Cesium Carbonate-Catalyzed Reduction of Amides with Hydrosilanes

Nov 15, 2013 - Cesium carbonate has been found to be an effective catalyst for the reduction of tertiary carboxamides with the simple, commercially av...
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Cesium Carbonate-Catalyzed Reduction of Amides with Hydrosilanes Weilong Xie, Mengdi Zhao, and Chunming Cui* State Key Laboratory and Institute of Elemento-Organic Chemistry, Nankai University, Tianjin, 300071, People’s Republic of China, and Collaborative Innovation Center of Chemical Science and Technology, Tianjin, People’s Republic of China S Supporting Information *

ABSTRACT: Cesium carbonate has been found to be an effective catalyst for the reduction of tertiary carboxamides with the simple, commercially available PhSiH3 under solvent-free conditions. The catalytic system can effectively reduce a range of amides under relatively mild conditions (from room temperature to 80 °C) to yield the corresponding amines in good to excellent yields (71−100%) and thus has the potential for practical applications.

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INTRODUCTION Amines constitute an important class of compounds in organic chemistry and chemical biology.1 The reduction of carboxamides represents an indispensable synthetic route to amino groups in organic synthesis. The most common approach for this transformation is based on the reduction of amides with stoichiometric amounts of aluminum and boron hydrides.2 However, the drawbacks of these hydrides lie in their air and moisture sensitivity as well as the poor selectivity. Hydrosilanes and hydrogen are relatively mild reducing reagents, but reduction with these reagents requires suitable catalysts. Thus, the development of highly effective and selective catalytic systems using these reducing reagents has attracted much attention. In the past several decades, many transition metalbased catalytic systems for the reduction of carboxamides with hydrogen and hydrosilanes have been reported.3,4 However, most of these catalytic systems still suffer from poor chemoselectivity and a limited substrate scope. Recently, several efficient and selective catalysts based on ruthenium clusters and iridium complexes have been developed by Nagashima et al.3d−i and Brookhart et al.5 The direct use of cheap and commercially available metal compounds as the catalysts is also of great interest in view of practicability. In 1962, Calas and co-workers reported the ZnCl2-catalyzed reduction of tertiary amides to tertiary amines with various trialkylsilanes at high temperatures (Scheme 1).6 Recently, Beller et al. reported on Zn(OAc)2 and Fe3(CO)12-catalyzed reduction of various amides at high temperature.7 These cheap catalysts are tolerant to several types of functional groups but generally require an excess of hydrosilanes and relatively high catalyst loadings (10−20 mol %). Cesium carbonate has been widely used as a strong base in organic synthesis due to its ease of handling, low hygroscopicity, and high solubility in organic solvents compared to alkali metal hydroxides. In the course of our investigation on Si−O coupling reaction, we found that cesium carbonate can catalyze the reduction of DMF in the presence of PhSiH3 to yield siloxanes at room temperature with only 1% molar loading of the catalyst. Since cesium carbonate is commercially available and cost-effective, we have investigated the cesium carbonatecatalyzed reduction chemistry in detail. Herein, we report on © XXXX American Chemical Society

Scheme 1. Selected Metal-Catalyzed Reduction of Amides with Silanes

the reduction of tertiary amides with only 1 equiv of PhSiH3 under relatively mild conditions.

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RESULTS AND DISCUSSION Initially, the reduction of DMF with Ph2SiH2 was investigated in the presence of 1.0 mol % Cs2CO3 under solvent-free conditions. The 1H NMR spectrum of the crude reaction mixture disclosed the reaction was complete in about 6 h. DMF can also be reduced by the secondary silane Ph2SiH2; the reaction yielded the cyclosiloxane (Ph2SiO)4 in nearly quantitative yield. Since reduction of DMF yielded the volatile Me3N as the product, the reduction of phenyl(piperidin-1yl)methanone (C6H5CONC5H10) with PhSiH3 was investigated as a model system to optimize reaction conditions. The reaction catalyzed by the other alkali carbonates Na2CO3 and K2CO3 has also been investigated under the same conditions. It was found that the reaction catalyzed by Na2CO3 and K2CO3 cannot take place probably due to their low solubility.8 However, the reaction catalyzed by Cs2CO3 proceeded smoothly at elevated temperature (Table 1, entries Received: September 25, 2013

A

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presence of 18-crown-6 ether at room temperature yielded a small amount of formic anion (HCOO−) as indicated by the 1H NMR analysis (see Figure S1 in the Supporting Information). On the basis of this observation, we proposed the possible activation mechanism shown in Scheme 2. The hypervalent

Table 1. Condition Selection for Cs2CO3-Catalyzed Tertiary Amide Formationa

entry

R

cat

temp (°C)

time (h)

silane

conv (%)

1 2 3 4 5 6 7 8 9 10 11 12b 13c 14c

H H H H H H H Cl Cl OMe H H H H

Na2CO3 K2CO3 Cs2CO3 Cs2CO3 Cs2CO3 Cs2CO3 Cs2CO3 Cs2CO3 Cs2CO3 Cs2CO3 Cs2CO3 Cs2CO3 Cs2CO3

80 80 80 25 40 40 60 60 80 25 60 80 80 80

24 24 24 24 12 24 12 24 24 24 5 24 24 24

PhSiH3 PhSiH3 PhSiH3 PhSiH3 PhSiH3 PhSiH3 PhSiH3 PhSiH3 PhSiH3 PhSiH3 PhSiH3 Ph2SiH2 PhMe2SiH (EtO)3SiH

0 0 0 0 0 83 100 80 95 100 0 0 0 0

Scheme 2. Possible Activation Mechanism

silicon species A formed by the attack of carbonate to PhSiH3 underwent hydride transfer to the carbon atom to form B followed by cleavage of the SiO−C bond to yield formic anion and the silicate C. This assumption is in agreement with our experimental observation that the reduction of phenyl(piperidin-1-yl)methanone (C6H5CONC5H10) with PhSiH3 can also be complete with 5.0 mol % loadings of SiMe3OK as the catalyst under the same conditions. After surveying the reaction conditions, various amides have been reduced with the Cs2CO3/PhSiH3 catalytic system. The results are given in Table 2. All of the amides listed in Table 2 can be completely reduced with only 1 equiv of PhSiH3. However, the amides with some functional groups such as carbonyl, ester, and nitro groups did not yield clean products, and the reduction of primary and secondary amides proved to be sluggish. As shown in Table 2, the steric hindrance of the substituents on the nitrogen atom and carbonyl group affects the reactivity: the reaction can take place at room temperature using only 1.0 mol % of catalyst for the small substituents (entries 4, 5, and 14 in Table 2); for sterically hindered substrates, the high catalyst loading (5.0 mol %) and the elevated temperature (80 °C) are required for a complete reduction. Cyclic tertiary amides can be easily reduced to the corresponding amines under room temperature (entries 5−7). The catalyst is selective in the presence of thiophene, furan, halogenm and ether groups (Table 2, entries 10−13). For the substrate with two amide bonds, the reaction can also give the desired product in high yield (Table 2, entry 16).

a

Reaction conditions: amide (3.0 mmol), Cs2CO3 (5.0 mol %), PhSiH3 (0.32 g, 3.0 mmol). Conversion was determined by 1H NMR spectroscopy of the crude reaction mixture. bPh2SiH2 (0.83 g, 4.5 mmol). c9 mmol of the silanes.

1−7) and achieved 100% conversion at 60 °C in 12 h (Table 1, entry 7). The substituents on the phenyl ring of the amide have pronounced effects on the reaction; the electron-donating group on the phenyl ring obviously facilitates the reaction, while the substrates with electron-withdrawing groups are less reactive (Table 1, entries 7−10). Hydrosilanes also have significant effects on the reaction; the primary silane PhSiH3 is the most reactive reagent for the reaction. Compared to the facile reduction of DMF with a low catalyst loading at room temperature, it can be concluded that steric factors of amides have pronounced effects on the catalytic activity. The experiment results demonstrated that the activation process is rather slow (Table 1, entry 11) since almost no conversions have been observed in 5 h. In order to investigate solvent effects, the reaction was also carried out in THF and toluene. It was found that reaction in THF is much faster than in toluene (see the Supporting Information, Table S1). The reaction under solvent-free conditions is the most efficient one. This might be related to the solubility of the catalyst. Under neat conditions, the highly polarized amides also acted as solvents and thus promote the catalytic reaction. The mechanism for the reduction chemistry is not clear at this stage. The solvent effects for the reduction chemistry indicate that the reaction may proceed via an ionic mechanism. It is quite possible that the “naked” carbonate acts as a strong base to initiate the catalytic process. In line with this assumption, the complete reduction of phenyl(piperidin-1yl)methanone with PhSiH3 catalyzed by 5% molar loadings of K2CO3 in the presence of 18-crown-6 ether was observed at 80 °C in 24 h. We reasoned that the most plausible initial step may involve the reduction of carbonate anion by PhSiH3. In order to have experimental support for this assumption, the reaction of Cs2CO3 with PhSiH3 was conducted. However, this reaction does not proceed under solvent-free conditions because Cs2CO3 cannot be dissolved in PhSiH3 in the absence of amides. Instead, the reaction of K2CO3 with PhSiH3 in the

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CONCLUSION In summary, we have developed the Cs2CO3-catalyzed reduction of carboxamides with 1 equiv of PhSiH3. Both the catalyst and reducing reagent are commercially available in large quantity; thus the reduction process can be easily performed in the laboratory and potentially on a large scale for practical applications. However, the limited substrate scope and unique chemistry involved in the catalytic cycle have yet to be investigated. Further studies dealing with applications of the catalytic system to reduction of other substrates and the mechanism of the activation mode are ongoing in our laboratory.

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EXPERIMENTAL SECTION

General Considerations. All solvents were freshly distilled from sodium/benzophenone. CDCl3 was purchased from Cambridge Isototope Laboratories. Amides (a, b, d−g, n), Cs2CO3 (99.9%), and silanes were purchased from Alfa-Aesar or J&K Scientific Ltd. B

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Table 2. Cs2CO3-Catalyzed Reduction of Tertiary Amidesa

a

Reaction conditions: amide (3.0 mmol), PhSiH3 (0.33 g, 3.0 mmol). bIsolated yield. cThe values in parentheses refer to the NMR yield. dAs the product is volatile, the conversion was determined by the 1H NMR spectroscopy of the crude reaction mixture. (4-Methoxyphenyl)(piperidin-1-yl)methanone7a (k). Using 4methoxybenzoyl chloride (8.53 g, 50 mmol) and piperidine (4.36 g, 50 mmol) in the presence of triethylamine (6.07 g, 60 mmol) in dichloromethane (50 mL) at room temperature yielded a colorless liquid (10.40 g, 47.5 mmol, 95%). 1H NMR (400 MHz, CDCl3): δ 7.35−7.37 (m, 2H), 6.88−6.90 (m, 2H), 3.82 (s, 3H), 3.53 (br s, 4H), 1.67 (br s, 2H), 1.58 (br s, 4H). Furan-2-yl(piperidin-1-yl)methanone7a (l). Using furan-2-carbonyl chloride (6.53 g, 50 mmol) and piperidine (4.36 g, 50 mmol) in the presence of triethylamine (6.07 g, 60 mmol) in dichloromethane (50 mL) at room temperature yielded a white solid (8.06 g, 45.0 mmol, 90%). 1H NMR (400 MHz, CDCl3): δ 7.47 (dd, J = 1.6, 0.7 Hz, 1H), 6.93 (dd, J = 3.4, 0.6 Hz, 1H), 6.46 (dd, J = 3.4, 1.8 Hz, 1H), 3.67 (br s, 4H), 1.66 (br s, 2H), 1.60 (br s, 4H). Piperidin-1-yl(thiophen-2-yl)methanone7a (m). Using thiophene2-carbonyl chloride (7.33 g, 50 mmol) and piperidine (4.36 g, 50 mmol) in the presence of triethylamine (6.07 g, 60 mmol) in dichloromethane (50 mL) at room temperature yielded a white solid (8.30 g, 42.5 mmol, 85%). 1H NMR (400 MHz, CDCl3): δ 7.35 (dd, J = 5.0, 1.0 Hz, 1H), 7.19 (dd, J = 3.6, 1.0 Hz, 1H), 6.96 (dd, J = 5.0, 3.7 Hz, 1H), 3.60 (br s, 4H), 1.62 (br s, 2H), 1.57 (br s, 4H). 2,2-Dimethyl-1-(piperidin-1-yl)propan-1-one (o). Using pivaloyl chloride (6.03 g, 50 mmol) and piperidine (4.36 g, 50 mmol) in the presence of triethylamine (6.07 g, 60 mmol) in dichloromethane (50 mL) at room temperature yielded a colorless liquid (7.36 g, 43.5 mmol, 87%). 1H NMR (400 MHz, CDCl3): δ 3.56 (br s, 4H), 1.62 (br s, 2H), 1.52 (br s, 4H), 1.25 (s, 9H). 13C NMR (101 MHz, CDCl3): δ 175.9, 46.1, 38.1, 28.3, 26.0, 24.6. HRMS (ESI): calcd for [C10H19NO, M + H]+ 170.1545, found 170.1539. 1,4-Phenylenebis(piperidin-1-ylmethanone) (p). Using terephthaloyl dichloride (10.15 g, 50 mmol) and piperidine (8.72 g, 100 mmol) in the presence of triethylamine (12.14 g, 120 mmol) in dichloromethane (50 mL) at room temperature yielded a white solid (10.96 g, 36.5 mmol, 73%). Mp: 220 °C. 1H NMR (400 MHz, CDCl3): δ 7.32 (s, 4H), 3.61 (br s, 4H), 3.23 (br s, 4H), 1.58 (br s, 8H), 1.40 (br s, 4H). 13C NMR (101 MHz, CDCl3): δ 169.4, 137.4, 126.8, 48.6, 43.0,

Other amides have been previously reported, and only 1H NMR spectroscopic data are presented. General Procedure for the Preparation of Amides.7a The acyl chloride (50.0 mmol) was slowly added to a solution of the amine (50.0 mmol) in the presence of triethylamine (60.0 mmol) in dichloromethane (50 mL) at room temperature, resulting rapidly in a boiling solution. The reaction mixture was stirred for 30−60 min at room temperature and then was diluted with dichloromethane (50 mL). The solution was transferred to a separation funnel and was washed with 1 N HCl (250 mL). The organic layer was filtered on a short silica gel column and washed with ethyl acetate/hexane (1:1). The combined fractions were concentrated under reduced pressure. Characterization of the Amides. N,N-Dibenzylbenzamide7b (c). Using benzoyl chloride (7.03 g, 50 mmol) and dibenzylamine (9.87 g, 50 mmol) in the presence of triethylamine (6.07 g, 60 mmol) in dichloromethane (50 mL) at room temperature yielded a white solid (13.6 g, 45 mmol, 90%). 1H NMR (400 MHz, CDCl3): δ 7.40−7.43 (m, 2H), 7.17−7.32 (m, 11H), 7.07 (s, 2H), 4.63 (br s, 2H), 4.32 (br s, 2H). Phenyl(piperidin-1-yl)methanone7a (h). Using benzoyl chloride (7.03 g, 50 mmol) and piperidine (4.26 g, 50 mmol) in the presence of triethylamine (6.07 g, 60 mmol) in dichloromethane (50 mL) at room temperature yielded a colorless liquid (8.52 g, 45 mmol, 90%). 1H NMR (400 MHz, CDCl3): δ 7.40 (s, 5H), 3.70 (br s, 2H), 3.33 (br s, 2H), 1.67 (br s, 4H), 1.52 (br s, 2H). Morpholino(phenyl)methanone7a (i). Using benzoyl chloride (7.03 g, 50 mmol) and piperidine (4.36 g, 50 mmol) in the presence of triethylamine (6.07 g, 60 mmol) in dichloromethane (50 mL) at room temperature yielded a colorless liquid (8.12 g, 42.5 mmol, 85%). 1 H NMR (400 MHz, CDCl3): δ 7.40−7.42 (m, 5H), 3.77 (br s, 4H), 3.63 (br s, 2H), 3.44 (br s, 2H). (4-Chlorophenyl)(piperidin-1-yl)methanone9 (j). Using 4-chlorobenzoyl chloride (8.75 g, 50 mmol) and piperidine (4.36 g, 50 mmol) in the presence of triethylamine (6.07 g, 60 mmol) in dichloromethane (50 mL) at room temperature yielded a white solid (10.62 g, 47.5 mmol, 95%). 1H NMR (400 MHz, CDCl3): δ 7.32−7.38 (m, 4H), 3.69 (br s, 2H), 3.33 (br s, 2H), 1.67 (br s, 4H), 1.52 (br s, 2H). C

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4-Benzylmorpholine.7a Using morpholino(phenyl)methanone (574 mg, 3 mmol), Cs2CO3 (49 mg, 0.15 mmol), and PhSiH3 (325 mg, 3 mmol) yielded a colorless liquid (404 mg, 2.28 mmol, 76%). 1H NMR (400 MHz, CDCl3): δ 7.26−7.33 (m, 5H), 3.70−3.72 (m, 4H), 3.50 (s, 2H), 2.43−2.45 (m, 4H). 13C NMR (101 MHz, CDCl3): δ 137.7, 129.2, 128.2, 127.1, 67.0, 63.4, 53.6. HRMS (ESI): calcd for [C11H15NO, M + H]+ 178.1232, found 178.1229. 1-(4-Chlorobenzyl)piperidine. Using (4-chlorophenyl)(piperidin-1yl)methanone (671 mg, 3 mmol), Cs2CO3 (49 mg, 0.15 mmol), and PhSiH3 (325 mg, 3 mmol) yielded a colorless liquid (528 mg, 2.52 mmol, 84%). 1H NMR (400 MHz, CDCl3): δ 7.16−7.21 (m, 4H), 3.36 (s, 2H), 2.28 (br s, 4H), 1.47−1.52 (m, 4H), 1.35−1.37 (m, 2H). 13 C NMR (101 MHz, CDCl3): δ 137.0, 132.5, 130.5, 128.2, 63.0, 54.4, 25.9, 24.3. HRMS (ESI): calcd for [C12H16ClN, M + H]+ 210.1050, found 210.1044. 1-(4-Methoxybenzyl)piperidine.7a Using (4-methoxyphenyl)(piperidin-1-yl)methanone (658 mg, 3 mmol), Cs2CO3 (49 mg, 0.15 mmol), and PhSiH3 (325 mg, 3 mmol) yielded a colorless liquid (585 mg, 2.85 mmol, 95%). 1H NMR (400 MHz, CDCl3): δ 7.20−7.23 (m, 2H), 6.83−6.86 (m, 2H), 3.80 (s, 3H), 3.41 (s, 2H), 2.35 (br s, 4H), 1.53−1.59 (m, 4H), 1.42−1.43 (m, 2H). 13C NMR (101 MHz, CDCl3): δ 158.5, 130.5, 130.4, 113.4, 63.2, 55.2, 54.3, 25.9, 24.4. HRMS (ESI): calcd for [C13H19NO, M + H]+ 206.1545, found 206.1540. 1-(Furan-2-ylmethyl)piperidine.7a Using furan-2-yl(piperidin-1-yl)methanone (538 mg, 3 mmol), Cs2CO3 (49 mg, 0.15 mmol), and PhSiH3 (325 mg, 3 mmol) yielded a colorless liquid (451 mg, 2.73 mmol, 91%). 1H NMR (400 MHz, CDCl3): δ 7.36 (dd, J = 1.8, 0.8 Hz, 1H), 6.30 (dd, J = 3.1, 1.9 Hz, 1H), 6.17 (dd, J = 3.1, 0.5 Hz, 1H), 3.49 (s, 2H), 2.39 (br s, 4H), 1.56−1.60 (m, 4H), 1.40−1.42 (m, 2H). 13C NMR (101 MHz, CDCl3): δ 152.1, 141.9, 109.9, 108.5, 55.6, 54.1, 25.8, 24.1. HRMS (ESI): calcd for [C10H15NO, M + H]+ 166.1232, found 166.1229. 1-(tThiophen-2-ylmethyl)piperidine.7a Using piperidin-1-yl(thiophen-2-yl)methanone (586 mg, 3 mmol), Cs2CO3 (49 mg, 0.15 mmol), and PhSiH3 (325 mg, 3 mmol) yielded a colorless liquid (457 mg, 2.52 mmol, 84%). 1H NMR (400 MHz, CDCl3): δ 7.14 (dd, J = 5.1, 1.2 Hz, 1H), 6.87 (dd, J = 5.1, 3.4 Hz, 1H), 6.82 (dd, J = 3.4, 0.9 Hz, 1H), 3.62 (s, 2H), 2.34 (br s, 4H), 1.48−1.54 (m, 4H), 1.34−1.36 (m, 2H). 13C NMR (101 MHz, CDCl3): δ 141.8, 126.3, 125.9, 124.7, 57.7, 54.0, 25.9, 24.2. HRMS (ESI): calcd for [C10H15NS, M + H]+ 182.1004, found 182.0996. N,N-Dimethylethanamine. Using N,N-dimethylacetamide (522 mg, 6 mmol), Cs2CO3 (20 mg, 0.06 mmol), and PhSiH3 (650 mg, 6 mmol). NMR yield: 100%. 1-Neopentylpiperidine. Using 2,2-dimethyl-1-(piperidin-1-yl)propan-1-one (508 mg, 3 mmol), Cs2CO3 (49 mg, 0.15 mmol), and PhSiH3 (325 mg, 3 mmol) yielded a colorless liquid (359 mg, 2.31 mmol, 77%). 1H NMR (400 MHz, CDCl3): δ 2.43 (br s, 4H), 1.99 (s, 2H), 1.51−1.54 (m, 4H), 1.36−1.47 (m, 2H), 0.85 (s, 9H). 13C NMR (101 MHz, CDCl3): δ 70.8, 57.3, 33.1, 27.8, 26.5, 24.1. HRMS (ESI): calcd for [C10H21N, M + H]+ 156.1752, found 156.1748. 1,4-Bis(piperidin-1-ylmethyl)benzene. Using 1,4-phenylenebis(piperidin-1-ylmethanone) (901 mg, 3 mmol), Cs2CO3 (49 mg, 0.15 mmol), and PhSiH3 (650 mg, 6 mmol) yielded a white solid (711 mg, 2.61 mmol, 87%). Mp: 93 °C. 1H NMR (400 MHz, CDCl3): δ 7.24− 7.26 (m, 4H), 3.45 (s, 4H), 2.36 (br s, 8H), 1.54−1.59 (m, 8H), 1.42− 1.43 (m, 4H). 13C NMR (101 MHz, CDCl3): δ 137.1, 129.0, 63.7, 54.5, 26.0, 24.4. HRMS (ESI): calcd for [C18H28N2, M + H]+ 273.2331, found 273.2328.

26.4, 25.5, 24.4. HRMS (ESI): calcd for [C18H24N2O2, M + H]+ 301.1916, found 301.1914. Typical Procedure for the Catalytic Reduction of Amides. N,N-Dimethyl-1-phenylmethanamine.3i A 25 mL Schlenk tube containing a stir bar was charged with 5.0 mol % Cs2CO3 (49 mg, 0.15 mmol). Subsequently, N,N-dimethylbenzamide (450 mg, 3.0 mmol) and PhSiH3 (325 mg, 3.0 mmol) were added. The mixture was stirred at room temperature for 24 h. Dichloromethane (0.5 mL) was added to the mixture. The mixture was purified on a short silica gel column and washed with ethyl acetate/hexane/Et3N (100:10:1). The solvents were removed to give the product as a colorless liquid (353 mg, 2.61 mmol, 87%). 1H NMR (400 MHz, CDCl3): δ 7.15−7.25 (m, 5H), 3.35 (s, 2H), 2.17 (s, 6H). 13C NMR (101 MHz, CDCl3): δ 138.6, 129.1, 128.2, 127.0, 64.3, 45.3. HRMS (ESI): calcd for [C9H13N, M + H]+ 136.1126, found 136.1118. Reduction of the Other Amides. The other reactions were performed similarly to that described for the amide a. For amides d−g, k, and n, the reactions were conducted at 80 °C; the others were performed at room temperature. The mixtures were stirred for 24 h (for amide d, 30 h; e, 12 h; f and g, 48 h). N-Benzyl-N-isopropylpropan-2-amine.7b Using N,N-diisopropylbenzamide (616 mg, 3 mmol), Cs2CO3 (49 mg, 0.15 mmol), and PhSiH3 (325 mg, 3 mmol) yielded a colorless liquid (528 mg, 2.76 mmol, 92%). 1H NMR (400 MHz, CDCl3): δ 7.39−7.41 (m, 2H), 7.28−7.31 (m, 2H), 7.19−7.22 (m, 1H), 3.66 (s, 2H), 3.03 (sept, 3J = 6.6 Hz, 2H), 1.04 (d, 3J = 6.6 Hz, 12H). 13C NMR (101 MHz, CDCl3): δ 143.3, 128.0, 127.9, 126.1, 48.9, 47.8, 20.8. HRMS (ESI): calcd for [C13H21N, M + H]+ 192.1752, found 192.1743. Tribenzylamine.7b Using N,N-dibenzylbenzamide (904 mg, 3 mmol), Cs2CO3 (49 mg, 0.15 mmol), and PhSiH3 (325 mg, 3 mmol) yielded a white solid (672 mg, 2.34 mmol, 78%). 1H NMR (400 MHz, CDCl3): δ 7.31−7.33 (m, 5H), 7.20−7.23 (m, 7H), 7.12− 7.14 (m, 3H), 3.46 (s, 6H). 13C NMR (101 MHz, CDCl3): δ 139.6, 128.7, 128.2, 126.8, 57.9. HRMS (ESI): calcd for [C21H21N, M + H]+ 288.1752, found 288.1743. 1-Methylpiperidine. Using piperidine-1-carbaldehyde (340 mg, 3 mmol), Cs2CO3 (10 mg, 0.03 mmol), and PhSiH3 (325 mg, 3 mmol) and distillation yielded a colorless liquid (152 mg, 1.53 mmol, 51%). 1 H NMR (400 MHz, CDCl3): δ 2.30−2.31(br s, 4H), 2.22 (s, 3H), 1.54−1.60 (m, 4H), 1.40 (br s, 2H). 13C NMR (101 MHz, CDCl3): δ 56.5, 46.9, 26.0, 23.7. HRMS (ESI): calcd for [C6H13N, M + H]+ 100.1126, found 100.1121. 1-Methylpyrrolidine. Using 1-methylpyrrolidin-2-one (594 mg, 6 mmol), Cs2CO3 (20 mg, 0.06 mmol), and PhSiH3 (650 mg, 6 mmol) and distillation yielded a colorless liquid (178 mg, 2.10 mmol, 35%). 1 H NMR (400 MHz, CDCl3): δ 2.43−2.46 (m, 4H), 2.34 (s, 3H), 1.76−1.79 (m, 4H). 13C NMR (101 MHz, CDCl3): δ 56.3, 42.1, 24.0. HRMS (ESI): calcd for [C5H11N, M + H]+ 86.0970, found 86.0961. 1-Methylazepane.10 Using 1-methylazepan-2-one (382 mg, 3 mmol), Cs2CO3 (49 mg, 0.15 mmol), and PhSiH3 (325 mg, 3 mmol) and distillation yielded a colorless liquid (241 mg, 2.13 mmol, 71%). 1H NMR (400 MHz, CDCl3): δ 2.54−2.57 (m, 4H), 2.35 (s, 3H), 1.66−1.68 (m, 4H), 1.60−1.62 (m, 4H). 13C NMR (101 MHz, CDCl3): δ 58.4, 47.3, 27.8, 26.6. HRMS (ESI): calcd for [C7H15N, M + H]+ 114.1283, found 114.1276. 1-Benzylpyrrolidine.3i Using 1-benzylpyrrolidin-2-one (526 mg, 3 mmol), Cs2CO3 (49 mg, 0.15 mmol), and PhSiH3 (325 mg, 3 mmol) yielded a colorless liquid (363 mg, 2.25 mmol, 75%). 1H NMR (400 MHz, CDCl3): δ 7.29−7.33 (m, 3H), 7.24−7.26 (m, 2H), 3.62 (s, 2H), 2.50−2.52 (m, 4H), 1.77−1.80 (m, 4H). 13C NMR (101 MHz, CDCl3): δ 139.2, 128.9, 128.2, 126.9, 60.7, 54.1, 23.4. HRMS (ESI): calcd for [C11H15N, M + H]+ 162.1283, found 162.1274. 1-Benzylpiperidine.7a Using phenyl(piperidin-1-yl)methanone (568 mg, 3 mmol), Cs2CO3 (49 mg, 0.15 mmol), and PhSiH3 (325 mg, 3 mmol) yielded a colorless liquid (473 mg, 2.70 mmol, 90%). 1H NMR (400 MHz, CDCl3): δ 7.16−7.24 (m, 5H), 3.41 (s, 2H), 2.31 (br s, 4H), 1.48−1.53 (m, 4H), 1.35−1.37 (m, 2H). 13C NMR (101 MHz, CDCl3): δ 138.3, 129.3, 128.1, 126.9, 63.8, 54.4, 25.9, 24.3. HRMS (ESI): calcd for [C12H17N, M + H]+ 176.1439, found 176.1434.

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ASSOCIATED CONTENT

S Supporting Information *

Text and figures giving general procedures and characterization data as well as 1H, 13C NMR spectra and HRMS for amides and amines. This material is available free of charge via the Internet at http://pubs.acs.org. D

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China and 973 Program (grant no. 2012CB821600).

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dx.doi.org/10.1021/om400951n | Organometallics XXXX, XXX, XXX−XXX