Abstract
Results from asymmetric Horner-Wadsworth-Emmons reactions between
chiral phosphonate reagents 3a-d, which contain
(1R,2S,5R)-8-phenylmenthol as a chiral auxiliary, and
meso-dialdehydes 6 and 14 are presented. It was found that both
the geometric selectivities and the levels of asymmetric induction
depended on the structure of the phosphonate (i.e., the alkyl
group R1 in the phosphoryl unit) and to a certain extent also on
the reaction conditions. Furthermore, the nature of the protecting
group used on the a-oxygen substituent in dialdehydes 14
influenced the outcome somewhat. By an appropriate choice of
reagent and conditions, either (E)- or (Z)-monoaddition products
could be obtained geometrically pure and with good to excellent
diastereoselectivities, in synthetically useful yields. Analyses
of the absolute configurations of the products showed that the
(E)-selective reagents (3a-c) and the (Z)-selective phosphonate 3d
reacted at opposite enantiotopic carbonyl groups in the
substrates. A mechanistic model which accounts for the products
formed is presented.
Original language | English |
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Journal | Journal of organic chemistry |
Volume | 63 |
Issue number | 23 |
Pages (from-to) | 8284-8294 |
Publication status | Published - 1998 |