4-Nitrobenzyl chloroformate → (4-Nitrophenyl)methyl 4-hydroxybut-2-ynoate

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Reaction Steps

A solution of 3.3 ml (23.2 mmols) of tetrahydro-2-(2-propinyloxy)-2H-pyran [R. A. Earl et al., Organic Syntheses 60, 81 (1981)] in 23 ml of anhydrous tetrahdrofuran was added dropwise to 7.8 ml (23.2 mmols) of a 3 molar solution of ethyl-magnesium bromide in ether at room temperature in the course of 30 minutes. The mixture was then subsequently stirred at room temperature for 1.5 hours. This solution was added dropwise to a well-stirred solution, cooled to -20° C., of 5.0 g (23.2 mmol) of 4-nitrobenzyl chloroformate in 25 ml of tetrahydrofuran in the course of 1.5 hours. The mixture was then subsequently stirred at -15° C. for 30 minutes and at 0° C. for 1.5 hours, and was then left to stand at 0° C. for 12 hours, whereupon the magnesium salts crystallized out. The salts were filtered off, with exclusion of moisture, and washed two times with a little toluene. The filtrate solution was washed 5 times with saturated NaCl solution and dried over MgSO4. The solvent was evaporated off in vacuo, the residue was dissolved in 25 ml of anhydrous methanol and the solution was stirred with 1 ml of the ion exchanger Dowex-50-X4 (H+ form, prewashed with anhydrous methanol) at room temperature for 1 hour. The ion exchanger was separated off, the filtrate solution was concentrated in vacuo and, finally, the residue was dried under a high vacuum. The treatment with the ion exchanger was repeated as described above. The crude product was chromatographed on 300 g of silica gel (toluene:ethyl acetate 4:1) and 2.07 g (38%) of 4-nitrobenzyl 4-hydroxy-2-butinoate were obtained as colorless crystals, melting point: 93°-94° C., RF : 0.27 (toluene:ethyl acetate 4:1).

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