- Regioselective 1,2-Diol Rearrangement by Controlling the Loading of BF3·Et2O and Its Application to the Synthesis of Related Nor-Sesquiterene- and Sesquiterene-Type Marine Natural Products
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The regiocontrolled rearrangement of 1,2-diols has been achieved by controlling the loading of BF3·Et2O. Its applicability is showcased by the divergent synthesis of austrodoral, austrodoric acid, and 8-epi-11-nordriman-9-one, as well as a formal synthesis of siphonodictyal B and liphagal. A new light is shed on piancol-type rearrangements that will be useful in diversity-oriented synthesis of related natural products.
- Wang, Jun-Li,Li, Hui-Jing,Wang, Hong-Shuang,Wu, Yan-Chao
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supporting information
p. 3811 - 3814
(2017/07/26)
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- Probing competitive enantioselective approach vectors operating in the Jacobsen-Katsuki epoxidation: A kinetic study of methyl-substituted styrenes
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This paper describes a study of reactivity and enantioselectivity for a series of methyl-substituted styrenes in the Jacobsen-Katsuki (Mn(salen)-catalyzed) epoxidation reaction. Competition experiments provided kinetic data for the reactivity of the seven possible methyl-substituted styrenes (mono-, di- and trisubstituted) relative to styrene itself, ee values were measured by chiral GC, and absolute configurations were secured by chemical correlation. Of particular interest was the switch in absolute configuration at the benzylic position of the epoxides derived from (Z)- and (E)-α,β-dimethylstyrene, respectively. The results could be rationalized in terms of an approach vector with the phenyl substituent proximal to the salen. As opposed to alkyl groups, a proximal phenyl group has very little effect on the rate of the reaction. Consideration of distal vs proximal approach allows prediction of absolute stereochemistry as a function of alkene substitution pattern. Trisubstituted alkenes with one phenyl group cis to the alkene hydrogen can be identified as a favored substrate class in the title reaction, with both rate and selectivity close to the classic (Z)-β-substituted styrene substrates.
- Fristrup, Peter,Dideriksen, Brian B.,Tanner, David,Norrby, Per-Ola
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p. 13672 - 13679
(2007/10/03)
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- Mg-promoted mixed pinacol coupling
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Mg-promoted reduction of a mixture of aromatic ketones (or imines) and aliphatic carbonyl compounds in N,N-dimethylformamide (DMF) brought about unique mixed pinacol type of cross coupling to give unsymmetrical vicinal diols (or amino alcohols) or α-hydroxyketones in good to moderate yields. The reaction may be initiated by electron transfer from magnesium metal to an aromatic carbonyl compound possessing a less negative reduction potential. The difference of reduction potential between aromatic ketones (or imines) and aliphatic carbonyl compounds was found to be one of the important key factors in this selective cross coupling.
- Maekawa, Hirofumi,Yamamoto, Yoshimasa,Shimada, Hisashi,Yonemura, Kazuaki,Nishiguchi, Ikuzo
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p. 3869 - 3872
(2007/10/03)
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- Preparation and Reactivities of Hexakisacetonitrile Iron(III) Perchlorate and Related Complexes as Strong Oxidizing Reagents
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The iron(III) complexes Fe(S)6(ClO4)3, S=solvent, were prepared from Fe(H2O)6(ClO4)3 in the donor solvents.Reactions of alkylbenzenes with Fe(AN)6(ClO4)3 (AN=acetonitrile) were explored because the AN complex has the highest formal redox potential, E0=1.73 V vs.SCE, among these complexes.Oxidation of the primary alkylbenzenes by the iron(III) AN complex gave the corresponding acetamides (Table II).Oxidation of the secondary alkylbenzenes, namely, cumene, 2-phenylbutane, and 2-exo-phenylnorbornane, afforded the corresponding acetates and acetamides (Charts 2 and 3), consuming over 4-mol eq of reagent.Reactions of p-xylene and hexamethylbenzene with Fe(CH2=CHCN)6(ClO4)3 also yielded the amides 31a and 31b.These results demonstrate the applicability of the iron(III) AN complexes as a powerful reagent to oxidize organic substrates which have onset potentials of anodic current of ca. 2.0 V vs.SCE.Keywords - oxidation; primary alkylbenzene; secondary alkylbenzene; oxidizing reagent; iron(III) perchlorate solvate; hexakisacetonitrile iron(III) perchlorate; hexakisacrylonitrile iron(III) perchlorate
- Kotani,Eiichi,Kobayashi, Shigeki,Ishii, Yoko,Tobinaga, Seisho
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p. 4281 - 4291
(2007/10/02)
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