t-Butyl 2-[(4R,6S)-6-formyl-2,2-dimethyl-1,3-dioxan-4-yl]acetate; tert-Butyl (3R,5S)-6-oxo-3,5-dihydroxy-3,5-O-isopropylidenehexanoate; t-Butyl (3R,5S)-3,5-isopropylidenedioxy-6-oxohexanoate