The first organocatalytic enantioselective direct
BORDER=0>-alkynylation of
beta2.gif" BORDER=0 ALIGN="middle">-ketoesters and 3-acyl oxindolesis descri
bed. It is demonstrated that activated
beta2.gif" BORDER=0 ALIGN="middle">-halo-alkynes undergo nucleophilic acetylenic su
bstitutioncatalyzed
by chiral phase-transfer compounds to afford the alkynylated products in high yields and excellentenantioselectivities. The potential of the reaction is first demonstrated for various alkynylating reagentshaving chloride and
bromide as the leaving groups and su
bstituents 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 num
ber of cyclic
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 enantioselectivitiesup to 98% ee. The procedure allows for the stereocontrolled attachment of an ethynyl unit in the
-positionto the car
bonyl compound
by facile removal of the activating group, and this has
been demonstrated for anum
ber 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-su
bstrate intermediate which might account forthe o
bserved enantioselectivity of the organocatalytic enantioselective
-alkynylation reaction. Furthermore,it is suggested that this intermediate is also the reactive species for a num
ber of other electrophiles addingto
beta2.gif" BORDER=0 ALIGN="middle">-ketoesters giving enantioselectivities in the range of 90-98% ee.