ALDOL CONDENSATION-REACTIONS OF (DIENONE) TRICARBONYLIRON COMPLEXES .3. ENANTIOSELECTIVE TOTAL SYNTHESIS OF 3,6-DIDEOXYHEXOSES FROM LACTALDEHYDE

The trimethylsilyl enol ether 2 of racemic (3,5-heptadien-2-one) trica rbonyliron 1 undergoes a completely stereoselective cross aldol reacti on with TiCl4-coordinated (S)-(-)-benzyloxylactaldehyde (-)-3, yieldin g two separable diastereomeric ketols, differing only in the configura tion of the metal-ligand attachment (resolution). Both were converted into protected 3,6-dideoxyhexoses [(+)-16 (R,S,S) and (-)-17 (S,S,S)] by successive stereoselective reduction into 1,3-diols, transformation into diacetates, decomplexation and ozonolysis. The same dideoxyhexos es, as well as the enantiomeric series, can be obtained from the racem ic lactaldehyde and the pure enantiomers of 2. (C) 1997 Elsevier Scien ce Ltd.