Written by Josephine S. Nakhla, Ph.D 

Chatani and coworkers have reported a complementary method to the Sonogashira-coupling for the alkynylation of the ortho C-H bond of various anilides. In the presence of catalytic Pd(OAc)₂, AgOTf, and K₂CO₃, ortho-C-H-bond metalation takes place (stoichiometric evidence for this palladacycle), followed by addition of the Pd-intermediate to the bromo alkyne, generating a vinyl palladium species, which upon beta-bromo-elimination generates the alkynylated product. It should be noted that ligand exchange of the bromide for triflate is necessary to generate a species capable of electrophilic metalation on the substrate. A variety of substrates can be utilized in this transformation, providing unprecedented molecular complexity and flexibility for alkynylations of aromatic substrates. In addition, the –Si(i-Pr)₃ provides an additional functional group handle for further manipulation.

Tobisu, M.; Ano, Y.; Chatani, N. Org. Lett. 2009, ASAP.

Written By: Mark Redlich, Ph.D.

I want to take a break from the heady, cutting-edge content that we normally blog about and hopefully open up a little more to your input.  As you may or may not be aware, Sigma-Aldrich has recently released a series of solutions of commonly used lab reagents that in their neat form are generally not fun to handle – they’re difficult to weigh out, sticky, or noxious – our list of currently available solutions is below.  We are working on more solutions based on our own experience with difficult to handle reagents, but I thought it might be a good idea to see if you have any suggestions – think of this as a “Please Bother Us” ChemBlog.

So, are there any reagents that are frequently used in your lab, which are a pain to handle, but might be viable as a solution?

Currently available solutions:
436267 Di-tert-butyl dicarbonate, 1M in THF
703753 Di-tert-butyl dicarbonate, 2M in THF
703737 Di-tert-butyl dicarbonate, 2M in dichloromethane
703745 Di-tert-butyl dicarbonate, 2M in ethyl acetate
706442 (S)-(-)-a,a-Diphenyl-2-pyrrolidinemethanol trimethylsilyl ether, 0.05M in toluene
706450 (R)-(+)-a,a-Diphenyl-2-pyrrolidinemethanol trimethylsilyl ether, 0.05M in toluene
705284 1,1'-Carbonyldiimidazole, 0.4M in dichloromethane
704083 Triflic anhydride, 1M in dichloromethane
704091 Tributyltin hydride 1M in cyclohexane
291048 Iodine monochloride, 1M in dichloromethane
708496 Acetyl chloride, 1M in dichloromethane

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 methid 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.