Douglas B. Grotjahn

Mild and selective deuteration and isomerization of alkenes by a bifunctional catalyst and deuterium oxide.

H/D exchange is achieved at allylic positions of alkenes using D(2)O in acetone and alkene isomerization catalyst 1, which features a bifunctional imidazolylphosphine. The basic nitrogen of the latter is thought to deprotonate an alkene substrate coordinated to the CpRu center; at this stage the protonated nitrogen could undergo H/D exchange with deuterium oxide. An exceptional degree of deuteration is achieved at positions accessible to isomerization, with a high degree of control. Using biphasic settings one can literally wash out reactive protons on the substrate without using organic solvents.

Stereoselective Alkene Isomerization over One Position

Although controlling both the position of the double bond and E:Z selectivity in alkene isomerization is difficult, 1 is a very efficient catalyst for selective mono-isomerization of a variety of multifunctional alkenes to afford >99.5% E-products. Many reactions are complete within 10 min at room temperature. Even sensitive enols and enamides susceptible to further reaction can be generated. Catalyst loadings in the 0.01-0.1 mol% range can be employed. E-to-Z isomerization of the product from diallyl ether was only <10(-6) times as fast as its formation, showing the extremely high kinetic selectivity of 1.

Finding the Proton in a Key Intermediate of anti-Markovnikov Alkyne Hydration by a Bifunctional Catalyst

The secondary structure of a bifunctional catalyst positions a crucial reactive proton in the final intermediate of anti-Markovnikov alkyne hydration to give an aldehyde. NMR coupling and isotopic labeling studies elucidate the location of this proton and its involvement in hydrogen bonding.

Coordination of chiral amines to coordinatively unsaturated Cp∗Ir-amino acid complexes allows determination of enantiomeric purity

Abstract Coordinatively unsaturated complexes of the Cp ∗ Ir fragment to the dianion of N-tosylamino acids combine with chiral amines in a highly diastereoselective fashion, such that metallacycle substituents R (amino acid side chain) and Cp ∗ are cis. Observation of adducts between the alanine- and phenylglycine-derived complexes and (S)-α-methylbenzylamine by NMR at low to ambient temperature allows determination of the enantiomeric purity of either component, 1 to 2% impurity being easily detectable. Furthermore, α-methylbenzylamine was analyzed for its enantiomeric purity independent of external chiral reagent, by its conversion to N,N′-bis(1-phenylethyl)urea.

Favoring alkene insertion over β-hydride elimination: aqueous media and ligands enable a double Heck reaction on a substrate for which β-hydride elimination is possible

Abstract Under Pd 0 catalysis, the (iodoaryl)diene N -methyl- N -(1,5-hexadiene-3-yl)-2-iodobenzoic acid amide ( 6 ) would normally be expected to give monocyclized product from initial oxidative addition of the Cue5f8I bond, followed by insertion of one alkene function and β-hydride elimination. Conditions were sought to favor insertion of the second alkene unit over β-hydride elimination, so as to increase the yield of polycyclic products. In fact, the use of phenanthroline ligand and aqueous media in reactions of 6 increased the total yield of expected tricyclic products ( 11–13 ) to 52%. Three other products ( 14–16 ) appear to be derived from an unusual rearrangement. By a process of elimination, control experiments point to the possibility of a chelation-assisted Pd-catalyzed Cope rearrangement in the formation of these unexpected products.

Aqueous Media in the Intramolecular Heck Reaction

In the last several years intramolecular variants of the Heck reaction [1] have been developed to produce complex polycyclic structures, as schematically illustrated by conversion of A to D. However, the successful formation of more than one ring in intramolecular Heck reactions of A has depended on substrate structure to prevent β-hydride elimination from intermediate(s) (e.g., B, R ≠ H). For B in which R = H, however, we wondered if aqueous media would favor further alkene insertion over β-hydride elimination in B, either because the alkenebearing chain would be poorly solvated by water (hydrophobic effect [2]) or because water would help to ionize the Pd-X bond. Intriguingly, our preliminary experiments suggest that changing from CH 3 CN to H 2 O-CH 3 CN or H 2 O-ethanol mixtures, with additives such as LiCl, indeed causes dramatic changes in product distribution for some substrates but not others.

Azide Tripodal Dendrons from Behera's Amine and Their Clicked Dendrimers.

Diazo transfer reactions on Beheras amine and its next-generation analogue formed G0 and G1 azide dendrons bearing three and nine tert-butyl-protected esters, respectively. The utility of the new dendrons was demonstrated by copper-catalyzed azide-alkyne cycloaddition, with 1,3,5-triethynylbenzene, forming two novel dendrimers in a convergent manner. Acid-mediated dendrimer deprotection was successful, and the resulting carboxy-terminated dendrimers were analyzed by NMR and DOSY experiments.