Total synthesis of 9-dihydroerythronolide B derivatives and of erythronolide B

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 α-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