostyrenes and 3-substituted oxindoles as starting materials. Michael–Henry cascade reactions, enabled through cinchona alkaloid organocatalysis, provided products in high yield and excellent enantioselectivity in a single step.

Spirooxindoles in one step

 DOI: 10.1021/ol300441z

http://pubs.acs.org/doi/abs/10.1021/ol300441z

If you just leaf through an organic chemistry journal, from JOC to Organic Letters, from EJOC to OBC, there is a huge number of papers describing synthesis of oxindoles! Indeed, the interest in the oxindoles scaffold rapidly increased in the last years and several methodologies have been published for the asymmetric synthesis of 3,3’-disubstituted oxindoles.

Cascade organacatalysis is a powerful tool for the for the asymmetric synthesis of very complex structures containing several stereogenic centers and oxindoles are optimal templates for the applications of these wonderful catalytic methodologies. For example, prof. Paolo Melchiorre, one the most expert in the organocatalysis field, published several works in the application of organocascade catalysis for the synthesis of quaternary oxindoles.

In this communication, Carlos Barbas, another pioneer of organocatalysis, reported a quindine-catalyzed synthesis of spirooxindoles through sequential Michael-Henry reactions.

They first performed a preliminary methodological study aimed at finding the most efficient catalyst, which turned out to be quindine derivative depicted below.

Subsequently the scope of the reaction has been expanded, by employing a wide range of substituted oxindoles, as well as different nitrostyrens. Performing the reaction at 0°C in CH2Cl2 as solvent in presence of quinidine derivative 1 permitted the isolation of the products in very high yield and optimal enantiomeric excess and diastereoisomeric ratio.

It is noteworthy to mention that this simple methodology permits the straightforward construction of the spirooxindole moiety containing four stereogenic centers,, with full control of the stereochemical outcome. This is another demonstration of the powerful of organocatalysis. 

http://pubs.acs.org/doi/abs/10.1021/ol300441z

Assembly of Spirooxindole Derivatives Containing Four Consecutive Stereocenters via Organocatalytic Michael–Henry Cascade Reactions

Klaus Albertshofer , Bin Tan , and Carlos F. Barbas, III*

The Skaggs Institute for Chemical Biology and the Departments of Chemistry and Molecular Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, United States

Org. Lett., 2012, 14 (7), pp 1834–1837

DOI: 10.1021/ol300441