Ceric ammonium nitrate in 70% aqueous acetonitrile oxidizes 5-phenyl-1-pentanol and 4-phenyl-1-butanol to 2-benzyl-and 2-phenyltetrahydrofuran, respectively. Competing processes include benzylic oxidation leading to ketone formation and to oxidative cleavage products. The effects on tetrahydrofuran formation by changing the cerium concentration and by varying the solvent are given. Oxidation of 3-phenyl-1-propanol yields chromanone as the only major reaction product when 2 equiv of ceric ammonium nitrate is employed. Chromanone is oxidized to chromone when >2 equiv of the oxidant is used. The mechanistic implications of these results are discussed.Cerium(1V) oxidations of primary alcohols, unlike those of benzylic,2 cyclopropylcarbinyl,3 or certain secondary alc o h o l~,~ yield tetrahydrofuran derivatives. Tetrahydrofuran formation represents but one of the three modes of reaction identified with cerium(1V) oxidations of alcohols, the others being oxidative cleavage resulting in substrate fragmentation and a-carbon-hydrogen cleavage yielding aldehydes or ket0nes.j Trahanovsky, Young, and Nave have studied the oxidation of 1-pentanol by ceric ammonium nitrate (CAN) and found 2-methyltetrahydrofuran as the only isolable reaction product.6 Although the similarity of this reaction to that of the corresponding lead tetraacetate oxidation7 has been pointed out, the synthetic utility and mechanistic course of cerium(1V) oxidations of primary alcohols have not been further documented.Phenyl-substituted alkanols have been used previously to determine the effect of the phenyl group on the course of lead tetraacetate oxidations.s The phenyl label is useful for identifying the hydrogen transfer step and for determining its specificity in reactions of alcohols with one-electron oxidants.Results 6-Phenyl-1-pentanol. Oxidation of 5-phenyl-1-pentanol (10 mmol) by ceric ammonium nitrate (20 mmol) in 25 ml of 70% aqueous acetonitrile at 75' afforded 2-benzyltetrahydrofuran (1) and benzoic acid as the only major identifiable reaction products (eq 1). Two other products, tentatively identified as benzaldehyde and 5-phenyl-1-pentyl nitrate, were observed by GLC analysis but in combined amounts of less than 8%; unreacted alcohol, by far the major constituent of the reaction mixture (77%), was also identified. The yield of 1, based on reacted 5-phenyl-1-pentanol, was 40%; benzoic acid was formed in less than 10% yield.
CAN
Das durch Umsetzung von α‐Chlorpropionsäure (I) mit Li‐diisopropylamid (II) leicht zugängliche Dianion (III) läßt sich von den Alkylhalogeniden (IV) zu den α‐Chlorcarbonsäuren (V) alkylieren.
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