• Title/Summary/Keyword: alkylation

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Theoretical Studies on the Gas-Phase Alkylation of Delocalized Ambident Anions with Methyl Fluoride

  • 이익춘;박형연;한인숙;김창곤;김찬경;이본수
    • Bulletin of the Korean Chemical Society
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    • v.20 no.5
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    • pp.559-566
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    • 1999

  • Gas-phase alkylations of delocalized ambident anions, Y---CH---X- where X, Y=CH2, O, or S, have been investigated theoretically at the MP2/6-31+G*//MP2/6-31+G* and QCISD/6-31+G*//MP2/6-31+G* lev-els. O-and S-alkylations (X=O and S) are more favored kinetically by ΔE^≠ = 4.6 and 9.8 kcal mol-1 than the respective C-alkylations even though they are thermodynamically less favored by 22.4 and 6.0 kcal mol-1 respectively. It was found that the transition structures for the C-alkylations are imbalanced due to the endoergic rehybridi-zation of the carbon center from sp2 to sp3 which leads to premature bond contraction of the C-Y bond and delayed bond stretching of the C-X bond. In the O-, or S-alkylation, such endoergic process is not required since the σ-lone pair on O or S is involved in the initial stage of alkylation. The imbalanced TSs for the C-alkylation are accompanied by higher intrinsic barriers and deformation energies.

  • https://doi.org/10.5012/bkcs.1999.20.5.559 인용 PDF

A Steroselective Synthesis of (22R, 23R)-Methylenecholesterol

  • Kim, Deuk-Joon
    • Archives of Pharmacal Research
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    • v.15 no.4
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    • pp.374-375
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    • 1992

  • The marine sterol (22R, 23R)-methylenecholesterol 1 has been synthesized from readily available C-22 steroidal ester 2 utilizing an intermolecular acyclic ester enolate alkylation as the key step.

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