## 2 Materials and Methods
### Chloromethyllation  
General procedure. The phenolic substrate (10 mmol) was mixed with PF (from 12 to 42 mmol, depending on the number of chloromethyl groups incorporated into the product) and aqueous 37% HCl (from 6.5 to 25.0 mL). Concentrated H\({}_{2}\)SO\({}_{4}\) (96%, up to 1.0 mL) was also added in the case of electron-poor phenolics. In some cases, dichloromethane (DCM, up to 2.0 mL) was added as a co-solvent. The reaction mixture was stirred at a specific temperature (from 25 \({}^{\circ}\)C to 100 \({}^{\circ}\)C) for several hours until the disappearance of the substrate, which was evaluated through TLC. Filtration on a Gooch glass filter (P3) followed by aqueous 10% NaHCO\({}_{3}\) (10 mL) and water washing (2 \(\times\) 10 mL) allowed for the isolation of the product. Alternatively, extraction with DCM (3 \(\times\) 10 mL) and washing of the organic phase with aq. 10% NaHCO\({}_{3}\) (2 \(\times\) 10 mL) and brine (2 \(\times\) 10 mL) allowed for the isolation of the product after vacuum-drying the organic phase. 3-(Chloromethyl)-4-hydroxy-5-methoxybenzaldehyde (**2a**). Following the general procedure, vanillin (**1a**, 10 mmol) was stirred with PF (12 mmol), conc. HCl (37%, 6.5 mL), and conc. H\({}_{2}\)SO\({}_{4}\) (0.5 mL) at 60 \({}^{\circ}\)C for 6 h. Filtration on a P3 glass filter allowed the isolation of the product as a brown solid in a 70% yield. \({}^{1}\)H NMR (400 MHz, CDCl\({}_{3}\)) \(\delta\)(ppm): 9.84 (s, 1H, Ar-C(=O) H), 7.53 (d, 1H, Ar-H), 7.40 (d, 1H, Ar-H), 6.43 (s, 1H, Ar-OH), 4.71 (s, 2H, Ar-CH\({}_{2}\)-Cl), 3.99 (s, 3H, O-CH\({}_{3}\)). \({}^{13}\)C NMR (400 MHz, CDCl\({}_{3}\)) \(\delta\)(ppm): 197.1 (C=O), 151.2 (C-Ar), 148.0 (C-Ar), 125.3 (C-Ar), 123.3 (C-Ar), 119.6 (C-Ar), 113.2 (C-Ar), 56.0 (OCH\({}_{3}\)), 40.2 (-CH\({}_{2}\)-). EA found: C 53.71%, H 4.69%; calcd for (C\({}_{9}\)H\({}_{9}\)O\({}_{3}\)Cl): C 53.88%, H 4.52%. Mp 116-119 \({}^{\circ}\)C (Lit. : 120-122 \({}^{\circ}\)C). 3,5-Bis(chloromethyl)-2-hydroxybenzaldehyde (**2b**). Following the general procedure, salicaldehyde (**1b**, 10 mmol) was stirred with PF (25 mmol), conc. HCl (37%, 17 mL), and conc. H\({}_{2}\)SO\({}_{4}\) (1.0 mL) at 70 \({}^{\circ}\)C for 20 h. After extraction with DCM, the product was obtained as a pale pink solid, in 99% yield. \({}^{1}\)H NMR (400 MHz, CDCl\({}_{3}\)) \(\delta\)(ppm): 11.49 (s, 1H, Ar-OH), 9.91 (s, 1H, Ar-C(=O)H), 7.68 (d, 1H, Ar-H), 7.59 (d, 1H, Ar-H), 4.68 (s, 2H, Ar-oCH\({}_{2}\)-Cl), 4.59 (s, 2H, Ar-pCH\({}_{2}\)-Cl). \({}^{13}\)C NMR (600 MHz, CDCl\({}_{3}\)) \(\delta\)(ppm): 196.3 (C=O), 159.4 (C-Ar), 137.8 (C-Ar), 134.1 (C-Ar), 129.3 (C-Ar), 126.8 (C-Ar), 120.4 (C-Ar), 45.1 (-CH\({}_{2}\)-), 39.6 (-CH\({}_{2}\)-). EA found: C 49.28%, H 3.71%; calcd for (C\({}_{9}\)H\({}_{8}\)O\({}_{2}\)Cl\({}_{2}\)): C 49.34%, H 3.68%. Mp 90-92 \({}^{\circ}\)C1-(3-(Chloromethyl)-4-hydroxyphenyl)ethan-1-one (**2c**). Following the general procedure, picoel (**1c**, 10 mmol) was stirred with PF (12 mmol), conc. HCl (37%, 6.5 mL), and conc. H\({}_{2}\)SO\({}_{4}\) (0.25 mL) at 40 \({}^{\circ}\)C for 6 h. Filtration on a P3 glass filter allowed the isolation of the product as a pink solid in 68% yield. \({}^{1}\)H NMR (600 MHz, CDCl\({}_{3}\)) \(\delta\)(ppm): 7.95 (d, 1H, Ar-H), 7.88 (dd, 8.4 Hz, 1H, Ar-H), 6.91 (d, 1H, 8.4 Hz, Ar-H), 5.81 (br s, 1H, Ar-OH), 4.70 (s, 2H, Ar-CH\({}_{2}\)-Cl), 2.57 (s, 3H, Ar-C(O)CH\({}_{3}\)). \({}^{13}\)C NMR (400 MHz, CDCl\({}_{3}\)) \(\delta\)(ppm): 196.6 (C=O), 158.5 (C-Ar), 131.6 (C-Ar), 131.4 (C-Ar), 130.8 (C-Ar), 123.9 (C-Ar), 116.3 (C-Ar), 41.8 (-CH\({}_{2}\)-), 26.6 (-CH\({}_{3}\)). EA found: C 58.60%, H 4.87%; calcd for (C\({}_{9}\)H\({}_{9}\)O\({}_{2}\)Cl): C 58.55%, H 4.91%. Mp n.d. (decomposed). 1-(3,5-Bis(chloromethyl)-4-hydroxyphenyl)ethan-1-one (**2c2**). Following the general procedure, picoel (**1c**, 10 mmol) was stirred with PF (25 mmol), conc. HCl (37%, 13 mL), and conc.