Keywords: Oxidation / Tetrahydrofuran / Catalysis / Asymmetric synthesis / Vanadium Vanadium(V) complexes 4 have been prepared from tridentate Schiff-base ligands 3 and VO(OEt) 3 . All vanadium(V) compounds were characterized (IR, UV/Vis, and 51 V NMR spectroscopy, and in selected examples by X-ray diffraction analysis) and were applied as oxidation catalysts for the stereoselective synthesis of functionalized tetrahydrofurans 2 starting from substituted bis(homoallylic) alcohols 1 (mono-or trisubstituted C−C double bonds). Oxidation of secondary or tertiary 1-alkyl-, 1-vinyl-, or 1-phenyl-substituted 5,5-dimethyl-4-penten-1-ols under optimized conditions [TBHP as primary oxidant and 1,2-(amino)indanol-derived vanadium(V) reagent 4g as catalyst] provided 2,5-cis-configured tetrahydrofurans in synthetically useful yields and diastereoselectivities (22−96% de). On the other hand, trans-disubstituted oxolanes (62%−96 de) were obtained from oxidations of 2-or 3-alkyl-and 2-or 3-phenyl-substituted 5,5-dimethyl-4-penten-1-ols bis(homoallylic) alcohols. Treatment of 4-penten-1-ols (i.e. substrates with monosubstituted olefinic π-bonds) with TBHP and catalytic amounts of vanadium(V) complex 4g furnished trans-disubstituted tetrahydrofurans as major products (20−96% de), no matter whether an alkyl or a phenyl substituent was located in position 1, 2, or 3 of the alkenol chain. The mechanism of this reaction has been investigated in detail. Based on re-

Diastereoselective syntheses Diastereoselective syntheses O 0031 (Schiff-Base)vanadium(V) Complex-Catalyzed Oxidations of Substituted Bis(homoallylic) Alcohols -Stereoselective Synthesis of Functionalized Tetrahydrofurans.-From several vanadium(V) complexes, chiral amino alcohol ligated complex VAN is found to be optimal to catalyze the title reaction. Depending on the position of substituents at the bis(homoallylic) alcohol, cis and trans substituted tetrahydrofurans are formed as sole or major products with 20 to >96% diastereoselectivity. -(HARTUNG*, J.; DREES, S.; GREB, M.; SCHMIDT, P.; SVOBODA, I.; FUESS, H.; MURSO, A.; STALKE, D.; Eur.

Oxidation of (3R)-linalool (2) with tert-butyl hydroperoxide (TBHP) occurs at the 6,7-position to selectively afford linalool oxide cis-1, if catalyzed by vanadium(V) Schiff base complexes 4. Substituted tetrahydrofuran cis-1 and its isomer trans-1 served as starting materials for short concise syntheses of β-carbolines cis-3 and trans-3 which are lower homologues of alkaloids (-)-isocyclocapitelline and (+)-cyclocapitelline.(-)-Isocyclocapitelline (Scheme 1), (+)-cyclocapitelline, and (+)-chrysotricine are tetrahydrofuran-derived β-carboline alkaloids, which have been extracted from far eastern medicinal plants. 1,2 From a biosynthetic point of view it seems likely that linalool oxides 1 and therefore linalool 2 serve as precursors for the formation of these alkaloids. 1,3 In organic synthesis, however, the abovementioned β-carbolines are generally obtained in multistep transformations that use other precursors than terpenol 2 as starting material for the following reasons. 4 Conversion of substrate 2 into functionalized tetrahydrofurans 1 requires selective oxygenation at the 6,7-π-bond which is attainable by e.g. peracids 5 or the combination of H 3 CReO 3 /H 2 O 2 . 6 Unfortunately, the observed diastereoselectivities in these reactions are negligible. If oxidized with tert-butyl hydroperoxide in the presence of an early transition metal catalyst such as VO(acac) 2 , 7 a selective conversion of linalool 1 into the corresponding 1,2-epoxyalcohol has been reported. 8,9 In view of the significance of linalool oxides 1 as versatile building blocks, 10 and the contemporary interest in tetrahydrofuran-derived β-carboline alkaloids, 1,2,4 we have developed a new stereoselective access to furanoid linalool oxide cis-1 and disclose our latest results in this communication as a part of the synthesis of hitherto unknown β-carbolines cis-3 and trans-3.The selected strategy for diastereoselectively oxidizing substrate 2 at the 6,7-position is based on the use of TBHP as primary oxidant and vanadium(V) Schiff base complexes 4 as catalysts. 11 The latter reagents were chosen for this purpose, since vanadium compound 4a does not catalyze the epoxidation of allylic alcohols 12 but efficiently mediates diastereoselective formation of functionalized tetrahydrofurans from bishomoallylic alcohols and TBHP. 11,13,14 In an initial experiment, terpenol 2 was treated with TBHP and 10 mol% of vanadium(V) catalyst 4a in CHCl 3 at 20°C for 12 hours. Previous optimization studies had shown that these conditions provide high selectivities for tetrahydrofuran formation in combination with a satisfactory peroxide efficiency. 14 Purification of the reaction mixture furnished furanoid linalool oxides 1 (62%, cis:trans = 61:39), 1,2-epoxylinalool oxides 5 (6%, cis:trans = 56:44), and pyranoid linalool oxides 6 (3%, cis:trans = 40:60) (Scheme 2). [15][16][17] No 1,2-epoxides of linalool were detected ( 1 H NMR, GC). 8,9 The relative configurations of major isomers of heterocycles 1, 5, and 6 were established by NMR experiments (NOE, HMBC, HM...

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