Selective Reduction of Carboxylic acids to Aldehydes Catalyzed by B(C 6 F 5 ) 3

Transcription

1 S1 Selective Reduction of Carboxylic acids to Aldehydes Catalyzed by B(C 6 F 5 ) 3 David Bézier, Sehoon Park and Maurice Brookhart* Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina mbrookhart@unc.edu Supporting Information 1. General remarks S1-S2 2. General procedures for the selective reduction of carboxylic acids to aldehydes catalyzed by B(C 6 F 5 ) 3 S2-S3 3. Characterization data of acetals 2a and 2q S3 4. Characterization data of aldehydes S4-S H NMR and 13 C{ 1 H} NMR spectra of acetals 2a and 2q S-S H NMR and 13 C{ 1 H} NMR spectra of aldehydes S12-S32 General remarks All manipulations were carried out using standard Schlenk, high-vacuum, and glovebox techniques. Argon was purified by passing through columns of BASF R3-11 catalyst (Chemalog) and 4 Å molecular sieves. Benzene-d 6, toluene-d 8 and CD 2 Cl 2 (Cambridge Isotope Laboratories) were used without purification. All silanes were purchased from Aldrich and Gelest and stored under argon over 4 Å molecular sieves. All carboxylic acid substrates were purchased from commercial sources and usually used without further purification except for -decanoic acid, 9- undecynoic acid and 2-thiopheneacetic acid which were sublimed. Technical grade petroleum

2 S2 ether (- C bp.), ethyl acetate and dichloromethane were used for chromatography. B(C 6 F 5 ) 3 was purchased from Acros and Gelest and dried by mixing with Me 2 Si(Cl)H for 1 h followed by evaporation under vacuum. NMR spectra were recorded on Bruker spectrometers (DRX-, AVANCE- and AVANCE-). 1 H and 13 C NMR spectra were referenced to residual solvent peaks. General procedures for the selective reduction of carboxylic acids to aldehydes catalyzed by B(C 6 F 5 ) 3 From aliphatic carboxylic acids (procedure A): To a J. Young NMR tube was added RCO 2 H (.5 mmol), C 6 D 6 (.3 ml), and R' 3 SiH (1.15 mmol, 2.3 equiv) in a glovebox. A stock solution of B(C 6 F 5 ) 3 was previously prepared by dissolving 26 g (5 mmol) of B(C 6 F 5 ) 3 in 3 ml of C 6 D 6. From 15 µl (5 mol %) to µl (1 mol %) was added to the reaction mixture. (When 2 mol % of B(C 6 F 5 ) 3 was used, the powder was first added into the J. Young NMR tube). The reaction was initiated at 23 C and followed by 1 H NMR spectroscopy. At the end of the reaction, the crude reaction mixture was transferred from the NMR tube to a Schlenk flask and all volatiles (solvent + excess of silane) were removed under vacuum. A1: For substrates 1a, 1b, 1h, 1j, 1k, 1m, 1n: Following the above procedure, 2 ml of THF was added, followed by 2 ml of 1 M HCl(aq) with vigorous stirring. The reaction mixture was further stirred for 3 h at room temperature and was extracted with diethyl ether (3 ml). The combined organic layers were dried over anhydrous MgSO 4, filtered and concentrated under vacuum. The residue was then purified by silica gel column chromatography using an ethyl acetate/petroleum ether mixture (1/) to afford the desired product. A2: For substrates 1c, 1d, 1e, 1f, 1g, 1i, 1l, 1o (volatile or sensitive aldehydes) : Following the above procedure, the reaction mixture was diluted with 2.5 ml EtOH, and to the mixture was added under vigorous stirring Brady s reagent [.15 g of 2,4-dinitrophenylhydrazine (% H 2 O),.5 ml of concentrated H 2 SO 4,.75 ml of H 2 O, and 2.5 ml of EtOH]. 1 A yellow or orange precipitate was formed immediately. The solid was collected through filtration using a glass frits and washed with H 2 O. Pure product was obtained by recrystallization from EtOH. From aromatic carboxylic acids (procedure B, substrates 1q, 1r, 1t, 1u, 1v, 1w): To a J. Young NMR tube was added B(C 6 F 5 ) 3 (2 mol %, 52 g), RCO 2 H (.5 mmol), and Ph 3 SiH ( M. Behforouz, J. L. Bolan, M. S. Flynt, J. Org. Chem. 1985,,

3 S3 mmol, 2.5 equiv,.326 g), followed by CD 2 Cl 2 (.6 ml) in a glove box. The hydrosilylation reaction was conducted at 23 C and monitored by 1 H NMR spectroscopy. At the end of the reaction, the crude reaction mixture was filtered through a plug of silica gel with CH 2 Cl 2 as an eluent in order to remove B(C 6 F 5 ) 3 and the filtrate was evaporated. Then 2.5 ml of Et 2 O was added followed by.5 ml of trifluoroacetic acid (99%) with vigorous stirring. The reaction mixture was stirred for 1.5 hour at room temperature and 2.5 ml of Et 2 O was added. The reaction was stirred for another 1.5 h followed by addition of 4 ml of H 2 O and extracted with diethyl ether (3 ml). The combined organic layers were dried over anhydrous MgSO 4, filtered and concentrated under vacuum. The yield of the aldehyde was first determined by 1 H NMR of the crude mixture using EtOAc (.5 mmol, 49 µl) as an internal standard in CD 2 Cl 2. For the substrates 1r, 1t, 1u, the residue was then purified by silica gel column chromatography using a CH 2 Cl 2 / petroleum ether mixture (4/) to afford the desired product. For the substrate 1s: the procedure A1 was followed. (2a) Characterization data of acetals 2a and 2q From crude reaction mixture, before quenching: 1 H NMR ( MHz, C 6 D 6 ): δ (m, 4H), (m, 1H), 5.35 (t, J = 4.9, 1H), (m, 2H), 5- (m, 2H), 1.12 (t, J =, 18H),.76 (q, J =, 12H). 13 C{ 1 H} NMR (1 MHz, CDCl 3 ): δ , , , , 93.19, 46, 31.39, 7.24 (6C), 5.91 (6C). (2q) From crude reaction mixture, before quenching: 1 H NMR ( MHz, CD 2 Cl 2 ): δ (m, 12H), (m, 6H), (m, 17H), 6.47 (s, 1H). 13 C{ 1 H} NMR (1 MHz, CDCl 3 ): δ , 138 (6C), (3C),.48 (4C), (2C), (6C), (2C),

4 S4 Characterization data for aldehydes Hydrocinnamaldehyde (5a) O H The compound was prepared as described using the procedure A1 (m = 58 mg, 86% isolated yield). 1 H NMR ( MHz, CDCl 3 ): δ 9.83 (t, J = 1.3, 1H), (m, 2H), (m, 3H), 2.97 (t, J = 7.6, 2H), 2.79 (td, J = 7.7, 1.3, 2H). 13 C{ 1 H} NMR (151 MHz, CDCl 3 ): δ 1.64,.42, , , , 45.35, 28.. Phenylacetaldehyde (5b) O H The compound was prepared as described using the procedure A1 (m = 43 mg, 71% isolated yield). 1 H NMR ( MHz, CDCl 3 ): δ 9.76 (t, J = 2.1, 1H), (m, 3H), (m, 2H), 3. (d, J = 2.1, 2H). 13 C{ 1 H} NMR (1 MHz, CDCl 3 ): δ , , , , , (Propylidene)-2-(2,4-dinitrophenyl)hydrazine (5c) The compound was prepared as described using the procedure A2 (m = 89 mg, 75% isolated yield). 1 H NMR ( MHz, CDCl 3 ): δ 12 (s, 1H), 9.12 (d, J = 2.3, 1H), 8. (dd, J = 9.6, 2.3, 1H), 7.94 (d, J = 9.6, 1H), 7.57 (t, J = 4.8, 1H), 2.47 (qd, J = 7.5, 4.8, 2H), 1.22 (t, J = 7.5, 3H). 13 C{ 1 H} NMR (1 MHz, CDCl 3 ): δ 153., , ,.9, , , , 26.17, (Hexylidene)-2-(2,4-dinitrophenyl)hydrazine (5d) The compound was prepared as described using the procedure A2 (m = 99 mg, 71% isolated yield). 1 H NMR ( MHz, CDCl 3 ): δ 12 (s, 1H), 9.12 (d, J = 2.5, 1H), 8. (dd, J = 9.6, 2.5, 1H), 7.93 (d, J = 9.6, 1H), 7.54 (t, J = 5.4, 1H), 2.43 (dt, J = 7.5, 5.6, 2H), (m, 2H), (m, 4H),.93 (t, J = 6.9, 3H). 13 C{ 1 H} NMR (151 MHz, CDCl 3 ): δ , , ,.7, , , , 32.61, 31.45, 26.12, 22.54, 18.

5 S5 Decanal (5e) The compound was prepared as described using the procedure A1 (m = 56 mg, 72% isolated yield). 1 H NMR ( MHz, CDCl 3 ): δ 9.75 (t, J = 1.7, 1H), 2. (dt, J = 1.7, 7.4, 2H), (m, 2H), (m, 12H),.87 (t, J = 6.8, 3H). 13 C{ 1 H} NMR (1 MHz, CDCl 3 ): δ 2.88, 44, 31.98, 29.49, 29.36, 29., 29.13, 22.77, 22.23, (2-Methylpropylidene)-2-(2,4-dinitrophenyl)hydrazine (5f) The compound was prepared as described using the procedure A2 (m = 5 mg, 83% isolated yield). 1 H NMR ( MHz, CDCl 3 ): δ.98 (s, 1H), 9. (d, J = 2.4, 1H), 8.28 (dd, J = 9.4, 2.1, 1H), 7.92 (d, J = 9.6, 1H), 7.48 (d, J = 4.8, 1H), (m, 1H), 1.21 (t, J =, 6H). 13 C{ 1 H} NMR (151 MHz, CDCl 3 ): δ , , ,.5, 128., , , 31.95, (Cyclohexylmethylene)-2-(2,4-dinitrophenyl)hydrazine (5g) The compound was prepared as described using the procedure A2 (m = 115 mg, 79% isolated yield). 1 H NMR ( MHz, CDCl 3 ): δ.97 (s, 1H), 9. (br.s, 1H), 8.28 (d, J = 8.9, 2.1, 1H), 7.91 (d, J = 9.5, 1H), 7.44 (d, J = 4.5, 1H), 2.41 (m, 1H), (m, 2H), (m, 3H), (m, 5H). 13 C{ 1 H} NMR (151 MHz, CDCl 3 ): δ , , ,.4, , , , 47,.16 (2C), 25.98, (2C). 2-Phenylpropionaldehyde (5h) The compound was prepared as described using the procedure A1 (m = 53 mg, 79% isolated yield). 1 H NMR ( MHz, CDCl 3 ): δ 9. (d, J = 1.3, 1H), (m, 2H), (m, 1H), (m, 2H), 3.64 (q, J = 7.2, 1H), 1.45 (d, J = 7.1, 3H). 13 C{ 1 H} NMR (1 MHz, CDCl 3 ): δ 1., , , , , 53.12,

6 S6 1-(2,2-dimethylmethylpropylidene)-2-(2,4-dinitrophenyl)hydrazine (5i) The compound was prepared as described using the procedure A2 (m = 1 mg, 76% isolated yield). 1 H NMR ( MHz, CDCl 3 ): δ.95 (s, 1H), 9.12 (d, J = 2.3, 1H), 8. (dd, J = 9.5, 2.1, 1H), 7.92 (d, J = 9.6, 1H), 7.44 (s, 1H), 1.21 (s, 9H). 13 C{ 1 H} NMR (1 MHz, CDCl 3 ): δ , , ,.2, , 123., , 35.69, (3C). 1-Adamantane carbaldehyde (5j) The compound was prepared as described using the procedure A1 (m = 68 mg, 83% isolated yield). 1 H NMR ( MHz, CDCl 3 ): δ 9. (s, 1H), 6 (m, 3H), (m, 12H). 13 C{ 1 H} NMR (1 MHz, CDCl 3 ): δ 6, 44.94, (3C), (3C), (3C). (Z)-9-Octadecenal (5k) The compound was prepared as described using the procedure A1 (m = 127 mg, 95% isolated yield). 1 H NMR ( MHz, CDCl 3 ): δ 9.74 (t, J = 1.7, 1H), (m, 2H), 2.39 (dt, J = 1.7, 7.4, 2H), (m, 4H), (m, 2H), (m, H),.86 (t, J = 6.8, 3H). 13 C{ 1 H} NMR (1 MHz, CDCl 3 ): δ 2.85,., ,, 31, 29.86, 29.76, 29.63, (2C), 29.36, 29.24, 29.15, 27.31, 27.24, 22.78, 22.16, (Hex-3-enylidene)-2-(2,4-dinitrophenyl)hydrazine (5l) The compound was prepared as described using the procedure A2 (m = mg, 65% isolated yield, containing 83% of 5l and 17% of the isomer 1-(hex-2-enylidene)-2-(2,4- dinitrophenyl)hydrazine). 5l : 1 H NMR ( MHz, CDCl 3 ): δ 14 (s, 1H), 9.12 (d, J = 2.4, 1H), 8. (dd, J = 9.5, 2.1, 1H), 7.94 (d, J = 9.6, 1H), 7.47 (t, J = 5.5, 1H), 5.67 (dt, J = 13.7, 6.3, 1H), 5.48 (dt, J = 13.7, 6.4, 1H), 3.13 (t, J = 5.6, 2H), 8 (dq, J = 13.7, 6.9, 2H), 1 (t, J =, 3H). 13 C{ 1 H} NMR (151 MHz, CDCl 3 ): δ 152, , , ,., , , , , 35., 25.78,

7 S7 9-Undecynal (5m) The compound was prepared as described using the procedure A1 (m = 76 mg, 91% isolated yield). 1 H NMR ( MHz, CDCl 3 ): δ 9.76 (t, J = 1.8, 1H), 2.42 (dt, J = 1.7, 7.4, 2H), (m, 2H), 1.77 (t, J = 2.5, 3H), (m, 2H), (m, 2H), (m, 6H). 13 C{ 1 H} NMR (1 MHz, CDCl 3 ): δ 2., 79.28, 75.49, 43.95, 29.12, 23, 28.96, 28.69, 29, 18.75, Bromodecanal (5n) The compound was prepared as described using the procedure A1 (m = 5 mg, 89% isolated yield). 1 H NMR ( MHz, CDCl 3 ): δ 9.76 (t, J = 1.7, 1H), 3. (t, J = 6.8, 2H), 2.42 (dt, J = 1.7, 7.4, 2H), (m, 2H), (m, 2H), (m, 2H), (m, 8H). 13 C{ 1 H} NMR (1 MHz, CDCl 3 ): δ 2.91, 43.95, 37, 32.85, 29., 29.27, 29.16, 28.73, 28.18, (2-Thiophen-2-yl)ethylidene)-2-(2,4-dinitrophenyl)hydrazine (5o) The compound was prepared as described using the procedure A2 due to light sensitivity of the pure aldehyde (m = 7 mg, % isolated yield). 1 H NMR ( MHz, CDCl 3 ): δ 18 (s, 1H), 9.12 (s, 1H), 8.33 (d, J =, 1H), 7.98 (d, J = 9.3, 1H), 7.61 (t, J = 4.6, 1H), 7.26 (s, 1H), (m, 2H), 3.97 (d, J = 4.4, 2H). 13 C{ 1 H} NMR (1 MHz, CDCl 3 ): δ , , , ,.7, , , 126., , , 116., Benzaldehyde (5q) The compound was prepared as described using the procedure B. The yield was determined by 1 H NMR of the crude mixture using EtOAc as an internal standard (yield = 72%). 1 H NMR ( MHz, CD 2 Cl 2 ): δ 9.98 (s, 1H), 7.87 (d, J = 7.3, 2H), (m, 3H).

8 S8 p-tolualdehyde (5r) The compound was prepared as described using the procedure B (m = 41 mg, 68% isolated yield). 1 H NMR ( MHz, CDCl 3 ): δ 9.93 (s, 1H), 7.74 (d, J = 8.1, 2H), 7.29 (d, J =, 2H), 2. (s, 3H). 13 C{ 1 H} NMR (1 MHz, CDCl 3 ): δ , , , , , o-tolualdehyde (5s) The compound was prepared as described using the procedure A1 (m = 42 mg, 69% isolated yield). 1 H NMR ( MHz, CDCl 3 ): δ.27 (s, 1H), 7. (dd, J = 7.6, 1.3, 1H), 7.48 (dt, J = 7.5, 1.4, 1H), 7.36 (t, J = 7.5, 1H), 7.26 (d, J = 7.5, 1H), 2.68 (s, 3H). 13 C{ 1 H} NMR (1 MHz, CDCl 3 ): δ ,.75, , , , , , 19.. Biphenyl-4-carboxaldehyde (5t) The compound was prepared as described using the procedure B (m = 68 mg, 75% isolated yield). 1 H NMR ( MHz, CDCl 3 ): δ 6 (s, 1H), 7.96 (d, J = 8.3, 2H), 7.76 (d, J = 8.2, 2H), (m, 2H), 7.49 (t, J = 7.6, 2H), 7.43 (t, J = 7.4, 1H). 13 C{ 1 H} NMR (151 MHz, CDCl 3 ): δ 197, , , ,., , 128., , Bromobenzaldehyde (5u) The compound was prepared as described using the procedure B (m = 66 mg, 72% isolated yield). 1 H NMR ( MHz, CDCl 3 ): δ 9.96 (s, 1H), 7.73 (d, J = 8.2, 2H), 7.67 (d, J = 8.2, 2H). 13 C{ 1 H} NMR (1 MHz, CDCl 3 ): δ , , , 137, Chlorobenzaldehyde (5v) The compound was prepared as described using the procedure B. The yield was determined by

9 1 H NMR of the crude mixture using EtOAc as an internal standard (yield = 87%). 1 H NMR ( MHz, CD 2 Cl 2 ): δ 9.94 (s, 1H), 7.86 (d, J = 7.3, 2H), 7.57 (d, J = 7.3, 2H). 4-(Trifluoromethyl)benzaldehyde (5w) S9 The compound was prepared as described using the procedure B. The yield was determined by 1 H NMR of the crude mixture using EtOAc as an internal standard (yield = 68%). 1 H NMR ( MHz, CD 2 Cl 2 ): δ 7 (s, 1H), 5 (d, J = 7.8, 2H), 7.87 (d, J = 7.8, 2H).

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12 S12 1 H NMR and 13 C{ 1 H} NMR spectra of aldehydes ppm (f1)

13 S13 ppm (f1) ppm (f1)

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19 S19 ppm (f1) ppm (f1)

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27 S Et2O + EtOAc EtOAc Ph3SiOSiPh3 Et2O EtOAc Ph3SiH

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32 S Ph3SiOSiPh3 EtOAc Et2O + EtOAc EtOAC Et2O Ph3SiH Et2O Et2O + EtOAc TFA Ph3SiOSiPh3 EtOAc EtOAc