Cross-metathesis reaction of vinyl sulfones and sulfoxides

Cross-metathesis reactions of α,β-unsaturated sulfones and sulfoxides in the presence of molybdenum and ruthenium pre-catalysts were tested. A selective metahesis reaction was achieved between functionalized terminal olefins and vinyl sulfones by using the ‘second generation’ ruthenium catalysts 1c-h while the highly active Schrock catalyst 1b was found to be functional group incompatible with vinyl sulfones. The cross-metathesis products were isolated in good yields with an excellent (E)-selectivity. Both the molybdenum and ruthenium-based complexes were, however, incompatible with α,β- and β,γ-unsaturated sulfoxides.     

C-C bond formation via C-H bond activation: catalytic arylation and alkenylation of alkane segments

A new system for catalytic arylation and alkenylation of alkane segments has been developed. The ortho-tert-butylaniline substrates and 2-pivaloylpyridine may be arylated and alkenylated at the tert-butyl group, while no functionalization occurred at more reactive C-H and other bonds. Arylation and alkenylation of these substrates are achieved in the presence of Ph2Si(OH)Me and Ph-CH=CH-Si(OH)Me2, respectively, and the catalytic amount of Pd(OAc)2 and stoichiometric oxidant (Cu(OAc)2, 2 equiv) in DMF. In contrast, the ortho-i-propylaniline substrate underwent cyclopalladation, but no arylation product was obtained. Complex compound 14 was synthesized via tandem arylation-alkenylation of tert-butylaniline 11. We hypothesize that the high selectivity of this system stems from the confluence of directing effect of the Schiff base or pyridine moiety and unique reactivity properties of a phenyl-palladium acetate species (Ph-Pd-OAc.Ln).     

Novel metathesis catalysts based on ruthenium 1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidenes: synthesis, structure, immobilization, and catalytic activity

The synthesis of novel ruthenium-based metathesis catalysts containing the saturated 1,3-bis(2,4,6-trimethylphenyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene ligand, that is, [RuCl2(NHC)[=CH-2-(2-PrO)-5-NO(2)-C6H3]] (1) and [Ru(CF3COO)2(NHC)[=CH-2-(2-PrO)-5-NO2-C6H3]] (2) (NHC=1,3-bis(2,4,6-trimethylphenyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene) is described. Both catalysts are highly active in ring-closing metathesis (RCM) and ring-opening cross-metathesis (ROCM). Compound 1 shows moderate activity in enyne metathesis. Compound 2 is not applicable to enyne metathesis since it shows high activity in the cyclopolymerization of diethyl dipropargylmalonate (DEDPM). Poly(DEDPM) prepared by the action of 2 consists of 95% five-membered rings, that is, poly(cyclopent-1-enevinylene)s, and 5 % of six-membered rings, that is, poly(cyclohex-1-ene-3-methylidene)s. The polymerization proceeds in a nonliving manner and results in polyenes with broad polydispersities (1.9< or =PDI< or =2.3). Supported analogues of 2 were prepared by immobilization on hydroxymethyl-Merrifield resin and a monolithic support derived from ring-opening-metathesis polymerization (ROMP). Catalyst loadings of 1 and 2.5%, respectively, were obtained. Both supported versions of 2 showed excellent reactivity. With 0.24-2% of the supported catalysts, yields in RCM and ROCM were in the range of 76-100%. Leaching of ruthenium was low and resulted in Ru contaminations of the products of less than 0.000014% (0.14 ppm).     

Simple and efficient recyclable catalytic system for performing copper-catalysed S-arylation reactions in the presence of water

A novel protocol for the copper-catalysed S-arylation of thiophenol derivatives with aryl halides leading to diaryl sulfides is reported. The reactions were catalysed by a combination of a copper salt and a 1,2-diamine derivative (acting both as the ligand and as the base) using exclusively water as the solvent. The recovery and successful reutilisation of the aqueous medium containing the active catalyst is described. Furthermore, one example of a "one-pot" process involving Br/I exchange of an aryl bromide and further S-arylation is presented.     

Iron-promoted C-C bond cleavage of 1,3-diketones: a route to 1,2-diketones under mild reaction conditions

A conceptual method for the preparation of 1,2-diketones is reported. The selective C-C bond cleavage of 1,3-diketones affords the 1,2-diketones in high yields under mild reaction conditions in air by the use of FeCl(3) as the catalyst and tert-butyl nitrite (TBN) as the oxidant without the use of solvent. The possible reaction mechanism is discussed. This protocol provides an expeditious route to the useful 1,2-diketones.     

C-C bond cleavage: Metal-free-catalyzed reaction of Betti bases with various heterocycles under microwave irradiation

The reaction of Betti bases with various heterocycles in the presence of p-toluenesulphonic acid (PTSA) under microwave irradiation gives bis(heterocycle)methanes through benzyl transfer. The reaction proceeds via the cleavage of C-N bond followed by C-C bond. The metal-free cleavage of C-C bond, which is in fact a C-dearylation, is rarely reported in the literature.     

Conversion of naringenin and hesperetin by heterogeneous catalytic Baeyer-Villiger reaction into lactones exhibiting apoptotic activity

Naringenin and hesperetin were converted into the corresponding lactones by hydrogen peroxide activated by poly(4-vinylpiridine)-supported methyltrioxorhenium in t-butanol, an environmentally friendly catalytic system. The products showed a marked apoptotic activity in the genetic tests.     

Extrusion of CO from aryl ketones: rhodium(I)-catalyzed C-C bond cleavage directed by a pyridine group

Snipping tool: the rhodium(I)-catalyzed extrusion of carbon monoxide from biaryl ketones and alkyl/alkenyl aryl ketones was developed to produce biaryls and alkyl/alkenyl arenes, respectively, in high yields. A wide range of functionalities are tolerated. Not only does this method provide an alternative pathway to construct useful scaffolds, but also offers a new strategy for C-C bond activation.