A mixture of 2.18 g (10.2 mmol) of 1,2-dihydro-8-hydroxy-3H-naphtho[2,1-b]pyran-3-one from the preceding example, 4.84 g (24.8 mmol) of t-butyl bromoacetate, 5.63 g (40.7 mmol) of anhydrous granular potassium carbonate and 55.5 mL of 2-butanone was heated at 60° C. for 24 hr. A second portion of t-butyl bromoacetate (0.5 mL, 3.1 mmol) was added and the reaction was allowed to proceed for another 17 hr. After being cooled to room temperature, the mixture was filtered and the solids were washed with ethyl acetate and ether. The filtrate and washes were combined and concentrated in vacuo, and the crude product was flash chromatographed on 360 g of silica gel, eluting with hexane-ethyl acetate (7:1 then 6:1) affording 3.04 g (91.0%) of the title compound as a white solid, mp 95°-96° C.
