- Molybdenum(II)- and tungsten(II)-catalyzed allylic substitution
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The molybdenum(II) complexes Mo(CO)5(OTf)2 (7a), [Mo(CO)4Br2]2 (8a), their tungsten(II) congeners 7b and 8b, and bimetallic complex Mo(CO)3(MeCN)2(SnCl3)Cl (9a) have been found to catalyze the C-C bond-forming allylic substitution with silyl enol ethers derived from β-dicarbonyls (e.g., 16 + 30 → 46) or from simple ketones (e.g., 16 + 32 → 50), aldehydes, and esters as nucleophiles under mild conditions (room temperature, 1-2 h). Methanol, as a prototype oxygen nucleophile, reacts in a similar fashion (e.g., 16 + MeOH → 43). Mechanistic and stereochemical experiments are indicative of Lewis-acid catalysis rather than a metal template-controlled process.
- Malkov, Andrei V.,Baxendale, Ian R.,Dvorak, Dalimil,Mansfield, Darren J.,Kocovsky, Pavel
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p. 2737 - 2750
(2007/10/03)
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- A Novel Methylation of Allylic Alcohols Using cis-Dichlorobis(triphenylphosphine)platinum(II)-Tin(II) Chloride Dihydrate Complex Catalyst
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The reaction of allylic alcohols in benzene-methanol (3:2) solvent in the presence of cis-dichlorobis(triphenylphosphine)platinum(II)-tin(II) chloride dihydrate complex catalyst afforded allylic methyl ethers.The structure of the obtained compounds was identified by direct comparison with authentic sample.Cholest-4-en-3α-ol, with a quasi-axial hydroxy group, gave a quantitative yield of 3α-methoxycholest-4-ene.On the other hand, cholest-4-en-3β-ol, with a guasi-equatorial hydroxy group, yielded 3β-methoxycholest-4-ene preferentially, but also yielded 3α-methoxycompound as a by-product, lowering the selectivity of the reaction.
- Sakamaki, Hiroshi,Kameda, Noriyuki,Iwadare, Tsukasa,Ichinohe, Yoshiyuki
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p. 3491 - 3496
(2007/10/03)
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- CLEAVAGES OF ETHERS BY CHLOROTRIMETHYLSILANE AND ACETIC ANHYDRIDE
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Methyl and benzyl ethers have been cleaved with a combination of reagents consisting of chlorotrimethylsilane and acetic anhydride containing a catalytic amount of concentrated sulfuric acid.Methylthiomethyl ethers yield the correponding acetoxymethyl ethers with chlorotrimethylsilane and acetic anhydride.Comparative study with the borontrifluoride etherate and acetic anhydride method of ether cleavage suggests that chlorotrimethylsilane and acetic anhydride (conc.H2SO4 catalysis) could be a useful alternative to it.
- Sarma, J. C.,Borbaruah, M.,Sarma, D. N.,Barua, N. C.,Sharma, R. P.
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p. 3999 - 4006
(2007/10/02)
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