Chiral N-Heterocyclic Carbene Gold Complexes: Synthesis, Properties and Application in Asymmetric Catalysis

Transcription

1 Chiral -Heterocyclic Carbene Gold Complexes: Synthesis, Properties and Application in Asymmetric Catalysis Dipshikha Banerjee, Andrea K. Buzas, Céline Besnard, and E. Peter Kündig* Index 1. General Synthesis of HC-gold complexes MR spectra of HC gold(i) complexes General method for the methoxycyclization of 1,6-enynes... 13

2 1. General Experiments were carried out under nitrogen atmosphere using standard Schlenk techniques. Solvents were dried with a Solvtek system (filtration over alumina). Methanol was dried over magnesium. All commercially available compounds were used as received. Deuterated solvents: from Cambridge Isotope Laboratories. MR spectra: Bruker AMX 500 and AMX 400 spectrometers at ambient probe temperature. IR spectra: Perkin-Elmer Spectrum One spectrometer. Melting points: Büchi 510 apparatus. [α] D values were recorded on a Perkin- Elmer 241 polarimeter using a quartz cell (l = 10 cm) and a a high-pressure lamp (λ = 589 nm). 2. Synthesis of HC-gold chloride complexes iii General method: To a solution of the imidazolium iodide (0.1 mmol, 1 equiv.) in CH 2 2 (3 ml), Ag 2 O (0.05 mmol, 0.5 equiv.) was added and the mixture was stirred at r.t. in the absence of light. The suspension became clear i.e. no more solid Ag 2 O was observed after stirring for 5-6h. Then a solution of [()(SMe 2 )] (0.1 mmol, 1 equiv.) in CH 2 2 (1 ml) was added drop wise. The resulted reaction mixture was stirred overnight, and then the solution was filtered through a short pad of celite and washed with CH 2 2. The filtrate was partially evaporated and addition of excess pentane to that resulted in the precipitation of the complexes as off white or yellow solids.

3 3. MR spectra of HC gold(i) chloride complexes Gold(I)(1,3-bis((S)-2,2-dimethyl-1-o-tolylpropyl)imidazolidin-2-ylidene) chloride (10) (S,S) 10 (S,S) 10

4 Gold(I)(1,3-bis((S)-2,2-dimethyl-1-o-tolylpropyl)-1H-imidazol-2(3H)-ylidene) chloride (11) (S,S) 11 (S,S) 11

5 Gold(I)(1,3-bis((R)-1-(2-methoxyphenyl)-2,2-dimethylpropyl)imidazolidin-2-ylidene) chloride (12) (R,R) 12 (R,R) 12

6 Gold(I)(1,3-bis((S)-1-(2-methoxyphenyl)-2,2-dimethylpropyl)-1H-imidazol-2(3H)- ylidene) chloride (13)

7 Gold(I)(1,3-bis((R)-1-(2-methoxyphenyl)-2-methylpropyl)imidazolidin-2-ylidene) chloride (14) (R,R) 14 (R,R) 14

8 Gold(I)(1,3-bis((R)-2,2-dimethyl-1-(naphthalen-2-yl)propyl)-1H-imidazol-2(3H)-ylidene) chloride (15)

9 Gold(I)(1,3-bis((S)-2,2-dimethyl-1-(naphthalen-1-yl)propyl)-1H-imidazol-2(3H)-ylidene) chloride (16)

10 Gold(I)(1,3-bis((R)-1-(4-methoxybiphenyl-3-yl)-2,2-dimethylpropyl)imidazolidin-2- ylidene) chloride (17) Ph Ph (R,R) 17 Ph Ph (R,R) 17

11 Gold(I)(1,3-bis((R)-1-(4-methoxybiphenyl-3-yl)-2,2-dimethylpropyl)-2,3-dihydro-1Himidazol-2-yl) chloride (18) Ph Ph (R,R) 18 Ph Ph (R,R) 18

12 MR spectra of Gold(I)(1,3-bis((R)-1-(2-methoxyphenyl)-2,2- dimethylpropyl)imidazolidin-2-ylidene) (1,1,1-trifluoro-- (trifluoromethylsulfonyl)methylsulfonamido) (19)

13 4. General method for the methoxycyclization of 1,6-enyne To a solution of the corresponding HC complex (0.05 equiv.) in CH 2 2 (2 ml), AgTf 2 (0.05 equiv.) was added and the mixture was stirred for 15 minutes at RT in the absence of light. H (5 equiv.) was added, followed by the addition of the substrate 1,6- enyne 20 (1 equiv.) and the mixture was stirred at r.t. for the time indicated in Table 4. After the reaction was finished the mixture was filtered over a plug of celite, washed with CH 2 2 and the solvents were removed under vacuum. The crude material was purified by f.c. on silica gel using cyclohexane/acoet (80/20 to 70/30) as eluent to give 21; spectroscopic analyses were in agreement with a previous literature report. iii 1 H MR (400 MHz, CD 3 ): δ (m, 4H), (m, 2H), (m, 2H), (m, 2H), (m, 4H), (m, 1H), 6.41 (s, 1H), 3.77 (dd, J = 8.2, 6.6 Hz, 1H), 3.69 (ddd, J = 15.9, 3.0, 1.8 Hz, 1H), 2.94 (s, 3H), 2.89 (d, J = 6.2 Hz, 1H), 2.82 (dd, J = 8.8, 1.5 Hz, 1H), 2.53 (d, J = 15.7 Hz, 1H), 0.89 (s, 3H), 0.80 (s, 3H). PhO 2 S PhO 2 S Ph Cat. HC (5 mol%) AgTf 2 (5 mol%) H (5 equiv.) CH 2 2, RT PhO 2 S PhO 2 S 20 (-) 21 Ph HPLC result obtained by using complex 18 is shown below. [Chiracel AS-H column, n- hexane/i-proh = 90:10, 1mL/min, 254 nm, t R = (major) and (minor)]

14 i Hu, X. L.; Castro-Rodriguez, I.; Olsen, K.; Meyer, K. Organometallics 2004, 23, ii de Fremont, P.; Scott,. M.; Stevens, E. D.; Ramnial, T.; Lightbody, O. C.; Macdonald, C. L. B.; yburne, J. A. C.; Abernethy, C. D.; olan, S. P. Organometallics 2005, 24, iii Mendez, M.; Munoz, M. P.; evado, C.; Cardenas, D. J.; Echavarren, A. M. J. Am. Chem. Soc. 2001, 123,