Liliana R. Orelli

Lanthanides in organic synthesis: Eu+3-catalyzed Michael addition of 1,3- dicarbonyl compounds

EuCl3 proves to be an efficient catalyst for Michael addition of 1,3-dicarbonyl compounds. The employment of Eu+3 chiral complex [Eu(tfc)3] allows the formation of Michael adducts in enantioselective way.

A new procedure for Horner-Wadsworth-Emmons olefination of carbonyl compounds

Abstract aldehydes undergo an efficient E-stereoselective Horner-Wadsworth-Emmons olefination by generation of phosphonate carbanion with lithium hydroxide. The reaction proceeds satisfactorily with linear, cyclic, polifunctional ketones in the presence of activated zeolites and and by the slow addition of the base.

A Convenient Synthesis of Unsymmetrical N,N′-Disubstitutedα,ω-Diaminoalkanes

Abstract A general procedure is described for regiospecific construction of unsymmetrical N-alkyl (or aralkyl)-N′-aryl-α,ω-diaminoalkanes 3 (n=2,3,4) by reduction of N-(ω -arylaminoalkyl)amides 2 with borane. Compounds 2 are readily obtained by condensation of N-(ω-haloalkyl)amides 1 with aromatic amines.

Convenient procedure of Horner–Wadsworth–Emmons olefination for the synthesis of simple and functionalized α,β-unsaturated nitriles

A mild and practical procedure of Horner–Wadsworth–Emmons olefination promoted by lithium hydroxide and α-cyano phosphonates has been set up for the synthesis of α,β-unsaturated nitriles. The reaction conditions are tolerated by functionalized ketones and the exclusive formation of E-γ-hydroxy α,β-unsaturated nitriles has been observed.

Atropisomerism in amidinoquinoxaline N-oxides: effect of the ring size and substituents on the enantiomerization barriers.

The atropisomerism of novel 2,3-dihydro-1H-pyrimido[1,2-a]quinoxaline 6-oxides 1 bearing dissymmetric (ortho-substituted) 5-aryl residues and the homologous 1,2-dihydroimidazo[1,2-a]quinoxaline 5-oxides 2 was investigated. The existence of a chiral axis was demonstrated for compound 1a by X-ray diffraction and by DFT calculations of the ground state geometry. The resolution of the atropisomeric enantiomers on chiral stationary phases is reported. The barriers to enantiomerization were determined by off-line racemization studies and/or by treatment of the plateau-shaped chromatograms during chromatography on chiral support. A clear ring size effect was evidenced. In all cases, six-membered amidine derivatives 1 showed higher barriers than the corresponding lower homologues 2, which also display lower sensitivity to the substituent size. Transition states for the interconversion of the atropisomers were located using DFT calculations, and involved the interaction of the ortho substituent with the formally sp(2) nitrogen in the amidine moiety. In contrast, in the most favored enantiomerization transition state of the 2-nitro derivative the ortho substituent is close to the N-oxide group.

A NEW SYNTHETIC APPROACH TO N,N′-DISUBSTITUTED 1,n-ALKANEDIAMINES

A general procedure is described for the synthesis of unsymmetrically substituted N-aryl-N′-alky1 (or aryl) 1,n-alkanediamines 1 (n = 2−5) by reduction of ω-alkyl (or aryl) aminoalkanamides 2 with borane. Compounds 2 are easily obtained by aminolysis of the corresponding ω-haloalkanamides 3.

Mass Spectra of Cyclic Amidines and Their Salts. Part II. 2-Aryl and L, 2-Diaryl-l, 4, 5, 6-Tetrahydropyrimidines and Their Corresponding Methiodides

Abstract Mass spectra of a series of 2-mono- and 1, 2-disubstituted- 1, 4, 5, 6-tetra hydropyrimidines 1 and their methiodides 2 under electron impact (EI) are analyzed. A typical fragmentation pattern was found for each series of compounds. One of the fragmentation routes proposed for compounds 1 was confirmed by high resolution techniques. A fast atom bombardment (FAB+) technique was employed in order to detect methiodides 2 molecular ion. The chemical ionization (CI) spectrum of compound 2d is also analyzed.

Amidinoquinoxaline N-oxides as novel spin traps

A novel type of spin traps 1 derived from the pyrimidoquinoxaline N-oxide heterocyclic core is reported. EPR technique was used to evaluate their ability to trap methyl radicals generated in a Fenton reaction in the presence of DMSO. All the synthesized nitrones showed spin trapping properties and the corresponding nitroxides 2 were characterized by EPR. The novel spin traps showed remarkably persistent signals, as confirmed in a competition experiment with DMPO. The addition rate constants leading to the spin adducts (kadd) were determined, and very good correlations were found with steric and electronic parameters of the parent nitrones. The spin adducts decomposition rate constants (kdec) and the corresponding half-life times (t1/2) were also determined. DFT and MP2 calculations were used in order to rationalize the adducts hfcc and the structural factors influencing their addition and decomposition rates.

1-Aryl-3-alkyl-1,4,5,6-tetrahydropyrimidinium salts. Part 2. Reactions with nucleophiles

The reactivity of 1-aryl-3-alkyl-1,4,5,6-tetrahydropyrimidinium salts (1) towards nucleophiles was studied. Hydrolysis of salts (1) afforded initially compounds (2, kinetic products) through the corresponding amidinium hydroxides (4). The regioselectivity of the reaction was analyzed considering the relative leaving group abilities and the stereoelectronic control theory. Amino amides (2a-c) in the reaction medium underwent spontaneous formyl migration, affording compounds (3, thermodynamic products). Reduction of salts (1) with sodium borohydride led to acyclic trimethylenediamines (5) or to the corresponding hexahydropyrimidines (6), according to the reaction conditions. Aminolysis of compound (1f) with isopropylamine yielded an acyclic formamidine (7f).

An Efficient Synthesis of N-Alkyl-N-arylputrescines and Cadaverines

N-Substituted 1,4-diaminobutane (putrescine) and 1,5-diaminopentane (cadaverine) derivatives are of biochemical and pharmacological interest as synthetic analogs of natural polyamines.1 Several der...