Stereoselective Synthesis of Vinylcyclopropa[b]indolines via a Rh-Migration Strategy.

A mild rhodium catalytic system has been developed to synthesize vinylcyclopropa[b]indolines through cyclopropanation of indoles with vinyl carbenoids generated from ring opening of cyclopropenes in situ. By employing a Rh-migration strategy, the products can be obtained with good to excellent E:Z ratios (≤99:1) and complete diastereoselectivity (≤99:1). This method is easy, has a low catalyst loading, and works for a broad range of functionalities.

Copper-Catalyzed Functionalization of Aza-Aromatic Rings with Fluoroalcohols via Direct C(sp2)-H/C(sp3)-H Coupling Reactions.

An efficient copper-catalyzed direct C(sp2)-H/C(sp3)-H coupling reaction of aza-aromatic rings with fluoroalcohols is developed. A variety of useful building blocks including hydroxyfluoroalkylated aniline, pyrrole, and indole derivatives bearing a quaternary carbon center could be constructed with high regioselectivity and good to excellent yields under very mild reaction conditions. The reaction is believed to undergo a fluoroalcohol oxidation and to follow an electronic addition reaction pathway.

2H-Azirines as Potential Bifunctional Chemical Linkers of Cysteine Residues in Bioconjugate Technology.

2H-Azirine-2-caboxamides have been designed to perform as a new type of bifunctional thiol linker under very mild reaction conditions. The cleavage of a C-N double bond of 2H-azirine furnishes an amino amide functional group in situ through a thiol addition and ring-opening process. It works with a broad scope of thiols and 2H-azirines in the absence of any catalysts at room temperature. Cysteine-containing peptides have also been demonstrated to work efficiently in a completely water solution.

Stereoselective synthesis of trifluoromethyl-substituted 2H-furan-amines from enaminones.

A straightforward strategy for synthesis of highly functionalized trifluoromethyl 2H-furans is described. The copper catalyzed method relies on a cascade cyclic reaction between enaminones and N-tosylhydrazones. This method allows the synthesis of 2-amino-3-trifluoromethyl-substituted 2H-furan derivatives carrying a quaternary stereogenic center as single diastereomers. The proposed reaction mechanism involves an amino-cyclopropane intermediate formed in the cyclopropanation of enaminones. The developed method tolerates a broad spectrum of functionalities, and the obtained 2H-furan derivatives are useful synthetic intermediates for preparing other trifluoromethyl-substituted compounds.

Synthesis of Functionalized α-Vinyl Aldehydes from Enaminones.

An efficient RhII -catalyzed synthesis of functionalized α-vinyl aldehydes with high E/Z stereoselectivity was developed. The reaction mediates the cyclopropanation of enaminones with vinyl carbenoids that are generated from cyclopropenes in situ to give the aminocyclopropane intermediates. Selective C-C bond cleavage of the cyclopropane intermediates leads to formation of α-vinyl aldehyde derivatives with high E/Z selectivity. This method proceeds at room temperature under very mild reaction conditions and works with a broad substrate scope.

Reactions of 5-Aminoisoxazoles with α-Diazocarbonyl Compounds: Wolff Rearrangement vs N-H Insertion.

A highly chemoselective reaction between 5-aminoisoxazoles and α-diazocarbonyl compounds has been described. Both Wolff rearrangement and N-H insertion products can be obtained selectively by the judicious choice of reaction conditions. In the case of the Wolff rearrangement reactions, the N-isoxazole amides are accessed as the sole products under thermal conditions. On the other hand, α-amino acid derivatives of N-isoxazolescan be obtained through N-H insertion reactions in the presence of catalytic Rh2(Oct)4. Both reactions proceed under mild reaction conditions and feature a broad substrate scope.

Synthesis of Polyaromatic Rings: Rh(III)-Catalyzed [5 + 1] Annulation of Enaminones with Vinyl Esters through C-H Bond Functionalization.

An expedient [5 + 1] annulation method via Rh(III)-catalyzed C-H bond functionalization of enaminones to synthesize polyaromatic rings is described. The reaction tolerates a broad range of functional groups and offers a new entry to construct polycyclic aromatic compounds with amino and formyl substituents. A possible reaction mechanism was proposed based on the results obtained from isotope labeling experiments.

Hoveyda-Grubbs II Catalyst: A Useful Catalyst for One-Pot Visible-Light-Promoted Ring Contraction and Olefin Metathesis Reactions.

A one-pot reaction to synthesize functionalized 2 H-azirines through visible-light-mediated ring contraction and olefin metathesis of isoxazoles is described. Hoveyda-Grubbs II catalyst was found to function as a photocatalyst for these transformations, allowing these processes to be carried out in a one-pot manner. This study offers a new entry for the application of Grubbs catalysts as efficient photocatalysts and the possibilities of carrying out other photoreactions and olefin metathesis in a one-pot process.

Asymmetric total synthesis of hedyosumin E aglycon, 7,10-epoxyhedyosminolide and ent-zedolactone A.

The asymmetric total syntheses of hedyosumin E aglycon, 7,10-epoxyhedyosminolide and ent-zedolactone A were realized, with the first two being achieved for the first time.

An asymmetric approach to bicyclo[2.2.1]heptane-1-carboxylates via a formal [4 + 2] cycloaddition reaction enabled by organocatalysis.

An organocatalytic formal [4 + 2] cycloaddition reaction has been realized that permits rapid access to a wide range of bicyclo[2.2.1]heptane-1-carboxylates in a highly enantioselective manner from simple starting materials under mild and operationally simple conditions.

Catalytic Asymmetric Total Synthesis of Hedyosumins A, B, and C.

The first and asymmetric total synthesis of hedyosumins A, B, and C was accomplished in 13-14 steps from simple starting materials. The essential tools that allow us to access the tetracyclic skeleton include an organocatalytic [4 + 3] cycloaddition reaction, an intramolecular aldol condensation, and an intramolecular carboxymercuration/demercuration enabled lactonization. A CBS-catalyzed asymmetric reduction was employed to boost the ee of the synthetic natural products to an excellent level. This synthesis established the absolute configurations of hedyosumins A, B, and C.

Diethyl 4-[4-(dimethyl-amino)phen-yl]-2,6-dimethyl-1,4-dihydro-pyridine-3,5-dicarboxyl-ate.

In the title compound, C(21)H(28)N(2)O(4), the dihydro-pyridine ring adopts a flattened boat conformation. The mean plane of the dihydro-pyridine ring and the attached benzene ring form a dihedral angle of 85.1 (1) Å. One of two ethyl fragments is disordered between two conformations in a 0.67 (4):0.33 (4) ratio. In the crystal structure, mol-ecules related by translation along the a axis are linked into chains via inter-molecular N-H⋯O hydrogen bonds.