Eur. J. Org. Chem. 2008 WILEY-VC Verlag Gmb & Co. KGaA, 69451 Weinheim, 2008 ISSN 1434 193X SUPPORTING INFORMATION Title: Enantio- and Diastereotopos Differentiation in the Palladium(II)-Catalyzed ydrosilylation of Bicyclo[2.2.1]alkene Scaffolds with licon-stereogenic lanes Author(s): Sebastian Rendler, Roland Fröhlich, Manfred Keller, Martin Oestreich* Ref. No.: O200800107
Contents 1 General Information S2 2 Synthesis of rac-8b S3 3 Copies of NMR Data for New Compounds S6 4 Copies of GLC and PLC Data for New Compounds S19 5 References and Footnotes S35
S2 1 General Information Reagents obtained from commercial suppliers were used without further purification unless otherwise noted. (phen)pdme 2, [S1] [(OEt 2 ) 2 ] + (BAr) 4, [S2] rac-2a and ( S)-2a, [S3] ( R)-[ 2 ]-2a, rac-2b and ( R)- 2b, [S4] 4, [S5] rac-8a, [S6] rac-9 [S7] were prepared according to known procedures. All reactions were performed in flame-dried glassware under a static pressure of argon. Liquids and solutions were transferred with syringes. Et 2 O and C 2 Cl 2 was dried by continuous distillation from Ca 2, TF was dried by continuous distillation from Potassium with bezophenone ketyl as an indicator prior to use. Melting points were determined using a Stuart Scientific SMP3 melting point apparatus (uncorrected values). Analytical thin-layer chromatography (TLC) was performed on silica gel SIL G-25 glass plates by Macherey-Nagel/Germany; for flash column chromatography silica gel 60 (40 63 μm, 230 400 mesh, ASTM) by Merck (Germany) and cyclohexane as a solvent were used. 1 and 13 C and 29 NMR spectra were recorded in CDCl 3 on Bruker AV300, Bruker AV 400, Varian INOVA 500 and Varian Unity plus 600 spectrometers. GLC analyses were performed using a Shimadzu GC-17A equipped with a SE-54 capillary column (30 m 0.32 mm, 0.25 µm, N 2 carrier gas, 250 C injection temperature, detector temperature 300 C; temperature program as indicated below). PLC analyses were performed with an Agilent 1200 instrument on a chiral stationary phase using a Daicel Chiralcel OD-R column (MeCN/ 2 O mixtures as solvent). Mass spectra were recorded with a Waters Micromass MAT 8200 GC-TOF (EI/RMS) instrument. IR spectra were recorded on a Varian 3100 FT-IR instrument equipped with a ATR unit. Optical rotations were measured in a 1 dm cuvette on a Perkin-Elmer 341 polarimeter. Elemental analyses were conducted on a Vario EL III instrument from Elementaranalysensysteme Gmb, anau (Germany). Analytical data for quaternary silanes rac- 7a, [S8] ( R)-7a, [S4] rac-7b and ( R)-7b, [S4] rac-11 [S9] were included in preliminary reports.
S3 2 Synthesis of rac-8b The cyclization precursors were prepared according to modified literature procedures: For dibromide 20 a four-step synthesis by Adamczyk [S10] was adapted for a larger scale (16 [S11] 20). The preparation of trichlorosilane 22 followed a slightly modified procedure reported earlier by Eaborn. [S12] Cyclization occurred cleanly under the conditions developed earlier by our group. [S3] Br Br KCN EtO/ 2 O Δ Br NC 16 17 KO 2 O 2 (cat.) EtO/ 2 O Δ 66% (2 steps) O 2 C Br 18 LiAl 4 Et 2 O Δ 89% O Br PBr 3 Br Br 100 C 79% 19 (46% from 16) 20 21 Cl i) Mg ii) Cl 4 Et 2 O Δ 44% Cl Cl 22 Cl i) Mg (activated) ii) LiAl 4 TF Δ 39% rac-8b Scheme S1. Synthesis of silaindane rac-8a. 2-(2-Bromophenyl)acetic acid (18): A 1-L three-necked flask equipped with reflux O 2 C condenser, a dropping funnel and a magnetic stirring bar was charged with a solution of Br KCN (76.0 g, 1.17 mol, 2.7 equiv.) in water (130 ml) and EtO (170 ml). After heating to reflux, a solution of dibromide 16 [S11] (108 g, 432 mmol, 1.00 equiv.) in EtO (130 18 ml) was added dropwise the stirred solution over a period of 30 min. After completion C 8 7 BrO 2 215.04 g/mol of the addition, reflux was maintained for a further 2.5 h. Subsequently, the cold reaction mixture was poured onto ice (400 ml), extracted with C 2 Cl 2 (4 150 ml), dried (Na 2 SO 4 ) and filtered. Evaporation of volatiles under reduced pressure furnished the crude nitrile 17 [S10] (70.6 g, 83%) as a yellowish oil, that was directly used in the following step without further purification. In a 1-L round-bottom flask equipped with reflux condenser and a magnetic stirring bar, a solution of nitrile 17 (70.6 g, 360 mmol, 1.00 equiv.) in EtO (400 ml) was treated with NaO (101 g, 1.80 mol, 5.00 equiv.) in water (200 ml) and 2 O 2 (2.5 ml, 30 wt.-% in water) and heated under reflux for 3 h. After cooling to room temperature, conc. Cl was added until p 2 was reached, and solid Na 2 SO 3 (5.0 g) was added to remove remaining peroxides. Extraction with ethyl acetate (3 200 ml), was followed by re-extraction of the organic phase with 10% NaO (3 100 ml). The aqueous phase was acidified with conc. Cl to p 2 and, again, extracted with ethyl acetate (3 200 ml). Subsequently,
S4 the organic phase was washed with brine (50 ml), dried (Na 2 SO 4 ) and filtered. Evaporation of volatiles in vacuo furnished the crude acid 18 (61.3 g, 66% over 2 steps) as a yellowish solid, which was sufficiently clean for the following step. The analytical data matched those reported in the literature. [S10] O Br 19 C 8 9 BrO 201.06 g/mol 2-(2-Bromophenyl)ethan-1-ol (19): A 1-L three-necked flask equipped with reflux condenser, a pressure-equalizing dropping funnel, an argon-inlet and a magnetic stirring bar was charged with LiAl 4 (16.2 g, 428 mmol, 1.50 equiv.) and suspended in Et 2 O (250 ml) at 0 C. At this temperature a solution of acid 18 (61.3 g, 285 mmol, 1.00 equiv.) was added dropwise to the stirred suspension over a period of 1.5 h. Subsequently, the reaction was to heated to reflux for 4 h. After cooling to room temperature, the reaction mixture was quenched at 0 C by careful addition of acetone (50 ml), water (400 ml) and finally, conc. Cl (100 ml) until p 4 was reached. The organic layer was separated and the aqueous phase was extracted with tert-butyl methyl ether (4 150 ml). The combined organic layers were washed with brine (100 ml), dried (Na 2 SO 4 ), filtered and volatiles were evaporated under reduced pressure. The crude primary alcohol 19 (51.0 g, 89%) was obtained as a yellowish oil, that was directly used in the following step. The analytical data matched those reported in the literature. [S10] Br Br 20 C 8 8 Br 2 263.96 g/mol 1-Bromo-2-(2-bromoethyl)benzene (20): A 250-mL round-bottom flask equipped with reflux condenser and a magnetic stirring bar was charged with alcohol 19 (51.0 g, 254 mmol, 1.00 equiv.). After careful addition of PBr 3 (17.9 ml, 51.6 g, 191 mmol, 0.750 equiv.) at 0 C over a period of 20 min, the mixture was heated to 100 C for 4 h. The mixture was then cooled to 0 C and carefully quenched with water (200 ml). Extraction with C 2 Cl 2 (4 100 ml), drying of the organic phase (Na 2 SO 4 ) and filtering, the volatiles were removed under reduced pressure. The crude product was distilled in vacuo (b.p. 108 C at 5 mbar) affording the dibromide 20 (52.8 g, 79%, 46% based on 16) as a colorless liquid. 1 NMR (300 Mz, CDCl 3 ): δ = 3.23 (t, J = 7.4 z, 2), 3.53 (t, J = 7.5 z, 2), 7.01 7.11 (m, 1), 7.16 7.25 (m, 2), 7.49 (d, J = 7.7 z, 1) ppm. The analytical data matched those reported in the literature. [S10] Cl Cl Cl Isopropyltrichlorosilane (22) [S11] : A 250-mL three-necked flask equipped with reflux condenser, a pressure-equalizing dropping funnel, an argon-inlet and a magnetic stirring bar was charged with magnesium turnings (11.6 g, 480 mmol, 1.20 equiv.). The 22 C 3 7 Cl 3 177.53 g/mol flask was subsequently flame dried in vacuo (3 times) with vigorous stirring, backfilled with argon and stirring was continued for 12 h. Addition of a small amount of 2- chloropropane (21) (3.7 ml, 3.1 g, 40 mmol, 0.10 equiv.) at room temperature initiated Grignard reagent formation upon which Et 2 O (60 ml) was added in one portion. To the stirred mixture, remaining 21 (32.9 ml, 28.3 g, 360 mmol, 0.900 equiv.) in Et 2 O (60 ml) was added dropwise over a period of 2 h. After complete addition, the reaction mixture was refluxed for a further 2 h.
S5 Another 500-mL three-necked flask equipped a reflux condenser, with pressure equalized dropping funnel, an argon-inlet and a magnetic stirring bar was charged with a solution of Cl 4 (107 ml, 158 g, 932 mmol, 2.33 equiv.) in Et 2 O (60 ml). The solution of the Grignard reagent was transferred into the dropping funnel and added dropwise to the reaction mixture while external heating to reflux was maintained. Subsequently, the reaction was stirred under reflux for a further 12 h under reflux. Then, approximately two thirds of total volume were distilled off at ambient pressure. Removal of the precipitated salts by filtration under inert gas atmosphere delivered a clear solution that was distilled at ambient pressure (b.p. 120 C) to give the trichlorosilane 22 (31.2 g, 44%) as a colorless liquid. 1 NMR (400 Mz, CDCl 3 ): δ = 1.20 (d, J = 7.4 z, 6), 1.54 (sept, J = 7.2 z, 1) ppm. 13 C NMR (100 Mz, CDCl 3 ): δ = 15.8, 22.8 ppm. The analytical data matched those reported in the literature. [S12] rac-8b C 11 16 rac-1-isopropyl-1-silaindane (rac-8b): A 1-L three-necked flask equipped with a reflux condenser, a 500-mL pressure-equalizing dropping funnel, an argon-inlet and a magnetic stirring bar was charged with magnesium turnings (16.8 g, 690 mmol, 10.0 equiv.). The flask was subsequently flame dried in vacuo (3 times) with vigorous stirring, backfilled with argon and stirring was continued for 12 h. Then, the 176.33 g/mol magnesium turnings were suspended in TF (100 ml) and a solution of 1,2- dibromoethane (6.05 ml, 13.0 g, 69.0 mmol, 1.00 equiv.) in TF (50 ml) was added dropwise. After complete addition, the mixture was heated to reflux and a solution of dibromide 20 (18.2 g, 69.0 mmol, 1.00 equiv.) and trichlorosilane 22 (12.2 g, 69.0 mmol, 1.00 equiv.) in TF (250 ml) was added slowly over a period of 4 h. The reaction mixture was maintained for a further 8 h at reflux. The resulting solution was transferred to another 1-L three-necked flask equipped with a reflux condenser, an argoninlet and a magnetic stirring bar, containing a suspension of LiAl 4 (4.71 g, 124 mmol, 1.80 equiv.) in TF (50 ml). eating at reflux for 4 h was followed by careful quenching of the resulting mixture at 0 C with acetone (50 ml), water (400 ml) and finally, conc. Cl (70 ml) until p 4 was reached. The organic layer was separated and the aqueous phase was extracted with tert-butyl methyl ether (4 120 ml). The combined organic layers were washed with brine (70 ml), dried (Na 2 SO 4 ), filtered and volatiles were evaporated under reduced pressure. The crude product was distilled in vacuo (b.p. 90 92 C at 14 mbar) affording the silane rac-8b (4.70 g, 39%) as a colorless liquid. R f = 0.72 (cyclohexane); GLC (SE-54; 40 C for 1 min, 10 C min 1, 280 C for 5 min): t R = 10.8 min; 1 NMR (500 Mz, CDCl 3 ): δ = 1.04 1.11 (m, 1), 1.12 1.15 (m, 6), 1.16 1.26 (m, 2), 3.16 (m c, 2), 4.55 (ddd, J = J = J = 3.0 z, 1), 7.23 (ddd, J = J = 7.3 z, J = 0.7 z, 1), 7.30 (d, J = 7.6 z, 1), 7.35 (ddd, J = J = 7.5 z, J = 1.4 z, 1), 7.65 (d, J = 7.1 z) ppm; 13 C NMR (125 Mz, CDCl 3 ): δ = 5.7, 12.3, 18.1, 18.2, 32.5, 125.6, 125.7, 129.6, 133.3, 135.3, 154.3 ppm; IR (ATR): ν ~ = 3056 (w), 2999 (w), 2940 (s), 2919 (s), 2890 (m), 2861 (s), 2108 (s) [ ], 1590 (w), 1549 (w), 1461 (m), 1441 (s), 1313 (w), 1119 (s), 1058 (w), 1004 (m), 908 (w), 880 (w), 805 (s), 772 (m), 741 (s), 719 (m), 663 (w). cm 1 ; RMS (EI): m/z: calcd for C 11 16 [M + ]: 176.1021, found: 176.0993; elemental analysis calcd (%) for C 11 16 (176.3): C 74.93,, 9.15; found: C 75.04, 9.27.
S6 3 Copies of NMR Data for New Compounds Table 1, Entry 5: rac-10a SR1091 Rendler/Oe 1 NMR (500 Mz) CDCl3 (7.26 ppm) rac-10a 10.43 3.01 0.06 1.00 0.06 0.06 3.00 1.00 1.00 1.00 ppm (t1) 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 SR840F1 Rendler/Oe 13C NMR (100 Mz) CDCl3 (77.10 ppm) 154.31 150.85 147.19 136.94 133.57 129.34 125.80 125.60 125.53 125.26 120.99 119.05 77.42 77.10 76.78 48.06 45.82 44.56 32.46 30.82 27.36 23.39 18.40 5.87 150 100 50 0
S7 SR1091 Rendler/Oe 29 {1} DEPT NMR (99.3 Mz) CDCl3 25.71 25.28 2552.54 2509.93 260025502500 z (t1) ppm (t1) 100 50 0-50 -100 Table 1, Entry 6: rac-10b SR1092 Rendler/Oe 1 NMR (600 Mz) CDCl3 (7.26 ppm) rac-10b 1.00 6.00 1.00 1.00 1.00 1.00 0.05 1.00 1.05 1.00 0.05 0.05 2.01 3.00 1.00 1.00 0.95 0.05 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0
S8 SR1092 Rendler/Oe 13C NMR (150 Mz) CDCl3 (77.10 ppm) 154.22 150.83 147.16 136.95 133.41 129.37 125.76 125.59 125.54 125.23 120.99 119.02 77.31 77.10 76.89 48.10 45.33 44.45 32.51 30.03 24.22 18.25 18.15 13.22 6.35 150 100 50 0 SR1092 Rendler/Oe 29 {1} DEPT NMR (99.3 Mz) CDCl3 23.69 23.23 2352.23 2306.35 23502300 z (f1) 100 50 0-50 -100
S9 Table 2, Entry 1: meso-13a (after flash chromatographical separation, contaminated with disiloxane) SR1100F3 Rendler/Oe 1 NMR (500 Mz) CDCl3 (7.26 ppm) meso-13a 24.00 1.51 2.48 1.00 1.00 4.00 ppm (t1) 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 SR1100F3 Rendler/Oe 13C NMR (125 Mz) CDCl3 (77.10 ppm) 150.07 135.55 132.81 128.60 128.43 124.83 77.35 77.10 76.85 41.35 37.99 37.30 35.99 34.02 31.87 27.72 26.04 23.90 18.52 7.93 ppm (t1) 150 100 50 0
S10 SR1100F3 Rendler/Oe 29{1} DEPT NMR (99.3 Mz) CDCl3-5.30-5.58-7.06-7.18-7.24 SR1100F3 Rendler/Oe 29{1} DEPT NMR (99.3 Mz) CDCl3 13.59 2.38-5.30-5.58-7.06-7.18-7.24 100 50 0-50 -100-3.0-4.0-5.0-6.0-7.0-8.0-9.0-10.0-11.0 Table 2, Entry 2: ( R, R)-13a SR1096 Rendler/Oe 1 NMR (500 Mz) CDCl3 (7.26 ppm) ( R, R)-13a 2 4.00 4.00 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0
S11 SR1096 Rendler/Oe 13C NMR (125 Mz) CDCl3 (77.10 ppm) 150.13 135.51 132.78 128.51 128.43 124.77 77.31 77.10 76.89 39.04 38.81 38.35 36.00 27.67 24.31 23.93 18.48 7.23 150 100 50 0 SR1096 Rendler/Oe 29{1} DEPT NMR (99.3 Mz) CDCl3-5.61-7.09 SR1096 Rendler/Oe 29{1} DEPT NMR (99.3 Mz) CDCl3 5.59 2.42-0.25-5.61-7.09 100 50 0-50 -100-3.0-4.0-5.0-6.0-7.0-8.0-9.0
S12 Table 2, Entry 3: ( S, S)-[ 2 2 ]-13a SR1097 Rendler/Oe 1 NMR (500 Mz) CDCl3 (7.26 ppm) D D ( S, S)-[ 2 2 ]-13a 2 4.00 ppm (t1) 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 SR1097 Rendler/Oe 13C NMR (125 Mz) CDCl3 (77.10 ppm) 150.13 135.52 132.79 128.52 128.43 124.77 77.35 77.10 76.85 38.80 38.73 38.65 38.50 38.31 36.01 27.67 24.17 23.93 18.48 ppm (t1) 150 100 50 0
S13 SR1097 Rendler/Oe 29{1} DEPT NMR (99.3 Mz) CDCl3-5.60 SR1097 Rendler/Oe 29{1} DEPT NMR (99.3 Mz) CDCl3-5.60 100 50 0-50 -100-2.0-3.0-4.0-5.0-6.0-7.0-8.0-9.0-10.0 Table 2, Entry 4: rac-13b & meso-13b (mixture of stereoisomers), SR1094 Rendler/Oe 1 NMR (500 Mz) CDCl3 (7.26 ppm) rac-13b meso-13b 2 4.00 0.41 1.18 0.41 4.00 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0
S14 SR1094 Rendler/Oe 13C NMR (125 Mz) CDCl3 (77.10 ppm) 149.93 149.85 135.06 135.00 132.95 132.91 128.54 128.48 125.00 124.95 77.31 77.10 76.89 40.39 38.56 37.76 37.58 37.49 37.45 35.90 32.97 32.71 25.82 23.62 23.59 18.42 18.34 18.15 18.05 13.02 12.92 7.63 7.26 150 100 50 0 SR1094 Rendler/Oe 29{1} DEPT NMR (99.3 Mz) CDCl3-7.07-8.51 100 50 0-50 -100
S15 Table 2, Entry 5: ( R, R)-13b SR1099 Rendler/Oe 1 NMR (500 Mz) CDCl3 (7.26 ppm) ( R, R)-13b 6.00 6.00 10.00 4.00 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 SR1099 Rendler/Oe 13C NMR (125 Mz) CDCl3 (77.10 ppm) 149.93 135.00 132.91 128.49 124.95 77.35 77.10 76.85 38.56 37.76 37.59 35.90 25.84 23.62 18.34 18.05 12.93 7.27 150 100 50 0
S16 SR1099 Rendler/Oe 29{1} DEPT NMR (99.3 Mz) CDCl3-7.07 100 50 0-50 -100 Table 2, Entry 6: rac-14a & meso-14a (mixture of stereoisomers) SR1095 Rendler/Oe 1 NMR (500 Mz) CDCl3 (7.26 ppm) rac-14a meso-14a 1.22 0.78 2 1.22 0.78 4.00 0.39 1.22 0.39 4.00 2.08 ppm (t1) 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0
S17 SR1095 Rendler/Oe 13C NMR (125 Mz) CDCl3 (77.10 ppm) 154.35 154.23 137.17 137.04 133.47 133.40 129.07 125.61 125.58 125.31 125.22 77.35 77.10 76.85 41.49 39.48 38.07 37.96 37.61 37.40 33.27 32.54 32.43 31.07 27.47 27.44 24.51 18.37 18.35 5.72 5.59 ppm (t1) 150 100 50 0 SR1095 Rendler/Oe 29{1} DEPT NMR (99.3 Mz) CDCl3 24.27 22.90 18.95 100 50 0-50 -100
S18 1-Isopropyl-1-silaindane (rac-8b) SR855 Rendler (1 NMR 500 Mz) CDCl3 = 7.26 ppm rac-8b 9.41 0.99 1.01 1.00 1.00 0.99 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 SR855 Rendler (13C NMR 125 Mz) CDCl3=77.1 ppm 154.32 135.31 133.34 129.63 125.74 125.67 77.35 77.10 76.85 32.52 18.22 18.06 12.30 5.68 150 100 50 0
S19 4 Copies of GLC and PLC Data for New Compounds Table 1, Entry 5: GLC
S20 Table 1, Entry 6: GLC
S21 Table 2, Entry 1: GLC (crude product before work-up)
S22 Table 2, Entry 1: GLC (after separation by flash chromatography: only meso-13a)
S23 Table 2, Entry 1: PLC (after purification by flash chromatography without separation of rac-13a and meso-13a)
S24 Table 2, Entry 1: PLC (after purification by flash chromatography with separation: only rac-13a)
S25 Table 2, Entry 1: PLC (after purification by flash chromatography with separation: only meso-13a)
S26 Table 2, Entry 2: GLC (crude product before work-up)
S27 Table 2, Entry 2: PLC (after purification by flash chromatography: only ( S, S)-13a)
S28 Table 2, Entry 3: GLC (crude product before work-up)
S29 Table 2, Entry 3: PLC (after purification by flash chromatography: only ( R, R)-[ 2 2 ]-13a)
S30 Table 2, Entry 4: GLC (crude product before work-up)
S31 Table 2, Entry 4: PLC (after purification by flash chromatography: rac-13b and meso-13b)
S32 Table 2, Entry 5: GLC (crude product before work-up)
S33 Table 2, Entry 5: PLC (after purification by flash chromatography: ( R, R)-13b)
S34 Table 2, Entry 6: GLC (crude product before work-up)
S35 5 References and Footnotes [S1] a) P. K. Byers, A. J. Canty, Organometallics 1990, 9, 210 220; b) W. de Graf, J. Boersma, A. L. Spek, G. van Koten, Organometallics 1989, 8, 2907 2917. [S2] a) M. Brookhart, B. Grant, A. F. Volpe Jr., Organometallics 1992, 11, 3920 3922; b) N. A. Yakelis, R. G. Bergman, Organometallics 2006, 24, 3579 3581. [S3] S. Rendler, G. Auer, M. Keller, M. Oestreich, Adv. Synth. Catal. 2006, 348, 1171 1182. [S4] S. Rendler, M. Oestreich, C. P. Butts, G. C. Lloyd-Jones, J. Am. Chem. Soc. 2007, 129, 502 503. [S5] G. Wittig, E. Knauss, Chem. Ber. 1958, 91, 895 907. [S6] O. Plefka, Diplomarbeit, Albert-Ludwigs-Universität, Freiburg (Germany), 2006; b) S. Rendler, O. Plefka, B. Karatas, G. Auer, R. Fröhlich, S. Grimme, M. Oestreich, Chem. Eur. J. 2008, 14, manuscript in preparation. [S7] a) G. L. Larson, E. Torres, J. Organomet. Chem. 1985, 293, 19 27; b) Isolation of intermediate chlorosilane was found to give superior yields: R. Tacke, K. Fritsche, A. Tafel, F. Wuttke, J. Organomet. Chem. 1990, 388, 47 55. [S8] M. Oestreich, S. Rendler, Angew. Chem. 2005, 117, 1688 1691; Angew. Chem. Int. Ed. 2005, 44, 1661 1664. [S9] S. Rendler, M. Oestreich, Beilstein J. Org. Chem. 2007, 3, 9. [S10] M. Adamczyk, D. S. Watt, D. S. Netzel, J. Org. Chem. 1984, 49, 4226 4237. [S11] M. Oestreich, U. K. Schmid, G. Auer, M. Keller, Synthesis 2003, 2725 2739 [S12] M. A. Cook, C. Eaborn, D. R. M. Walton, J. Organomet. Chem. 1971, 29, 389 396.