A BUTYROLACTONE-]1,3-DIOL STRATEGY FOR THE OBTENTION OF TOLYPOTHRIX POLYETHERS - TOTAL SYNTHESIS OF THE TOLYPOTHRIX PENTAETHER FROM ENANTIOMERICALLY ENRICHED S-GLYCIDOL
H. Priepke et R. Bruckner, A BUTYROLACTONE-]1,3-DIOL STRATEGY FOR THE OBTENTION OF TOLYPOTHRIX POLYETHERS - TOTAL SYNTHESIS OF THE TOLYPOTHRIX PENTAETHER FROM ENANTIOMERICALLY ENRICHED S-GLYCIDOL, Liebigs Annalen, (8), 1997, pp. 1645-1655
Permethyl ether 1 from Tolypothrix conglutinata was synthesized follow
ing the retrosynthetic analysis of Scheme 1. According to it, we combi
ned aldehyde 3 [prepared from S-glycidol (7); cf. Schemes 2, 3] and la
ctone 4 (also prepared from S-glycidol (7); cf, the preceding communic
ation(\2\) and Scheme 4) to the enantiopure and diastereopure trimetho
xy lactone 2 (Scheme 5). The C=O group of this lactone was removed thr
ough the Criegee rearrangement of a derived lactol peroxonosylate (Sch
eme 6); thereby, the C-C=O bond of lactone 2 was replaced with complet
e retention of configuration by one C-OH bond of the resulting syn-con
figured diol 18. Protecting group manipulations (Schemes 6, 7) and oxi
dation of the resulting alcohol 21 to aldehyde 31 (Scheme 10) initiate
d the three final operations: Cz-homologation with Ph3P=CH-CH=O (--> e
nal 32), tosyl hydrazone formation (--> 34), and reduction/concomitant
C=C bond migration. They led to the target ether 1 as a 89:11 mixture
with the CH=CH-richer ether 36.