Compound 6 was identified as trans-l, 3, 4-trideoxy-5, 6-O-isopropylidene-3-C-methyl-D- glycero-hex-3-enulose. It had 2ma X 230 nm (e 11830), which is close to the absorption reported a'4 for this kind of e, fl-unsaturated ketone. The 1H-nmr signal at~ 6.38, assigned to H-4, indicated the deshielding effect of the carbonyl group on H-4. The structure of 6 was confirmed by its synthesis from 5 by hydrolysis followed by reaction with methyl-lithium.
