Enantioselective conjugate additions of silylketene acetals to 2-carboxycyclopentenones promoted by chiral Ti complexes

Article abstract of DOI:10.1016/S0040-4020(97)00825-9

The conjugate addition of silylketeneacetals to 2-carbalkoxycyclopentenones 1 promoted by TADDOL · TiCl₂ complexes was studied. The reactions are highly syn selective. The enantioselectivity depends on the size of the substrate ester group, wit

Full text of DOI:10.1016/S0040-4020(97)00825-9

Enantioselective conjugate additions of silylketene acetals
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the reaction between la and 23 in
in lh at
to give
4
5% of the addition product.
2
2
2
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yields, and characterize it by NMR spectroscopy. It
0
X 0
Ar
was proved that a solution of
and
is
stable for 1 h at
and 21 appears only after the
addition of 2b to the mixture
2
7. Although the configuration of these compounds was not rigorously established they are likely to be the cis
and trans isomers on the cyclopentenone ring, since the reaction of 19 with the acetate equivalent also
gives two isomers in 6: ratio.
28. The relative configuration of these compounds was determined by decarbethoxylation and
NMR
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2
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3
3
1. Other potential achiral promoters in the reaction mixtures are the molecular sieves, and, possibly, some
that can be formed by silylation of the
liberated in solution during the formation of the
Ti