Recebido em 17/1/08; aceito em 7/4/08; publicado na web em 30/4/08 NATURAL OCCURRENCE, BIOLOGICAL ACTIVITIES AND SYNTHESIS OF EIGHT-, NINE-, AND ELEVEN-MEMBERED RING LACTONES. The natural occurrence, biological activities and synthetic approaches to natural eight-, nine-, and elevenmembered lactones is reviewed. These medium ring lactones are grouped according to ring size, and their syntheses are discussed. The structures of some natural products early identified as medium-ring lactones were revised after total synthesis.
The strategies for the synthesis of naturally occurring ten-membered-ring lactones, which are the most abundant of the medium-ring lactones, are discussed. According to their structures and/or biosynthesis, the molecules are classified in monocyclic polyketides, monocyclic oxylipins, aliphatic bicyclic and aromatic bicyclic lactones. In each subsection, the lactones are presented in chronological order of their isolation. Representative complex systems bearing multiple functionalities in addition to the lactone moiety, as well as a selection of recent synthetic approaches to nonnatural medium-ring lactones, are briefly presented.
In the present work, we describe the preparation of ten amino acid ionic liquids (AAILs) formed from ammonium salts as cations, derivatives of glycerol, and natural amino acids as anions. All of them are viscous oils, colorless or pale yellow, and hygroscopic at room temperature. They have appreciable solubility in many protic and aprotic polar solvents. The AAILs were used as catalysts in a Morita-BaylisHillman (MBH) reaction. The ionic liquids derivative from L-proline and L-histidine demonstrated the ability to catalyze the reaction between methyl vinyl ketone and aromatic aldehydes differently substituted in the absence of an additional co-catalyst under organic solvent-free conditions. The AAIL derivatives from L-valine, L-leucine, and L-tyrosine catalyzed the MBH reaction only in the presence of imidazole. The MBH adducts were obtained in moderate to good yields. Although the catalytic site in the ILs was in its enantiomerically pure form, all the MBH adducts were obtained in their racemic form.
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