General procedure for the synthesis of mono-tert-butyl hexadecanedioate from hexadecanedioic acid and N,N-dimethylformamide di-tert-butyl acetal: Hexadecanedioic acid (4.5 g, 15.71 mmol) was suspended in toluene (28.1 mL) and heated to reflux. 1,1-di-tert-butoxy-N,N-dimethylmethylamine (10.10 mL, 42.1 mmol) was added slowly and dropwise over 30 minutes. The reaction mixture was refluxed overnight. Subsequently, the solvent was removed by distillation under reduced pressure at 50 °C, and the crude product obtained was suspended in a CH2Cl2/EtOAc solvent mixture (75 mL, 1:1 v/v) and stirred for 15 min. The insoluble material was removed by filtration and the filter cake was washed with CH2Cl2 (25 mL). The filtrates were combined and concentrated under reduced pressure. The resulting material was dissolved in CH2Cl2 (6 mL), cooled in an ice bath for 10 min and filtered. The solvent was removed again under reduced pressure to give the crude product, which was purified by fast column chromatography (silica gel, EtOAc/hexane as eluent) to give the final 16-(tert-butoxy)-16-oxohexadecanoic acid (2.56 g, 7.47 mmol, 47.6% yield). Analytical conditions D: retention time = 5.04 min; ESI-MS (+) m/z 269.3 [M-OC(CH3)3]; 1H NMR (500 MHz, methanol-d4) δ 2.33-2.18 (m, 4H), 1.66-1.54 (m, 4H), 1.50-1.43 (m, 9H), 1.40-1.25 (m. 20H).
