Enantioselective Claisen Rearrangement Research Articles

Enantioselective construction of branched 1,3-dienyl substituted quaternary carbon stereocenters by asymmetric allenyl Claisen rearrangement.

The availability of enantiomerically enriched 1,3-dienyl substituted quaternary stereocenters is highly valuable for the synthesis of complex natural compounds. Despite great advances in the area of construction of alkenyl-substituted types, a general, practical catalytic system that works for enantioselective formation of 1,3-diene derivatives still remains to be developed. Herein, we disclose the first asymmetric Claisen rearrangement of allenyl vinyl ethers to access optically active β-ketoesters, containing branched 1,3-butadienyl substituted stereocenters. A variety of substrates bearing a range of useful functional groups were well tolerated, thus affording the corresponding products with excellent enantioselectivities (up to 99% ee) and high yields (up to 91%).

ChemInform Abstract: Microwave Effect on Catalytic Enantioselective Claisen Rearrangement.

Catalytic enantioselective Claisen rearrangement was drastically enhanced under microwave irradiation conditions without any loss of the enantioselectivity. Based on Arrhenius plots it was revealed that enantioselectivity decreased as the internal reaction temperature increased. Therefore, this reaction acceleration would NOT be caused by only a simple thermal effect.

ChemInform Abstract: Catalytic Asymmetric Claisen Rearrangement of Enolphosphonates: Construction of Vicinal Tertiary and All‐Carbon Quaternary Centers.

AbstractA copper‐catalyzed enantioselective Claisen rearrangement of easily accessible enolphosphonates using commercially available PhBOX as chiral ligand is developed.

Microwave effect on catalytic enantioselective Claisen rearrangement

Catalytic enantioselective Claisen rearrangement was drastically enhanced under microwave irradiation conditions without any loss of the enantioselectivity. Based on Arrhenius plots it was revealed that enantioselectivity decreased as the internal reaction temperature increased. Therefore, this reaction acceleration would NOT be caused by only a simple thermal effect.

Copper(II)- and palladium(II)-catalyzed enantioselective Claisen rearrangement of allyloxy- and propargyloxy-indoles to quaternary oxindoles and spirocyclic lactones.

In this Article, a strategy to obtain highly enantioselective catalysts for the Claisen rearrangement of allyloxy- and propargyloxy-indoles is outlined. Ultimately, copper BOX and palladium BINAP or PHOX catalysts were discovered as superior in catalyzing Claisen rearrangements of allyloxy- or proparyloxy-substituted indoles to generate oxindoles bearing allyl- or allenyl-substituted quaternary centers. This method proved to be tolerant of a broad range of functional groups. Tandem reactions of the silyl-allene products provide rapid access to a variety of spirocyclic oxindoles in one operation.

Catalytic asymmetric Claisen rearrangement of enolphosphonates: construction of vicinal tertiary and all-carbon quaternary centers.

A Cu-catalyzed enantioselective Claisen rearrangement of easily-accessible enolphosphonates using commercially available (R, R)-PhBOX as the chiral ligand was developed. A wide range of rearrangement products with contiguous tertiary and all carbon quaternary centers were obtained in excellent yields and stereoselectivities. The α-ketophosphonate products could be easily transformed into other functional groups in high efficiency.

Asymmetric Synthesis of Allenyl Oxindoles and Spirooxindoles by a Catalytic Enantioselective Saucy–Marbet Claisen Rearrangement

Asymmetric Synthesis of Allenyl Oxindoles and Spirooxindoles by a Catalytic Enantioselective Saucy–Marbet Claisen Rearrangement

Transition-state charge stabilization through multiple non-covalent interactions in the guanidinium-catalyzed enantioselective Claisen rearrangement.

The mechanism by which chiral arylpyrrole-substituted guanidinium ions promote the Claisen rearrangement of O-allyl α-ketoesters and induce enantioselectivity was investigated by experimental and computational methods. In addition to stabilization of the developing negative charge on the oxallyl fragment of the rearrangement transition state by hydrogen-bond donation, evidence was obtained for a secondary attractive interaction between the π-system of a catalyst aromatic substituent and the cationic allyl fragment. Across a series of substituted arylpyrrole derivatives, enantioselectivity was observed to vary predictably according to this proposal. This mechanistic analysis led to the development of a new p-dimethylaminophenyl-substituted catalyst, which afforded improvements in enantioselectivity relative to the parent phenyl catalyst for a representative set of substrates.

Chiral Guanidinium-Catalyzed Enantioselective Claisen Rearrangement

Jacobsen and co-workers disclose the enantioselective Claisen rearrangement of O-allyl β-keto esters catalyzed by chiral guanidinium salt 1. The desired products were obtained with good yields and enantioselectivities from a broad variety of different substrates, including substituted O-allyl β-keto esters leading to the ­formation of vicinal stereocenters. The utility of the products was demonstrated in the enantio­selective construction of the hyperforin core structure. Furthermore, the recyclability of the catalyst was demonstrated, and computational studies modeling the reaction pathway and a plausible transition state are provided.

An enantioselective Claisen rearrangement catalyzed by N-heterocyclic carbenes.

In the presence of a chiral azolium salt (10 mol %), enols and ynals undergo a highly enantioselective annulation reaction to form enantiomerically enriched dihydropyranones via an N-heterocyclic carbene catalyzed variant of the Claisen rearrangement. Unlike other azolium-catalyzed reactions, this process requires no added base to generate the putative NHC-catalyst, and our investigations demonstrate that the counterion of the azolium salt plays a key role in the formation of the catalytically active species. Detailed kinetic studies eliminate a potential 1,4-addition as the mechanistic pathway; the observed rate law and activation parameters are consistent with a Claisen rearrangement as the rate-limiting step. This catalytic system was applied to the synthesis of enantioenriched kojic acid derivatives, a reaction of demonstrated synthetic utility for which other methods for catalytic enantioselective Claisen rearrangements have not provided a satisfactory solution.

Enantioselective Catalysis of Claisen Rearrangement by DABNTf—Pd(II) Complex.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Enantioselective catalysis of Claisen rearrangement by DABNTf–Pd(II) complex

Two types of palladium complexes, cationic ( R ) - BINAP – Pd 2 + ( SbF 6 - ) 2 and neutral ( R)-DABNTf–Pd(CH 3CN) 2 were examined as chiral catalysts for enantioselective Claisen rearrangement. DABNTf–Pd(CH 3CN) 2 complex gave high enantio- and anti-diastereoselectivity, and good yield. This Claisen rearrangement should proceed via six-membered boat transition state through bi-dentate coordination to the Pd catalyst.

Catalysis of the Claisen Rearrangement of Aliphatic Allyl Vinyl Ethers

The thermal Claisen rearrangement of allyl vinyl ethers is generally regarded as high-performance method for diastereoselective C−C bond formation. Substrate-induced diastereoselectivity and reagent-induced enantioselectivity with stoichiometric amounts of external chiral auxiliaries have frequently been exploited to control the stereochemical course of the Claisen rearrangement. This review summarizes the attempts to catalyze the Claisen rearrangement of acyclic aliphatic allyl vinyl ethers with chiral and achiral catalysts. The best suited catalysts for the Claisen rearrangement so far identified are Lewis acids. Finally, bis(oxazoline)copper(II) complexes have found a further useful application as chiral catalysts for the first catalytic, enantioselective Claisen rearrangement − 90 years after Ludwig Claisen originally reported a [3,3]-sigmatropic rearrangement of an allyl vinyl ether.

The Catalytic Enantioselective Claisen Rearrangement of an Allyl Vinyl Ether This work was financially supported by the Deutsche Forschungsgemeinschaft, the Fonds der Chemischen Industrie, and the Dr. Otto Röhm Gedächtnisstiftung. M.H. thanks Prof. P. Metz and Prof. H.-U. Reissig for their support.

The Catalytic Enantioselective Claisen Rearrangement of an Allyl Vinyl Ether This work was financially supported by the Deutsche Forschungsgemeinschaft, the Fonds der Chemischen Industrie, and the Dr. Otto Röhm Gedächtnisstiftung. M.H. thanks Prof. P. Metz and Prof. H.-U. Reissig for their support.

Enantioselective Claisen rearrangement of difluorovinyl allyl ethers

The enantioselective Claisen rearrangement of difluorovinyl allyl ethers was achieved, for the first time, in moderate to good enantioselectivity using a chiral boron reagent as the Lewis acid.

ChemInform Abstract: Highly Enantioselective Claisen Rearrangement of Imidates Derived from Primary Allyl Alcohols.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Highly Enantioselective Claisen Rearrangement of Imidates Derived from Primary Allyl Alcohols.

A highly enantioselective and diastereoselective Claisen rearrangement of N-arylimidates derived from an axially chiral binaphthylamine auxiliary is reported. Upon deprotonation of the imidates with lithium diethylamide, the resultant azaenolates rearrange at 0 degrees C to give anti alpha,beta-disubstituted, gamma,delta-unsaturated N-binaphthyl amides. A iodolactonization/zinc reduction sequence readily converts these amides into the corresponding carboxylic acids of 91-95% ee and allows an efficient recovery of the chiral auxiliary.