David P. Day

Asymmetric Epoxidation Using Iminium Salt Organocatalysts Featuring Dynamically Controlled Atropoisomerism

Introduction of a pseudoaxial substituent at a stereogenic center adjacent to the nitrogen atom in binaphthyl- and biphenyl-derived azepinium salt organocatalysts affords improved enantioselectivities and yields in the epoxidation of unfunctionalized alkenes. In the biphenyl-derived catalysts, the atropoisomerism at the biphenyl axis is controlled by the interaction of this substituent with the chiral substituent at nitrogen.

Enantioselective Total Synthesis of (+)-Scuteflorin A Using Organocatalytic Asymmetric Epoxidation

We report the first enantioselective total synthesis of (+)-scuteflorin A in 14% overall yield, employing a chiral iminium salt to effect an organocatalytic asymmetric epoxidation of xanthyletin in >99% ee as the key step.

Synthesis, Photochemical, and Redox Properties of Gold(I) and Gold(III) Pincer Complexes Incorporating a 2,2′:6′,2″-Terpyridine Ligand Framework

Reaction of [Au(C6F5)(tht)] (tht = tetrahydrothiophene) with 2,2′:6′,2″-terpyridine (terpy) leads to complex [Au(C6F5)(η1-terpy)] (1). The chemical oxidation of complex (1) with 2 equiv of [N(C6H4Br-4)3](PF6) or using electrosynthetic techniques affords the Au(III) complex [Au(C6F5)(η3-terpy)](PF6)2 (2). The X-ray diffraction study of complex 2 reveals that the terpyridine acts as tridentate chelate ligand, which leads to a slightly distorted square-planar geometry. Complex 1 displays fluorescence in the solid state at 77 K due to a metal (gold) to ligand (terpy) charge transfer transition, whereas complex 2 displays fluorescence in acetonitrile due to excimer or exciplex formation. Time-dependent density functional theory calculations match the experimental absorption spectra of the synthesized complexes. In order to further probe the frontier orbitals of both complexes and study their redox behavior, each compound was separately characterized using cyclic voltammetry. The bulk electrolysis of a solution of complex 1 was analyzed by spectroscopic methods confirming the electrochemical synthesis of complex 2.

Kinetic Resolution in Asymmetric Epoxidation using Iminium Salt Catalysis

The first reported examples of kinetic resolution in epoxidation reactions using iminium salt catalysis are described, providing up to 99% ee in the epoxidation of racemic cis-chromenes.

“Janus” Calixarenes: Double-Sided Molecular Linkers for Facile, Multianchor Point, Multifunctional, Surface Modification

We herein report the synthesis of novel “Janus” calix[4]arenes bearing four “molecular tethering” functional groups on either the upper or lower rims of the calixarene. These enable facile multipoint covalent attachment to electrode surfaces with monolayer coverage. The other rim of the calixarenes bear either four azide or four ethynyl functional groups, which are easily modified by the copper(I)-catalyzed azide–alkyne cycloaddition reaction (CuAAC), either pre- or postsurface modification, enabling these conical, nanocavity reactor sites to be decorated with a wide range of substrates to impart desired chemical properties. Redox active species decorating the peripheral rim are shown to be electrically connected by the calixarene to the electrode surface in either “up” or “down” orientations of the calixarene.

New Non-Toxic Semi-Synthetic Derivatives from Natural Diterpenes Displaying Anti-Tuberculosis Activity

We report herein the synthesis of six diterpene derivatives, three of which are new, generated through known organic chemistry reactions that allowed structural modification of the existing natural products kaurenoic acid (1) and copalic acid (2). The new compounds were fully characterized using high resolution mass spectrometry, infrared spectroscopy, 1H- and 13C-NMR experiments. We also report the evaluation of the anti-tuberculosis potential for all compounds, which showed some promising results for Micobacterium tuberculosis inhibition. Moreover, the toxicity for each of the most active compounds was also assessed.

Silver-Catalyzed 1,3-Acyloxy Migration/Diels–Alder Reaction of 1,9-Dien-4-yne Esters to Partially Hydrogenated Isoquinolines

A synthetic method to prepare partially hydrogenated isoquinolines efficiently from silver-mediated [3,3]-sigmatropic rearrangement/Diels-Alder reaction of 1,9-dien-4-yne esters is described. The reactions were shown to be robust with a wide variety of substitution patterns tolerated to provide the corresponding nitrogen-containing heterocyclic products in good to excellent yields. This includes examples containing a bridgehead sp3 quaternary carbon center as well as the cycloisomerization of one substrate to give the corresponding bicyclic adduct in excellent yield at the gram scale.

Brønsted Acid-Catalysed Allylic Amination of 1-(2-Aminoaryl)prop-2-en-1-ols to 1,2-Dihydroquinolines

A highly efficient synthetic method to prepare 1,2-dihydroquinolines that relies on trifluoromethanesulfonic acid (TfOH)-catalysed allylic amination of 1-(2-aminoaryl)prop-2-en-1-ols is described. Achieved at a catalyst loading of 0.01 mol-% under mild conditions at room temperature, the reaction was found to be robust, with a wide range of substitution patterns tolerated. The corresponding N-heterocyclic adducts were obtained in good to excellent yields of 45–93 %.

Brønsted Base-Mediated Aziridination of 2-Alkyl-Substituted-1,3-Dicarbonyl Compounds and 2-Acyl-Substituted-1,4-Dicarbonyl Compounds by Iminoiodanes

The synthesis of α,α-diacylaziridines and α,α,β-triacylaziridines from reaction of 2-alkyl-substituted-1,3-dicarbonyl compounds and 2-acyl-substituted-1,4-dicarbonyl compounds with arylsulfonyliminoiodinanes (ArSO2N=IPh) under Bronsted base-mediated atmospheric conditions is described. The reaction mechanism is thought to involve the formal oxidation of the substrate followed by aziridination of the ensuing α,β-unsaturated intermediate by the hypervalent iodine(iii) reagent.