Simona Selva

Synthesis and reactivity of a new Fe(II) 5-(4-pyridyl)-tetrazolate complex and X-ray structure of its doubly protonated derivative.

Abstract The synthesis of the new Fe(II) complex [CpFe(CO)2(N4C–C5H4N)] (2) is described. 1H- and 13C-NMR spectroscopy data of (2) indicate the presence of interannular conjugation in the pyridyl-tetrazolate ligand, implying coplanarity between the two rings. Addition of electrophiles to 2 resulted in the formation of cationic complexes such as [CpFe(CO)2(4-MeN4C–C5H4N)][O3SCF3] (3), [CpFe(CO)2(4-HN4C–C5H4N)][O3SCF3] (4) and of the doubly protonated complex [CpFe(CO)2(4-HN4C–C5H4N–H)][O3SCF3]2 (5). In all cases, the out-of-plane rotation of the pyridyl ring occurred as a consequence of the quaternization of the N-4 of tetrazole ring. X-ray structure of complex 5 indicates a torsion angle of 20.9(2)° between the aromatic rings. Protonation reactions were found to be reversible and complexes 4–5 were easily converted into the starting complex 2 by addition of a base.

Synthesis and desilylation of (2R,3S)-α-methyl-α-silyl-α,β-2,3-dihydroxycarboxylic methyl esters

Abstract Addition reactions of the chiral lithium (2 S )-enolates of the (2 S ,5 S )-2- tert -butyl-5-methyl-[1,3]dioxolan-4-one and (2 S ,5 S )-2- tert -butyl-2,5-dimethyl-[1,3]dioxolan-4-one with linear aliphatic acylsilanes yield the corresponding (2 S ,5 R ,1′ R )-1′-trimethylsilyl-dioxolanone alcohols. Sodium methoxide-induced removal of the acetal center at C-2 affords the corresponding methyl (2 R ,3 R )-2,3-dihydroxy-2-methyl-3-trimethylsilyl alkanoates. The desilylation of these esters occurs with complete retention of configuration yielding the corresponding (2 R ,3 S )-2,3-dihydroxy-2-methyl-alkanoic acids.

Enantioselective synthesis of aziridine 2,2-dicarboxylates. Part II: Determination of the absolute configuration

Abstract The absolute configuration of aziridine-2,2-dicarboxylates was determined through their transformation into the corresponding diastereomeric (S)-(−)-α-methylbenzylamido derivatives. The data obtained allows establishment of the stereochemistry of the first step of the conjugate addition reaction catalyzed by chiral bisoxazoline–Cu complex.

Unexpected reactivity between aromatic nitro compounds and PCl3/AlCl3. A new one-pot synthesis of phenazines

The reaction between 4-nitroalkoxybenzenes 7 and PCl 3 /AlCl 3 , when carried out in appropriate molar ratio, gives a prevalent formation of diazenes 8 and 2,7-dialkoxyphenazines 9 with their new chlorinated derivatives 10 – 13 . These compounds are obtained, in satisfactory yield, in a one-pot procedure, in mild conditions, from commercially available and safe starting materials. In this reaction both the reagents PCl 3 and AlCl 3 play a fundamental role in obtaining the products, and this method might be applicable to other 4-alkoxynitrobenzenes.

Synthesis and characterization of new thioether derivatives of [Os3(CO)12] and [H2Os3(CO)10]; crystal and molecular structures of [Os3(CO)11(L)] [Et2S, Pr2S, S(CH2)5] and [Os3(CO)9(μ-H)(μ-X){SMe(But)}] (X=H, OH)

Reaction of [Os3(CO)11(NCMe)] with R2S (R = Et, nPr) and MeSBut results in the formation of [Os3(CO)11(L)] (L = thioether) clusters in which the thioethers are coordinated in an equatorial site of the triosmium framework. Such monosubstituted clusters are also formed when [Os3(CO)10(NCMe)2] is reacted with R2S (R = Et, nPr) while reaction of the same cluster with Ph2S or MeSPh results in the formation of orthometalated clusters, viz. [Os3(m-H)(CO)10(m-h2-C6H4SR)] and [Os3(m-H)(CO)9(m3-C6H4SPh)]. The similar reaction of [Os3(m-H)2(CO)10] with Pr2S, MeSBut, MeSPh or Ph2S does not lead to discernable products except when carried out in the presence of trimethylamine N-oxide, which leads to clusters of the general formula [Os3(CO)9(m-H)2(thioether)]. The crystal and mol. structures of [Os3(CO)11(L)] (L = Et2S, Pr2S, S(CH2)5) and [Os3(CO)9(m-H)(m-X){SMe(But)}] (X = H, OH) are presented. (Less)

Design of boron bis-oxazolinate (B-BOXate) complexes: a new class of stable organometallic catalysts

A new class of remarkably stable B-BOXate complexes has been synthesised, isolated and employed as chiral catalysts for asymmetric reduction of variously substituted prochiral ketones.