(Schiff‐base)vanadium(V) Complex‐Catalyzed Oxidations of Substituted Bis(homoallylic) Alcohols − Stereoselective Synthesis of Functionalized Tetrahydrofurans

Abstract

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-

Polymer and Silica Supported Tridentate Schiff Base Vanadium Catalysts for the Asymmetric Oxidation of Ethyl Mandelate – Activity, Stability and Recyclability

“…The V À O bond distances are comparable with literature precedents and decrease in the order of phenolate oxygen [1.895(5) ], alcoholato oxygen [1.839(6) ], ethanolato oxygen [1.756(6) ] and V=O oxygen [1.602(6) ]. [19] The V1 À N1 distance is 2.079(5) , which is well within the range of reported literature values of similar complexes. The ORTEP diagram and metric parameters of metalated-2 are given in Figure 1.…”

“…[20] Also, the V=O stretch is seen at 986 cm À1 in the homopolymer and 984 cm À1 in the copolymer, and these values are in line with reported literature values. [13,[19][20][21] Figure 1. Molecular structure of metalated 2 with thermal ellipsoids at the 30% probability level.…”

Mechanistic Analysis of Nucleophilic Substrates Oxidation by Functional Models of Vanadium‐Dependent Haloperoxidases: A Density Functional Theory Study

“…These results demonstrate the importance of protons in catalytic process. Many vanadium catalysts have been presented in the literature for a variety of oxidations: alcohol oxidations, [38] olefin epoxidation, [1,[39][40][41] sulfide oxidation, [6,7,9,11,41] and phosphane oxidation. [1,8] Many of these processes use in-situ-derived catalytic systems from vanadium starting materials, vanadyl sulfate and vanadyl acetylacetonate being the most common, with a variety of ligands.…”

The (Schiff base)vanadium(V) Complex Catalyzed Oxidation of Bromide − A New Method for the in situ Generation of Bromine and Its Application in the Synthesis of Functionalized Cyclic Ethers

“…[7] A major objective of this study was associated with the search for an adequate combination of bromide source and primary oxidant that would reduce the inherent propensity of (Schiff base)vanadium() complexes in the presence of tert-butyl hydroperoxide (TBHP) to convert alkenols 1 directly into hydroxy-functionalized tetrahydrofurans. [15,16] Thus, reactivity-selectivity studies on the vanadium()-catalyzed oxidation of bromide were conducted. The results were supplemented by information obtained from spectroscopic and spectrometric investigations in order to interpret crucial steps in the process such as peroxide activation and the generation of an active brominating reagent.…”