Supporting information Oxidative cleavage of α-arylaldehydes using iodosylbenzene Nizam Havare and Dietmar A. Plattner S1 General: All used substrate were prepared following published procedures [a-m]. Starting materials: (diacetoxyiodo)benzene, Dess-Martin reagent, 2-(4-nitrophenyl)ethanol, 2-(4- chlorophenyl)ethanol, phenylacetaldehyde, 2-(2-naphthyl)ethanol, 2-(4-methoxy)ethanol, 2- methoxy-2-phenylethanol, 2-phenylpropanal, 2-phenyl-1-butanol, cyclohexyl- phenylacetonitrile, α-tetralone, 2-acetylnaphthalene, anethol, 4-nitroacetophenone and solvents were obtained commercially from ABCR , Sigma-Aldrich , Fluka , Alfa Aesar and Acros. Dichloromethane was dried over potassium carbonate, freshly distilled and stored under Ar prior to use. Cyclohexane was dried over sodium, freshly distilled and stored under Ar prior to use. Ethyl acetate was dried over phosphor pentaoxide, freshly distilled and stored under Ar prior to use. Column chromatography: Silica gel 60 : 0.06-0.2 mm, Carl Roth GmbH. 1 TLC: Silica gel 60 F 254 25 Aluminium sheets 20x20 cm from Merck KGaA co. Darmstadt. H- spectra: Varian 300 and Bruker 500 spectrometer. GC-MS: (GC Varian 3400 , achiral GC column Macherey-Nagel optima 5 MS 30 m x0.25 mmØ, 0.25 µm film). MS: Thermo TSQ 700. Preparation of CO detection reagent (PdCl 2/HCl): 100 ml of water is added to 130 mg of palladium(II)chloride (0.733 mmol, 99.7%) in a 250 ml volumetric flask. 1 ml of HCl solution is added, which was prepared from mixture of conc. HCl/water (V/V = 1:10). The suspension is stirred for one day at room temperature, until giving a clear solution. Then the flask is filled to the mark with water. The solution can be stored for up to eight months. Preparation of CO 2 detection reagent (Ba(OH) 2): In a 500 ml two-necked flask 200 ml of water is saturated with barium hydroxide, filtered, and stored under argon. (The saturated solution reacts rapidly with air-carbon dioxide). Synthesis of iodosylbenzene: To 32 g of (diacetoxyiodo)benzene (0.1 mol, 1 eq.) in a 1 l Erlenmeyer flask is added 532 ml of sodium hydroxide solution (1.88 M) dropwise at room temperature. The light yellow suspension is stirred for three hours at room temperature. The precipitate is filtered under high vacuum and washed with water until the washing water is neutral. The slightly yellow solid was dried in the air and then mortared into fine powder. The result of iodometric titration of one sample gave 99.5% (W/W) of iodosylbenzene. Yield: 86-90% S2 Entry 1 O PhIO/HBF4 (Et2O) no reaction CH2Cl2, r.t. Method A1 Entry 2 O O O PhIO / HBF4 (48 % in water) Ph Ph OH CH2Cl2, 1.5 h, r.t. Method B1 In a two-necked flask equipped with two bubble counters, which are connected and filled with the CO 2 detection reagent (barium hydroxide) and with the CO detection reagent (PdCl 2/HCl in water), respectively, 608 mg of phenylglyoxal (4 mmol, 1 eq.) is dissolved in 20 ml CH 2Cl 2. 1.32 g of iodosylbenzene (6 mmol, 1.5 eq) is added to the solution. Under stirring, 630 µL of tetrafluoroboric acid (4.82 mmol, 1.2 eq., 48% in water) is added within a few minutes dropwise to the suspension. The reaction mixture is stirred for 1.5 hours at room temperature (TLC control after 1.5 hours). After 1.5 hours, BaCO 3 and Pd metal precipitated in bubble counter. The reaction mixture is concentrated under reduced pressure. The product is isolated by column chromatography (eluent: cyclohexane / ethyl acetate = 20:1 → 10:1). Yield: 73 % O Ph OH 1 H-NMR (300 MHz, CDCl 3): δ = 8.13 (d, J = 8.0 Hz, 2H, Ar-H), 7.62 (t, J = 7.4 Hz, 1H, Ar-H), 7.52-7.45 (t, J = 7.4 Hz, 2H, Ar-H). S3 GC/MS-EI m/z(%): 123.1(6), 122.0(100), 106.1(6), 105.0(88), 77.1(38). Entry 3 OMe O O O PhIO/HBF4 Et2O Ph + 1,4-dioxane Ph H Ph OMe Method A2 In a 100 ml flask, 150 mg of 2-methoxy-2-phenylacetaldehyde (1 mmol, 1 eq.) and 50 mg of 1,4-dichlorobenzene (0.347 mmol) (internal standard) are dissolved in 10 ml of 1,4-dioxane (abs.) under argon atmosphere. 330 mg of iodosylbenzene (1.5 mmol, 1.5 equiv.) is added. The suspension is stirred for 5 minutes at room temperature. Then, 220 µl of tetrafluoroboric acid etherat complex (395 mg, 2.2 mmol, 2.2 eq., 50-55% in ether), diluted with CH 2Cl 2 (abs.) to the total volume of 10 ml with 1,4-dioxane, is injected within 10 minutes to the suspension. After 10, 20, 40 and 60 minutes, and finally after 15 hours are taken each 700 µl sample of the reaction environment. (The preparation of GC sample: the sample is first diluted to 2 ml with S4 diethyether, and then washed with saturated sodium thiosulfate. The aqueous solution is removed. The sample is washed then with saturated sodium bicarbonate. The aqueous phase is removed. The organic phase is dried with little sodium sulfate and filtered. After 15 hours, the reaction is processed with the same work up of the samples. The solvent is removed. The product is isolated by column chromatography (eluent: cyclohexane / ethyl acetate = 10:1). Yield: 65% (GC-yield), 3% (GC-yield) methyl benzoate (oxidative cleavage product). O Ph H Benzaldehyde: 1 H-NMR (300 MHz, CDCl 3): δ = 10.02 (s, 1H, C HO), 7.85 (d, 2H, Ar-H), 7.61 (t, 1H, Ar-H), 7.51 (t, 2H, Ar-H). S5 O Ph OMe Methylbenzoate 1 H-NMR (300 MHz, CDCl 3): δ = 8.028 (d, 2H, Ar-H), 7.56-7.26 (m, 3H, Ar-H), 3.89 (s, -COOC H3). Synthesis of 2-methoxy-2-phenylacetaldehyde OMe OMe OH Oxalyl chloride / DMSO / Et3N Ph O Ph CH2Cl2, -78°C, 25 min. 1.26 ml (14.5 mmol, 1.1 eq.) oxalyl chloride is disolved in 60 ml of dichloromethane. The solution is cooled to -78 °C. 2.05 ml of DMSO (28.9 mmol, 2.2 eq.), dissolved in 10 ml of dichloromethane is added dropwise. The solution is stirred 20 min. at -78 ° C. 2 g of 2- methoxy-2-phenylethanol (13.1 mmol, 1 eq.) were added dropwise in 7 ml of dichloromethane. The solution is stirred for a further five minutes at -78 °C. Then 9.16 ml of S6 triethylamine is added at the same temperature. The mixture fades a yellow suspension. The reaction mixture is allowed to warm to 0°C and hydrolyzed with 20 ml of water. The aqueous phase is extracted three times with dichloromethane. The combined organic phase is washed once with saturated sodium chloride solution and dried over sodium sulfate. The organic phase is concentrated. The residue is diluted with ether and washed three times with 20 ml of 1% cold HCl solution and once with brine. The organic phase is dried over magnesium sulphate and the solvent is removed. The product is isolated by column chromatography (eluent: cyclohexane / ethyl acetate = 20:1). Yield: 43% (842 mg) OMe O Ph 1 H-NMR (300 MHz, CDCl 3): δ = 9.60 (d, J = 1.5 Hz, 1H, -CHO), 7.46-7.32 (m, 5H, Ar-H), 4.64 (d, J = 1.5 Hz, 1H, PhC H(OCH 3)CHO), 3.45 (s, 3H, PhCH(OC H3)CHO). S7 Entry 4 O2N O O PhIO / HBF4 H Ph N NO2 Ph Ph N 1.2 g of phenylacetaldehyde (10 mmol, 1 eq.) is dissolved in 30 ml of dioxane-water (15:15). 3.3 g of iodosylbenzene (15 mmol, 1.5 eq.) is added. Under stirring, 1:58 ml of tetrafluoroboric acid (12 mmol, d = 1.4 g/ml, 48% in water) is added dropwise to the suspension. The reaction mixture is stirred for six days at room temperature. After six days, the freshly prepared 2,4-dinitrophenylhydrazine solution is added to give the corresponding hydrazone compound. The precipitate is filtered and washed several times with water. The hydrazone is then dried. Preparation of 2,4-dinitrophenylhydrazine solution: To 3.1 g of 2,4-dinitrophenylhydrazine (11 mmol, 1.1 eq, 70%) are added 11.74 ml of sulfuric acid and 17.6 ml of water. 60 ml tech. S8 Ethanol is then added to hot solution. The solution is stirred for 10 minutes at room temperature. Yield: 98 % (2.82 g) O2N H Ph N NO2 N 1-Benzylidene-2-(2,4-dinitrophenyl)hydrazine 1 H-NMR (300 MHz, DMSO-d6): δ = 11.7 (bs,1H, -CHNN H-), 8.88 (d, J = 2.7 Hz, 1H, Ar-H), 8.73 (s, 1H, -CHNNH- ), 8.43- 8.36 (dd, J = 2.70 Hz, J = 9.70 Hz, 1H, Ar-H), 8.15-8.10 (d, J = 9.70, 1H, Ar-H), 7.85-7.75 (dd, J = 4.2 Hz, J = 2.06 Hz, 2H, Ar-H), 7.54-7.46 (m, 3H; Ar-H). S9 Entry 5 O PhIO / HBF4 (48% in H2O) O 1,4-dioxane / water: 1 / 1 Method B2 170 mg of 2-(naphthalene-6-yl)acetaldehyde (1 mmol, 1 eq.) is dissolved in mixture of 20 ml 1,4-dioxane-water (1:1). And then, 330 mg of iodosylbenzene (1.5 mmol, 1.5 equiv.) is added to the solution. 220 µl of HBF 4 (1.7 mmol, 1.7 eq. 48% in water) is added dropwise to the suspension. The suspension is stirred for 6 days at room temperature.