Intramolekulare konzertierte Insertion von Vinylkationen in C H-Bindungen:

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1 Intramolekulare konzertierte Insertion von Vinylkationen in C H-Bindungen: Cyclisierende Hydroalkylierung von Alkinen mit Chlorameisensäurealkylestern zu Cyclopentanen** Ursula Biermann, Rainer Koch und Jürgen O. Metzger* Supporting Information. Experimental Section All reactions were performed under nitrogen. Solvents were dried and distilled according to standard procedures. 4-Octyne (2a), 5-decyne (2b), 3-hexyne (2c), and 1-octyne (2d) were obtained from Aldrich and used as received. Et 3 Al 2 Cl 3 was purchased from Crompton GmbH and isopropyl (1a) and 2-butyl chloroformate (1b) were obtained from BASF and Laxness, respectively. Analytical GC was performed on a Carlo Erba GC series 4160 with a FID detector and fused silica capillary column DB1, 29m. Tetradecane (Aldrich) was used as internal standard for quantitative GC-analyses of cyclopentanes 9 and H and 13 C NMR spectra were recorded in CDCl 3 on a Bruker AM 300 or Bruker AM 500 spectrometer at 20 C using TMS ( 1 H NMR) and CDCl 3 (δ = 77.0 ppm, 13 C NMR) as internal standard. Mass spectra were recorded on a Finnigan MAT 95. Unsaturated hydroalkylation products 4 were identified and separated by addition of bromine. Reaction of 4-octyne (2a) and isopropyl chloroformate (1a): A mixture of 4-octyne (2a, 1.1g, 10mmol) and of isopropyl chloroformate (1a, 1.2g, 10mmol) in CH 2 Cl 2 (10 ml) was stirred in a N 2 atmosphere (1 bar) for 5 min at 15 C. Then a mixture of triethylsilane (1.16g, 10mmol) and Et 3 Al 2 Cl 3 (2.48 g, 10mmol) was added dropwise over 1h at 15 C and the solution was stirred at room temperature for a further 1h. Diethyl ether 1

2 (100 ml), H 2 O (40 ml), and 10% HCl to dissolve precipitated aluminum salts were then added. The organic phase was separated and washed with H 2 O (3 x 30 ml). The combined extracts were dried over Na 2 SO 4, the solvent was removed in vacuo and the residue filtrated over silica gel 60 with pentane (150 ml) to remove triethylsilyl derivatives. Purification of the crude product by Kugelrohr distillation (16mbar, 100 C) gave 1.21g (79%) of 1- isopropyl-2-propylcyclopentane (5a) as a mixture of two diastereomers (ratio: 4.6 : 1).- 13 C NMR (125.8 MHz), main product: δ = (prim.), (prim.), (sec.), 23.0 (prim.), (sec.), (sec.), (tert.), (sec.), (sec.), (tert.), (tert.); minor product: δ = (prim.), (prim.), (sec.), (prim.), (sec.), (sec.), (tert.), 30.0 (sec.), (sec.), (tert.), (tert.).- GC/MS (EI), main product: m/z (%) 154 (7) [M + ], 139 (3), 126 (2), 112 (5), 111 (66), 110 (35), 84 (4), 83 (6), 70 (11), 69 (100), 55 (40), 41 (32); minor product: m/z (%) 154 (6) [M + ], 139 (2), 126 (3), 112 (7), 111 (73), 110 (31), 84 (7), 83 (10), 70 (15), 69 (100), 55 (41), 41 (32)..- HR-MS (EI) C 11 H 22 calcd ; found Comparison of the mass spectra with mass spectra of 1,2-dipropylcyclopentane 1 give evidence that the major product should be trans-5a and the minor product cis-5a. Reaction of 5-decyne (2b) and isopropyl chloroformate (1a): A mixture of 5-decyne (2b, 1.38g, 10mmol) and of isopropyl chloroformate (1a, 1.2g, 10mmol) in CH 2 Cl 2 (10 ml) was stirred in a N 2 atmosphere (1 bar) for 5 min at 15 C. Then a mixture of triethylsilane (1.16g, 10mmol) and Et 3 Al 2 Cl 3 (2.48 g, 10mmol) was added dropwise over 1h at 15 C and the solution was stirred at room temperature for a further 1h. Diethyl ether (100 ml), H 2 O (40 ml), and 10% HCl to dissolve precipitated aluminum salts were then added. The organic phase was separated and washed with H 2 O (3 x 30 ml). The combined extracts were dried over Na 2 SO 4, the solvent was removed in vacuo and the residue was dissolved in pentane and filtrated over silica gel 60 to remove triethylsilyl derivatives. 2

3 Purification of the crude product by Kugelrohr distillation (16mbar, 85 C) gave 1.35g (74%) of 2-butyl-1-isopropyl-3-methylcyclopentane (5b) as a mixture of four diastereomers (ratio: a) : b) : c) : d) = 11 : 1: 6: 1).- 13 C NMR (125.8 MHz), main diastereomer: δ = 14.16, 18.52, 22.26, 23.14, 23.66, 26.37, 30.08, (tert.), (sec.), (sec.), (tert.), (tert.), (tert).- GC/MS (EI), main diastereomer a): m/z (%) 182 (6)[M + ], 140 (6), 139 (39), 138 (47), 126 (5), 125 (7),112 (6), 111 (5), 98 (8), 97 (46), 96 (8), 84 (14), 83 (100), 70 (17), 69 (73), 56 (24), 55 (56), 41 (35); diastereomer b): m/z (%) 182 (4)[M + ], 140 (7), 139 (31), 138 (28), 126 (8), 125 (28), 112 (6), 111 (5), 98 (9), 97 (39), 96 (5), 84 (19), 83 (98), 70 (26), 69 (100), 56 (37), 55 (52), 41 (32); diastereomer c): m/z (%) 182 (12) [M + ], 140 (6), 139 (32), 138 (30), 126 (10), 125 (18), 112 (14), 111 (6), 98 (10), 97 (48), 96 (8), 84 (20), 83 (100), 70 (23), 69 (92), 56 (42), 55 (64), 41 (42); diastereomer d): m/z (%) 182 (9)[M + ], 140 (8), 139 (38), 138 (25), 126 (10), 125 (9), 112 (16), 111 (6), 98 (11), 97 (49), 96 (7), 84 (28), 83 (100), 70 (35), 69 (97), 56 (69), 55 (82), 41 (63)..- HR-MS (EI) C 13 H 26 calcd ; found Comparison of the mass spectra of the diastereomers of 5b with the mass spectra of authentic diastereomers of 1-ethyl-2,3-dimethylcyclopentane and 2-ethyl-1,3-dimethylcyclopentane 2 give evidence that the major diastereomer should be trans, trans-5b. Reaction of 3-hexyne (2c) and isopropyl chloroformate (1a): A mixture of 3-hexyne (2c, 0.82g, 10mmol) and of isopropyl chloroformate (1a, 1.2g, 10mmol) in CH 2 Cl 2 (10 ml) was stirred in a N 2 atmosphere (1 bar) for 5 min at 15 C. Then a mixture of triethylsilane (1.16g, 10mmol) and Et 3 Al 2 Cl 3 (2.48 g, 10mmol) was added dropwise over 1h at 15 C and the solution was stirred at room temperature for a further 30min. with occasionally cooling (-10 C). Diethyl ether (100 ml), H 2 O (40 ml), and 10% HCl to dissolve precipitated aluminum salts were then added. The organic phase was separated and washed with H 2 O (3 x 30 ml). The combined extracts were dried over Na 2 SO 4, 3

4 the solvent was removed in vacuo and the residue was dissolved in pentane and filtrated over silica gel 60 to remove triethylsilyl derivatives. Purification of the crude product by Kugelrohr distillation (17mbar, 65 C) gave 0.61g (38%) of 3-chloro-4-isopropyl-3-hexene (6c) as a mixture of the [E]- and [Z]-stereoisomer (3 : 1).- HR-MS (EI) C 9 H 17 Cl calcd ; found Reaction of 1-octyne (2d) and isopropyl chloroformate (1a): A mixture of 1-octyne (2d, 0.55g, 5mmol) and of isopropyl chloroformate (1a, 0.61g, 5mmol) in CH 2 Cl 2 (10 ml) was stirred in a N 2 atmosphere (1 bar) for 5 min at 15 C. Then Et 3 Al 2 Cl 3 (1.86g, 7.5mmol) was added dropwise over 1h at 15 C and the solution was stirred at room temperature for a further 30min with occasionally cooling (-5 C). Diethyl ether (100 ml), H 2 O (40 ml), and 10% HCl to dissolve precipitated aluminum salts were then added. The organic phase was separated and washed with H 2 O (3 x 30 ml). The combined extracts were dried over Na 2 SO 4, the solvent was removed in vacuo and the residue was dissolved in pentane and filtrated over silica gel 60 to remove triethylsilyl derivatives. Purification of the crude product by Kugelrohr distillation (4mbar, 85 C) gave 0.33g (35%) of 4-chloro-2- methyl-3-decene (6d) as a mixture of the [E]- and [Z]-stereoisomer (1 : 1).- HR-MS (EI) C 11 H 21 Cl calcd ; found Reaction of 4-octyne (2a) and 2-butyl chloroformate (1b): A mixture of 4-octyne (2a, 1.1g, 10mmol) and of 2-butyl chloroformate (1b, 1.36g, 10mmol) in CH 2 Cl 2 (10 ml) was stirred in a N 2 atmosphere (1 bar) for 5 min at 15 C. Then a mixture of triethylsilane (1.16g, 10mmol) and Et 3 Al 2 Cl 3 (2.48 g, 10mmol) was added dropwise over 1h at 15 C and the solution was stirred at room temperature for a further 1h. Diethyl ether (100 ml), H 2 O (40 ml), and 10% HCl to dissolve precipitated aluminum salts were then added. The organic phase was separated and washed with H 2 O (3 x 30 ml). The combined 4

5 extracts were dried over Na 2 SO 4, the solvent was removed in vacuo and the residue filtrated over silica gel 60 with pentane (150 ml) to remove triethylsilyl derivatives. Purification of the crude product by Kugelrohr distillation (16mbar, 100 C) gave 0.88g (52 %) of a mixture of 1-methyl-2,3-dipropylcyclopentane (9a) and 1-sec.butyl-2-propylcyclopentane (10a) in a ratio of 1 : 3. 9a and 10a, respectively, was formed as a mixture of 4 diastereomers. GC/MS (EI), main diastereomer of 9a: m/z (%)168 (23)[M + ], 126 (32), 125 (54), 112 (15), 111 (16), 98 (18), 97 (15), 84 (57), 83 (57), 70 (40), 69 (100), 56 (57), 55 (65), 41 (34); main diastereomer of 10a: m/z (%)168 (4) [M + ], 126 (0.5), 125 (4); 139 (24), 111 (58), 110 (38), 98 (3), 97 (17), 84 (6), 83 (46), 70 (25), 69 (100), 56 (15), 55 (52), 41 (30). Reaction of 3-hexyne (2c) and 2-butyl chloroformate (1b): A mixture of 3-hexyne (2c, 0.41g, 5mmol), tetradecane (0.4g, 2mmol) and 2-butyl chloroformate (1b, 0.68g, 5mmol) in CH 2 Cl 2 (10 ml) was stirred in a N 2 atmosphere (1 bar) for 5 min at 15 C. Then a mixture of triethylsilane (0.58g, 5mmol) and Et 3 Al 2 Cl 3 (1.24g, 5mmol) was added dropwise over 1h at 15 C and the solution was stirred at room temperature for a further 1h with occasionally cooling (-5 C). Diethyl ether (100 ml), H 2 O (40 ml), and 10% HCl to dissolve precipitated aluminum salts were then added. The organic phase was separated and washed with H 2 O (3 x 30 ml). The combined extracts were dried over Na 2 SO 4, the solvent was removed in vacuo and the residue was dissolved in pentane and filtrated over silica gel 60 to remove triethylsilyl derivatives. Quantitative analysis was performed by GC, based on tetradecane as internal standard, giving as main product 1,2- diethyl-3-methylcyclopentane (9c) as a mixture of four diastereomers (ratio: 3.8:1.9:1.4:1) in a yield of 0.18g (26 %).- GC/MS (EI), main diastereomer a): m/z (%) 140 (15) [M + ], 112 (10), 111 (75), 98 (22), 84 (33), 70 (50), 69 (100), 56 (32), 55 (71), 41 (46); diastereomer b): m/z (%) 140 (6) [M + ], 112 (5), 111 (41), 98 (25), 84 (22), 70 (65), 69 (100), 56 (40), 55 (89), 41 (73); diastereomer c): m/z (%) 140 (12) [M + ], 112 (9), 111 (66), 98 (25), 84 (56), 70 (43), 5

6 69 (100), 56 (54), 55 (73), 41 (46); diastereomer d): m/z (%) 140 (7) [M + ], 112 (6), 111 (25), 98 (35), 84 (52), 70 (69), 69 (98), 56 (86), 55 (100), 41 (89). Comparison of the mass spectra of the diastereomers of 9c with the mass spectra of authentic diastereomers of 1-ethyl-2,3-dimethylcyclopentane and 2-ethyl-1,3-dimethylcyclopentane [2] give evidence that the major diastereomer should be trans, trans-9c and the less diastereomer cis, cis-9c. Reaction of 1-octyne (2d) and 2-butyl chloroformate (1b): A mixture of 1-octyne (2d, 1.1g, 10mmol), tetradecane (0.99g, 5mmol) and 2-butyl chloroformate (1b, 1.36g, 10mmol) in CH 2 Cl 2 (10 ml) was stirred in a N 2 atmosphere (1 bar) for 5 min at 15 C. Then a mixture of triethylsilane (1.16g, 10mmol) and Et 3 Al 2 Cl 3 (2.48 g, 10mmol) was added dropwise over 1h at 15 C and the solution was stirred at +10 C for a further 1h. Diethyl ether (100 ml), H 2 O (40 ml), and 10% HCl to dissolve precipitated aluminum salts were then added. The organic phase was separated and washed with H 2 O (3 x 30 ml). The combined extracts were dried over Na 2 SO 4, the solvent was removed in vacuo and the residue was dissolved in pentane and filtrated over silica gel 60 to remove triethylsilyl derivatives. Quantitative analysis was performed by GC, based on tetradecane as internal standard, giving as main product 1-hexyl-3-methylcyclopentane (9d) in a yield of 0.22g (13%). 9d was obtained as a mixture of two diastereomers which could not be separated by GC.- GC/MS (EI), m/z (%) 168 (12)[M + ], 140 (22), 139 (10), 112 (9), 111 (11), 98 (10), 97 (38), 83 (100), 82 (49), 70 (37), 69 (31), 56 (37), 55 (69), 41 (30). Mass spectra give evidence of the formation of 9d by comparison with literature data. However, the mass spectra of cis- and trans-isomers are most similar and could not be differentiated. [1] 6

7 Table S1: Energies of calculated structures. MP2/6-31G(d) MP2/6-311+G(d,p) SP MP2/6-31G(d) MP2 SP + ZVPE Absolute energies ZPVE ZPVE scaled Rel. energies a.u. kcal/mol kj/mol 2-Propylcation Octyne 2a Reactants Vinyl cation 3a TS Cyclopentyl cation 7a Vinyl cation 3e TS endo TS exo Cyclopentyl cation 7e Cyclopentyl cation H 7e 3e 11 Scheme S1: Model reaction of vinyl cation 3e via the endo- (top) and exocyclic (bottom) pathways to give cyclopentyl cation 7e and 11, respectively. H 7

8 Figure S1: Model transition structure for the formation of the exocyclic cyclopentyl cation 11. Carbon atoms 2 and 3 are situated above the plane formed by carbon atoms 1, 4, 5 and the transferred hydrogen atom. The angle between C 1, H, C 5 is

9 Cartesian coordinates of MP2/6-31G(d)-optimized structures Vinyl cation 3a C C C C C C C C C C C H H H H H H H H H H H H H H H H H H H H H

10 TS concerted of the formation of cyclopentyl cation 7a (see Figure 1 of the main text) C C C C C C C C C C C H H H H H H H H H H H H H H H H H H H H H

11 Cyclopentyl cation 7a C C C C C C C C C C C H H H H H H H H H H H H H H H H H H H H H

12 TS formation of endocyclic cyclopentyl cation 7e C C C C C C C C C C C C H H H H H H H H H H H H H H H H H H H H H H H

13 TS formation of exocyclic cyclopentyl cation 11 C C C C C C C C C C C C H H H H H H H H H H H H H H H H H H H H H H H

14 Endocyclic cyclopentyl cation 7e C C C C C C C C C C C C H H H H H H H H H H H H H H H H H H H H H H H

15 Exocyclic cyclopentyl cation 11 C C C C C C C C H H H H H H H H H H H C H H H C H H C C H H H H H H H L. S. Golovkina, G. V. Rusinova, A. A. Petrov, Izvestiya Akad. Nauk, Seriya Khimicheskaya 1979, 68-73; engl. 1979, L. S. Golovkina, G. V. Rusinova, A. A. Petrov, Izvestiya Akad. Nauk, Seriya Khimicheskaya 1979, 73-80; engl. 1979,