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Dediazoniation of 2,4,6-trimethylbenzenediazonium tetrafluoroborate, 1-ArN 2 BF 4 (for the z-Ar compounds described in this paper, z refers to the length of the carbon chain of the substituent at C4 of the benzene ring), in aqueous solutions containing sodium methyl sulfate, NaMeSO 4 , or sodium methanesulfonate, NaMeSO 3 , yields 2,4,6-trimethylphenol, 1-ArOH, 2,4,6-trimethylphenyl methyl sulfate, 1-ArOSO 3 Me and 2,4,6-trimethylphenyl methanesulfonate, 1-ArO 3 SMe, respectively. The relative yields of 1-ArO 3 SMe or 1-ArOSO 3 Me and 1-ArOH depend on the NaMeSO 4 or NaMeSO 3 concentrations. 4-n-Hexadecyl-2,6-dimethylbenzenediazonium tetrafluoroborate, 16-ArN 2 BF 4 , was used to determine the local head group concentration in sodium dodecyl sulfate and sodium dodecanesulfonate micelles by chemical trapping comparing the relative product yields with those obtained in water using the short chain analogs.Ab initio calculations of the spontaneous dediazoniation of phenyldiazonium ion in the gas phase, as well as in aqueous solution with, or without, added MeSO 3 Ϫ , yield potential energy surfaces for the reaction. For this model the calculated and experimental values of the spontaneous dediazoniation rate constants in aqueous solution, as well as the product composition, were similar to those obtained with 1-ArN 2 ϩ . These results suggest that in aqueous solution nucleophiles can only compete with water if a diazonium ionؒnucleophile complex is formed prior to N 2 loss. Calculations show that the addition of nucleophiles to the arenediazonium ion occurs without a saddle point in the potential energy surface, suggesting that the free phenyl cation is not an obligatory intermediate in aqueous solutions.

The first synthesis of the natural product (+)-mutisianthol was accomplished in 11 steps and in 21% overall yield from 2-methylanisole. The synthesis of its enantiomer was also performed in a similar overall yield. The absolute configuration of the sesquiterpene (+)-mutisianthol was assigned as (1S,3R). Key steps in the route are the asymmetric hydrogenation of a nonfunctionalized olefin using chiral iridium catalysts and the ring contraction of 1,2-dihydronaphthalenes using thallium(III) or iodine(III). The target molecules show moderate activity against the human tumor cell lines SF-295, HCT-8, and MDA-MB-435.

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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.

Dedicamos este artigo ao Prof. Dr. Sílvio do Desterro Cunha, da UFBA, pelo constante estímulo, esperando contribuir com mais uma "inevitável" leitura para seu grupo de pesquisa.

The reaction of a series of cis-fused bicyclic beta-hydroxytetrahydrofurans with ruthenium tetraoxide, generated in situ from ruthenium trichloride and sodium periodate, afforded 9- and 10-membered keto-lactones in moderate to good yields, in a clean and straightforward fashion. The starting beta-hydroxyethers were obtained from the corresponding 3-alkenols by two alternative procedures, depending on their pattern of substitution: (a) epoxidation by dimethyldioxirane, followed by base-catalyzed cyclization of the resulting epoxyalcohol, and (b) thallium trinitrate-mediated cyclization of the 3-alkenols, a method already described by our group.

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