The first org
anocatalytic en
antioselective direct
gifchars/alpha.
gif"
BORDER=
0>-alkynylation of
gifchars/beta2.
gif" BORDER=
0 ALIGN="middle">-ketoesters
and 3-acyl oxindolesis described. It is demonstrated that activated
gifchars/beta2.
gif" BORDER=
0 ALIGN="middle">-halo-alkynes undergo nucleophilic acetylenic substitutioncatalyzed by chiral phase-tr
ansfer compounds to afford the alkynylated products in high yields
and excellenten
antioselectivities. The potential of the reaction is first demonstrated for various alkynylating reagentshaving chloride
and bromide as the leaving groups
and substituents such as allyl
and alkyl esters, amides,ketones,
and sulfones. These reactions proceed with 74-99% yield
and 88-97% ee. Then the scope innucleophile is demonstrated for a large number of cyclic
gifchars/beta2.
gif" BORDER=
0 ALIGN="middle">-ketoesters with various ring-sizes
and for oxindolesas well. The corresponding optically active products are formed in high yields
and with en
antioselectivitiesup to 98% ee. The procedure allows for the stereocontrolled attachment of
an ethynyl unit in the
gifchars/alpha.
gif" BORDER=
0>-positionto the carbonyl compound by facile removal of the activating group,
and this has been demonstrated for
anumber of the optically active allyl esters. Furthermore, the synthesis of optically active 1,4-enynes is alsoshown. The isolation
and characterization by X-ray
analysis of the catalyst with
p-nitrophenolate as thecounterion allowed us to propose a model of the catalyst-substrate intermediate which might account forthe observed en
antioselectivity of the org
anocatalytic en
antioselective
gifchars/alpha.
gif" BORDER=
0>-alkynylation reaction. Furthermore,it is suggested that this intermediate is also the reactive species for a number of other electrophiles addingto
gifchars/beta2.
gif" BORDER=
0 ALIGN="middle">-ketoesters giving en
antioselectivities in the r
ange of 9
0-98% ee.