Article Cite This: J. Org. Chem. 2017, 82, 13414−13422
pubs.acs.org/joc
Conformational Preferences of the Phenyl Group in 1‑Phenyl-1-X-1silacyclo-hexanes (X = MeO, HO) and 3‑Phenyl-3-X-3silatetrahydropyrans (X = HO, H) by Low Temperature 13C NMR Spectroscopy and Theoretical Calculations Bagrat A. Shainyan,*,† Svetlana V. Kirpichenko,† and Erich Kleinpeter‡ †
A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Division of the Russian Academy of Sciences, 1 Favorsky Street, 664033 Irkutsk, Russian Federation ‡ Chemisches Institut der Universität Potsdam, Karl-Liebknecht-Str. 24-25, D-14476 Potsdam (Golm), Germany S Supporting Information *
ABSTRACT: New Si-phenyl-substituted silacyclohexanes and 3silatetrahydropyrans have been synthesized and studied with respect to the conformational equilibria of the heterosixmembered ring by low temperature 13C NMR spectroscopy and quantum chemical calculations. For 1-methoxy-1-phenylsilacyclohexane 1 and 3-phenyl-3-silatetrahydropyran 4 the conformational equilibria could be frozen and assigned. The Phax ⇆ Pheq equilibrium constants at 103 K are 2.21 for 1 and 4.59 for 4. In complete agreement with former studies of similar silicon compounds, molecules 1 and 4 prefer to adopt the Pheq conformation. The conformational equilibria of 1-hydroxy-1phenylsilacyclohexane 2 and 3-hydroxy-3-phenyl-3-silatetrahydropyran 3 could not be frozen at 100 K and proved to be heavily one-sided (if not anancomeric). Obviously, there is a general trend of predominance of Phax conformer in the gas phase and of Pheq in solution. For the isolated molecules of silanols 2 and 3, calculations allowed to explain the axial predominance of the phenyl group by a larger polarization of the Si−Ph than of the Si−O bond in the Phax conformer and additional destabilization of 3-Pheq conformer by repulsion of unidirectional dipoles of the endocyclic oxygen lone pair and of the highly polar axial Si−O bond.
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phenyl-1-silacyclohexane2 and in all the so far studied 3-methyl3-phenyl-3-silaheterocyclohexanes (heteroatom = nitrogen, oxygen,7 sulfur2) the Pheq conformers predominate comprising from 62 to 68%. It is worth noting that all the above-mentioned results refer to solution; in gas phase the situation may change, as was recently shown by gas-phase electron diffraction for 1-methyl-1phenyl-1-silacyclohexane.8 Moreover, while in solution the rotational conformers about the Si−Ph bond can be assumed to be averaged, in gas phase different rotamers must be considered for each conformer,8 which complicates the analysis and interpretation of the experimental results. As to geminally substituted 1-X-1-phenylsilacyclohexanes having an electron acceptor group X, a series of such compounds [X = F, Cl, Br, MeO, OH, Me2N, OSi(Ph)C5H10] was synthesized by us recently9 and the first two (X = F, Cl) were studied conformationally.10 In solution, the ratio of the conformers Pheq:Phax is ∼3:1 for X = F and ∼4.5:1 for X = Cl. Note that while for X = Cl the gas-phase electron diffraction determined ratio of ∼4:1 is close to that in solution, for X = F it is reversed slightly in favor of the Phax conformer (represented by two rotamers about the Si−Ph bond).10 Until now, the only
INTRODUCTION Phenyl group as a substituent on the cyclohexane ring has conformational energy A of 2.87 kcal/mol and can be considered as an anancomeric (conformationally fixed) group.1 In going from cyclohexanes to silacyclohexanes the conformational energies of all substituents attached to silicon are reduced or even invert the sign, indicating the variations of the conformational equilibrium due to altered C−Si−C bond angles and decisively longer Si−C bond lengths.2 Noteworthy, the differences in the conformational energies for the substituents at silicon are leveled out: thus, while the phenyl and methyl substituents have notably different conformational energies in the cyclohexane series (2.87 and 1.74 kcal/mol, respectively1) they are practically equal when attached to silicon in silacyclohexanes: 0.22−0.252 and 0.21 kcal/mol.3 In geminally disubstituted cyclohexanes, the phenyl group demonstrates specific conformational behavior due to steric interactions with its geminal counterpart. For example, in spite of being more bulky, the phenyl group in 1-methyl-1-phenylcyclohexane prefers the axial position4 because of destabilizing nonvalent interactions of the phenyl ring with the 2,6-Heq and Me protons in the Ph-equatorial conformer.5 In silacyclohexanes, steric effects play a subordinate role with respect to electrostatic and hyperconjugation effects6 and, as a result, in 1-methyl-1© 2017 American Chemical Society
Received: October 3, 2017 Published: November 24, 2017 13414
DOI: 10.1021/acs.joc.7b02505 J. Org. Chem. 2017, 82, 13414−13422
Article
The Journal of Organic Chemistry
dichloromethane as the solvent. The results of the low temperature 13C NMR study are included as well. As a model molecule, 3-methoxy-3-phenyl-3-silatetrahydropyran 8 was also calculated. It clearly follows from the computational results in Table 1 and from comparison with previous results for 1phenylsilacyclohexane,2 that the axial or equatorial preference of the phenyl group in compounds 1−4, 8 depends on the second substituent at silicon, the presence and nature of endocyclic heteroatom in the ring, and on both specific and nonspecific solvent effects. Although the phenyl group is a bulkier substituent than all other groups at silicon in compounds 1−4, 8 (H, OH, OMe), practically for all species, except for H-complexes 1·CHCl3, 3· CHCl3 and 8·2CHCl3, the Phax conformers have lower ΔE values while the Pheq conformers are entropically preferable (the values of ΔG° are less positive or more negative than the corresponding ΔE values). Evidently, this is due to more easy rotation of the phenyl group in Pheq conformers increasing their entropy and, hence, decreasing ΔG° values. The exception is 3-methoxy-3phenyl-3-silatetrahydropyran 8, for which the restrictions to rotation of the axial methoxy group are larger than those for the phenyl group, so the 8-Phax conformer is entropically preferable. In silanol 2 the phenyl group prefers the axial position irrespective the theoretical method (DFT or MP2) or the considered medium (gas or solution) and only the formation of H-complexes of the conformers of 2 with chloroform, simulating specific solvation, decreases the relative free energy of the Phax conformer by 0.3−0.4 kcal/mol making the conformational equilibrium practically degenerate. These seemingly unexpected results can be rationalized by careful consideration of the electronic structure of the two conformers. The polarization of the Si−Ph bond calculated as Δq = qSi − qCipso is larger in the 2Phax conformer by 0.026e, whereas the polarization of the Si−O bond in the two conformers is practically the same, Δq = qSi − qO = 0.001e. Moreover, strange as it might seem, the absolute polarization of the Si−Ph bond is larger than that of the Si−O bond: 1.891e vs 1.843e for the 2-Phax and 1.865e vs 1.844e for the 1-Pheq conformer. Therefore, the preference for the 2-Phax conformer is consistent with the general rule of preferable axial location of more electronegative group. Close values of the dipole moments for the two conformers (1.86D for 2-Phax and 1.79D for 2-Pheq) cannot cause any changes in going from gas to solution and, indeed, using the PCM model gives the results close to those for the gas phase (Table 1). On the other hand, a larger negative charge on the hydroxy group in the 2-Pheq than in the 2Phax conformer (−0.420e vs −0.408e) favors the formation of Hcomplex 2-Pheq·CHCl3 and counterbalances the predominance of 2-Phax in the isolated conformers (Table 1). Silanol 3 differs from its analogue 2 by the presence of the endocyclic oxygen atom, which might cause a shift of the conformational equilibrium 3-Phax ⇆ 3-Pheq to the right as compared to 2-Phax ⇆ 2-Pheq because of formation of
known Si(Ph)-monosubstituted silaheterocyclohexane was 3phenyl-1-thia-3-silacyclohexane,2 so, the effect of the heteroatom in the ring on the conformational energy of the phenyl group at silicon is still a “state-of-the-art” problem. In the present paper, we have synthesized 1-methoxy-1-phenylsilacyclohexane (1), 1hydroxy-1-phenylsilacyclohexane (2), 3-hydroxy-3-phenyl-3-silatetrahydropyran (3) and 3-phenyl-3-silatetrahydropyran (4) and studied their conformational behavior by low-temperature 13 C NMR spectroscopy and quantum-chemical calculations.
Silacyclohexanes 1 and 2 make an interesting pair for comparison to each other because of unobvious reasons for the theoretically predicted difference in conformational preferences between the hydroxy and methoxy groups attached to silicon11 and to the carbon predecessor of silanol 2, 1-phenylcyclohexanol, which exist practically exclusively in the Pheq conformation.12 Conformational analysis of 3-phenyl-3-silatetrahydropyrans 3 and 4 may through light on the effect of endocyclic oxygen atom on the conformational preferences of the phenyl and hydroxy groups, in particular, by comparing compound 4 to its sulfur analogue, 3-phenyl-1-thia-3-silacyclohexane.2
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RESULTS AND DISCUSSION Synthesis. Silacyclohexanes 1 and 2 were prepared from 1chloro-1-phenylsilacyclohexane by its methanolysis or hydrolysis, respectively, as described earlier.9 Heterocycles 3 and 4 have been synthesized in one-pot procedure, starting from 3,3diphenyl-3-silatetrahydropyran 5 (Scheme 1). Thus, treatment of compound 5 with trifluoromethanesulfonic acid, followed by hydrolysis of monotriflate 6 in the presence of aniline yielded silanol 3 in 78% yield (calculated from 1H NMR). Pure compound 3 was isolated by column chromatography in moderate yield (45%) and showed no changes in 1H NMR spectrum after 7 weeks storage at ambient temperature. This proves relative stability of silanol 3 with respect to condensation to disiloxane 7, which is the main product when the hydrolysis of triflate 3 is carried out in the presence of triethylamine. Note that preparation of compound 3 is the first purposeful synthesis of 1,3-silaheterocyclohexanes bearing the hydroxy group at silicon. Removal of the phenyl group from 5 with triflic acid followed by the treatment with i-propanol/triethylamine mixture gave the corresponding i-propoxy derivative which was characterized by 1 H, 13C and 29Si NMR spectroscopies. The resulting compound was reduced with lithium aluminum hydride to afford heterocycle 4 with 35% overall yield (Scheme 1). Quantum Chemical Calculation and Low Temperature 13 C NMR Study. Table 1 summarizes the results of calculations for compounds 1−4 and their solvate H-complexes in gas phase and in solution using polarizable continuum model (PCM) and Scheme 1
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DOI: 10.1021/acs.joc.7b02505 J. Org. Chem. 2017, 82, 13414−13422
Article
The Journal of Organic Chemistry
Table 1. Relative Energies ΔE [E(Pheq) − E(Phax)], Free Energies ΔG° [G°(Pheq) − G°(Phax)] (298 K, kcal/mol) and Ratios of the Conformers of 1-Methoxy-1-phenyl-1-silacyclohexane 1, 1-Hydroxy-1-phenyl-1-silacyclohexane 2, 3-Hydroxy-3-phenyl-3silatetrahydropyran 3, 3-Phenyl-3-silatetrahydropyran 4, and 3-Methoxy-3-phenyl-3-silatetrahydropyran 8 and Their Solvate Complexes in Gas Phase and Solution Pheq:Phax species 1
1·CHCl3 2
2·CHCl3 3
3·CHCl3b 3·CHCl3c 3·2CHCl3 4
4·CHCl3 8
8·2CHCl3
method
ΔE
ΔG° 298 K (103 K)
298 K
low temp. 13C NMR study
103 K
M062X/6-311G**
0.03
−0.70 (−0.33)
77:23
84:16
MP2/6-311G** MP2/cc-pVTZ M062X/6-311G** (PCM, CH2Cl2) M062X/6-311G** (PCM, CH2Cl2) M062X/6-311G** MP2/6-311G** MP2/cc-pVTZ M062X/6-311G** (PCM, CH2Cl2) M062X/6-311G** (PCM, CH2Cl2) M062X/6-311G** MP2/6-311G** MP2/cc-pVTZ M062X/6-311G** (PCM, CH2Cl2) M062X/6-311G** (PCM, CH2Cl2) M062X/6-311G** (PCM, CH2Cl2) M062X/6-311G** (PCM, CH2Cl2) M062X/6-311G**
0.53 0.30 0.38
−0.06 (0.28) −0.29 (0.05)a −0.50 (0.09)
52:48 38:62 70:30
20:80 56:44 61:39
−0.34
−1.15 (−0.51)
87:13
92:8
0.49 0.77 0.65 0.55
0.45 (0.59) 0.41 (0.62) 0.29 (0.50)a 0.30 (0.51)
32:68 33:67 38:62 38:62
5:95 5:95 8:92 8:92
0.005
0.01 (−0.12)
50:50
64:36
0.90 0.53 0.84 1.40
0.56 (0.73) 0.02 (0.29) 0.33 (0.60)a 0.91 (1.25)
28:72 49:51 36:64 18:82
3:97 20:80 5:95 0:100
0.18
0.46 (0.35)
32:68
15:85
−1.27
−0.73 (−1.14)
77:23
99.6:0.4
1.97
1.11 (2.02)
13:87
0:100
1.32
1.33 (1.41)
10:90
0.1:99.9
MP2/6-311G** MP2/cc-pVTZ M062X/6-311G** (PCM, CH2Cl2) M062X/6-311G** (PCM, CH2Cl2) M062X/6-311G** MP2/6-311G** MP2/cc-pVTZ M062X/6-311G** (PCM, CH2Cl2) M062X/6-311G** (PCM, CH2Cl2)
1.48 1.26 1.38
0.67 (1.10) 0.45 (0.88)a 0.74 (1.16)
24:76 32:68 22:78
0.4:99.6 1:99 0.3:99.7
3.80
2.83 (3.07)
0.8:99.2
0:100
0.71 0.71 0.30 0.15
0.64 (0.10) 1.02 (0.79) 0.61 (0.38)a 0.53 (−0.28)
25:75 15:85 26:74 29:71
38:62 2:98 14:86 80:20
−3.02
0.77 (−1.35)
21:79
100:0
68.8:31.2, K = 2.21 (103 K); ΔG° = −RT ln K = −0.16 kcal/mol
No decoalescence of 13C signals of C-2 to C-6
No decoalescence of 13C signals of C-2 to C-6
82.9:17.1 K = 4.59 (103 K) ΔG° = −RT ln K = −0.31 kcal/mol
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ΔG° calculated using thermodynamic parameters obtained at the MP2/6-311G** level of theory. bFor CHCl3 molecule coordinated to the endocyclic oxygen atom in the Pheq conformer. cFor CHCl3 molecule coordinated to the OH oxygen atom in the Pheq conformer; in the Phax conformer the CHCl3 molecule is coordinated to both oxygen atoms forming a bifurcated hydrogen bond. a
Pheq. The obvious and most probable reason for that is an additional destabilization of the 3-Pheq conformer due to electrostatic repulsion of the dipoles of the endocyclic oxygen and of the highly polar axial Si−O bond. Unfortunately, neither for 2 nor for 3 the decoalescence of the 13C signals of the participating conformers at low temperature (95% purity as determined by 1H NMR. Elemental analysis on C, H, and Si was performed on a Thermo Finnigan Flash EA microanalyzer (Italy) or by combustion method. Room temperature 1H, 13C, and 29Si NMR spectra were registered on a Bruker DPX 400 spectrometer at working frequencies 400 (1H), 100 (13C) and 79 MHz (29Si). The low temperature 13C NMR spectra were recorded on a Bruker AV-600 instrument (at 150.95 MHz). Chemical shifts were determined relative to residual CHCl3 (1H, δ 7.27 ppm), internal CDCl3 (13C, δ 77.0 ppm), and internal CD2Cl2 (13C, δ 53.73 ppm) downfield from TMS (for 1H, 13C). Analysis and assignment of the 1H NMR data were supported by homonuclear (COSY) and heteronuclear (HSQC and HMBC) correlation experiments. A solvent mixture of CD2Cl2, CHFCl2, and CHF2Cl in a ratio of 1:1:3 was employed for the low temperature measurements because of being still liquid at around 100 K. The probe temperature was calibrated by means of a thermocouple PT 100 inserted into a dummy tube. The low temperature measurements were estimated to be accurate to ±1°. The equilibrium constants (K) of conformational equilibria were determined by integration of separated signals of the two participating conformers in the 13C NMR spectra at 103 K, and the free energy differences were calculated as ΔG° = −RT ln K in kcal/mol. 3-Phenyl-3-(trifluoromethylsulfonyloxy)-3-silatetrahydropyran (6). Trifluoromethanesulfonic acid (0.286 g, 1.91 mmol) was added dropwise to the solution of 5 (0.486 g, 1.91 mmol) in CH2Cl2 (3 mL) at room temperature. After refluxing the mixture for 6 h, the volatiles were removed under reduced pressure to afford triflate 6 in almost quantitative yield as a dark brown oil: 1H NMR (400 MHz, CDCl3) δ 1.42−1.52 (m, 2H, 4−CH2), 1.98−2.16 (m, 2H, 5−CH2), 3.71−3.73 (m, 2H, 6−CH2), 3.98 (s, 2H, 2−CH2), 7.48−7.52 (m, 2H, Hm), 7.56− 7.60 (m, 1H, Hp), 7.68−7.70 (m, 2H, Ho). 13C NMR (100 MHz, CDCl3) δ 10.0 (4-CH2), 24.9 (5-CH2), 61.6 (2-CH2), 71.3 (6-CH2), 128.0 (Ci), 128.7 (Cm), 132.3 (Cp), 133.8 (Co). CF3 quartet could not be acquired in a reasonable time. 19F NMR (376 MHz, CDCl3) δ −76.12. 29Si NMR (79 MHz, CDCl3) δ: 5.9. 3-Phenyl-3-hydroxy-3-silatetrahydropyran (3). To the solution of silyl triflate 6 freshly prepared from compound 5 (0.486 g,1.91 mmol) as described above and cooled to 0 °C, ether (5 mL), aniline (0.180 g, 1.93 mmol) and water (0.36 mL, 20 mmol) was added, the reaction mixture stirred for 10 min and diluted with water (1 mL). The organic layer was washed with water (10 mL) and brine (20 mL). The organic phase was
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CONCLUSIONS Both theoretical and experimental low temperature 13C NMR studies of 1-methoxy-1-phenylsilacyclohexane 1 confirmed the dominance of the Pheq conformer in the present conformational equilibrium at 103 K, which is in compliance with steric constraints caused by phenyl group versus methoxy group. Opposite to this result, especially the theoretical study of 3phenyl-3-silatetrahydropyran 4 and of the hydroxy compounds 2 and 3 suggested the preference of the Phax conformer. In case of 2 and 3 this result could not be checked up experimentally; due to heavily preferred or anancomeric conformers of 2 and 3, so that the minor conformer could not be seen even in the conforma13420
DOI: 10.1021/acs.joc.7b02505 J. Org. Chem. 2017, 82, 13414−13422
Article
The Journal of Organic Chemistry dried over Na2SO4, filtered, and concentrated in vacuum to give the crude product (0.301 g) consisting of unreacted compound 5 and silanol 3 in 1:10 molar ratio. At this stage the yield of 78% was calculated from 1 H NMR spectrum using 5 (δ= 3.96 ppm in CDCl3, 2H) as an internal standard. Pure silanol 3 was isolated by column chromatography (gradient eluent: hexane/ether, 15/3 to 0/1) in 45% yield (0.166 g, 0.85 mmol) as a colorless liquid. IR νmax (neat) 1115 (PhSi) and 3331 (br, OH) cm−1. 1H NMR (400 MHz, CDCl3) δ 1.07−1.11 (m, 2H, 4−CH2), 1.88−1.97 (m, 1H, 5−CHA), 1.98−2.08 (m, 1H, 5−CHB), 3.55−3.60 (ddd, 1H, J = 12.3, 7.9, 2.3 Hz, 6−CHA), 3.69 (s, 2H, 2−CH2), 3.69− 3.75 (ddd, 1H, J = 12.3, 6.1, 2.8 Hz, 6−CHB), 4.17 (br s, 1H, HO−Si), 7.38−7.46 (m, 3H, Hm+p), 7.65−7.67 (m, 2H, Ho). 13C NMR (100 MHz, CDCl3) δ 12.0 (4-CH2), 25.5 (5-CH2), 64.4 (2-CH2), 71.3 (6-CH2), 128.0 (Cm), 130.1 (Cp), 133.6 (Co), 135.0 (Ci). 29Si NMR (79 MHz, CDCl3) δ−10.9. Anal. Calcd for C10H14SiO2: C, 61.81; H, 7.26; Si, 14.45. Found: C, 61.82; H, 7.34; Si, 14.60. When the hydrolysis of triflate 6 was carried out in the presence of triethylamine silanol 3 was obtained in a low yield (13%), whereas disiloxane 7 was isolated in 32% yield by column chromatography (eluent: hexane/ether). Compound 7 is a mixture of diastereomers in 1:1 ratio due to the presence of two chiral silicon atoms in the molecule. IR νmax (neat) 1070 (SiOSi) and 1117 (SiPh) cm−1.1H NMR (400 MHz, CDCl3) δ 1.04−1.11 (ddd, 1H, J = 14.8, 8.3, 3.8 Hz, 4−CHA), 1.13−1.20 (ddd, 1H, J = 14.8, 8.3, 5.4 Hz, 4−CHB), 1.85−1.94 (m, 1H, 5−CHA), 1.95−2.04 (m, 1H, 5−CHB), 3.63−3.66 (m, 4H, 6−CH2), 3.66 (d, 1H, J = 15.0 Hz, 2−CHA), 3.72 (dd, 1H, J = 15.0, 4.3 Hz, 2−CHB), 7.39−7.47 (m, 3H, Hm+p), 7.66−7.68 (m, 2H, Ho). 13C NMR (100 MHz, CDCl3) δ 12.58, 12.65 (4-CH2), 25.8 (5-CH2), 64.3, 64.4 (2-CH2), 71.3 (6CH2O), 128.0 (Cm), 130.1 (Cp), 133.6 (Co), 135.4 (Ci). Anal. Calcd for C20H26Si2O3: C, 64.82; H, 7.07; Si, 15.16. Found: C, 64.68; H, 7.00; Si, 15.14. 3-Phenyl-3-silatetrahydropyran (4). Triflate 6 prepared from compound 5 (0.761 g, 3.0 mmol) was dissolved in pentane (2 mL), and the solution was cooled to 0 °C. A mixture of i-propanol (0.208 g, 3.3 mmol) and triethylamine (0.334 g, 3.3 mmol) was added dropwise at 0 °C, followed by refluxing the reaction mixture for 5 h. The upper layer of the formed two-phase system was separated from the lower layer (triethylammonium triflate) and the solvent was removed under reduced pressure to give 3-phenyl-3-isopropoxy-3-silatetrahydropyran as a colorless oil (0.506 g, 71% yield). 1H NMR (400 MHz, CDCl3) δ 1.11−1.16 (m, 2H, 4−CH2), 1.21−1.22 (d, 6H, J = 6.0 Hz, Me2CH), 1.84−1.92 (m, 1H, 5−CHA), 1.94−2.04 (m, 1H, 5−CHB), 3.57−3.69 (m, 2H, 6-CH2), 3.71 (d, 1H, J = 15.1 Hz, 2−CHA), 3.77 (d, 1H, 2− CHB), 4.16 (hept, 1H, Me2CH), 7.38−7.46 (m, 3H, Hm+p), 7.67−7.69 (m, 2H, Ho). 13C NMR (100 MHz, CDCl3) δ 11.2 (4-CH2), 25.7 (Me2CH), 25.9 (5-CH2), 63.3 (2-CH2), 66.1 (Me2CH), 71.4 (6-CH2), 127.9 (Cm), 130.0 (Cp), 134.0 (Co), 135.6 (Ci). 29Si NMR (79 MHz, CDCl3) δ −13.0. Without isolation and purification, crude 3-phenyl-3isopropoxy-3-silatetrahydropyran was dissolved in diethyl ether (1 mL) and added dropwise to a stirred suspension of lithium aluminum hydride (0.076 g, 2.0 mmol) in diethyl ether (3 mL) at 0 °C. The mixture was refluxed for 3 h, cooled to room temperature and added to a stirred mixture of pentane (2 mL), concentrated hydrochloric acid (5 mL), water (15 mL) and ice. The organic phase was separated and the aqueous phase extracted with ether (2 × 3 mL). The combined organic phases were dried over MgSO4. After removal of the volatiles under reduced pressure (45 mmHg), the residue (0.239 g) was purified by column chromatography on silica gel (eluent: hexane/ether) to give 5 as colorless oil in 35% yield (0.171 g, 1.05 mmol): 1H NMR (400 MHz, CDCl3) δ 1.06−1.15 (m, 1H, 4−CHA), 1.19−1.29 (m, CHB), 1.88−2.03 (m, 2H, 5−CH2), 3.58−3.64 (ddd, 1H, J = 12.0 Hz, 7.4 and 2.9 Hz, 6− CHA), 3.70−3.73 (m, 1H, 6−CHB), 3.73 (dd, 1H, J = 14.9, 3.9 Hz, 2− CHA), 3.89 (d, 1H, 2−CHB), 4.45 (m, 1H, H−Si), 7.38−7.46 (m, 4H, Hm+p), 7.63−7.65 (m, 2H, Ho). 13C NMR (100 MHz, CDCl3) δ 7.8 (4CH2), 25.3 (5-CH2), 61.4 (2-CH2), 71.4 (6-CH2), 128.0 (Cm), 129.9 (Cp), 133.4 (Ci), 134.7 (Co). 29Si NMR (79 MHz, CDCl3) δ −28.8. Anal. Calcd for C10H14SiO: C, 67.36; H, 7.91; Si 15.75. Found: C, 67.19; H, 7.72; Si, 15.56. Theoretical Calculations. All geometric and vibrational calculations were performed with no restrictions on the geometry by using
M06-2X correlation functional with 6-311G(d,p) basis set or at the MP2 level of theory with 6-311G(d,p) and cc-pVTZ basis sets. 13C GIAO NMR calculations were performed at the MP2/6-311G(d,p) level using the MP2/6-311G(d,p) optimized geometries. All calculations were performed with Gaussian 09 program suite.19
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.joc.7b02505. IR and NMR spectra of the key products and Cartesian coordinates for the calculated structures (PDF)
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Bagrat A. Shainyan: 0000-0002-4296-7899 Notes
The authors declare no competing financial interest.
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REFERENCES
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DOI: 10.1021/acs.joc.7b02505 J. Org. Chem. 2017, 82, 13414−13422
