Barbara Sechi

Aryloxypropanoic herbicides by asymmetric hydroformylation catalyzed by rhodium carbonyl complexes modified with phosphorus ligands

Abstract Three aryl vinyl ethers have been subjected to enantioselective Rh(I) catalyzed hydroformylation using diphosphites 10 and 11 described in the literature and diphosphites 12–16 synthesized in our laboratories as ligands. All these ligands afforded in most cases 80–90% yields 2-aryloxypropanals as valuable precursors of the very selective herbicides, 2-aryloxypropanoic acids. The same unsaturated substrates have been also hydroformylated in the presence of Rh complexes with commercially available ferrocenylphosphines 17–19: these catalytic complexes showed generally satisfactory reaction rates as well as regioselectivities, but in some cases, lower chemoselectivities than those containing diphosphites. The enantioselectivities obtained with all described ligands were rather low (up to 9%).

Enantioselective Hydroformylation of Vinyl-aromatics using a Rhodium Complex with the (1R,2R,4R)-2-(2-Diphenylphosphinyl-1,7,7-trimethylbicyclo[2.2.1]hept-2-yl)pyridine

The rhodium complex of a pyridylphosphinite derived from (+)-camphor was prepared and assessed in the hydroformylation reaction of some vinyl-aromatic substrates. The complex exhibit good catalytic activity. The prevalent formation of the branched aldehyde was obtained with all examined substrates. The enantioselectivities were low to moderate (up to 45%).

Single and double reductive cleavage of CO bonds of aromatic dimethyl acetals and ketals: Generation of benzylic mono- and dicarbanions

Abstract The reductive cleavage of aromatic dimethyl acetals and ketals, 1 , with Li metal in THF at low temperature allows the generation of stable α-alkoxy-α-arylsubstituted carbanions, avoiding the Wittig rearrangement. Reaction of these carbanions with various electrophiles afforded the expected products 2 . Further in situ reaction of compounds 2 afforded the products of reductive electrophilic disubstitution, 3 .

Reductive Electrophilic Substitution of Diarylmethyl Methyl Ethers: Synthetic Applications

Abstract The reductive cleavage of diarylmethyl methyl ethers with Li metal in THF led to quantitative formation of the corresponding diarylmethyl anions. Quenching with electrophiles afforded substituted diarylmethanes in good to excellent yields.

Osmium complexes in catalysis of olefin hydrogenation and isomerization

This review focuses on the evolution of the use of osmium complexes as catalysts in the hydrogenation and isomerization of olefins. Osmium systems show good catalytic activities and selectivities in the hydrogenation of olefins via both dihydrogen and transfer hydrogenation. Such systems therefore have significant potential to become a powerful tool in organic synthesis.

Synthesis, structural properties, and pharmacological evaluation of 2-(acylamino)thiophene-3-carboxamides and analogues thereof

We have previously reported the synthesis and the pharmacological characterization of a family of methyl 2-(acylamino)thiophene-3-carboxylates as GABAB positive allosteric modulators active both in vitro and in vivo. In the present work, we describe the synthesis of new compounds based on the bioisosteric replacement of the ester moiety with amido or heterocyclic groups as well as of thieno[2,3-d]pyrimidine derivatives as rigid analogues thereof. 4H-Thieno[2,3-d][1,3]oxazin-4-ones were used as synthetic intermediates for the preparation of some of these compounds. The structures of oxazinones 11b, 16, and 17 were assigned by X-ray crystallographic studies, which definitely ruled out the isomeric beta-lactam structure previously hypothesized for these compounds. None of the new molecules exhibited significant activity at the GABAB receptor, either as allosteric or orthosteric ligands.