The degraded C-21 sesterterpenoid (+)-3, enantiomeric with (−)-untenospongin B, has been isolated from the Mediterranean sponge Spongia virgultosa. The absolute stereochemistry of 3 was assigned by applying Mosher's method. On the basis of this work, the absolute stereochemistry at C-11 of nitenin (1) and dihydronitenin (2) has been reanalyzed by applying Mosher's method, whereas the R chirality at C-8 of 2 was determined by recording NOE spectra.The structures of two known C-21 furanoterpenes, tetradehydrofurospongin-1 (8) and 7, have been revised as (+)-3 (named “revised tetradehydrofurospongin-1”) and its acetyl derivative 5, respectively. Finally, a comparison between the Mosher and Horeau methods was carried out, paying attention to the reliability of the stereochemical predictions obtained by the two approaches applied to compounds (+)-3, nitenin (1), and dihydronitenin (2), containing aliphatic-type alcohols.

An improved procedure for the ruthenium tetraoxide catalysed oxidation of 1,5-dienes, employing 0.05 equiv. of the catalyst RuO 2 ·2H 2 O, 2.5 equiv. of NaIO 4 as a stoichiometric oxidant, and a biphasic solvent system of AcOEt/(CH 3 ) 2 CO/ H 2 O (2:1:1, v/v/v), is presented. Reactions of 1,5-dienes 1, 3, and 5 furnished the new cis-tetrahydrofuran products 2, 4, 6, and 7 with total stereospecificity. The structures of the products have been established on the basis of NMR and MS data, as well as chemical evidence. Application of this procedure to geranyl acetate (8) and neryl acetate (12) afforded the cis-tetrahydrofuran derivatives 9, 10, and 13 in high yields, accompanied by small amounts of trans-tetrahydrofu-

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Ruthenium Tetraoxide Oxidation of Alkenes.Part 7. A More Complete Picture.-The main oxidation products of a number of linear and cyclic alkenes are 1,2-diols and/or α-ketols sometimes accompanied by small amounts of scission products such as aldehydes and/or ketones which can be further oxidized to carboxylic acids or can react with the diols to form cyclic acetals, e.g. (XVIII). All reactions proceed through a common intermediate ruthenium(VI) diester, which is presumably the first-formed product from a (3 + 2) cycloaddition of RuO4 to the olefin. -(ALBARELLA, L.; PICCIALLI, V.; SMALDONE, D.; SICA, D.; J.