Travis Dudding

Hydroxyproline-derived pseudoenantiomeric [2.2.1] bicyclic phosphines: asymmetric synthesis of (+)- and (-)-pyrrolines.

We have prepared two new diastereoisomeric 2-aza-5-phosphabicyclo[2.2.1]heptanes from naturally occurring trans-4-hydroxy-l-proline in six chemical operations. These syntheses are concise and highly efficient, with straightforward purification. When we used these chiral phosphines as catalysts for reactions of γ-substituted allenoates with imines, we obtained enantiomerically enriched pyrrolines in good yields with excellent enantioselectivities. These two diastereoisomeric phosphines functioned as pseudoenantiomers, providing their chiral pyrrolines with opposite absolute configurations.

Evidence for Alkene cis‐Aminocupration, an Aminooxygenation Case Study: Kinetics, EPR Spectroscopy, and DFT Calculations

Alkene difunctionalization reactions are important in organic synthesis. We have recently shown that copper(II) complexes can promote and catalyze intramolecular alkene aminooxygenation, carboamination, and diamination reactions. In this contribution, we report a combined experimental and theoretical examination of the mechanism of the copper(II)-promoted olefin aminooxygenation reaction. Kinetics experiments revealed a mechanistic pathway involving an equilibrium reaction between a copper(II) carboxylate complex and the γ-alkenyl sulfonamide substrate and a rate-limiting intramolecular cis-addition of N-Cu across the olefin. Kinetic isotope effect studies support that the cis-aminocupration is the rate-determining step. UV/Vis spectra support a role for the base in the break-up of copper(II) carboxylate dimer to monomeric species. Electron paramagnetic resonance (EPR) spectra provide evidence for a kinetically competent N-Cu intermediate with a Cu(II) oxidation state. Due to the highly similar stereochemical and reactivity trends among the Cu(II)-promoted and catalyzed alkene difunctionalization reactions we have developed, the cis-aminocupration mechanism can reasonably be generalized across the reaction class. The methods and findings disclosed in this report should also prove valuable to the mechanism analysis and optimization of other copper(II) carboxylate promoted reactions, especially those that take place in aprotic organic solvents.

Origin of Enantioselection in Hetero-Diels−Alder Reactions Catalyzed by Naphthyl-TADDOL

The asymmetric hetero-Diels-Alder reaction of benzaldehyde with 1-dimethylamino-3- tert-butyldimethylsiloxy butadiene catalyzed by ( R, R)-1-Np-TADDOL was studied using computational methods. A theoretical rationale was developed through the combined use of molecular mechanics and ONIOM(B3LYP/6-31G(d):AM1) calculations. The origins of stereoselection in this process were identified, and excellent correlation between experiment and theory was found.

Desymmetrizations forming tetrasubstituted olefins using enantioselective olefin metathesis.

Highly reactive chiral Ru-based catalysts possessing C(1)-symmetric N-heterocyclic carbene ligands adorned with one N-alkyl group and one N-aryl group were evaluated in asymmetric desymmetrizations to form cyclic products possessing a tetrasubstituted olefin.

NHC-Catalyzed Intramolecular Redox Amidation for the Synthesis of Functionalized Lactams

A very efficient NHC-catalyzed lactamization reaction is reported. For most cases, the ring expansion reaction proceeds to cleanly furnish five- and six-membered N-Ts and N-Bn lactams, without the need for further purification. Evidence is presented suggesting a dual role for the stoichiometric base: (1) deprotonation of the triazolium precatalyst and (2) activation of the nitrogen leaving group through hydrogen bonding.

A Coordination Compound of Ge0 Stabilized by a Diiminopyridine Ligand

Reduction of the cationic Ge(II) complex [dimpyrGeCl][GeCl3] (dimpyr=2,6-(ArN=CMe)2NC5H3, Ar=2,6-iPr2C6H3) with potassium graphite in benzene affords an air sensitive, dark green compound of Ge(0), [dimpyrGe], which is stabilized by a bis(imino)pyridine platform. This compound is the first example of a complex of a zero-valent Group 14 element that does not contain a carbene or carbenoid ligand. This species has a singlet ground state. DFT studies revealed partial delocalization of one of the Ge lone pairs over the π*(C=N) orbitals of the imines. This delocalization results in a partial multiple-bond character between the Ge atom and imine nitrogen atoms, a fact supported by the X-ray crystallography and IR spectroscopy data.

A structure-activity study of spermicidal and anti-HIV properties of hydroxylated cationic surfactants

The syntheses of 2-hydroxy-N-(2-hydroxyethyl)-N,N-dimethylhexadecan-1-aminium chloride [1(16)Cl] and iodide [1(16)I], 2-hydroxy-N,N,N-trimethylhexadecan-1-aminium chloride (6), N-(2-hydroxyethyl)-N,N-dimethylhexadecan-1-aminium chloride (8), N,N-bis(2-hydroxyethyl)-N-methylhexadecan-1-aminium chloride (11), and 2-hydroxy-N-(2-hydroxyethyl)-N,N-dimethyl-4-oxahexadecan-1-aminium chloride (14) are reported along with the critical micelle concentrations (cmcs), as measured by conductivity at 25 degrees C, of 1(16)Cl, 1(16)I, 6, 8, 11, and N,N,N-trimethylhexadecan-1-aminium chloride (12). All compounds display spermicidal and virucidal activity. A plot of minimum effective concentration (MEC) in the Sander-Cramer spermicidal assay and cmc shows that 1(16)Cl and 6 have the best spermicidal activity and highest cmcs. Compounds 8, 11, and 1(16)Cl are the most active at 0.05 mg mL(-1) against cell-free and cell-associated virus. In conclusion, 1(16)Cl shows the best combination of dual activity against sperm and HIV; it is a promising candidate for further preclinical studies as a topical, contraceptive microbicide.

Molecular mechanics calculations as predictors of enantioselectivity for chiral nucleophile catalyzed reactions

We present molecular mechanics (MM) calculations as models of activated complexes for the β-lactam forming [2+2] cycloaddition between imino ester 4 and the zwitterionic intermediates derived from ketenes and various chiral nucleophilic catalysts. Our method employs the use of Monte Carlo conformational searches utilizing the MMFF force field contained within the Macromodel program. These models accurately predict the sense of stereochemical induction observed experimentally. Also, the predicted energetic differences for minima leading to (R) or (S)-derived ketene facial selectivity correlate in a general sense with the magnitude of the enantioselectivity. This work establishes that our approach represents a viable method for the design of new nucleophilic catalysts a priori using MM calculations.

Catalytic, Enantioselective Alkylations of N,O- and N, N-Acetals and Hemiacetals

Abstract We report the first examples of catalytic, enantioselective alkylation of N,O-acetals to produce useful amino acid derivatives 5 in high yield (73–93%) and enantioselectivity (70–96%). We have extended the utility of our reaction to include a simple one-pot procedure from readily available starting materials. We also provide several different N-based protecting groups that greatly increase the flexibility of the reaction. In addition, we have elucidated novel mechanistic information including the discovery of unique transilylations that start off the catalytic reactions of enol silane nucleophiles with N,O-acetals. These details will guide us in further explorations of the reactions scope and utility.

Synthesis and Theoretical Investigation of a 1,8‐Bis(bis(diisopropylamino)cyclopropeniminyl)naphthalene Proton Sponge Derivative

We report herein the synthesis and characterization of a new proton sponge derivative, 1,8-bis(bis(diisopropylamino)cyclopropeniminyl)naphthalene 4 (DACN), as well as its bis-protonated counterpart 6. A crystal structure of 6 is presented, along with variable temperature (1)H NMR data on the BF4(-) salt (6⋅BF4). DFT calculations were performed to investigate the structure of the monoprotonated species 7 and to gain insight into the structural and electronic nature of all three species. The proton affinity (PA) of 4, calculated at the B3LYP/6-311G++(d,p)//B3LYP/6-31G(d,p) level, taking into account thermal corrections from the B3LYP/6-31G(d,p) method, was 282.3 kcal mol(-1), while its pKa was estimated at 27.0. NICS calculations were performed to examine the changes in aromaticity within these systems upon each successive protonation. Lastly, homodesmotic reaction schemes were used in order to estimate the factors contributing to the strong PA predicted for 4.