Isopropenyl acetate (13.5 mL, 123 mmol, 2 eq) and Amano-PS lipase (1.2 g, 1/10 w/w) were added to a solution of chroman-4ols 1b or 1c (61.4 mmol, 1 eq) in t-BuOMe (150 mL), and the resulting mixture was stirred at 50 °C until the conversion of reaction was approximately 50%. The reaction progress was monitored by 1 H NMR spectroscopy. Then, the lipase was filtered out and washed with t-BuOMe. The filtrate was evaporated in vacuo to give a mixture of the alcohol and acetate. This mixture was separated by column chromatography on silica gel using nhexane -THF (10/1, v/v) as the eluent to afford pure products (2R,4S)-1a-c and (2R,4S)-3a-c.