Direct Enantio- and Diastereoselective Oxidative Homocoupling of Aldehydes.

A novel strategy for the direct enantioselective oxidative homocoupling of α-branched aldehydes is presented. The methodology employs open-shell intermediates for the construction of chiral 1,4-dialdehydes by forming a carbon-carbon bond connecting two quaternary stereogenic centers in good yields and excellent stereoselectivities for electron-rich aromatic aldehydes. The 1,4-dialdehydes were transformed into synthetically valuable chiral pyrrolidines. Experimental mechanistic investigations based on competition experiments combined with computational studies indicate that the reaction proceeds through a radical cation intermediate and that reactivity and stereoselectivity follow different trends.

Catalytic Enantioselective [10+4]†Cycloadditions.

The first peri- and stereoselective [10+4] cycloaddition between catalytically generated amino isobenzofulvenes and electron-deficient dienes is described. The highly stereoselective catalytic [10+4] cycloaddition exhibits a broad scope with high yields, reflecting a robust higher-order cycloaddition. Experimental and computational investigations support a kinetic distribution of intermediate rotamers dictating the enantioselectivity, which relies heavily on additive effects.

Organocatalytic Enantioselective Higher-Order Cycloadditions of In Situ Generated Amino Isobenzofulvenes.

The [8+2] cycloaddition of indene-2-carbaldehydes and nitro olefins is described to provide benzonorbornene scaffolds in a highly peri-, diastereo-, and enantioselective fashion in the presence of a C2 -symmetric aminocatalyst. This reaction, which proceeds through a transient semi-aromatic amino isobenzofulvene, represents the first example of catalytic formation and transformation of these species. Quantum chemical calculations suggest a kinetically controlled stepwise mechanism where the stereochemistry is determined in the first bond-forming event. Beyond the useful [8+2] cycloadducts, [10+4] cycloadducts have been identified in silico as potential off-pathway intermediates.

Organocatalytic Formation of Chiral Trisubstituted Allenes and Chiral Furan Derivatives.

A novel reaction that provides chiral allenes by amino catalytic activation of either aldehydes or α,ß-unsaturated aldehydes for reaction with alkynyl-substituted enones is presented. The reaction forms a variety of trisubstituted allenes in high yields and with excellent stereoselectivities. The utility of the reaction concept is demonstrated by the synthesis of chiral furan derivatives in high yields and stereoselectivities.

One-Pot Synthesis of Benzo[4,5]imidazo[2,1-a]isoquinolines and Isoquinolino[3,4-b]quinoxalines via Tandem Cyclization Strategies.

Two operationally simple one-pot protocols have been developed for the synthesis of amino-functionalized benzo[4,5]imidazo[2,1-a]isoquinolines and isoquinolino[3,4-b]quinoxalines. Optimization data and substrate scope for these atom-economical transformations, which engage commercially available o-phenylenediamines and o-cyanobenzaldehydes, are discussed.

Predicting hydration propensities of biologically relevant α-ketoamides.

Quantum chemical calculations coupled to experiments were used to predict covalent hydration propensities of biologically relevant α-ketoamides. Experimentally determined hydration equilibrium constants for related ketones and aldehydes were compared to computationally determined values to develop a method for predicting hydration equilibrium constants. This method was used on six newly synthesized α-ketoamides to experimentally verify computational predictions. A correlation between calculation and experiment was observed and applied to models of several pertinent APIs. Our results indicate that the keto form is favored for practically all α-ketoamides in biological environs.

Inhibition of myeloperoxidase: evaluation of 2H-indazoles and 1H-indazolones.

Myeloperoxidase (MPO) produces hypohalous acids as a key component of the innate immune response; however, release of these acids extracellularly results in inflammatory cell and tissue damage. The two-step, one-pot Davis-Beirut reaction was used to synthesize a library of 2H-indazoles and 1H-indazolones as putative inhibitors of MPO. A structure-activity relationship study was undertaken wherein compounds were evaluated utilizing taurine-chloramine and MPO-mediated H2O2 consumption assays. Docking studies as well as toxicophore and Lipinski analyses were performed. Fourteen compounds were found to be potent inhibitors with IC50 values <1µM, suggesting these compounds could be considered as potential modulators of pro-oxidative tissue injury pertubated by the inflammatory MPO/H2O2/HOCl/HOBr system.

Cyclic azacyanines: experimental and computational studies on spectroscopic properties and unique reactivity.

The absorption and fluorescence properties of cyclic azacyanine (CAC) derivatives were examined in several solvents. The presence of electron donating or withdrawing groups on the CAC impacts spectroscopic properties. The general solvent relaxation displayed by azacyanine derivatives is in accordance with Lippert-Mataga's prediction but exception is noted in the case of protic solvent due to specific hydrogen bonding interactions. Fluorescence lifetime decay studies indicate a relaxation time in the nanosecond timescale with mono exponential decay. Donating substituents markedly increase the excited state lifetime, whereas withdrawing groups marginally decrease the excited state lifetime. Quantum chemical computations were used to explore the origins of the reactivity and spectroscopic properties of CACs; results are consistent with a model in which regioselectivity results from differences in mechanistic steps occurring after initial attack by hydroxide on the CAC.

Synthesis of Highly Stereodefined Tetrasubstituted Acyclic All-Carbon Olefins via a Syn-Elimination Approach.

An efficient synthesis of stereodefined tetrasubstituted acyclic all-carbon olefins has been developed via a bis(2,6-xylyl)phosphate formation of stereoenriched tertiary alcohols, followed by in situ syn-elimination of the corresponding phosphates under mild conditions. This chemistry tolerates a wide variety of electronically and sterically diverse substrates and generates the desired tetrasubstituted olefins in high yields and stereoselectivities (>95:5) in most cases. This stereocontrolled olefin synthesis has been applied to the synthesis of anticancer drug tamoxifen in three steps from commercially available 1,2-diphenylbutan-1-one in 97:3 stereoselectivity and 78% overall yield.

Dibenzonaphthyridinones: Heterocycle-to-Heterocycle Synthetic Strategies and Photophysical Studies.

A heterocycle-to-heterocycle strategy is presented for the preparation of highly fluorescent and solvatochromic dibenzonaphthyridinones (DBNs) via methodology that leads to the formation of a tertiary, spiro-fused carbon center. A linear correlation between the results of photophysical experiments and time dependent density functional theory calculations was observed for the λ(max) of excitation for DBNs with varying electronic character.

Facile one-pot assembly of imidazotriazolobenzodiazepines via indium(III)-catalyzed multicomponent reactions.

An operationally simple, one-pot multicomponent reaction has been developed for the assembly of 9H-benzo[f]imidazo[1,2-d][1,2,3]triazolo[1,5-a][1,4]diazepines adorned with three diversification points via an atom-economical transformation incorporating α-diketones, o-azidobenzaldehydes, propargylic amines, and ammonium acetate. This process involves tandem InCl3-catalyzed cyclocondensation and intramolecular azide-alkyne 1,3-dipolar cycloaddition reactions; optimization data, substrate scope, and mechanistic insights are discussed.

Heterocycle-heterocycle strategies: (2-nitrophenyl)isoxazole precursors to 4-aminoquinolines, 1H-indoles, and quinolin-4(1H)-ones.

Reductive heterocycle-heterocycle (heterocycle → heterocycle; H-H) transformations that give 4-aminoquinolines, 3-acylindoles, and quinolin-4(1H)-ones from 2-nitrophenyl substituted isoxazoles are reported. When this methodology is applied to 3,5-, 4,5-, and 3,4-bis(2-nitrophenyl)isoxazoles, chemoselective heterocyclization gives quinolin-4(1H)-ones, and 4-aminoquinolines, exclusively.