Highly enantioselective catalytic asymmetric Claisen rearrangement of 2-alkoxycarbonyl-substituted allyl vinyl ethers

Progress in the catalytic asymmetric Claisen rearrangement of 2-alkoxycarbonyl-substituted allyl vinyl ether is reported. Application of a more Lewis acidic catalyst, [Cu{(S,S)-t-Bu-box}](H₂O)₂(SbF₆)₂, afforded β-chiral α-keto ester with an enantiomeric excess up to 99%. We suggest a highly polarized transition state for the Lewis acid-catalyzed Claisen rearrangement in order to explain the experimental results.     

Catalytic thia-Sommelet-Hauser rearrangement: application to the synthesis of oxindoles

A series of 3-arylthio-1,3-disubstituted-oxindoles were prepared in good yields by the reaction of α-diazocarbonyl compounds and sulfenamides. The reaction involves a Rh-catalyzed thia-Sommelet-Hauser-type rearrangement.     

Catalytic enantioselective fluorination of oxindoles

We have developed a highly efficient catalytic enantioselective fluorination of oxindole derivatives. In the presence of a catalytic amount of chiral Pd complex 2 (2.5 mol %), various substrates, including aryl- and alkyl-substituted oxindoles, were fluorinated in a highly enantioselective manner (up to 96% ee). In addition, when R was a hydrogen atom, enantioselective fluorination followed by solvolysis gave a monofluorinated ester with up to 93% ee. To our knowledge, this is the first example of catalytic enantioselective fluorination of oxindoles.     

The Claisen rearrangement of protonated allyl phenyl ether

Molecular protonated ions of allyl phenyl ether undergo a Claisen rearrangement both in the ion source and along the flight path. The rearranged ions undergo fragmentation, the predominat loss being ethene, and only a small contribution from loss of carbon monoxide is observed. Collision-induced dissociation spectra are used to verify the structures of the daughter ions. These spectra, together with other evidence of an acid-induced ortho rearrangement, allow a mechanism to be proposed for the ethene loss. In contrast, molecular protonated ions of propargyl phenyl ether lose exclusively carbon monoxide.     

Catalytic asymmetric synthesis of 3,3-disubstituted oxindoles: diazooxindole joins the field

The catalytic asymmetric synthesis of 3,3-disubstituted oxindoles, a big family of privileged scaffolds in natural products and drugs, is of current interest. Recently, the catalytic asymmetric functionalization of diazooxindoles emerges as a potentially general and flexible strategy for this purpose, with several notable examples coming out in 2013. In this digest, synthetic applications of diazooxindoles have been summarized and discussed, which might be helpful for readers to understand the special properties of this type of donor/acceptor cyclic diazo reagent and to develop new catalytic asymmetric reactions.     

Claisen rearrangement of allyl aryl ethers under adsorption conditions

Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1934–1935, August, 1990.     

Bismuth triflate catalyzed Claisen rearrangement of allyl naphthyl ethers

Bismuth triflate was found to be an efficient catalyst for the Claisen rearrangement of allyl naphthyl ethers. The reaction proceeds smoothly with a catalytic amount of bismuth triflate (20 mol %) to afford the corresponding ortho-allyl naphthol in moderate to good yields in most cases.     

Catalytic enantioselective synthesis of fluoromethylated stereocenters by asymmetric hydrogenation

Fluoromethyl groups possess specific steric and electronic properties and serve as a bioisostere of alcohol, thiol, nitro, and other functional groups, which are important in an assortment of molecular recognition processes. Herein we report a catalytic method for the asymmetric synthesis of a variety of enantioenriched products bearing fluoromethylated stereocenters with excellent yields and enantioselectivities. Various N,P-ligands were designed and applied in the hydrogenation of fluoromethylated olefins and vinyl fluorides.

Herein, a catalytic asymmetric hydrogenation to synthesize various products bearing fluoromethylated stereocenters has been developed.     

Regioselective boron trichloride-mediated aromatic Claisen rearrangement of resorcinol allyl ethers

The regioselective Claisen rearrangement of resorcinol allyl ethers with boron trichloride was achieved with good selectivity (ca. 13:1) to afford the 6-isomer as major product.     

Catalytic asymmetric domino Michael addition-alkylation reaction: enantioselective synthesis of dihydrofurans

A catalytic enantioselective synthesis of dihydrofurans has been developed. 1,3-Dicarbonyl derivatives react with (E)-β,β-bromonitrostyrenes in the presence of a chiral bifunctional thiourea catalyst providing mild and efficient access to diverse polysubstituted dihydrofurans in good yields and enantioselectivities.     

Catalytic asymmetric synthesis of spirooxindoles by a mannich-type reaction of isothiocyanato oxindoles

Easy access: a strontium/Schiff base complex as catalyst for the title reaction provided straightforward access to enantiomerically enriched spiro[imidazolidine-4,3'-oxindole] compounds, as well as a spiro[imidazoline-4,3'-oxindole] through a two-step conversion from the Mannich adduct.     

Highly diastereoselective Claisen rearrangement leading to vicinal quaternary carbons construction of oxindoles

An efficient approach to spirocyclic oxindole architecture with vicinal quaternary carbon centers is described. The reaction of 2-allyloxyindolin-3-ones with cyanomethylphosphonate at low reaction temperature proceeds smoothly with consecutive olefination, isomerization, deacylation, and anion-accelerated Claisen rearrangement to give the 3,3-disubstituted oxindoles with vicinal quaternary all-carbon centers in high yield and diastereoselectivity. The oxindoles are readily converted into more synthetically advanced spiro-products.     

Catalytic asymmetric cyclocarbonylation of o-isopropenylphenols: enantioselective synthesis of six-membered ring lactones

Cyclocarbonylation of o-isopropenylphenols with CO (500 psi) and H(2) (100 psi), using Pd(OAc)(2) and (+)-DIOP as the chiral catalyst, in CH(2)Cl(2) affords 3,4-dihydro-4-methylcoumarins in 60-85% yield and in up to 90% enantiomeric excess. The stereoselectivity is influenced by the structure of the chiral phosphine ligands and substrates, as well as by the reaction conditions.     

Catalytic asymmetric aza-Michael-Michael addition cascade: enantioselective synthesis of polysubstituted 4-aminobenzopyrans

A catalytic asymmetric aza-Michael-Michael addition cascade of anilines to nitroolefin enoates in the presence of chiral bifunctional thiourea catalysts has been disclosed. This reaction provides a mild and efficient approach to polysubstituted chiral 4-aminobenzopyrans bearing three consecutive stereocenters in high yields with excellent stereoselectivities.     

A spin-coupled study of the Claisen rearrangement of allyl vinyl ether

The spin-coupled (SC) form of modern valence bond (VB) theory is utilised to examine the electronic structure of the transition state (TS) and the electronic reaction mechanism of the Claisen rearrangement of allyl vinyl ether. The differences between the spin-coupling patterns and orbital overlap integrals at the optimised TS geometries obtained using B3LYP/6-31G^*, MP2/6-31G^* and MP4(SDQ)/6-31G^* wavefunctions are minimal, and the SC picture suggests that the TS is non-aromatic. SC calculations along the intrinsic reaction coordinates computed at these three levels of theory also produce near identical results. The SC wavefunctions at different stages of the reaction provide easily interpretable orbital diagrams which, in combination with the changes in the orbital overlap integrals, indicate an electronic reaction mechanism involving concerted, though not entirely synchronous, bond breaking and bond formation processes. The evolution of the active space spin-coupling pattern, which is closely related to the classical VB concept of resonance, combined with the changes in the orbital overlap integrals, show that the reaction path involves a region in which the electronic structure of the reacting system becomes similar to that of benzene. This suggests that during the Claisen rearrangement the reacting system can attain moderately aromatic character but that this does not necessarily happen at the TS. The results of the SC analysis indicate that the most appropriate schematic representation of the Claisen rearrangement is furnished by a homolytic mechanism in which six harpoons describe the changes in the bonding pattern from reactant to product     

Catalytic asymmetric sulfenylation of unprotected 3-substituted oxindoles

Catalytic asymmetric sulfenylation of unprotected 3-substituted oxindoles has been developed via cooperative catalysis of a chiral N,N'-dioxide-Sc(OTf)(3) complex and a Br?nsted base. Utilizing readily available N-(phenylthio)phthalimide as the sulfur source, a wide range of optically active 3-phenylthiooxindoles were obtained in excellent yields with excellent enantioselectivities under mild reaction conditions.