The Unusual Mechanistic Course of Some NHC-Mediated Transesterifications

Transcription

1 Supporting Information The Unusual Mechanistic Course of Some NHC-Mediated Transesterifications Luca Pignataro, *,± Teresa Papalia, Alexandra M. Z. Slawin, Stephen M. Goldup, *, ± Dipartimento di Chimica Organica e Industriale, Università degli Studi di Milano, via Venezian 21, I Milano, Italy; Dipartimento di Chimica Organica e Biologica, Università Degli Studi di Messina, Salita Sperone 31 (vill. S. Agata), Messina, Italy; School of Chemistry, University of St. Andrews, Purdie Building, St. Andrews, Fife, KY16 9ST, UK, School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, United Kingdom luca.pignataro@unimi.it; s.m.goldup@qmul.ac.uk Table of Contents 1. General Experimental Methods S3 2. Experimental Procedures S4 3. Experiments in d 8 -THF S6 4. Transesterification Procedures S8 Figure S1: Stack Plot of Transesterification Experiments and 4a S8 5. NMR Spectra of Compounds S9-S35 S1

2 1. General Experimental Methods Unless otherwise stated, all reagents and solvents, including anhydrous THF, were purchased from Aldrich Chemicals and used without further purification. d 8 -THF was purchased from Goss Scientific Instruments Ltd. 2,6-di-iso-propyl-4-iodoaniline, 1,2 1,3-Bis(2,6-di-iso-propylphenyl)imidazolium chloride (IPr HCl, 1a) 3 and 1,3-di-tertbutylimidazolium chloride (ItBu HCl, 1c) 4 were prepared using literature procedures. All reactions were performed under a nitrogen atmosphere in anhydrous solvents unless otherwise stated. Reactions in d 8 -THF were carried out under argon in a Wilmad NMR tube with J. Young valve. A VWR Ultrasonic Cleaner ultrasound bath was used to agitate reactions performed in an NMR tube. Column chromatography was carried out using Silica 60A (particle size μm, Fisher, UK) as the stationary phase, and TLC was performed on precoated silica gel plates (0.25 mm thick, 60 F 254, Merck, Germany) and observed under UV light. 1 H and 13 C NMR spectra were recorded on Bruker AV 400. Chemical shifts are reported in parts per million (ppm) from high to low frequency and referenced to the residual solvent resonance. Carbon NMR spectra were recorded as pendant experiments. 5 Coupling constants (J) are reported in hertz (Hz). Standard abbreviations indicating multiplicity were used as follows: s = singlet, d = doublet, t = triplet, dd = double doublet, q = quartet, m = multiplet, b = broad, AB-q = AB quartet. Infrared spectra were recorded in the solid state using a Pike MIRacle ATR accessory fitted to a Bruker Tensor 27 spectrometer. Melting points (m.p.) were determined using Gallenkamp melting point apparatus and are reported uncorrected. Mass spectrometry was carried out by the services at the University of Edinburgh and the EPSRC National Mass Spectrometry Service Centre, Swansea, UK. S2

3 2. Experimental procedures Bis(2,6-diisopropyl-4-iodophenyl)diazabutadiene (S1): A solution of glyoxal (40% aqueous solution: 18.5 ml, 23.5 g, 162 mmol, 1.1 eq) was diluted with n-proh-h 2 O (4:9, 65 ml) and added to a stirred solution of 2,6-di-iso-propyl-4-iodoaniline 1 (44.6 g, 147 mmol) in n-proh (100 ml) at rt. A drop of HCO 2 H was added and the mixture was heated to 70 C for 1 h, during which time a yellow precipitate formed. H 2 O (50 ml) was added, the mixture allowed to cool to rt, and the solid collected by suction filtration. The residue was washed with ice-cold MeOH (50 ml) and dried in vacuo to give diimine S1 (25.0 g, 54%) as a yellow crystalline solid. The filtrate was evaporated to dryness and resubjected to the same reaction conditions to give a further portion of diimine S1 (10.9 g, 24%: total yield 79%): m.p C; 1 H NMR (CDCl 3, 400 MHz) δ 8.03 (s, 2H, H d ), 7.46 (s, 4H, H a ), 2.83 (sept, J sept = 6.7, 4H, H c ), 1.17 (d, J d = 6.9, 24H, H b ); 13 C NMR (CDCl 3, 100 MHz) δ 163.1, 147.6, 139.3, 132.5, 90.2, 28.0, 23.2; IR 2961, 2931, 2871, 1632, 1565, 1449, 1429, 1384, 1364, 1324, 1244, 1175; LRFAB-MS (3-NOBA matrix) m/z 629 [M + H] +, 585 [M + H C 3 H 8 ] + ; HRFAB-MS (3-NOBA matrix) m/z [M + H] + (calcd. for C 26 H 35 N 2 I 2, ). 1,3-Bis(2,6-diisopropyl-4-iodophenyl)imidazolium chloride (1b): Paraformaldehyde (1.5 g, 50 mmol) was dissolved with heating in a solution of HCl in dioxane (4 M, 15 ml) and added to a solution of diimine S1 (25.0 g, 41.4 mmol, 1 eq.) in THF (79 ml). The reaction mixture was stirred for 1 h during which time a white precipitate formed. The suspension was cooled to 26 C for 2 h and the precipitate collected by suction filtration, washed with cold Et 2 O and dried in vacuo to give imidazolium chloride 1b (15.8 g, 62%) as a white solid: m.p. 220 C (dec.); 1 H NMR (d 6 -DMSO, 400 MHz) δ (t, J t = 1.5, 1H, H e ), 8.55 (d, J d = 1.5, 2H, H d ), 7.87 (s, 4H, H a ), 2.24 (sept, J sept = 6.8, 4H, H c ), 1.23 (d, J d = 6.8, 12H, 12 of H b ), 1.13 (d, J d = 6.8, 12H, 12 of H b ); 13 C NMR (d 6 -DMSO, 100 MHz) δ 147.0, 133.5, 129.8, 126.1, 99.7, 28.5, 23.8, 22.7; IR 3155, 3133, 2869, 2837, 2760, 1567, 1530, 1463, 1366, 1326, 1266, 1204, 1070 cm 1 ; LRFAB-MS (3-NOBA matrix) m/z 641 [M + H] +, 515 [M + H I] + ; HRFAB-MS (3-NOBA matrix) m/z [M + H] + (calcd. for C 27 H 35 N 2 I 2, ). S3

4 2-(1-(Benzoyloxy)ethyl)-1,3-bis(2,6-diisopropylphenyl)-1H-imidazol-3-ium (4a): THF (3 ml) was added to a mixture of IPr HCl (1a) (100 mg, mmol) and t-buok (28.0 mg, mmol, 1.05 eq), and the slightly turbid colorless solution which formed was stirred for 10 min before addition of vinyl benzoate (39 μl, mmol, 1.2 eq.). The mixture immediately took on an orange color which became deep red over time. After 2.5 h HCl (2 M in Et 2 O, 0.25 ml, 0.5 mmol) was added and the solvent removed in vacuo to give a white solid. Chromatography (8% MeOH in CH 2 Cl 2 ) gave adduct 4a as a white solid (124 mg, 92%): m.p. 202 C (dec.); 1 H NMR (CDCl 3, 400 MHz) δ 8.65 (br s, 2H, H e ), 7.60 (t, J d = 7.8, 2H, H a ), (m, 1H, H j ), 7.38 (dd, J d = 7.8, 1.0, 2H, H h ), (m, 6H, H b and H i ), 6.18 (q, J q = 6.8, 1H, H g ), 2.94 (sept, J sept = 6.8, 2H, 2 of H d ), 2.34 (sept, J sept = 6.8, 2H, 2 of H d ), 1.29 (d, J d = 6.8, 3H, H f ), (m, 18H, 18 of H c ), 1.31 (d, J d = 6.8, 6H, 6 of H c ), 1.27 (d, J d = 6.8, 6H, 6 of H c ), 1.14 (d, J d = 6.8, 6H, 6 of H c ); 13 C NMR (CDCl 3, 100 MHz) δ 163.8, 145.0, 144.6, 142.7, 134.3, 132.2, 130.0, 129.7, 129.0, 128.4, 127.3, 125.2, 125.0, 62.7, 29.4, 29.3, 26.1, 26.1, 22.5, 22.3, 18.3; IR 1963, 2930, 2870, 1727, 1600, 1500, 1454, 1461, 1251, 1087, 1067 cm 1 ; LR-MS (ES +ve) m/z 537 [M] + ; HR-MS (ES +ve) m/z [M] + (calcd. for C 36 H 45 N 2 O 2, ). 2-(1-(Benzoyloxy)ethyl)-1,3-bis(2,6-diisopropyl-4-iodo-phenyl)-1H-imidazol-3- ium (4b): Following the procedure described for the synthesis of 4a with imidazolium 1b (151 mg, mmol) gave, after chromatography (8% MeOH in CH 2 Cl 2 ), adduct 4b as a pale yellow solid (147 mg, 77%): m.p. 179 C (dec.); 1 H NMR (CDCl 3, 400 MHz) δ 8.73 (bs, 2H, H d ), 7.74 (d, J d = 1.8, 2 of H a ), 7.62 (d, J d = 1.8, 2 of H a ), 7.62 (m, 1H, H i ), 7.42 (t, J t = 7.7, 2H, H h ), 7.29 (d, J d = 7.4, 2H, H g ), 6.21 (q, J q = 6.7, 1H, H f ), 2.34 (m, 2H, 2 of H c ), 2.22 (m, 2H, 2 of H c ), 1.36 (d, J d = 6.8, 3H, H e ), (m, 18H, 18 of H b ), 1.11 (d, J d = 6.7, 6H, 6 of H b ); 13 C NMR (CDCl 3, 100 MHz) δ 163.8, 147.0, 146.4, 143.4, 135.0, 134.7, 129.8, 129.7, 129.3, 128.8, 127.1, 99.5, 62.9, 29.6, 29.5, 26.2, 26.0, 22.2, 19.1; IR 1934, 291, 2902, 1721, 1566, 1499, 1453, 1325, 1262, 1086, 1069 cm 1 ; LR-MS (ES +ve) m/z 789 [M] + ; HR-MS (ES +ve) m/z [M] + (calcd. for C 36 H 43 I 2 N 2 O 2, ). Crystals suitable for single crystal X-ray diffraction were obtained by slow diffusion of a pentane into a solution of 1b in CH 2 Cl 2 : S4

5 Crystal data and structure refinement for 4b. Empirical formula C37 H45 Cl3 I2 N2 O2 Formula weight Temperature 93(2) K Wavelength Å Crystal system Orthorhombic Space group Pbca Unit cell dimensions a = (8) Å = 90. b = (7) Å = 90. c = (10) Å = 90. Volume (6) Å 3 Z 8 Density (calculated) Mg/m 3 Absorption coefficient mm -1 F(000) 3632 Crystal size x x mm 3 Theta range for data collection 2.51 to Index ranges -23<=h<=22, -20<=k<=20, -28<=l<=30 Reflections collected Independent reflections 7830 [R(int) = ] Completeness to theta = % Absorption correction Multiscan Max. and min. transmission and Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 7830 / 4 / 443 Goodness-of-fit on F Final R indices [I>2sigma(I)] R1 = , wr2 = R indices (all data) R1 = , wr2 = Largest diff. peak and hole and e.å -3 S5

6 2-(1-Acetoxy-1-ethyl)-1,3-bis(2,6-diisopropylphenyl)imidazolium chloride (11): Following the procedure described for the synthesis of adduct 4a with imidazolium 1a (100 mg, mmol) and vinyl acetate (26.0 μl, mmol) gave, after chromatography (8% MeOH in CH 2 Cl 2 ), adduct 11 as a tan solid (112 mg, 97%): m.p. 193 C (dec.); 1 H NMR (CDCl 3, 400 MHz) δ 8.59 (s, 2H, H e ), 7.59 (t, J t = 7.9, H a ), 7.33 (dd, J d = 8.1, 1.1, 2H, 2 of H b ), 7.31 (dd, J d = 8.0, 1.1, 2H, 2 of H b ), 5.77 (q, J q = 6.9, 1H, H g ), 2.27 (sept, J sept = 6.8, 2H, 2 of H d ), 2.22 (sept, J sept = 6.8, 2H, 2 of H d ), 1.77 (s, 3H, H h ), 1.25 (d, J d = 6.8, 6H, 6 of H c ), (m, 18H, 18 of H c ), 1.08 (d, J d = 6.9, 3H, H f ); 13 C NMR (CDCl 3, 100 MHz) δ 167.7, 144.9, 144.7, 142.2, 132.5, 129.3, 128.6, 124.9, 124.9, 61.2, 29.3, 29.2, 26.0, 25.7, 22.6, 22.0, 20.4, 17.1; IR 2964, 2930, 2871, 1755, 1498, 1369, 1329, 1218, 1063 cm 1 ; LR-MS (ES +ve) m/z 475 [M] +, 431 [M Ac] +, 11%, 389 (6%, [M- EtOAc + H] + ; HR-MS (ES +ve) m/z [M] + (calcd. for C 31 H 43 N 2 O 2, ). 3. Experiments in d 8 -THF In all cases a Wilmad NMR tube with J. Young valve was used under argon at rt and the reaction progress was monitored by 1 H NMR. A 0.5 M solution of t-buok in d 8 - THF was prepared under nitrogen in a volumetric flask where the base was initially dissolved by agitation with an ultrasound bath and diluted to the required concentration. The solution was then kept under nitrogen in a Schlenk tube. b a c d e N k O 3a 1-(1,3-bis(2,6-diisopropylphenyl)-1H-imidazol-2(3H)-ylidene)ethyl benzoate 3a: d 8 -THF (0.75 ml) was added to a mixture of compound 1a (20.1 mg, mmol, 1 eq) and t-buok (5.3 mg, mmol, 1 eq). The suspension was sonicated for 10 min to give a pale yellow, slightly turbid solution to which vinyl benzoate (6.5 μl, mmol, 1 eq) was added, and the mixture agitated with an ultrasound bath for 10 min to give a solution of adduct 3a which was not isolated, but characterized in situ using 1D and 2D NMR techniques: 1 H NMR (400 MHz, d 8 -THF) δ (m, 2H, H a and H n ), 7.25 (d, J d = 7.6, H b ), 7.21 (dd, J d = 8.0, 1.3, 2H, H l ), 7.11 (t, J d = 8.0, 2H, H m ), 6.92 (s, 3H, H i and H j ), 6.12 (d, J d = 2.5, 1H, H e ), 6.06 (d, J d = 2.5, 1H, H f ), 3.48 (sept, J sept = 6.9, 2H, H d ), 3.34 (sept, J sept = 6.9, 2H, H g ), 1.40 (d, J = 6.9 Hz, 6H, 6 of H c ), 1.32 (s, 3H, H k ), 1.26 (d, J = 6.9 Hz, 6 of H c )), 1.21 (d, J d = 6.9, 6 of H h ), 1.18 (d, J d = 6.9, 6 of H h ); 13 C NMR (100 MHz, d 8 -THF) δ 165.8, 149.5, 148.2, 139.2, f N O g h l i j m n S6

7 139.0, 137.7, 132.7, 131.8, 130.3, 129.8, 128.7, 128.3, 124.8, 124.3, 118.5, 117.0, 100.9, 29.6, 29.5, 25.3, 25.0, 23.5, 23.4, b a c d e N f N g h i j k O O 10 1-(1,3-Bis(2,6-diisopropylphenyl)-1H-imidazol-2(3H)-ylidene)ethyl acetate 10: d 8 - THF (0.75 ml) was added to a mixture of compound 1a (20.1 mg, mmol, 1 eq) and t-buok (5.3 mg, mmol, 1 eq). The suspension was agitated with an ultrasound bath for 10 min to give a pale yellow, slightly turbid solution to which vinyl acetate (4.4 μl, mmol, 1 eq) was added. The mixture tube was agitated with an ultrasound bath for 10 min to give a solution of adduct 10 which was not isolated, but characterized in situ using 1D and 2D NMR techniques: 1 H NMR (400 MHz, d 8 -THF) δ 7.32 (t, J t = 7.8, 1H, H a ), (m, 3H, H b and H j ), 7.16 (d, J d = 7.5, 2H, H i ), 6.05 (AB-q, J q = 2.5, 2H, H e and H f ), 3.4 (sept, J sept = 6.9, 2H, H d or H g ), 3.33 (sept, J sept = 6.9, 2H, H d or H g ), (m, 9H, H l and 6 of H c or H h ), 1.23 (d, J d = 6.9, 6H, 6 of H c or H h ), 1.19 (d, J d = 6.9, 6H, 6 of H c or H h ), 0.98 (s, 3H, H k ); 13 C NMR (100 MHz, d 8 -THF) δ , , , , , , , , , , , , , 30.47, 30.37, 25.56, 24.89, 23.47, 23.24, 19.84, Transesterification Procedures Stoichiometric Conditions d 8 -THF (0.75 ml) was added to a mixture of compound 1a (20.1 mg, mmol, 1 eq) and t-buok (5.3 mg, mmol, 1 eq). The mixture was agitated using an ultrasound bath for 10 min, then vinyl benzoate (6.5 μl, mmol, 1 eq) and EtOH (2.75 μl, mmol, 1 eq) were added and the mixture once again agitated briefly using an ultrasound bath. The reaction was followed using 1 H NMR. Catalytic Conditions d 8 -THF (0.75 ml) was added to compound 1 (7.5 μmol, 0.01 eq. followed by t-buok solution in d 8 -THF (0.50 M, 15 μl, 7.5 μmol). The mixture was agitated using an ultrasound bath for 10 min, then the vinyl ester (0.75 mmol, 1 eq) and EtOH (44 μl, 0.75 mmol, 1 eq) were added and the reaction mixture agitated briefly in an ultrasound bath. The reaction was followed using 1 H NMR. (1) Brboric, J. S.; Vladimirov, S.; Jovanovic, M. S.; Dogovic, N. Monats. Chem. 2004, 135, ; (2) Monnereau, C.; Blart, E.; Odobel, F. Tetrahedron Lett. 2005, 46, ; (3) Arduengo, A. J.; Krafczyk, R.; Schmutzler, R.; Craig, H. A.; Goerlich, J. R.; Marshall, W. J.; Unverzagt, M. Tetrahedron 1999, 55, ; (4) Scott, N. M.; Dorta, R.; Stevens, E. D.; Correa, A.; Cavallo, L.; Nolan, S. P. J. Am. Chem. Soc. 2005, 127, ; (5) Homer, J.; Perry, M. C. J. Chem. Soc., Perkin Trans , ; l S7

8 Figure S1: Stack Plot of Transesterification Experiments and Adduct 4a (400 MHz, d 8 -THF, 300 K) a b a d e N N 2a d` e` f` g` b` N N i` a` j` OBz 3a A HO O A` 3a+ 4a + Ph O HCl b`` a`` d`` e`` N N g`` OBz 4a a Partial 1 H NMR spectra (400 MHz, d 8 -THF, 300 K) of a) IPr, b) IPr + vinyl benzoate (adduct 3a), c) IPr + vinyl benzoate + EtOH after 3.5 h, d) adduct 4a. S8

9 5. NMR Spectra of Compounds: S1 1 H NMR (400 MHz, CDCl 3 ) S9

10 S1 13 C NMR (100 MHz, CDCl 3 ) S10

11 1b 1 H NMR (400 MHz, d 6 -DMSO) S11

12 1b 13 C NMR (100 MHz, d 6 -DMSO) S12

13 3a 1 H NMR (400 MHz, d 8 -THF) S13

14 3a COSY (d 8 -THF) S14

15 3a 13 C NMR (100 MHz, d 8 -THF) S15

16 3a HSQC (d 8 -THF) S16

17 3a HMBC (d 8 -THF) S17

18 3a NOESY (d 8 -THF) S18

19 4a 1 H NMR (400 MHz, CDCl 3 ) S19

20 4a COSY (CDCl 3 ) S20

21 4a 13 C NMR (100 MHz, CDCl 3 ) S21

22 4a HSQC (CDCl 3 ) S22

23 4b 1 H NMR (400 MHz, CDCl 3 ) S23

24 4b COSY (CDCl 3 ) S24

25 4b 13 C NMR (100 MHz, CDCl 3 ) S25

26 10 1 H NMR (400 MHz, d 8 -THF) S26

27 10 COSY (d 8 -THF) S27

28 10 13 C NMR (100 MHz, d 8 -THF) S28

29 10 HSQC (CDCl 3 ) S29

30 10 HMBC (CDCl 3 ) S30

31 11 1 H NMR (400 MHz, CDCl 3 ) S31

32 11 COSY (CDCl 3 ) S32

33 11 13 C NMR (100 MHz, CDCl 3 ) S33

34 11 HSQC (CDCl 3 ) S34

35 11 HMBC (CDCl 3 ) S35