Asymmetric synthesis of (3S) 3-benzoyloxymethylisobenzofuranone and its 3R enantiomer as analogues of α,β-butenolides

Both enantiomers of 3-benzoyloxymethylisobenzofuranone have been obtained in good yield in six steps from phthalaldehyde using a d-xylose derivative as a chiral protecting group. The two chiral heterocycles are γ-hydroxymethyl-α,β-butenolide analogues having a benzene ring in positions 2 and 3. The key step was the dihydroxylation using both OsO4 and AD-mix developed by Sharpless. The asymmetric dihydroxylation using AD-mix required a double diastereoselectivity and gave excellent diastereoisomeric excess.