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2001
diastereoselective syntheses, enantioselective syntheses
diastereoselective syntheses, enantioselective syntheses (incl. cis/trans-isomerism)
O 0031
Highly
Enantioselective
Protonation
of
the
3,4-Dihydro-2— The
16 - 034 methylnaphthalen-1(2H)-one Li-Enolate by TADDOLs.
enantioselective protonation of the lithium enolate of tetralone (III) is studied employing nine chiral tetraaryl-1,3-dioxolane-4,5-dimethanol (TADDOL)
derivatives such as (I) or TDD as proton sources. The Li-enolate is generated
either from the enol acetate (II) or directly from racemic ketone (III) or from the
silyl enol ether (IV), and is then treated with the TADDOL derivatives. Best
results with up to 99% e.e. of the (S)-enantiomer are obtained with 1-naphthylsubstituted TADDOL derivatives whereas tetrakis(2-naphthyl)-, tetraphenyl- or
tetraphenanthryl-substituted derivatives only give moderate enantioselectivities
favoring the S-enantiomer (III). Among the tested TADDOL derivatives, only
TDD affords the (R)-enantiomer mainly. Non-linear effects in the protonation
of the Li-enolate by addition of (Ib) are discussed.
— (CUENCA, ANA;
MEDIO-SIMON, MERCEDES; ASENSIO AGUILAR, GREGORIO; WEIBEL,
DANIEL; BECK, ALBERT K.; SEEBACH, DIETER; Helv. Chim. Acta 83
(2000) 12, 3153-3162; Dep. Quim. Org., Univ. Valencia, E-46100 Burjassot,
Valencia, Spain; EN)
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