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.
In this work we describe the cyclofunctionalization of eleven differently substituted alkenyl-beta-dicarbonyl compounds, employing three electrophilic reagents, namely, iodine, p-methoxyphenyltellurium trichloride, and phenylselenenyl bromide. The reactions occur through the enolic form of the substrates, to afford the corresponding iodo-, telluro-, or selenocyclic enol ethers. Substrates bearing trisubstituted double bonds failed in reacting with the selenium and tellurium reagents. In general, beta-diketones reacted faster than beta-keto esters with the three studied electrophiles.
This work describes the use of aryltellurium trichloride and iodine as suitable cyclization reagents for alkenyl substituted β-keto esters. The reaction takes place via the enolic form of the dicarbonyl compounds, giving the corresponding five-membered cyclic ethers in good yields.
Este trabalho descreve a reação de desidroiodação, promovida por base, de uma série de β-iodoenol éteres cíclicos. Os produtos são tetraidrofuranos contendo duas ligações duplas exocíclicas, die tetraidrobenzofuranos e um derivado de diidropirano, todos obtidos em ótimos rendimentos. This work describes the base-promoted dehydroiodination of differently substituted cyclic β-iodo-enol ethers. The products are tetrahydrofuran derivatives bearing two exocyclic double bonds, di-and tetrahydrobenzofurans and a dihydropyran derivative, which were obtained in very good yields.
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