Biomedical subjects

Paul R Rablen

Publications and source records attributed to Paul R Rablen.

4 recordsLinked to original sources

PubMed2005

Dichlorocarbene addition to cyclopropenes: a computational study.

Reaction paths for addition of dichlorocarbene to 1,2-disubstituted cyclopropenes were calculated using hybrid density functional theory (B3LYP/6-31G) in the gas phase and in the presence of a continuum solvation model corresponding to acetonitrile. In both the gas phase and acetonitrile, :CCl2-cyclopropene addition follows an asymmetric, non-least-motion approach. Barriers to addition range from 0 to 2 kcal/mol. The reactions proceed in concerted fashion in both the gas phase and solution to yield 1,3-dienes or bicyclobutanes. The reaction pathway on this complex potential energy surface of this reaction appears to bifurcate, and the product distribution is believed to be controlled by reaction dynamics. At the present level of theory, there appears to be no minimum on the potential energy surface corresponding to a dipolar intermediate.

Computer Simulation↗

PubMed2003

Are the enolates of amides and esters stabilized by electrostatics?

The fact that amides and esters form less stable enolates than ketones might be seen as evidence that electrostatic stabilization is unimportant in these anions. However, ab initio molecular orbital calculations show that electrostatic stabilization does in fact lie beneath the competing resonance effect that causes the decrease in acidity. The electrostatic contribution is revealed by examining torsionally twisted amide and ester structures in which the pi resonance interactions are largely inhibited. These twisted amides and esters have greater enolate acidity than the corresponding ketones. Qualitatively similar behavior is observed with respect to protonation, such that twisted amides and esters are generally less basic than the reference ketones, in striking contrast to their behavior in the normal geometries.

Journal Article↗

PubMed2003

Directed ring-opening of 1,5-dioxaspiro[3.2]hexanes: selective formation of 2,2-disubstituted oxetanes.

1,5-Dioxaspiro[3.2]hexanes undergo ring-opening reactions with many heteroatom nucleophiles to provide alpha-substituted-beta'-hydroxy ketones. However, certain Lewis acidic nucleophiles provide 2,2-disubstituted oxetanes. Herein, the results of reactions of 3-phenyl-1,5-dioxaspiro[3.2]hexane with a variety of nitrogen-containing heteroaromatic bases are reported. There appears to be a correlation between the pK(a) of the nucleophile and the reaction outcome with more acidic nucleophiles providing 2,2-disubstituted oxetanes. Moreover, the mode of ring opening can be directed toward the substituted oxetane by the addition of a Lewis acid. These results are rationalized by calculation of stationary points on the potential energy surfaces for the various possible reaction pathways using ab initio molecular orbital methods.

Journal Article↗

PubMed2003

Simultaneous and stereoselective formation of planar and axial chiralities in enantiopure sulfinyl iron diene complexes.

[reaction: see text] Enantiopure (1Z,3E)-1-sulfinyl dienes bearing an o-dithianylphenyl group can be prepared and complexed with (bda)Fe(CO)(3) to afford the corresponding sulfinyl diene iron(0) tricarbonyl complexes. This diastereoselective complexation introduces planar and axial chirality simultaneously, with a high degree of facial selectivity as well as atropselectivity. Dynamic kinetic resolution is likely to be the origin of the atropselectivity.

Journal Article↗