Wittig Homologation Research Articles

An alternative approach to mevinic acid analogues from methyl (3R)-(–)-3-hydroxyhex-5-enoate and an extension to unambiguous syntheses of (6R)-(+)-and (6S)-(–)-goniothalamin

Ozonolysis of the 3-silyloxyhexenoate 12, derived from the yeast reduction product methyl (3R)-(–)-3-hydroxyhex-5-enoate 6 and having an enantiomeric enrichment of 78%, followed by Wittig homologation and selenolactonization leads to the unsaturated mevinic acid analogues 17 and 18. Subsequent dehydration gives both enantiomers of the natural product goniothalamin 20 and 21.

4-alkoxycarbonyloxazoles as β-hydroxy-α-amino acid synthons: efficient stereoselective syntheses of 3-amino-2,3,6-trideoxyhexoses and a hydroxy amino acid moiety of Al-77-B

5-Substituted 4-alkoxycarbonyloxazoles 13a-c have been easily prepared by direct C-acylation of isocyanoacetic esters with O-protected α-hydroxycarboxylic acids 12a-c by use of diphenyl phosphorazidate (DPPA). Acid treatment of the oxazole derivatives 13a-c affords 5-substituted 3-aminotetronic acids 14a-c, which are stereoselectively hydrogenated to give 5-substituted 2-amino-3-hydroxy-1,4-lactones 15a, 16b, and so on. From the L-lyxo-1,4-lactone 15a, three 3-amino-2,3,6-trideoxyhexoses, L-daunosamine ( 7), L-vancosamine ( 8), and D-ristosamine ( 9) have been conveniently prepared by use of the Wittig homologation. Similar treatment of the D-ribo-1,4-lactone 16b has produced a hydroxy amino acid moiety A of Al-77-B ( 11) as its protected form 10.

Synthesis of trioxilin B 3

Both C(10) diastereomers of trioxilin B 3, presumed to be a mixture of 10( R/ S), 11( R), 12( R)-trihydroxyeicosa-5( Z), 8( Z), 14( Z)-trienoic acids, were prepared from a carbohydrate derived precursor by Wittig homologation and Mitsunobu inversion.