Rhodium-Catalyzed Enantioselective Intramolecular Hydroacylation of Trisubstituted Alkenes.

We report the first examples of transition metal-catalyzed enantioselective alkene hydroacylations with 1,1,2-trisubstituted alkenes. DFT and mechanistic studies are consistent with a reaction pathway for these rhodium-catalyzed processes including intramolecular alkene hydroacylation and α-epimerization to generate highly enantioenriched, polycyclic architectures. This reaction sequence enables the hydroacylation of 2-(cyclohex-1-en-1-yl)benzaldehydes to form hexahydro-9H-fluoren-9-ones in moderate to high yields (68-91 %) with high enantioselectivities (up to 99 % ee) and diastereoselectivities (typically >20:1).

Rhodium-Catalyzed, Enantioselective Hydroacylation of ortho-Allylbenzaldehydes.

The development of a rhodium catalyst for endo- and enantioselective hydroacylation of ortho-allylbenzaldehydes is reported. A catalyst generated in situ from [Rh(COD)Cl]2, (R)-DTBM-SEGPHOS, and NaBARF promotes the desired hydroacylation reactions and minimizes the formation of byproducts from competitive alkene isomerization and ene/dehydration pathways. These rhodium-catalyzed processes generate the 3,4-dihydronaphthalen-1(2H)-one products in moderate-to-high yields (49-91%) with excellent enantioselectivities (96-99% ee).

Palladium-catalyzed synthesis of N-tert-prenylindoles.

Palladium-catalyzed N-tert-prenylations of indoles, tricarbonylchromium-activated indoles, and indolines that occur in high yields (up to 94%) with high tert-prenyl-to-n-prenyl selectivity (up to 12:1) are reported.

Spectroscopic properties of nanotube-chromophore hybrids.

Recently, individual single-walled carbon nanotubes (SWNTs) functionalized with azo-benzene chromophores were shown to form a new class of hybrid nanomaterials for optoelectronics applications. Here we use a number of experimental and computational techniques to understand the binding, orientation, and nature of coupling between chromophores and the nanotubes, all of which are relevant to future optimization of these hybrid materials. We find that the binding energy between chromophores and nanotubes depends strongly on the type of tether that is used to bind the chromophores to the nanotubes. The pyrene tethers form a much stronger attachment to nanotubes compared to anthracene or benzene rings, resulting in more than 80% retention of bound chromophores post-processing. Density functional theory (DFT) calculations show that the binding energy of the chromophores to the nanotubes is maximized for chromophores parallel to the nanotube sidewall, even with the use of tethers; optical second harmonic generation measurements show that there is nonetheless a partial radial orientation of the chromophores on the nanotubes. We find weak electronic coupling between the chromophores and the SWNTs, consistent with noncovalent binding. This weak coupling is still sufficient to quench the chromophore fluorescence through a combination of static and dynamic processes. Photoluminescence measurements show a lack of significant energy transfer from the chromophores to isolated semiconducting nanotubes.