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Schlagwörter:
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Zusammenfassung:
A convergent total synthesis (22 steps on the longest linear route) of
(-)-erythronolide B (5) and two 9-dihydro derivatives (52 and 54)
thereof from (R)-2,3-O-isopropylideneglyceraldehyde (20) as the only
source of chirality is described. A key step of the synthesis is the
regio- and stereocontrolled coupling of the allyl sulfide anion 39 and
ketone 26, which can be directed to either alpha-adduct 40 or 41 by an
appropriate choice of the conditions (Scheme V, Table II). From 40 and
41 the seco acids 47 and 49 are prepared, which are smoothly
macrolactonized to 50 and 51 according to a modified Yamaguchi
procedure. Hydroboration of 50 and 51 proceeds under macrocyclic
stereocontrol to afford the 9-dihydroerythronolide B derivatives 52 and
54, of which 54 is converted into 5 by a known oxidation-deketalizaton
sequence.
