Diethyl Pyrocarbonate → (S)(-)-Ethyl N-(3,4-dihydro-2-naphthoyl)prolinate

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To a DMF solution (60 ml) containing 3,4-dihydro-2-naphthoic acid (9a, 7.12 g, 40.0 mmole), and (S)(-)-ethyl prolinate (6.41 g, 44.8 mmole), a DMF solution (60 ml) containing DEPC (7.17 g, 44.0 mmole) and a DMF solution (60 ml) containing triethylamine (4.05 g, 40.0 mmole) are dropwise added at 0° C. in 5 minutes. The resultant mixture is stirred at 0° C. for 2 hours and then at room temperature for 2 days. The reaction mixture is diluted with ethyl acetate (1.8 liters), and the ethyl acetate solution is washed with 5% hydrochloric acid (130 ml×2), water (130 ml×2), a saturated aqueous solution of sodium chloride (130 ml×2), a saturated aqueous solution of sodium hydrogen carbonate (130 ml×2) and water (130 ml×2) in order and then dried over anhydrous magnesium sulfate. After filtration and evaporation, a crude product (10a) is obtained as a yellow caramel (13.9 g, 116%), which is purified by column chromatography (silica gel, 300 g; solvent, ether) to obtain an almost pure product (10a) as colorless needles (11.1 g, 91%). M.P. 55°-57° C. Recrystallization from ether-hexane affords an analytical sample as colorless needles melting at 56°-57° C. [α]D20 -18.6° (c=1.03, ethanol). IRνmaxNujol cm-1 : 1750 (ester), 1650 (C=C), 1610 (CON), NMR (in CDCl3): 1.27 (3H, t, J=7 Hz, CO2CH2CH3), 1.64-2.40 (4H, m, NCH2CH2CH2), 2.40-3.20 (4H, m, CH2CH2C=), 3.72 (2H, t, J=6 Hz, N--CH2), 4.16 (2H, q, J= 7 Hz, CO2CH2CH3), 4.58 (1H, t, J=6 Hz, NCHCO2), 6.77 (1H, s, CH=C), 7.12 (4H, s, aromatic proton).

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