Ana Paula Esteves

Room temperature ionic liquids, such as N,N,N-trimethyl-N-(2-hydroxyethyl)ammonium bis(trifluoromethylsulfonyl)imide, [N_{1 1 1 2(OH)}][NTf₂] and 1-ethyl-3-methylimidazolium ethylsulfate, [C₂mim][C₂SO₄], have been used for the electroreductive intramolecular cyclization of unsaturated bromo derivatives 1 in Ni(II)-catalyzed reactions. Controlled-potential electrolyses led to five-membered-ring compounds in moderate to good yields. Cyclic voltammetry in these ionic liquid systems was also investigated.

We investigated the reductive intramolecular cyclization of bromopropargyl ethers derivatives, catalyzed by electrogenerated (1,4,8,11-tetramethyl-1,4,8,11-tetraaza-cyclotetradecane)nickel(I), [Ni(tmc)]⁺ as the catalysts in N,N,N-trimethyl-N-(2-hydroxyethyl)ammonium bis(trifluoromethylsulfonyl)imide,[N_{1 1 1 2(OH)}][NTf₂] and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C₂mim][NTf₂] by cyclic voltammetry and controlled-potential electrolysis. The results show that the reaction leads to the formation of the expected cyclic compounds, which are important intermediates in the synthesis of natural products with possible biological activities.

Radical cyclization continues to be a central methodology for the preparation of natural products containing heterocyclic rings. Hence, some electrochemical results obtained by cyclic voltammetry and controlled-potential electrolysis in the study of electroreductive intramolecular cyclization of ethyl (2S, 3R)-2-bromo-3-propargyloxy-3-(2^′,3^′,4^′,6^′-tetra-O-acetyl-β-D-glucopyranosyloxy) propanoate (1a), 2-bromo-3-allyloxy-3-(2^′,3^′,4^′,6^′-tetra-O-acetyl-β-D-glucopyranosyloxy)propanoate (1b), 2-bromo-[1-(prop-2-yn-1-yloxy)propyl]benzene (1c) and [1-bromo-2-methoxy-2-(prop-2^′-yn-1-yloxy)ethyl]benzene (1d) promoted by (1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane)nickel(I), [Ni(tmc)]⁺, electrogenerated at glassy carbon cathodes in ethanol and ethanol:water mixtures containing tetraalkylammonium salts, are presented. During controlled-potential electrolyses of solutions containing [Ni(tmc)]²⁺ and bromoalkoxylated compounds (1) catalytic reduction of the latter proceeds via one-electron cleavage of the carbon–bromine bond to form a radical intermediate that undergoes cyclization to afford the substituted tetrahydrofurans.

Radical cyclization continues to be a central methodology for the preparation of natural products containing heterocyclic rings. The use of electrogenerated nickel(I) complexes as mediators for cathodic intramolecular cyclizations proved to be successful in the formation of carbocyclic products. In this work, the indirect electroreductive intramolecular cyclization of bromoalkoxylated derivatives 1 catalyzed by electrogenerated (1,4,8,11-tetramethyl-1,4,8,11-tetraaza-cyclotetradecane)nickel(I), [Ni(tmc)]⁺, as the catalysts in the ionic liquids, N,N,N-trimethyl-N-(2-hydroxyethyl)ammonium bis(trifluoromethylsulfonyl)imide, [N_{1 1 1 2(OH)}][NTf₂] and 1-ethyl-3-methylimidazolium ethylsulfate, [C₂mim][C₂SO₄] has been investigated by cyclic voltammetry and controlled-potential electrolysis. During controlled-potential electrolyses of solutions of Ni(II) complex in the presence of bromoalkoxylated derivatives 1, only five-membered-ring esters were obtained in moderate to good yields as the main products.

2,3,4,6-Tetra-o-acetyl-1-[4-(2-hydroxyethyl)-1H-1,2,3-triazol-1-yl]-β-D-glucopyranose was prepared and reacted with several acids, either commercially available or prepared. These included, aliphatic or aromatic acids (phenylacetic acid derivatives, benzoic derivatives), palmitic acid and the protected amino acids N-(benzyloxycarbonyl)glycine and N-(tert-butyloxycarbonyl)-phenylalanine. Two other acids, 2-(3-bromopropoxy)benzoic acid and 2-(5-bromopentoxy)benzoic acid (analogues of salicylic acid were synthesized), whose preparation is also described in this work. The esterification was performed either with N,N'-dicyclohexylcarbodiimide (DCC)/4-dimethylaminopyridine (DMAP) or by reacting the acyl chlorides with the alcohol in the presence of triethylamine. The products were isolated in fair yields and fully characterized by the usual analytical techniques.

The synthesis of a series of novel 1,4-disubstituted 1,2,3-triazole compounds bearing a D-glucose derivative and an heteroaromatic system is described. Alkylation of isatin, 3-methyl-carbazole, and one tetrahydro-γ-carboline with propargyl bromide gave their N-propargyl derivatives in good yields. These compounds further reacted with acetylated D-glucose with the azide group in position 1 to give three final products and with peracetylated 6-azido-6-deoxy-α-D-methylglucoside, giving the corresponding derivative of tetrahydro-γ-carboline. Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file.