SYNTHESIS OF ETHYL BENZOYLFORMATE

Ethyl 𝜶-oxo-1H-imidazole-1-acetate

• Ethyl oxalyl chloride (20.0 ml, 0.1 79 mol) (Aldrich) (1) in tetrahydrofuran (80 ml) (2) is added to a stirred solution of imidazole (24.3g, 0.35 mol) in tetrahydrofuran (500 ml) at 0°C under nitrogen over a 1-hour period. 

• After an additional 1 hour of being stirred at °C, the mixture is filtered and the precipitate washed with anhydrous tetrahydrofuran (100 ml). 

• The tetrahydrofuran is removed from the filtrate and washings under vacuum, and the residue is distilled to furnish 27.2g (90%) of product, b.p. 100°C/1 mmHg; i.r. (neat) 1730 (ester) and 1770 (amide) cm⁻¹; p.m.r. (CDCl₃, TMS) 𝜹1 .45 (t, 3H), 4.45 (q, 2H), 7.05 (s, 1H), 7.60 (s, 1H), and 8.40 (s, 1H); m/z 168 (M). 

• This material undergoes slow discoloration at room temperature and is stored at 5 °C.

Ethyl benzoylformate:

• The foregoing imidazolide (3.03g, 24mmol) is dissolved in tetrahydrofuran (75 ml) under nitrogen and cooled to -50 °C in a dry-ice-acetone bath. 

• Phenylmagnesium bromide (1.0 equiv. in 50 ml of tetrahydrofuran) is added by a dropping funnel over 1 hour with stirring. 

• The solution is allowed to come to room temperature over 3 hours and poured into ice-water (200 ml). 

• The solution is extracted with ether (a few drops of acetic acid are added to break up emulsions), and the ether extract is washed with brine and dried over magnesium sulphate. 

• Removal of solvents under reduced pressure and distillation affords ethyl benzoylformate (72%), b.p. 88°C/0.5mmHg.

Notes to keep in mind:

1. Ethyl oxalyl chloride should be handled with care in a fume cupboard since it is lachrymatory.

2. The tetrahydrofuran should be distilled from sodium benzophenone ketyl immediately prior to use.