## 2 Materials and Methods
### SARA-AERC towards **3** or **6**  
Preparation of **3**. In an oven-dried Schlenk tube (previously rinsed with 10% aqueous NH\({}_{4}\)OH and water in sequence), Na\({}_{2}\)CO\({}_{3}\) (0.2 mmol, 21 mg), NaBr (4 mmol, 0.412 g), amide **1** (4 mmol, 1.032 g), and metallic copper wire (length 40 mm, diameter 1 mm, 99.9%) were inserted. After three cycles of vacuum/argon (around 10 min, each), AcOEt (2 mL), EtOH (96 vol%, 1 mL), and TPMA (1 mL of 0.04 mol/L solution in absolute ethanol) were added under an argon atmosphere. The Schlenk tube was heated at 37 \({}^{\circ}\)C and stirred at 700 rpm for 16 h. The reaction was then quenched with water (6 mL), acidified with 10% aqueous HCl (1 mL) and extracted with CH\({}_{2}\)Cl\({}_{2}\) (3 \(\times\) 5 mL). The combined organic layers were concentrated to dryness at the rotary evaporator, giving the crude product **3** as a brownish solid (95%, 3.8 mmol, 1.150 g), which resulted contaminated by a small amount (-5% GC) of ATRC dichlorocarbam **2**, and a small amount (-5% GC) of isomeric dibromolactam **3b** (see Figures 3 and S1). A purer version of **3** was obtained through (unoptimized) recrystallization from a mixture of CH\({}_{2}\)Cl\({}_{2}\):toluene:Et\({}_{2}\)O in a 65:15:20 ratio, giving a beige solid with an 82% yield, as an inseparable mixture of cis/trans diastereomers (97:3). Compound **3**: (_cis_-isomer, 97%): \({}^{1}\)H NMR (600 MHz, CDCl\({}_{3}\)): \(\delta\) = 1.86 (s, 3 H, CH\({}_{3}\)), 2.75 (m, 1 H, CH), 3.65 (pq, J = 9.4 Hz, 2 H, CH\(H\)Br, CH\(H\)NCO), 3.71 (pdd, J = 4.74, 10.4 Hz, 1 H, CH\(H\)Br), 4.02 (pdd, J = 6.9, 9.9 Hz, 1 H, CHHNCO), 7.21 (pt, J = 7.4 Hz, 1 H, \(p\)-ArH), 7.40 (pt, J = 7.6 Hz, 2 H, \(m\)-ArH), 7.65 (pd, J = 8.1 Hz, 2H, \(o\)-ArH) ppm. \({}^{13}\)C NMR (150 MHz, CDCl\({}_{3}\)): \(\delta\) = 25.0 (CH\({}_{3}\)), 29.2 (CH\({}_{2}\)Br), 47.3 (CH), 50.6 (CH\({}_{2}\)NCO), 120.3 (\(o\)-ArC), 125.7 (\(p\)-ArC), 129.2 (\(m\)-ArC), 138.7 (N-ArC), 170.0 (NCO) ppm. (_trans_-isomer, 3%): \({}^{1}\)H NMR (600 MHz, CDCl\({}_{3}\)): \(\delta\) = 1.72 (s, 3 H, CH\({}_{3}\)), 3.15 (m, 1 H, CH), 3.36 (t, J = 10.4 Hz, 1 H,CHHBr), 3.69 (m, 1 H, CHHNCO), 4.04 (m, 1 H, CHHBr), 4.18 (pdd, J = 6.8, 10.1 Hz, 1 H, CHHNCO), 7.21 (pt, J = 7.4 Hz, 1 H, \(p\)-ArH), 7.40 (pt, J = 7.6 Hz, 2 H, \(m\)-ArH), 7.65 (pd, J = 8.1 Hz, 2H, \(o\)-ArH) ppm. EA found: C 47.7 H 4.2 N 4.8; calcd for (C\({}_{12}\)H\({}_{13}\)NOClBr): C 47.63 H 4.33 N 4.63  
MS molecular peak [3]\({}^{+}\) isotopic pattern: calcd \(m/z\) = 300.9 (76.8%); 301.9 (10.4%); 302.9 (100.0%); 303.9 (13.5%); 304.9 (24.9%); 305.9 (3.3%); 306.9 (0.3%). Found \(m/z\) = 300.9 (76.2%); 301.9 (10.6%); 302.9 (100.0%); 303.9 (13.9%); 304.9 (25.2%); 305.9 (3.0%). Preparation of **6**. In an oven-dried Schlenk tube (previously rinsed with 10% aqueous NH\({}_{4}\)OH and water in sequence), Na\({}_{2}\)CO\({}_{3}\) (0.2 mmol, 21 mg), NaBr (4 mmol, 0.412 g), amide **4** (4 mmol, 1.312 g), and a piece of copper wire (length 40 mm, 1 mm diameter, 99.9%) were inserted. After three cycles of vacuum/argon (around 10 min, each), AcOEt (3 mL), EtOH (96 vol%, 1.5 mL), and TPMA (1 mL of 0.04 mol/L solution in absolute ethanol) were added under an argon atmosphere. The Schlenk tube was heated at 37 \({}^{\circ}\)C and stirred at 700 rpm for 16 h. The reaction was then quenched with water (6 mL), acidified with 10% aqueous HCl (1 mL) and extracted with CH\({}_{2}\)Cl\({}_{2}\) (3 \(\times\) 5 mL). The combined organic layers were concentrated to dryness at the rotary evaporator, giving the crude product **6** as a brownish solid (96%, 1.260 g), which resulted contaminated by a small amount (-9% GC) of trichlorolactam **5** (see also Figure S2). A purer version of **6** was obtained through (unoptimized) recrystallization from a mixture of CH\({}_{2}\)Cl\({}_{2}\):petroleum ether in 1:2 ratio, giving a yellowish solid with a 78% yield.