Zinc(II)-Assisted Aryl Finkelstein Reaction for the Synthesis of Aryl Iodides

Abstract

Aryl iodides play an important role in synthetic organic chemistry as they are frequently utilized in cross-coupling reactions and in oxidation processes using hypervalent iodine compounds. Their synthesis is, however, often cumbersome and may lead to unwanted side products. Here, we report on an improved protocol for the aryl Finkelstein reaction in which dehalogenation is prevented by addition of zinc iodide in lieu of copper(I). Generally, electron-poor ortho-bromo methyl benzoates, amides, and even unprotected phenols are well-suited for this method.

Aryl iodides play a fundamental role in synthetic organic chemistry. In addition to cross-coupling reactions,[1] aryl iodides have an outstanding synthetic relevance as educts for hypervalent oxidants (Scheme [1]).[2]

Yet, only a limited number of applicable iodination reactions are known that allow for the efficient preparation of aryl iodides. Well-established protocols are mainly based on the use of either elemental iodine[3] also after directed lithiation[4] or iodide in Sandmeyer-type[5] reactions. In particular, the iodination of deactivated aromatic systems is highly challenging, due to the frequency of dehalogenation during synthesis.[6] Thus, new strategies are required. We report here a protocol for the efficient synthesis of a 2-iodobenzoic acid, which serves as a starting point for hypervalent iodo compounds[7] and for the generation of numerous 2-substituted 5-hydroxybenzoic acid derivatives. A literature search on the synthesis of 5-hydroxy-2-iodobenzoic acid 3 revealed that its synthesis involves outdated protocols such as a diazotation–reduction, diazotation, an iodination reaction sequence (from 1891),[8] or the use of explosive NI₃ (from 1937).[9]

In contrast to 3, the corresponding bromo methyl ester 4 is readily accessible.[10] Thus, we aimed to establish an aryl Finkelstein reaction for the bromine–iodine exchange. Even though there are new reaction conditions for the aryl Finkelstein reaction like nickel[11] and ruthenium[12] catalysis or light-induced[13] halogen exchange, the substrate scope rarely includes a free phenolic hydroxyl group.

Pilot experiments utilizing various α,β-diamines, N ¹,N ¹-dimethylethane-1,2-diamine, N ¹,N ²-dimethylethane-1,2-diamine[14] (5), N ¹,N ¹-N ²,N ²-tetramethylethane-1,2-diamine,[15] and rac-cyclohexane 1,2-diamine,[16] showed that 5 gave traces of the desired product. To improve the reaction conditions, we first tested various different reaction temperatures and reaction times and monitored educt and product contents by GC/FID-MS. We found that reaction temperatures of 140 °C and above gave higher turnover rates but led at the same time to an increased dehalogenation. The formation of the dehalogenated product methyl 3-hydroxybenzoate 6 increases, which is in unison with other reports (Figure [1], reactions a–e).[17] Despite numerous variations of the tested conditions, based on GC/FID-MS analyses not more than 45.1% yield of 7 were obtained, even if additional equivalents of NaI were added. With the aim to finding conditions for improved product yields, we carefully re-examined the reaction conditions including all of its additives. We found that the methyl carboxylate in ortho position to the halogen may complex copper(I) (8), thus preventing higher yields. Notably, the complexation of copper by binding to the halogen substituents has been reported as crucial step for the Finkelstein reaction.[18] Thus, the effect of additional equivalents of copper(I) iodide was tested (Figure [1], reaction f). Even though the GC/FID-MS plot displayed an increased turnover for 4, only the amount of the dehalogenated product 6 was increased. This finding and the fact that without the addition of copper(I) iodide (Figure [1], reaction h) no conversion could be observed, we reasoned that copper catalyzes both, the Finkelstein reaction as well as the undesired dehalogenation step.

In order to prevent the dehalogenation reaction, we searched for a suitable weak Lewis acid as substitution for the unfavorable copper(I). Zinc(II) may have similar ionic properties and also act as a weak Lewis acid. Additionally an iodide is available which is also of benefit for the chemical equilibrium by the product view. Initial experiments gave promising results with over 80% yield (Figure [1], reaction g). A preparative-scale reaction was performed in a standard laboratory autoclave (pressure raised not above 2 bar).[19] All test reactions were performed in standard 5 mL HPLC vials sealed with PTFE septa and heated in an aluminum rack at the stated temperature. After aqueous workup and recrystallization 66% of the iodide 7 were isolated. The higher yield is attributable to the proposed metal-exchange reaction with copper(I) by zinc(II) (9), which prevents dehalogenation of the product (Scheme [2]).[18a] [20] Since halogen dance reactions occur frequently during higher temperatures and especially in catalytic environment[21] we confirmed the substitution pattern of the product. Saponification led to 5-hydroxy-2-iodobenzoic acid (3), as proven by comparison of the NMR signals with those reported.[22]

To verify the proposed beneficial effect of the zinc(II) iodide during the catalytic reaction we tested a series of aryl bromides using the conditions for the synthesis of 7 (Figure [2]).[19b] We tested each substrate in a reaction with 1.1 equivalents of zinc(II) iodide and one equivalent of sodium iodide or without zinc(II) iodide but three equivalents sodium iodide to keep the iodide concentration almost constant. The reaction was monitored after aqueous workup with GC/FID-MS, monitoring the amounts of the starting material as well as the dehalogenation product and the desired iodo product. Since bromobenzene did not show any conversion irrespective of the presence or absence of zinc(II) iodide (data not shown) all isomers of the methyl bromo 3-hydroxy benzoate (4, 10–12 with X = Br) were tested. Only in cases where the bromine was in ortho position to the methylester (4, 10 with X = Br) a conversion into the corresponding iodide was observed. In the absence of zinc(II) iodide the reaction resulted in dehalogenation yielding 10 (X = H). The substrates in which the bromine was in meta (11) or para (12) position to the methyl benzoate practically no conversion could be detected. In cases where the substrate did not have any phenol substituent (13–15 with X = Br) the yield of the iodo product is increased by the factor of 3.4 in the presence of zinc(II) iodide, albeit only in the ortho-substituted substrate. To evaluate the beneficial effect of zinc(II) iodide in the Finkelstein reaction in ortho-bromo carbonyl systems we next tested aldehyde 16 and amide 17. In the presence of zinc(II) iodide the 2-bromo benzamide (17 with X = H) is converted into the corresponding iodide with almost 90% yield (based on GC/FID integrals). In contrast, without zinc(II) iodide only 48% of the desired product are obtained. However, when using 2-bromo benzaldehyde as a substrate, the reaction did not benefit from the presence of the zinc; rather an adverse effect was noted. Likewise, an unfavorable effect was observed for the electron-rich 2-bromo anisole (18). These results consolidate our proposed role of zinc during the catalytic cycle in the Finkelstein reaction as a copper exchange cation.

In this report we have demonstrated a new, efficient synthetic route involving the Buchwald procedure for an aryl Finkelstein reaction to prepare aryl iodides. The protocol was optimized for the preparation of the important building block methyl 5-hydroxy-2-iodo benzoate. Using the new method, the valuable chemical is now readily accessible from commercially available reagents, bypassing the use of toxic anilines and diazonium salts and avoiding any chromatographic steps. A major advantage of the scheme is the use of zinc(II) iodide in place of copper(I). In this way, dehalogenation of the product is effectively prevented. A broader survey of the scope of the reaction revealed that the presence of zinc(II) iodide is particularly favorable for ortho bromo methyl benzoates and ortho bromo amides in electron-poor aromatic systems. It is also noteworthy that the method is well suitable for bromo phenols without the need for protection groups. In general, the protocol is simple and applicable to generate aryl iodides that may be used for various applications such as aryl cross-couplings or oxidations by hypervalent iodine.

Acknowledgment

We thank A. Perner and H. Heinecke for performing MS and NMR measurements, respectively.

• References

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• 19a All reagents were obtained from commercial suppliers and used without further purification unless otherwise stated. All solvents used were spectral grade or distilled prior to use. Reactions were carried out under inert gas (Ar) by using the Schlenk technique. 1,2-Dioxane was dried by distillation from a sodium/benzophenone suspension and zinc(II) iodide was sublimed in high vacuum prior to use. Gas-chromatographic analytics were executed on a Thermo Trace GC Ultra equipped with Combi PAL auto sampler and coupled with a FID and a Thermo Polaris Q electron impact (EI) – ion-trap mass spectrometer. We used a SGE forte capillary column BPX5 30 m; 0.25 mm inner diameter and 0.25 μm film. The column was operated with helium carrier gas 1.5 mL/min and split injection (injector temperature 200 °C, detector temperature 250 °C after initial 1 min at 40 °C the oven temperature was raised to 100 °C with 30 °C/min and then to 300 °C with 10 °C/min. Total ion count (TIC) was obtained using the mass range of 50–650 amu; FID temperature: 250 °C. Reaction progress was monitored by GC/FID-MS or thin layer chromatography (TLC; silica gel on aluminum sheets with fluorescent dye 254 nm, Merck KGaA). All test reactions were executed in 5 mL HPLC vials with a PTFE-coated rubber seal. NMR spectra were recorded in deuterated solvents on a Bruker AVANCE II 300 or 400 MHz instrument. The chemical shifts are reported in ppm relative to the solvent residual peak; ¹H NMR (CDCl₃): δ = 7.24 ppm, ¹³C NMR (CDCl₃): δ = 77.23 ppm, ¹H NMR (DMSO-d ₆) δ = 2.50 ppm, ¹³C NMR (DMSO-d ₆) δ = 39.52 ppm. Following abbreviations are used for multiplicities of resonance signals: s = singlet, d = doublet, br = broad. ESI-HRMS measurements were conducted on a Thermo Q Exactive plus apparatus.
• 19b Methyl 2-bromo-5-hydroxybenzoate (4, 1.25 g, 5.41 mmol, 1 equiv), Cu(I)I (103 mg, 541 mmol, 0.1 equiv), Zn(II)I₂ (1.9 g, 5.95 mmol, 1.1 equiv), and NaI (892 mg, 5.95 mmol, 1.1 equiv) were placed into a laboratory autoclave and flushed three times with argon. Then, 1,4-dioxane (50 mL) and N ¹,N ²-dimethyl­ethane-1,2-diamine (5, 136 μL, 1.08 mmol, 0.2 equiv) were added, and the autoclave was sealed. After 24 h at 120 °C (the pressure within the autoclave rises not above 2 bar) the solvent was evaporated under reduced pressure. The white residue was taken up in water (100 mL) and extracted three times with EtOAc (100 mL). The combined organic phases were dried over sodium sulfate and concentrated to dryness under reduced pressure. The product was recrystallized from a mixture of cyclohexane and EtOAc (200 mL, 4:1 v/v). The title compound 7 was isolated in 66% yield by filtration as white solid (990 mg, 3.56 mmol). R_f = 0.31 (silica gel 60; CHCl₃–MeOH = 95:5). ¹H NMR (600 MHz; CDCl₃): δ = 7.76 (d, 1 H, CH-3, ³ J _H–H = 8.6 Hz), 7.31 (d, 1 H, CH-6, ³ J _H–H = 8.6 Hz, ⁴ J _H–H = 3.0 Hz), 6.70 (dd, 1 H, CH-4, ⁴ J _H–H = 3.0 Hz), 5.87 (s, 1 H, OH), 3.90 (s, 3 H, COOCH₃) ppm. ¹³C NMR (150 MHz, CDCl₃): δ = 167.2 (C=O), 155.8 (C–OH), 142.1 (CH, C-3), 135.8 (C, C-1a), 120.7 (CH, C-4), 118.4 (CH, C-6), 82.1 (C-I), 52.7 (COOCH₃) ppm. IR (ATR): ν (%T) = 3844 (w), 3742 (w), 3679 (w), 3319 (m), 2954 (w), 1706 (s), 1559 (s), 1463 (s), 1430 (m), 1256 (s), 1217 (s), 1094 (s), 1009 (m), 980 (m), 812 (m), 672 (m) cm^–1. ESI-MS (ESI⁺): m/z = 301 (42) [M + Na]⁺, 333 (100) [M + Na + MeOH]⁺, 579 (15) [2 M + Na]⁺. HRMS (ESI⁺): m/z calcd for C₈H₇O₃I [M + H]⁺: 278.9513; found: 278.9512.
• 20 Casitas A, Canta M, Sola M, Costas M, Ribas X. J. Am. Chem. Soc. 2011; 133: 19386
  CrossrefSearch in Google Scholar
• 21 Proust N, Chellat MF, Stambuli JP. Synthesis 2011; 3083
  Thieme Connect
• 22a Uyanik M, Akakura M, Ishihara K. J. Am. Chem. Soc. 2009; 131: 251
  CrossrefPubMedSearch in Google Scholar
• 22b The methyl benzoate 7 (11.6 mg, 42 μM, 1 equiv) was placed into a round-bottom flask followed by the addition of MeOH (100 μL) and 1 N NaOH solution (200 μL, 210 μmol, 5 equiv). The progress of the reaction was monitored with TLC, and the reaction was stopped 15 min after complete consumption of the methyl ester by adding 1 N HCl (500 μL). After extraction with EtOAc (3 × 5 mL) the solvent was dried over Na₂SO₄ and evaporated under reduced pressure to give a pale yellow crystalline solid. The solid was dried in fine vacuum overnight yielding the title compound 5-hydroxy-2-iodobenzoic acid (3) (10.0 mg, 38 μmol, 91%). The ¹H NMR data are identical to the reported values from ref. 22a. ¹H NMR (400 MHz, DMSO-d ₆): δ = 13.11 (br s, 1 H, COOH), 9.97 (s, 1 H, ArOH), 7.71 (d, 1 H, ³ J _H–H = 8.6 Hz, ArCH-3), 7.13 (d, 1 H, ⁴ J _H–H = 3.0 Hz, ArCH-6), 6.68 (dd, 1 H, ³ J _H–H = 8.6 Hz, ⁴ J _H–H = 3.0 Hz, ArCH-4) ppm. ¹³C NMR (100 MHz, DMSO-d ₆): δ = 167.8 (ArCOOH), 157.4 (ArCOH), 141.2 (ArCH-3), 137.5 (Ar C COOH), 120.2 (ArCH-4), 117.3 (ArCH-6), 80.0 (ArCI) ppm. HRMS (ESI^–): m/z calcd for C₇H₄IO₃ [M – H]^– = 262.9211; found: 262.9208.

• References

• 1 Brückner R. Reaktionsmechanismen: Organische Reaktionen, Stereochemie, Moderne Synthesemethoden. 3rd ed. Spektrum Akademischer Verlag; Heidelberg: 2009
  Search in Google Scholar
• 2 Silva JL. F, Olofsson B. Nat. Prod. Rep. 2011; 28: 1722
  CrossrefSearch in Google Scholar
• 3 Schwetlick K. Organikum. Vol. 21. Wiley-VCH; Weinheim: 2001
  Search in Google Scholar
• 4 Snieckus V. Chem. Rev. 1990; 90: 879
  Search in Google Scholar
• 5a Krasnokutskaya EA, Semenischeva NI, Filimonov VD, Knochel P. Synthesis 2007; 81
  Thieme Connect
• 5b Filimonov VD, Trusova M, Postnikov P, Krasnokutskaya EA, Lee YM, Hwang HY, Kim H, Chi KW. Org. Lett. 2008; 10: 3961
  CrossrefPubMedSearch in Google Scholar
• 5c Hodgson HH. Chem. Rev. 1947; 40: 251
  CrossrefPubMedSearch in Google Scholar
• 6 Cannon KA, Geuther ME, Kelly CK, Lin S, MacArthur AH. R. Organometallics 2011; 30: 4067
  CrossrefSearch in Google Scholar
• 7a Ma H, Li W, Wang J, Xiao G, Gong Y, Qi C, Feng Y, Li X, Bao Z, Cao W, Sun Q, Veaceslav C, Wang F, Lei Z. Tetrahedron 2012; 68: 8358
  CrossrefSearch in Google Scholar
• 7b Miles KC, Le CC, Stambuli JP. Chem. Eur. J. 2014; 20: 11336
  CrossrefSearch in Google Scholar
• 7c Reed NN, Delgado M, Hereford K, Clapham B, Janda KD. Bioorg. Med. Chem. 2002; 12: 2047
  CrossrefSearch in Google Scholar
• 7d Mülbaier M, Giannis A. Angew. Chem. Int. Ed. 2001; 40: 4393
  CrossrefSearch in Google Scholar
• 8 Limpricht H. Liebigs Ann. Chem. 1891; 263: 224
  CrossrefSearch in Google Scholar
• 9 Datta RL, Prosad N. J. Am. Chem. Soc. 1917; 39: 441
  CrossrefSearch in Google Scholar
• 10a Ueberschaar N, Dahse H.-M, Bretschneider T, Hertweck C. Angew. Chem. Int. Ed. 2013; 52: 6185
  CrossrefSearch in Google Scholar
• 10b Ueberschaar N, Xu Z, Scherlach K, Metsä-Ketelä M, Bretschneider T, Dahse H.-M, Goerls H, Hertweck C. J. Am. Chem. Soc. 2013; 135: 17408
  CrossrefSearch in Google Scholar
• 11 Cant AA, Bhalla R, Pimlott SL, Sutherland A. Chem. Commun. 2012; 48: 3993
  CrossrefSearch in Google Scholar
• 12 Imazaki Y, Shirakawa E, Ueno R, Hayashi T. J. Am. Chem. Soc. 2012; 134: 14760
  CrossrefSearch in Google Scholar
• 13 Li L, Liu W, Zeng H, Mu X, Cosa G, Mi Z, Li C.-J. J. Am. Chem. Soc. 2015; 137: 8328
  CrossrefSearch in Google Scholar
• 14 Sejberg JJ. P, Smith LD, Leatherbarrow RJ, Beavil AJ, Spivey AC. Tetrahedron Lett. 2013; 54: 4970
  CrossrefSearch in Google Scholar
• 15 Bennacef I, Haile CN, Schmidt A, Koren AO, Seibyl JP, Staley JK, Bois F, Baldwin RM, Tamagnan G. Bioorg. Med. Chem. 2006; 14: 7582
  CrossrefSearch in Google Scholar
• 16 Hapke M, Kral K, Spannenberg A. Synthesis 2011; 642
  Thieme Connect
• 17 Hekmatshoar R, Sajadi S, Heravi MM. J. Chin. Chem. Soc. 2008; 55: 616
  CrossrefSearch in Google Scholar
• 18a Sheppard TD. Org. Biomol. Chem. 2009; 7: 1043
  CrossrefPubMedSearch in Google Scholar
• 18b Klapars A, Buchwald SL. J. Am. Chem. Soc. 2002; 124: 14844
  CrossrefPubMedSearch in Google Scholar
• 19a All reagents were obtained from commercial suppliers and used without further purification unless otherwise stated. All solvents used were spectral grade or distilled prior to use. Reactions were carried out under inert gas (Ar) by using the Schlenk technique. 1,2-Dioxane was dried by distillation from a sodium/benzophenone suspension and zinc(II) iodide was sublimed in high vacuum prior to use. Gas-chromatographic analytics were executed on a Thermo Trace GC Ultra equipped with Combi PAL auto sampler and coupled with a FID and a Thermo Polaris Q electron impact (EI) – ion-trap mass spectrometer. We used a SGE forte capillary column BPX5 30 m; 0.25 mm inner diameter and 0.25 μm film. The column was operated with helium carrier gas 1.5 mL/min and split injection (injector temperature 200 °C, detector temperature 250 °C after initial 1 min at 40 °C the oven temperature was raised to 100 °C with 30 °C/min and then to 300 °C with 10 °C/min. Total ion count (TIC) was obtained using the mass range of 50–650 amu; FID temperature: 250 °C. Reaction progress was monitored by GC/FID-MS or thin layer chromatography (TLC; silica gel on aluminum sheets with fluorescent dye 254 nm, Merck KGaA). All test reactions were executed in 5 mL HPLC vials with a PTFE-coated rubber seal. NMR spectra were recorded in deuterated solvents on a Bruker AVANCE II 300 or 400 MHz instrument. The chemical shifts are reported in ppm relative to the solvent residual peak; ¹H NMR (CDCl₃): δ = 7.24 ppm, ¹³C NMR (CDCl₃): δ = 77.23 ppm, ¹H NMR (DMSO-d ₆) δ = 2.50 ppm, ¹³C NMR (DMSO-d ₆) δ = 39.52 ppm. Following abbreviations are used for multiplicities of resonance signals: s = singlet, d = doublet, br = broad. ESI-HRMS measurements were conducted on a Thermo Q Exactive plus apparatus.
• 19b Methyl 2-bromo-5-hydroxybenzoate (4, 1.25 g, 5.41 mmol, 1 equiv), Cu(I)I (103 mg, 541 mmol, 0.1 equiv), Zn(II)I₂ (1.9 g, 5.95 mmol, 1.1 equiv), and NaI (892 mg, 5.95 mmol, 1.1 equiv) were placed into a laboratory autoclave and flushed three times with argon. Then, 1,4-dioxane (50 mL) and N ¹,N ²-dimethyl­ethane-1,2-diamine (5, 136 μL, 1.08 mmol, 0.2 equiv) were added, and the autoclave was sealed. After 24 h at 120 °C (the pressure within the autoclave rises not above 2 bar) the solvent was evaporated under reduced pressure. The white residue was taken up in water (100 mL) and extracted three times with EtOAc (100 mL). The combined organic phases were dried over sodium sulfate and concentrated to dryness under reduced pressure. The product was recrystallized from a mixture of cyclohexane and EtOAc (200 mL, 4:1 v/v). The title compound 7 was isolated in 66% yield by filtration as white solid (990 mg, 3.56 mmol). R_f = 0.31 (silica gel 60; CHCl₃–MeOH = 95:5). ¹H NMR (600 MHz; CDCl₃): δ = 7.76 (d, 1 H, CH-3, ³ J _H–H = 8.6 Hz), 7.31 (d, 1 H, CH-6, ³ J _H–H = 8.6 Hz, ⁴ J _H–H = 3.0 Hz), 6.70 (dd, 1 H, CH-4, ⁴ J _H–H = 3.0 Hz), 5.87 (s, 1 H, OH), 3.90 (s, 3 H, COOCH₃) ppm. ¹³C NMR (150 MHz, CDCl₃): δ = 167.2 (C=O), 155.8 (C–OH), 142.1 (CH, C-3), 135.8 (C, C-1a), 120.7 (CH, C-4), 118.4 (CH, C-6), 82.1 (C-I), 52.7 (COOCH₃) ppm. IR (ATR): ν (%T) = 3844 (w), 3742 (w), 3679 (w), 3319 (m), 2954 (w), 1706 (s), 1559 (s), 1463 (s), 1430 (m), 1256 (s), 1217 (s), 1094 (s), 1009 (m), 980 (m), 812 (m), 672 (m) cm^–1. ESI-MS (ESI⁺): m/z = 301 (42) [M + Na]⁺, 333 (100) [M + Na + MeOH]⁺, 579 (15) [2 M + Na]⁺. HRMS (ESI⁺): m/z calcd for C₈H₇O₃I [M + H]⁺: 278.9513; found: 278.9512.
• 20 Casitas A, Canta M, Sola M, Costas M, Ribas X. J. Am. Chem. Soc. 2011; 133: 19386
  CrossrefSearch in Google Scholar
• 21 Proust N, Chellat MF, Stambuli JP. Synthesis 2011; 3083
  Thieme Connect
• 22a Uyanik M, Akakura M, Ishihara K. J. Am. Chem. Soc. 2009; 131: 251
  CrossrefPubMedSearch in Google Scholar
• 22b The methyl benzoate 7 (11.6 mg, 42 μM, 1 equiv) was placed into a round-bottom flask followed by the addition of MeOH (100 μL) and 1 N NaOH solution (200 μL, 210 μmol, 5 equiv). The progress of the reaction was monitored with TLC, and the reaction was stopped 15 min after complete consumption of the methyl ester by adding 1 N HCl (500 μL). After extraction with EtOAc (3 × 5 mL) the solvent was dried over Na₂SO₄ and evaporated under reduced pressure to give a pale yellow crystalline solid. The solid was dried in fine vacuum overnight yielding the title compound 5-hydroxy-2-iodobenzoic acid (3) (10.0 mg, 38 μmol, 91%). The ¹H NMR data are identical to the reported values from ref. 22a. ¹H NMR (400 MHz, DMSO-d ₆): δ = 13.11 (br s, 1 H, COOH), 9.97 (s, 1 H, ArOH), 7.71 (d, 1 H, ³ J _H–H = 8.6 Hz, ArCH-3), 7.13 (d, 1 H, ⁴ J _H–H = 3.0 Hz, ArCH-6), 6.68 (dd, 1 H, ³ J _H–H = 8.6 Hz, ⁴ J _H–H = 3.0 Hz, ArCH-4) ppm. ¹³C NMR (100 MHz, DMSO-d ₆): δ = 167.8 (ArCOOH), 157.4 (ArCOH), 141.2 (ArCH-3), 137.5 (Ar C COOH), 120.2 (ArCH-4), 117.3 (ArCH-6), 80.0 (ArCI) ppm. HRMS (ESI^–): m/z calcd for C₇H₄IO₃ [M – H]^– = 262.9211; found: 262.9208.

• Supplementary Material