270594-13-3Relevant academic research and scientific papers
Unique diastereoselectivity trends in aminyl radical cyclizations onto silyl enol ethers
Zlotorzynska, Maria,Zhai, Huimin,Sammis, Glenn M.
supporting information; experimental part, p. 864 - 872 (2010/05/18)
(Chemical Equation Presented) The cyclization of nitrogen-centered radicals onto silyl enol ethers is an efficient method for the synthesis of polyhydroxylated alkaloids as the 2-hydroxymethylpyrrolidine core can be readily accessed from a linear precursor. During our studies on the synthesis of polyhydroxylated alkaloid CYB-3, we found that the diastereoselectivity of the cyclization was dependent on a complex combination of sterics and olefin geometry. A more thorough understanding of the factors that lead to high diastereoselectivites would greatly expand the utility of this methodology in complex natural product synthesis. We have found that cyclization diastereoselectivities of substrates with alkyl or aryl substitution were excellent regardless of olefin geometry or substitution pattern. When electronegative substituents were introduced adjacent to the silyl enol ether, only Z-silyl enol ethers provide high diastereoselectivites. Temperature, steric size of the silyl group, and sterics and electronics of the metal hydride affected the selectivity to a lesser extent.
Lipase-catalyzed transesterification of primary alcohols: Resolution of 2-ethylhexan-1-ol and 2-ethylhex-5-en-1-ol
Baczko, Krystyna,Larpent, Chantal
, p. 521 - 526 (2007/10/03)
Both the (R) and (S) enantiomers of 2-ethylhex-5-en-1-ol (R)-(-)-1, (S)-(+)-1 and 2-ethylhexan-1-ol (R)-(-)-2, (S)-(+)-2 were prepared in good yields and in high enantiomeric excess via lipase-catalyzed transacetylation of racemic alcohols 1 and 2 with vinyl acetate. Various experimental conditions (lipase PSL or PLF, solvent and temperature ranging from 30 to -30°C) are used and their influence on the enantioselectivity and on the reaction rate is evaluated. The (S) unsaturated alcohol 1 is specifically esterified by lipase PS in CH2Cl2 at 0°C with a very high enantiomeric ratio (E ～ 750) thus allowing the production of both enantiomers (R)-(-)-1 and (S)-(+)-1 with fairly good yields from the same enzymatic transformation. The comparison of unsaturated and saturated primary alcohols 1 and 2 shows that, for a similar atomic framework, the enantioselectivity of PSL is greatly enhanced by the presence of a terminal double bond. On the other hand, an enhancement of PSL enantioselectivity without loss of catalytic activity is achieved by decreasing the temperature to -30°C thus giving access to both enantiomers.
