Ethyl 4-methylbenzoate could be produced through the following synthetic routes.

A. [m-(1,4-Diazabicyclo[2.2.2]octane-kN1:kN4)]hexamethyldialuminum DA-Me₃ (1). A 250-mL, three-necked, round-bottomed flask is equipped with an egg-shaped, teflon-coated, magnetic stir bar (ca. 25 mm), a glass stopper, a reflux condenser and a 100-mL pressure-equalizing dropping funnel. The reflux condenser is fitted at the top with a two-tap Schlenk adaptor connected to a bubbler and an argon/vacuum manifold. A modest flow of argon is applied as judged by the exit bubbler (1-2 bubbles per second) and the reaction is kept under argon during the entire procedure. The glass stopper is removed and dry DABCO (5.40 g, 48.1 mmol, 1.00 equiv) is added in one portion using a powder funnel. The open joint is sealed with a rubber septum and dry deoxygenated toluene (30 mL) is added via syringe. The solution is stirred for 10 min until all DABCO has dissolved and the rubber septum is replaced by a 0-150 °C thermometer in a gas-tight adaptor. The dropping funnel is charged with 2 m trimethylaluminum in toluene (47.0 mL, 94.0 mmol, 1.95 equiv) using a syringe. The trimethylaluminum solution is then added to the DABCO solution over 25 min at room temperature causing the formation of a white precipitate after ca. 10 min. Residual trimethylaluminum in the dropping funnel is rinsed with additional dry deoxygenated toluene (3 mL). The solution is stirred for 30 min at room temperature before DABAL-Me₃ (1) is allowed to settle for ca. 10 min. The dropping funnel is replaced by a rubber septum (Note 10, 11) and the toluene is removed by cannular filtration. The colorless DABAL-Me₃ (1) is washed by injection of dry deoxygenated diethyl ether (40 mL), brief stirring and removal of the solvent by cannular filtration. This procedure is repeated twice (2 × 40 mL of dry deoxygenated diethyl ether). The product is dried under high vacuum (0.05 mmHg) at room temperature to afford DABAL-Me₃ (1) (9.97 g, 38.9 mmol, 81%) as a colorless solid.

B. Ethyl 4-methylbenzoate (2). A 500-mL, two-necked, round-bottomed flask is equipped with an egg-shaped, teflon-coated, magnetic stir bar (ca. 25 mm), a rubber septum and a reflux condenser fitted at the top with a two-tap Schlenk adaptor connected to a bubbler and an argon manifold. The flow of argon is reduced to a modest level as judged by the exit bubbler (1-2 bubbles per second), the rubber septum is removed and solid Pd₂(dba)₃ (550 mg, 0.600 mmol, 1.50 mol%) and X-Phos (573 mg, 1.20 mmol, 3.00 mol%) are added. The joint is sealed again with the rubber septum and dry THF (200 mL) and ethyl 4-bromobenzoate (9.16 g, 40.0 mmol, 1.00 equiv) are added by syringe. The joint is opened again to add DABAL-Me₃ (1) (8.31 g, 32.4 mmol, 0.801 equiv) using a powder funnel. The open socket is sealed with a glass stopper and the dark purple reaction mixture is heated at reflux for 4 h in an oil bath (90 °C). Completion of the reaction can by confirmed by working up an aliquot (1 mL) of the reaction mixture, as described below, and recording its 1H NMR spectrum. The argon flow is slightly increased (3-4 bubbles per second), heating is stopped and the reaction mixture is allowed to cool to room temperature over an hour. The flask is further cooled in an ice bath for 15 min and the reaction is quenched by cautious, portionwise, addition of 2 m aqueous HCl (160 mL). The resulting biphasic mixture is transferred into a separatory funnel (1 L) with diethyl ether (2 × 100 mL). The layers are separated, retained separately and the aqueous fraction is re-extracted with diethyl ether (3 × 150 mL). The organic layers are combined, dried over MgSO₄ (30 g) and filtered though a plug of activated charcoal (5 g) layered on the top of SiO₂ (50 g). The plug is further washed with diethyl ether (1 L). Removal of the solvent by rotatory evaporation (25 °C, 150 mmHg) affords the crude product as a clear brown oil in quantitative yield. Short-path distillation under reduced pressure (118-120 °C at 0.1 mmHg) gives the product 2 (6.11 g, 37.2 mmol, 93%) as a colorless oil.

Notice: Trialkylaluminum compounds are pyrophoric and must not be allowed to come into contact with air or moisture. These compounds should only be handled by individuals trained in their proper and safe use.