Article pubs.acs.org/joc
Cite This: J. Org. Chem. 2018, 83, 2250−2255
An Additive-Free, Base-Catalyzed Protodesilylation of Organosilanes Wubing Yao, Rongrong Li, Huajiang Jiang, and Deman Han* Department of Chemistry, Taizhou University, Jiaojiang 318000, China S Supporting Information *
ABSTRACT: We report an additive-free, base-catalyzed C−, N−, O−, and S−Si bond cleavage of various organosilanes in mild conditions. The novel catalyst system exhibits high efficiency and good functional group compatibility, providing the corresponding products in good to excellent yields with low catalyst loadings. Overall, this transition-metal-free process may offer a convenient and general alternative to current employing excess bases, strong acids, or metal-catalyzed systems for the protodesilylation of organosilanes.
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INTRODUCTION The cleavage of carbon−silicon bond is one of the most valueadded processes in organic synthesis and has achieved broad attentions.1 The traditional methods, for the C−Si bond cleavage, involve the use of large molar excess of fluoride ion donors,2 oxygenated bases,3 or strong acids.1a,b,4 These noncatalytic transformations have been presented in various introductory organic chemistry courses. Nevertheless, such methods always suffer from serious limitations: (1) the restriction of the substrate scope and the labile decomposition of the products or substrates; (2) the formation of significant amounts of inorganic salts as wastes; and (3) the harsh reaction conditions (super bases or acids). An alternative, but less developed, method for the C−Si bond cleavage is the use of transition metal as the catalyst. In the past decades, precious metal catalysts, involving Ag,5 Pd,6 and Ln7 were employed for the desilyation. However, toxic reagents,5a high catalyst loadings,5b and high temperatures6 were required to achieve good conversions. Thus, the low abundance, high cost, and environment unfriendly metals motivated the investigation of more practical protocols for alternatives. In 1967, Price reported a stoichiometric protodesilylation of SiMe4 and Bn-SiMe3 using KOtBu as the promoter.8 Subsequently, Hudrlik reported the KOtBu catalyzed C−Si bond cleavage of β-hydroxysilanes (Scheme 1, a).9 This work represented a breakthrough in the catalytic protodesilylation of organosilanes, but was restricted to reactions with serveral β-hydroxysilanes, and an additive (18crown-6) must was required for good conversions. In 2003, the group of Yoshida disclosed a highly efficient method for the cleavage of various C(sp2)−, C(sp3)−Si bonds.10 The reaction occurred at 390 °C and 27 MPa using supercritical water as a promoter (Scheme 1, b). In a subsequent report, Zafrani employed montmorillonite KSF clay for the protodesilylation of several aryltrimethylsilanes.11 Recently, Phillips disclosed the protodesilylation of the Si−O bond using catalytic fluoride at neutral pH in anhydrous dimethyl sulfoxide-methanol.12 © 2018 American Chemical Society
Scheme 1. Protodesilylation of Organosilanes
Despite these advances in the desilylation reactions, the highly efficient and practical nonmetal catalytic systems for cleavage of C−, O−, N−, and S−Si bonds are extremely rare, and the substrate scopes of most current methods are also very restricted. Herein we demonstrate that potassium trimethylsilanolate (KOTMS) is remarkably active for the catalytic desilylation of various organosilanes containing C−, O−, N−, and S−Si bonds (Scheme 1, c). Most reactions proceeded to completion with 1−5 mol % of KOTMS employing wet DMSO as the solvent. Beyond high activity, this novel catalyst system offers broad substates and good functional group tolerance and affords the desirable products in good to excellent yields.
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RESULTS AND DISCUSSION We commenced by investigating the effect of different solvents on the protodesilyation of trimethylphenylsilane (1a). The Received: December 13, 2017 Published: January 26, 2018 2250
DOI: 10.1021/acs.joc.7b03139 J. Org. Chem. 2018, 83, 2250−2255
Article
The Journal of Organic Chemistry
of 5 mol % of nBu4NCl. It is noteworthy that 1a remained intact without catalysts (entry 19). To evaluate the scope and limitation of this base-catalyzed system, we used KOTMS as the catalyst for the protodesilylation of various aryltrimethylsilanes. As shown in Table 2, most reactions proceeded smoothly at 70 °C and gave the
results are summarized in Table 1. Obviously, the solvents had dramatic effects on the C−Si bond cleavage. The reaction Table 1. Optimization of Reaction Conditionsa
Table 2. Protodesilylation of Aryltrimethylsilanesa 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15c 16c 17c 18d 19c
[cat.]
[cat.] (mol %)
solvent
yield (%)b
KOtBu KOtBu KOtBu KOtBu KOtBu KOtBu KOtBu KOAc K2CO3 KOMe NaOMe KOH NaOTMS KOTMS KOTMS KOTMS KOTMS KOTMS --
20 20 20 20 20 20 5 5 5 5 5 5 5 5 5 1 0.5 1 1
tBuOH THF PhMe DMF DMA DMSO DMSO DMSO DMSO DMSO DMSO DMSO DMSO DMSO DMSO DMSO DMSO DMSO DMSO
0 0 0 38 80 99 51 0 0 56 49 77 95 99 95 94 78 17 0
Reaction conditions: PhTMS 1a (1.0 mmol), base (50 μmol, 5 mol %), solvent (2.0 mL), at 100 °C, 6 h. bDetermined by GC and GC-MS analysis. c70 °C. d25 °C. a
a Reaction conditions: ArTMS 1 (1.0 mmol), KOTMS (50 μmol, 5 mol %), wet DMSO (2.0 mL), at 70 °C, 6 h; the yield is determined by GC and GC-MS analysis, and the value in parentheses is isolated yield. bKOTMS (0.1 mmol, 10 mol %), 12 h.
provided the most satisfied result (99%) when using DMSO as solvent in the presence of 20 mol % of KOtBu (entry 6). However, the reactions ran in tBuOH, THF, toluene (PhMe), or DMF showed relative poor catalytic activities in comparison with DMSO (entries 1−5). The superior catalytic activity of the catalyst in DMSO may be attributed to that DMSO can serve as a decent ligand for potassium, causing the stronger orders of magnitude than the KOTMS in conventional solvents.13 With the most suitable solvent in hand, we next investigated the influence of different catalysts employed on this desilylation process. NaOTMS and KOTMS were proved the best catalysts for this transformation, offering 2a in 95% and 99% yields (entries 13 and 14). Other common base catalysts, such as KOAc, K2CO3, KOMe, NaOMe, and KOH, were inactive for the desilylation (entries 8−12). To our delight, the process also occurred smoothly even at 70 °C (entry 15). More importantly, the loadings of the catalyst could be reduced to 1 mol % without influencing the conversation obviously (entry 16). Performing the reaction at 70 °C with 0.5 mol % KOTMS also gave the desired product in useful yield (entry 17). Gratifyingly, this reaction can even proceed at 25 °C, albeit with low yield of the product (entry 18). Inspired by the fact that Bu4N+ can improve the reactivity by increasing both the solubility of the base and the nucleophilicity of the trimethylsilyl oxide,14 we envisioned that Bu4NOTMS may allow for lowering the reaction temperature. To test this hypothesis, we examined the catalytic protodesilylation reactions with 5 mol % of KOTMS and nBu4NCl at 25−70 °C in DMSO or THF (Table S1, entries 15−18). However, these conditions all afforded 2a in low yields with the addition
desired products in high yields. A methyl group at all the positions on the benzene rings were compatible (1b−d), offering product yields ranging from 80% to 93%. In addition, this transformation was compatible with fluoro, chloro, or bromo substituent (1e−g), giving the expected products in 88−90% yields. Furthermore, functional groups including methoxyl (1h), phenyl (1i), or N,N-dimethyl (1j) all underwent the desilylation process successfully. Disubstituted aryltrimethylsilanes, such as 1n and 1o, were also investigated and gave the corresponding product (benzene) in 90% and 75% yields, respectively. It is noteworthy that this method similarly exhibited highly efficient for silanol 1k, methoxysilane 1l, and siloxane 1m, giving the corresponding products in excellent yields. Notably, the reaction of 1p or 1q with 5 mol % of KOTMS selectively offered the sole product (benzene or diphenyl) in 98% and 99% yields after 6 h. To our delight, aryltrimethylsilanes containing O− and S−Si bonds (1r, 1s) were also compatible with the present conditions. Delightfully, this process underwent smoothly to afford cyclohexanone (2t) and cyclopentanone (2u) in good yields. These good results encouraged us to evaluate the protodesilylation of alkynylsilanes. As shown in Table 3, alkynyltrimethylsilanes containing electron-donating (3b−e) or -withdrawing groups (3f−h) in the para position of benzene rings underwent facile desilylation to form the products in excellent yields. By utilizing the basic conditions, functional groups including cyanide (3i), mercaptomethyl (3j), acetyl (3k), formyl (3l), nitryl (3m), and lactam (3o) could be 2251
DOI: 10.1021/acs.joc.7b03139 J. Org. Chem. 2018, 83, 2250−2255
Article
The Journal of Organic Chemistry Table 3. Protodesilylation of Alkynylsilanesa
Table 4. Protodesilylation of Alkylsilanesa
Reaction conditions: 3 (1.0 mmol), KOTMS (50 μmol, 5 mol %), DMSO (2.0 mL), at 70 °C, 6 h; the yield is determined by GC and GC-MS analysis, and the value in parentheses is isolated yield. b KOTMS (0.1 mmol, 10 mol %), 12 h. a
Reaction conditions: 5 (1.0 mmol), KOTMS (50 μmol, 5 mol %), wet DMSO (2.0 mL), at 70 °C, 6 h; the yield is determined by GC and GC-MS analysis.
a
allowed, for the first time, for the highly efficient and selective formation of toluene in 98% yield. With the highly active catalyst in hand, we sought to develop procedures to conduct the process on a gram-scale (Scheme 2).
tolerated. Moreover, 2-ethynylthiophene (4n) was successfully synthesized as well by treatment of 5 mol % KOTMS in wet DMSO. To our delight, this catalytic protocol also could be applicable to the protodesilylation of the disubstituted silane 3p and 3s and provided 1, 4-diethynylbenzene in 88% and 71% yields. Similarly, the reactions of tert-butyldimethylsilane 3q and triethylsilane 3r also proceeded smoothly. The reactions of 3t and 3u were tried. To our satisfaction, the desired desilylation products were obtained in useful yields. We next turned our attention to challenge the alkylsilanes (Table 4). Significantly, all the substrates performed smoothly using the standard conditions, furnishing the products in useful to excellent yields. The benzyltrimethylsilane containing alkyl (5b), amino (5d), alkoxy (5e), fluorine (5f), trifluoromethyl (5g), and mercaptomethyl (5h) groups all gave the products in good yields. Notably, this novel catalyst system was insensitive to the steric of the substrate: benzyltrimethylsilane possessing an o-methyl group smoothly gave 6c in 89% yield. Moreover, the reactions of the unprecedented 1,3-siladihydrobenzofuran derivates could smoothly occur in this mild condition. 1,3-Siladihydrobenzofuran containing methoxy or alkyl underwent the desilylation process smoothly, providing the unique anisole analogues ranging from moderate to excellent yields. Furthermore, we found that the C−Si bond cleavage of N-(trimethylsilylmethyl)-benzylamine derivates 5n and 5o also took place efficiently using this protocol. To further explore the scope, the C−Si bond cleavage of alkynyl dimethylsilane 5p and 5q were tested, offering toluene (5p, 5q) or phenylacetylene (5q) in useful yields. Interestingly, alkylsilanes containing N−Si bonds (5r, 5s) could be carried out successfully. Having identified an effective catalyst, KOTMS, for the protodesilylation, we next examined the more complex (E)-1-(benzyldimethylsilyl)-1-buten-3-yne 5t. To our delight, our catalyst system
Scheme 2. Gram-Scale C−Si Bond Cleavage
Employing only 1 mol % of catalyst, the desilylation of 1a, 3a, and 5a could be scaled up to 7 mmol and afforded the corresponding products in 90%, 80%, and 94% yield, respectively. In addition, to distinguish homogeneous from heterogeneous catalysis, we conducted the protodesilylation of 1a in the presence of commonly used heterogeneous catalyst poison liquid Hg15 and PMe315c (Table 5). The addition of Hg or PMe3 showed no inhibition effect on the yield of 2a in comparison with the blank test. Therefore, these results suggest that this base catalyst is likely to be homogeneous under the standard conditions. 2252
DOI: 10.1021/acs.joc.7b03139 J. Org. Chem. 2018, 83, 2250−2255
Article
The Journal of Organic Chemistry Table 5. Homogeneity Test with Hg and PMe3a
entry
additive
equivalent
yield (%)
1 2 3
− Hg PMe3
− 100 1.0
95 95 94
a
Reaction conditions: PhTMS 1a (1.0 mmol), KOTMS (50 mmol, 5 mol %), x equiv of additive relative to KOTMS, DMSO (2.0 mL), at 70 °C, 6 h. The yield was determined by GC analysis.
To understand the reaction mechanism of this protodesilylation process, several control and deuterium-labeling experiments were performed (Scheme 3). No desired product was
Figure 1. Reaction conditions: 5a (0.5 mmol), KOTMS (5 mol %), x equiv of H2O relative to 5a, anhydrous DMSO (2.0 mL), at 70 °C, 6 h. The yield was determined by GC and GC-MS analysis.
Scheme 3. Control and Deuterium-Labeling Experiments
Figure 2. Reaction conditions: (TMS)2O (0.2 mmol), x equiv of KOH relative to (TMS)2O, wet DMSO (2.0 mL), at 70 °C, 1 h. The yield was determined by GC and GC-MS analysis.
Scheme 4. Plausible Reaction Pathway detected when the process conducted in the presence of anhydrous molecular sieves (MS), wet DMSO (eq 1). Similarly, the transformation also could not perform in the anhydrous DMSO-d6 (eq 2). However, the catalytic protodesilylation process in wet DMSO offered 6a′ in 99% yield with 92% D incorporation (eq 3). In addition, treatment of 5a with 1.0 equiv of D2O and KOTMS (5 mol %) in anhydrous DMSO also smoothly produced the product in 99% yield (eq 4). These results clearly indicated that H2O is the proton source of the protodesilylation and must be required for the process. Prompted by the above results, we proceeded to thoroughly investigate the relation of H2O with the protodesilylation process. The effect of the amount of H2O is clearly illustrated in Figure 1. We found that protodesilylation of 5a by treatment with 5 mol % KOTMS in anhydrous DMSO (2.0 mL) containing 0.5−50 equiv of H2O occurred with high yields. Based on the previous report,5b and with the anlaysis of the 1 H NMR and29Si NMR experiment (S3.3−3.4), TMSOH in our catalytic system could immediately undergo condensation to give 0.5 equiv of (TMS)2O and H2O. This interpretation was also confirmed by the result of treatment 0.2 mmol of (TMS)2O with 0−1.5 equiv of KOH (Figure 2). These reactions, which were carried out at 70 °C for 1 h, proved to be selective and provided the yield of (TMS)2O ranging from 0% to 27%. In our opinion, the results obtained in the reactions of (TMS)2O with KOH could partly explain the catalytic cycle reported in Scheme 4.
Based on the mechanistic investigation and the reported works,5b,9,13 we proposed a plausible mechanistic description of this protodesilylation process involving Lewis base initiation of an autocatalytic cycle (Scheme 4). The addition of trimethylsilanolate ion A to RSiMe 3 could afford a pentacoordinated silicon intermediate B, which would generate the carbanion C and disiloxane in situ. Protonation of this carbanion species facilely affords the corresponding product and hydroxide ion. Then, the reaction of the hydroxide ion with 2253
DOI: 10.1021/acs.joc.7b03139 J. Org. Chem. 2018, 83, 2250−2255
Article
The Journal of Organic Chemistry
MHz, CDCl3, 20 °C) δ 7.62 (d, J = 8.0 Hz, 4H), 7.46 (t, J = 8.0 Hz, 4H), 7.37 (t, J = 6.0 Hz, 2H). 4-[(Trimethylsilyl)ethynyl]benzonitrile 3i.21 Purification by silica gel column chromatography using EtOAc/petroleum ether gave a white solid, 0.79 g, 80%. 1H NMR (400 MHz, CDCl3, 20 °C) δ 7.56 (dd, J = 24.0, 8.0 Hz, 4H), 0.26 (s, 9H). Trimethyl{[4-(methylthio)phenyl]ethynyl}silane 3j.22 Purification by silica gel column chromatography using petroleum ether gave a pale yellow oil, 0.77 g, 70%. 1H NMR (400 MHz, CDCl3, 20 °C) δ 7.37 (d, J = 8.0, 2H), 7.15 (d, J = 8.0, 2H), 2.48 (s, 3H), 0.24 (s, 9H). 1-{4-[(Trimethylsilyl)ethynyl]phenyl}ethan-1-one 3k.22 Purification by silica gel column chromatography using petroleum ether/ EtOAc gave a yellow oil, 0.71 g, 66%.1H NMR (400 MHz, CDCl3, 20 °C) δ 7.88 (d, J = 8.0 Hz, 2H), 7.53 (d, J = 8.0 Hz, 2H), 2.59 (s, 3H), 0.26 (s, 9H). 4-[(Trimethylsilyl)ethynyl]benzaldehyde 3l.22 Purification by silica gel column chromatography using petroleum ether/EtOAc gave a white solid, 0.78 g, 77%. 1H NMR (400 MHz, CDCl3, 20 °C) δ 10.55 (s, 1H), 7.90 (d, J = 8.0, 1H), 7.58−7.51 (m, 2H), 7.43 (t, J = 8.0 Hz, 1H), 0.28 (s, 9H). Trimethyl[(4-nitrophenyl)ethynyl]silane 3m.21 Purification by silica gel column chromatography using petroleum ether/EtOAc gave a yellow solid, 0.76 g, 70%. 1H NMR (400 MHz, CDCl3) δ 8.17 (d, J = 8.0 Hz, 2H), 7.59 (d, J = 8.0 Hz, 2H), 0.27 (s, 9H). Trimethyl(thiophen-2-ylethynyl)silane 3n.23 Purification by silica gel column chromatography using petroleum ether gave a pale yellow oil, 0.39 g, 66%. 1H NMR (400 MHz, CDCl3, 20 °C) δ 7.48 (d, J = 4.0 Hz, 1H), 7.23 (q, J = 4.0 Hz, 1H), 7.13 (d, J = 4.0 Hz, 1H), 0.24 (s, 9H). 1-{4-[(Trimethylsilyl)ethynyl]phenyl}piperidin-2-one 3o.23 Purification by silica gel column chromatography using petroleum ether/ EtOAc gave a pale yellow solid, 0.85 g, 63%. 1H NMR (400 MHz, CDCl3, 20 °C) δ 7.46 (d, J = 8.5 Hz, 2H), 7.20 (d, J = 8.5 Hz, 2H), 3.62 (d, J = 5.6 Hz, 2H), 2.55 (t, J = 5.9 Hz, 2H), 2.01−1.89 (m, 5H), 0.24 (s, 9H). 13C NMR (101 MHz, CDCl3, 20 °C) δ 170.1, 132.8, 125.9, 51.4, 33.1, 23.6, 21.5, 0.1. 1,4-Bis[(trimethylsilyl)ethynyl]benzene 3p.21 Purification by silica gel column chromatography using petroleum ether gave a white solid, 1.2 g, 89%. 1H NMR (400 MHz, CDCl3, 20 °C) δ 7.38 (s, 4H), 0.24 (s, 18 H). Triethyl(phenylethynyl)silane 3r.21 Purification by silica gel column chromatography using petroleum ether gave a colorless oil, 0.87 g, 80%. 1H NMR (400 MHz, CDCl3, 20 °C) δ 7.49−7.47 (m, 2H), 7.30 (d, J = 8.0 Hz, 3H), 1.05 (t, J = 8.0 Hz, 9H), 0.68 (q, J = 8.0 Hz, 6H). tert-Butyldimethyl{[4 ((trimethylsilyl)ethynyl)phenyl] ethynyl}silane 3s.24 Purification by silica gel column chromatography using petroleum ether gave a white solid, 1.1 g, 71%. 1H NMR (400 MHz, CDCl3, 20 °C) δ 7.38 (s, 4H), 0.99 (s, 9H), 0.24 (s, 9H), 0.18 (s, 6H). 4-Ethylphenylacetylene 4c.25 Purification by silica gel column chromatography using petroleum ether gave a pale yellow oil, 0.11 g, 90%. 1H NMR (400 MHz, CDCl3, 20 °C) δ 7.42 (d, J = 8.0 Hz, 2H), 7.15 (d, J = 8.0 Hz, 2H), 3.03 (s, 1H), 2.65 (q, J = 8.0 Hz, 2H), 1.23 (t, J = 8.0 Hz, 3H). 4-Ethynylanisole 4d.26 Purification by silica gel column chromatography using petroleum ether gave a colorless oil, 0.13 mg, 93%. 1H NMR (400 MHz, CDCl3, 20 °C) δ 7.43 (d, J = 8.0 Hz, 2H), 6.84 (d, J = 8.0 Hz, 2H), 3.81 (s, 3H), 2.99 (s, 1H). 4-Ethoxyphenylacetylene 4e.27 Purification by silica gel column chromatography using petroleum ether gave a pale yellow oil, 0.14 mg, 96%. 1H NMR (400 MHz, CDCl3, 20 °C) δ 7.42 (d, J = 8.0 Hz, 2H), 6.82 (d, J = 12.0 Hz, 2H), 4.03 (q, J = 8.0 Hz, 2H), 2.99 (s, 1H), 1.41 (t, J = 8.0 Hz, 3H). 4-Chlorophenylacetylene 4g.28 Purification by silica gel column chromatography using petroleum ether gave a white solid, 0.11 g, 83%. 1 H NMR (400 MHz, CDCl3, 20 °C) δ 7.42 (d, J = 8.0 Hz, 2H), 7.29 (d, J = 12.0 Hz, 2H), 3.10 (s, 1H). 4-Bromophenylacetylene 4h.28 Purification by silica gel column chromatography using petroleum ether gave a white solid, 0.16 g, 86%. 1 H NMR (400 MHz, CDCl3, 20 °C) δ 7.46 (d, J = 8.0 Hz, 2H), 7.35 (d, J = 8.0 Hz, 2H), 3.12 (s, 1H).
hexamethyldisiloxane (TMS2O) would give trimethylsilanol (TMSOH) and regenerated trimethylsilanolate ion. TMSOH immediately undergoes condensation to give 0.5 equiv of TMS2O and 0.5 equiv of H2O.
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CONCLUSIONS In conclusion, we have developed a general and practical basecatalyzed protodesilylation of various alkynyl-, aryl-, and even the challenging arylsilanes with high efficiency. Featuring the use of the novel catalyst, mild reaction conditions, broad substrate scopes, and high functional group tolerance, this protocol could be an attractive route for the value-added C−, N−, O−, and S−Si bonds cleavage.
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EXPERIMENTAL SECTION
General Considerations. All manipulations were carried out in air without using standard Schlenk, high vacuum, and glovebox techniques. Glassware was dried in a 100 °C oven over 4 h before used. The 1-(trimethylsilyl)-1-alkynes,16 (E)-1-(benzyldimethylsilyl)1-buten-3-yne,17 and 2-(3-butenyl)bromobenzene18 were synthesized according to literature procedures. KOTMS (98%), KOH (85%), and PMe3 (97%) were purchased from a commercial supplier and used as received. DMSO (99.9%) and Hg (99.999%) were purchased from a commercial supplier and used as received. Flash colum chromatography was performed on silica gel (particle size 300−400 mesh ASTM), purchased from a commercial supplier. The other solvents, bases, and organosilanes were obtained from commerical sources and used as received. NMR spectra data were obtained on AVANCE (III) HD 400 MHz instruments. 1H NMR spectra were referenced to residual protio solvent peaks or TMS signal (0 ppm). Data for 1H NMR are recorded as follows: chemical shift (δ, ppm) and multiplicity (s = singlet, d = doublet, t = triplet, m = multiplet or unresolved, br = broad singlet, coupling constant (s) in Hz, integration). GC was performed on a Shimadzu GC-2010 plus spectrometer. GC/MS was performed on a Shimadzu GCMS-QP2010 Plus spectrometer. Typical Procedure for the Protodesilylation of the Silane. In air, a 10 mL dried Schlenk tube equipped with a magnetic stir bar was charged with the KOTMS (50 μmol, 5 mol %), arylsilane (1.0 mmol), and DMSO (2.0 mL). Then, the tube was sealed with a Teflon plug under air atmosphere and stirred at 70 °C oil bath for 6 h. After that, the reaction mixture was cooled to room temperature and dissolved in dichloromethane. Then, the mixture was filtrated though Celite and analyzed by GC and GC-MS with n-undecane or p-xylene (1.0 mmol, 1.0 equiv) as an interal standard to obtain the averaging yield of GC and GC-MS. After that, the total crude products were purified by silica gel column chromatography using petroleum ether. The Procedure for the Deuterium Experiment. In air, a 10 mL dried Schlenk tube equipped with a magnetic stir bar was charged with the KOTMS (50 μmol, 5 mol %), trimethylbenzylsilane (1.0 mmol), D2O (3.0 equiv), and anhydrous DMSO-d6 (1.0 mL). Then, the tube was sealed with a Teflon plug under air atmosphere and stirred at 70 °C oil bath for 6 h. After that, the reaction mixture was cooled to room temperature and dissolved in dichloromethane. Then, the mixture was filtrated though Celite and analyzed by GC, GC-MS and 1H NMR with 1, 2-dimethoxybenzene (1.0 mmol, 1.0 equiv) as an interal standard to obtain the deuteration and the yield of the product. The Procedure for the 29Si NMR Experiment. A valved NMR tube was charged with potassium trimethylsilanolate (KOTMS) (0.2 mmol). Then, trimethylphenylsilane 1a (0.2 mmol, 1.0 equiv) in wet DMSO-d6 (0.5 mL) was added to the tube, and it was placed in a 70 °C oil bath for 1 h. After that, the above mixture, trimethylphenylsilane 1a, and trimethylsilanolate were then analyzed by 29Si NMR spectroscopy at 20 °C in DMSO-d6, respectively. Spectral data are similar to the reported works.19 Biphenyl 2i.20 Purification by silica gel column chromatography using petroleum ether gave a white solid, 0.13 g, 86%. 1H NMR (400 2254
DOI: 10.1021/acs.joc.7b03139 J. Org. Chem. 2018, 83, 2250−2255
Article
The Journal of Organic Chemistry 1, 4-Diethynylbenzene 4p.29 Purification by silica gel column chromatography using petroleum ether gave a white solid, 0.1 g, 83%. 1 H NMR (400 MHz, CDCl3, 20 °C) δ 7.44 (s, 4H), 3.17 (s, 2H).
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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.7b03139. Conditions optimization, unreactive substrates, mechanistic studies, pH changes, deuterium experiment, 1H NMR and 29Si NMR experiments, and NMR spectra (PDF)
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Deman Han: 0000-0003-1995-0770 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was supported by the China Postdoctoral Science Foundation (2017M621972), Chemical Engineering and Technology of Zhejiang Province First-Class Discipline (Taizhou University), and the National Natural Science Foundation of China (21375092). We also acknowledge Prof. Zheng Huang and Mr. Huaquan Fang kindly offered 5,5dimethylbenzo[b]benzosilole 1q and 1,3-siladihydrobenzofuran derivates (5i−5m).
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DOI: 10.1021/acs.joc.7b03139 J. Org. Chem. 2018, 83, 2250−2255
