Tuning the Reducing Properties of 1,2-Diaryl-1,2-disodiumethanes

We investigated the reducing properties of a series of 1,2-diaryl-1,2-disodiumethanes by means of equilibration reactions. The electron-donor power of these vic-diorganometals is strongly affected by the nature of substituents present either on the aromatic ring(s) or on the carbanionic centers, and it can be correlated with their ability to delocalize the arylmethyl carbanions. These findings are supported by electrochemical analysis of the reduction behavior of the parent 1,2-diarylalkene. Applications of these results to the reduction of selected substrates are described

BH₃-Promoted Stereoselective β-Lithiation of <i>N</i>-Alkyl-2-phenylaziridines

BH3 complexes of N-alkyl-2-phenylaziridines have been synthesized and their structure and stereochemistry proved with DFT calculations and NMR experiments. It has been demonstrated that the Lewis acid complexation is able to promote a regioselective β-lithiation in 2-phenylaziridino−borane complexes. The lithiated intermediates were configurationally stable, allowing an enantioselective preparation of cis-2,3-disubstituted aziridines

V^IVO Versus V^IV Complex Formation by Tridentate (O, N_arom, O) Ligands: Prediction of Geometry, EPR ⁵¹V Hyperfine Coupling Constants, and UV–Vis Spectra

Systems formed using the V^IVO²⁺ ion with tridentate ligands containing a (O, N_arom, O) donor set were described. Examined ligands were 3,5-bis­(2-hydroxyphenyl)-1-phenyl-1<i>H</i>-1,2,4-triazole (H₂hyph^Ph), 4-[3,5-bis­(2-hydroxyphenyl)-1<i>H</i>-1,2,4-triazol-1-yl]­benzoic acid (H₃hyph^C), 4-[3,5-bis­(2-hydroxyphenyl)-1<i>H</i>-1,2,4-triazol-1-yl]­benzenesulfonic acid (H₃hyph^S), and 2,6-bis­(2-hydroxyphenyl)­pyridine (H₂bhpp), with H₃hyph^C being an orally active iron chelator that is commercially available under the name Exjade (Novartis) for treatment of chronic iron overload arising from blood transfusions. The systems were studied using EPR, UV–Vis, and IR spectroscopies, pH potentiometry, and DFT methods. The ligands bind vanadium with the two terminal deprotonated phenol groups and the central aromatic nitrogen to give six-membered chelate rings. In aqueous solution the main species were the mono- and bis-chelated V^IVO complexes, whereas in the solid state neutral non-oxido V^IV compounds were formed. [V­(hyph^Ph)₂] and [V­(bhpp)₂] are hexacoordinated, with a geometry close to the octahedral and a meridional arrangement of the ligands. DFT calculations allow distinguishing V^IVO and V^IV species and predicting their structure, the ⁵¹V hyperfine coupling constant tensor <i><b>A</b></i>, and the electronic absorption spectra. Finally, EPR spectra of several non-oxido V^IV species were compared using relevant geometrical parameters to demonstrate that in the case of tridentate ligands the ⁵¹V hyperfine coupling constant is related to the geometric isomerism (meridional or facial) rather than the twist angle Φ, which measures the distortion of the hexacoordinated structure toward a trigonal prism

Data_Sheet_1_Stereo- and Enantioselective Addition of Organolithiums to 2-Oxazolinylazetidines as a Synthetic Route to 2-Acylazetidines.docx

A new synthetic route to N-alkyl-2-acylazetidines was developed through a highly stereoselective addition of organolithiums to N-alkyl-2-oxazolinylazetidines followed by acidic hydrolysis of the resulting oxazolidine intermediates. This study revealed an unusual reactivity of the C=N bond of the oxazoline group when reacted with organolithiums in a non-polar solvent such as toluene. The observed reactivity has been explained considering the role of the nitrogen lone pair of the azetidine ring as well as of the oxazolinyl group in promoting a complexation of the organolithium, thus ending up with the addition to the C=N double bond. The high level of stereoselectivity in this addition is supported by DFT calculations and NMR investigations, and a model is proposed for the formation of the oxazolidine intermediates, that have been isolated and fully characterized. Upon acidic conditions, the oxazolidine moieties were readily converted into 2-acylazetidines. This synthetic approach has been applied for the preparation of highly enantioenriched 2-acylazetidines starting from chiral not racemic N-alkyl-2-oxazolinylazetidines.</p

Nitrogen Stereodynamics and Complexation Phenomena as Key Factors in the Deprotonative Dynamic Resolution of Alkylideneaziridines: A Spectroscopic and Computational Study

The present work is aimed at shedding light on the origin of the stereoselectivity observed in the reactions of chiral heterosubstituted organolithiums, generated by lithiation of alkylideneaziridines. Factors such as the nitrogen inversion barrier, the stereochemistry at the nitrogen atom, the substitution pattern of the alkylideneaziridines, and the reaction conditions are taken into consideration. The interplay between nitrogen stereodynamics and complexation phenomena seems to be crucial in determining the stereochemical outcome of the lithiation/trapping sequence. The findings were rationalized by a synergistic use of NMR experiments, run on the lithiated intermediates, alongside computational data. It has been demonstrated that, in such systems, the stereochemistry-determining step is the deprotonation reaction, and a model based on a deprotonative dynamic resolution has been proposed. Such findings could find application in dynamic systems other than aziridines