Alejandra Salerno

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.

Synthesis of Substituted 1H,5-Dihydroimidazolium Salts by Dehydrogenation of Imidazolidines

Abstract A study is presented on the scope of the method to obtain 1H-4,5-dihydroimidazolium salts 3 by dehydrogenation of 1,3-di and 1,2,3-trisubstituted imidazolidines 2. Of the dehydrogenating agents used, N-bromoacetamide leads to the best results, providing a simple and general method to prepare salts 3.

A Convenient “One-Pot” Reaction for Selective Monoalkylation of N,N′-Disubstituted Ethylenediamines

Abstract A study on the scope of the method to obtain N,N,N′-trisubstituted ethylenediamines III by monoalkylation of N,N′-disubstituted ethylenediamines I through a “one-pot” reaction is presented. It involves condensation of compounds I with aldehydes followed by reduction of the formed imidazolidines II without previous isolation.

1H NMR Spectroscopy and Conformational Analysis of N-Benzylimidazolidines

1H NMR spectra of a series of 1-benzyl- and 1,3-dibenzylimidazolidines are analyzed and correlated with their conformational features. The spectra are assigned on the basis of chemical shifts and proton coupling constant values, and confirmed by NOESY spectra. C 2 -Unsubstituted imidazolidines (1, 9) show a fast inversion of the nitrogen atoms. By contrast, 1,2,3-trisubstituted imidazolidines display a preferential conformation with a transoid orientation of the N 1 , N 3 , and C 2 substituents.

An efficient synthesis of 1-acyl-3-arylimidazolidines catalyzed by Montmorillonite K-10 clay under microwave irradiation

The synthesis of 1-acyl-3-arylimidazolidines were performed by reaction of N-acyl-N -arylethylenediamines with formaldehyde and Montmorillonite clay K-10 as a catalyst under microwave irradiation. INTRODUCTION Tetrahydroimidazoles (imidazolidines) are cyclic aminals of pharmacological interest due to the bioactivity shown by some members which is closely related to the substitution type. The most studied compounds are those N,N -disubstituted ones with alkyl or aryl groups, functionalized sometimes. Accordingly, a large number of these compounds with diverse properties such as strogenic activity and mammary tumor inhibition, anti inflammatory and analgesic activity have been described in the literature. Fungicide, bactericide and antiviral activities had also been reported. On the other hand, due to the hydrophobic nature of imidazolidines they can be used to increase the bioavailability of biologically active precursors in the form of a pro-drug and they had been employed as carriers of pharmacologically active ethylenediamines or carbonyl compounds. They are also closely related to the coenzyme N,N-methylenetetrahydrofolic acid, which participate in single carbon transfer at the oxidation level of formaldehyde. Synthesis and study of this type of compounds present interest from a chemical point of view, as synthetic intermediates of cyclic and acyclic compounds with the ethylenediamine structural unit. Thus, dehydrogenation of imidazolidines leads to 4,5-dihydro-1H-imidazolium salts and their selective reduction to N,N,N -trisubstituted ethylenediamines. The imidazolidine system has been widely employed as protecting group of vicinal diamines in peptide synthesis, due to its easy cleavage in mild acid medium. Besides, imidazolidines were also employed as heterocyclic chiral auxiliaries in asymmetric synthesis. Opposite to compounds HETEROCYCLES, Vol. 78, No. 3, 2009 771

(1)H- and (13)C-NMR analysis of a series of 1,2-diaryl-1H-4,5-dihydroimidazoles.

An analysis of the 1H- and 13C-NMR spectra of a series of 1,2-diaryl-1H-4,5-dihydroimidazoles and comparisons with 4,5-dihydroimidazoles having different substitution patterns are presented. The influence of different 1-aryl and 2-aryl group substituents on spectroscopic parameters of the heterocyclic ring and on the contributions of possible mesomeric structures in the system was determined. Spectroscopic features are coherent with the presence of two conjugated systems (Ar1-N and Ar2-C=N) which compete with the delocalization characteristics of the amidine system.

Synthesis and Synthetic Applications of 1-Aryl-2-alkyl-4,5-dihydro-1H-imidazoles

Abstract An easy synthesis of 1-aryl-2-alkyl-4,5-dihydro-1H-imidazoles 1 by cyclo-condensation of N-acyl-N′-arylethylenediamines 2 is described. Such precursors were synthesized by aminolysis of the corresponding N-(2-bromoethyl)amides 3. Cyclizations were performed using trimethylsilyl polyphosphate as a mild dehydrating agent, under microwave irradiation. Chemical properties of 1-aryl-2-alkyl-4,5-dihydro-1H-imidazoles, typical of the amidine system, were studied. Reduction of dihydroimidazoles with sodium cyanoborohydride leads regiospecifically to N-alkyl-N′-arylethylenediamines 4, and nucleophilic attack to methyl iodide leads to the corresponding 1-aryl-2-alkyl-3-methyl-4,5-dihydro-1H-imidazolium salts 5. GRAPHICAL ABSTRACT

Mass Spectra of Cyclic Amidines and their Salts. Part I: 1,2-diaryl-lH-4,5-Dihydro- Imidazoles and their Corresponding Methiodides.

Abstract Mass spectra under electron impact of certain l,2-diaryl-lH-4,5-dihidroimidazoles (1) and their corresponding l,2-diaryl-3-methyl-lH-4,5-dihydroimidazolium iodides (2) were measured and their patterns analyzed. A fragmentation model is proposed for both series of compounds.

Spectroscopic Analysis of Imidazolidines. Part IV: 13C-NMR Spectroscopy

13C NMR spectra of a series of 1,3-di- and 1,2,3-trisubstituted imidazolidines with aryl, alkyl and aralkyl groups are analyzed and their spectroscopic parameters correlated with conformational features. Assignments were confirmed by means of two dimensional spectra of heteronuclear correlation HMQC and HMBC. Heterocyclic carbons are highly influenced by the nature of the substituent on adjacent nitrogen. Thus, carbon atoms adjacent to a nitrogen substituted with an alkyl or aralkyl group appear in the spectrum at 6 ca. 53 ppm as double doublets with 1 J C - H 134 and 145 Hz, due to a definite orientation of the substituent. Instead, carbon atoms adjacent to an N-aryl group appear at higher fields (6 ca. 47 ppm) as triplets with 1 J C - H ca 141-143 Hz.

Detection of a covalent-ionic carbinolamine intermediate in aqueous media by SDTLC on silica gel plates

When the components of a reaction mixture cannot be quantified by UV-visible spectrophotometry, because the λmax values of their absorption bands overlap, the components can be separated and quantified by spectrodensitometric thin-layer chromatography (SDTLC). In this work an aminolysis reaction mixture in aqueous medium was studied by TLC on silica gel plates with densitometric detection. The reaction, an intramolecular rearrangement involving migration of an acyl group, was studied by monitoring a carbinolamine intermediate for which λmax was identical with those of the substrate and product. SDTLC not only enabled detection of all three components of the mixture when the plate was developed but also enabled detection of covalent and ionic forms of the reaction intermediate by comparison of their absorbance/reflectance spectra with those of structurally related imidazolidine and amidinium salt derivatives, respectively, used as model compounds. Kinetic studies, among others, may also be performed by SDTLC to determine the mechanism of the reaction.