Generation and characterization of a distonic biradical anion formed from an enediynone prodrug in the gas phase.

A negatively charged biradical intermediate was successfully generated in the gas phase via cyclization of the deprotonated bicyclo[8.3.0]trideca-12-ene-2,7-diyn-1-one precursor.

A surprising mechanistic "switch" in Lewis acid activation: a bifunctional, asymmetric approach to alpha-hydroxy acid derivatives.

We report a detailed synthetic and mechanistic study of an unusual bifunctional, sequential hetero-Diels-Alder/ring-opening reaction in which chiral, metal complexed ketene enolates react with o-quinones to afford highly enantioenriched, alpha-hydroxylated carbonyl derivatives in excellent yield. A number of Lewis acids were screened in tandem with cinchona alkaloid derivatives; surprisingly, trans-(Ph(3)P)(2)PdCl(2) was found to afford the most dramatic increase in yield and rate of reaction. A series of Lewis acid binding motifs were explored through molecular modeling, as well as IR, UV, and NMR spectroscopy.

Scalable methodology for the catalytic, asymmetric alpha-bromination of acid chlorides.

The optimization of a practical, catalytic, asymmetric process for the alpha-bromination of acid chlorides to produce synthetically versatile, optically active alpha-bromoesters is reported. A range of products is produced in high enantioselectivity and moderate to good chemical yields with retention of both upon scale-up. The reactions herein are catalyzed by cinchona alkaloid derivatives, with the best performance achieved by the use of a proline cinchona alkaloid conjugate designed in a de novo fashion.

Ring size and substituent effects in oxyanion-promoted cyclizations of enyne-allenes: observation of a Myers-Saito cycloaromatization at cryogenic temperature.

A series of acetoxy-substituted enyne-allenes, fused to cyclopentene and cyclohexene ring systems, were synthesized and treated with methyllithium to generate the corresponding enolates. It was found that whereas the cyclohexannulated examples underwent either C2-C7 (Myers-Saito) cycloaromatization or C2-C6 (Schmittel) cyclization depending on their terminal subsituents, the cyclopentannulated examples either failed to cyclize altogether or underwent C2-C7 cyclization. Both of these results lie in contrast to the behavior of their benzannulated analogues, which underwent exclusive C2-C6 cyclization independent of substituents.

Conformation-specific spectroscopy of 3-benzyl-1,5-hexadiyne.

3-Benzyl-1,5-hexadiyne (BHD) was studied by a combination of methods, including resonance-enhanced-two-photon ionization, UV-UV hole-burning spectroscopy, resonant ion-dip infrared spectroscopy, and rotational band contour analysis. There are five conformations of BHD observed in the expansion with their 1<-- S0 origins occurring at 37520, 37565, 37599, 37605, and 37631 cm(-1). DFT calculations predict six low energy conformations.

Catalytic, enantioselective [4 + 2]-cycloadditions of ketene enolates and o-quinones: efficient entry to chiral, alpha-oxygenated carboxylic acid derivatives.

We report catalytic, enantioselective [4 + 2]-cycloadditions of o-quinones with ketene enolates (derived from readily available acid chlorides) using cinchona alkaloid derivatives as catalysts to produce products in high enantiomeric excess (ee) and good to excellent yields. The thermodynamic driving force for these reactions is due in part to the restoration of aromaticity to the products. The resulting chiral, bicycloadducts can be synthetically manipulated in a variety of useful ways, for example to provide a flexible synthesis of alpha-oxygenated carboxylic acid derivatives.

"Concerted" transition state, stepwise mechanism. Dynamics effects in C2-C6 enyne allene cyclizations.

The C2-C6 (Schmittel)/ene cyclization of enyne-allenes is studied by a combination of kinetic isotope effects, theoretical calculations, and dynamics trajectories. For the cyclization of allenol acetate 9, the isotope effect (k(CH3)/k(CD3) is approximately 1.43.

Synthesis and cycloaromatization of a cyclic enyne-allene prodrug.

A simple and stable cyclic enediynone (4) has been synthesized using an intramolecular Nozaki-Hiyama-Kishi cyclization as the key step. Reaction with a thiolate nucleophile led to rapid cycloaromatization of 4. Trapping experiments using 1,4-cyclohexadiene support the intermediacy of an aromatic diradical in the cycloaromatization.