ABSTRACT:The use of the hypervalent iodine reagents in oxidative processes has become a staple in modern organic synthesis. Frequently, the reactivity of λ 3 iodanes is further enhanced by acids (Lewis or Brønsted). The origin of such activation, however, has remained elusive. Here, we use the common combination of PhI(OAc)2 with BF3·Et2O as model to fully explore this activation phenomenon. In addition to the spectroscopic assessment of the dynamic acid-base interaction, for the first time the putative PIDA·BF3 complex has been isolated and its structure determined by X-Ray diffraction. Consequences of such activation are discussed from a structural and electronic (DFT) points of views, including the origins of the enhanced reactivity.

Chloro[2,6-bis{1-(phenyl)iminoethyl}pyridine]rhodium(I) complexes (RhCl(N,N,N); 1-11) have been prepared by reaction of the dimer [Rh(μ-Cl)(η 2 -C 2 H 4 ) 2 ] 2 with the corresponding nitrogen donor ligand. These complexes afford nanoparticles with a mean diameter of 1.5 ( 0.2 nm stabilized by the partially hydrogenated ligand, under 1 atm of hydrogen, in 2-propanol as solvent, at 60°C, and in the presence of K t BuO. Under a constant atmospheric pressure of hydrogen, the nanoparticles catalyze the dehalogenation of the chlorobenzene 1,2-, 1,3-, and 1,4-dichlorobenzene, 1,2,4-trichloro benzene, fluorobenzene, 2-, 3-, and 4-chlorobiphenyl, and 4,4 0 -and 3,5-dichlorobiphenyl and the hydrogenation of benzene, toluene, p-xylene, styrene, R-methylstyrene, biphenyl, aniline, phenol, and pyridine. A Hg(0) poisoning test reveals that homogeneous and heterogeneous catalysis coexist during the dehalogenation reactions, whereas the hydrogenation processes are heterogeneous. The nanoparticles can be also generated in the presence of basic aluminum oxide of 150 mesh, which at the same time acts as a support. When they are deposited on the alumina, the nanoparticles do not significantly modify their catalytic activity.

The α-arylation of carbonyl compounds is generally accomplished under basic conditions, both under metal catalysis and via aryl transfer from the diaryl λ(3)-iodanes. Here, we describe an alternative metal-free α-arylation using ArI(O2CCF3)2 as the source of a 2-iodoaryl group. The reaction is applicable to activated ketones, such as α-cyanoketones, and works with substituted aryliodanes. This formal C-H functionalization reaction is thought to proceed through a [3,3] rearrangement of an iodonium enolate. The final α-(2-iodoaryl)ketones are versatile synthetic building blocks.

High enantioselection is obtained in Michael additions of cyclic beta-ketoesters in the presence of lanthanium triflates and (S,S)-ip-pybox. Intermediates based on simultaneous coordination of the lanthanide to both (S,S)-ip-box and beta-ketoester (in keto and enolate forms) are detected by means of ESI mass spectrometry and NMR experiments, and a possible mechanism is proposed through theoretical calculations.