Written by Dr. Sharbil J. Firsan

Using a chiral ionic liquid (IL) as solvent and the exclusive source of chiral information, Schmitkamp et al. have reported the first examples of an enantioselective, homogeneous, rhodium-catalyzed hydrogenation that employs tropoisomeric (tropos) ligands.   In light of the fact that rotation of the phenyl rings in tropos ligands takes place rapidly and, hence, these ligands do not possess permanent chirality, the enantioselectivities obtained in the hydrogenation are remarkable.  Also remarkable is the reusability of the catalyst system after the product is extracted out with supercritical carbon dioxide (scCO₂).  Curiously enough, the addition of water to the reaction system did not adversely affect the enantioselectivity: a comparable level of enantioselection was observed.

Schmitkamp, M.; Chen, D.; Leitner, W.; Klankermayer, J.; Franciò, G. Chem. Commun. 2007, 4012.

Written by William Sommer, PhD 

Substituted ureas are of the utmost importance for the synthesis of common pharmacores. Kotecki and coworkers, from the Abbott Laboratories, developed a general method for the synthesis of subsituted ureas using palladium catalyzed amidation reaction. It is importatn to note that the common method to synthesize substituted ureas involve the use of phosgene. The authors reported the synthesis of various unsymmetrically substituted ureas using Pd₂(dba)₃ and bippyphos as a ligand. Isolated yield of up to 92% were reported for the coupling of various aryl halides with various substituted ureas.

 

Written By: Mark Redlich, Ph.D.
Organic Letters just published on the web an article by Lipshutz detailing the first palladium-catalyzed allylic amination of allylic alcohols in pure water.  The reaction is easily achieved at room temperature with either dppf or biphep ligands when methyl formate was added to the reaction along with 2 wt % of the amphiphile PTS . A few cases result in the formation of limited quantities of the branched material, but most cases selectively favor the linear product.  The methodology was applied to the one pot synthesis of the antifungal naftifin, obtaining the target product in 83% isolated yield under exceptionally mild conditions.

If you’re interested in more information on PTS, check out http://tr.im/kcVq

Nishikata, T.; Lipshutz, B. H. Org. Lett. 2009, ASAP.

Written by: Dr. Sharbil J. Firsan

Castillón, Claver, and co-authors have reported a new synthesis of air-stable and water-soluble zwitterionic phosphine ligands and their application in the Suzuki–Miyaura cross-coupling reaction in neat, non-dearated water.   For aryl bromides and arylboronic acids, this palladium-catalyzed reaction took place with high conversions, with and without microwave irradiation, and was characterized by very low catalyst loadings (0.025–0.05 mol %) and relatively short reaction times.  In the case of the much less reactive aryl chlorides, the reaction with arylboronic acids proceeded under microwave irradiation and low catalyst loadings (0.2–2.0 mol %), but resulted in only moderate conversions.

(1) García Suárez, E. J.; Ruiz, A.; Castillón, S.; Oberhauser, W.; Bianchini, C.; Claver, C. Dalton Trans. 2007, 2859.  (2) For a recent review on transition-metal-catalyzed cross-couplings in water, see Lipshutz, B. H.; Ghorai, S. Aldrichimica Acta 2008, 41, 59.