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Palladium-Catalyzed Allylic Acyloxylation of Terminal Alkenes in the Presence of a Base Emilie Thiery, Chahinez Aouf, Julien Belloy, Dominique Harakat, Jean Le Bras,* and Jacques Muzart Institut de Chimie Mol eculaire de Reims, UMR 6229 CNRSUniversit e de Reims Champagne-Ardenne, UFR des Sciences exactes et naturelles, BP 1039, 51687 REIMS Cedex 2, France
[email protected] Received December 7, 2009
The efficiency and the selectivity of the Pd-catalyzed oxidation, in carboxylic acids, of terminal alkenes are strongly improved in the presence of a base. The methodology is particularly well adapted for the oxidation of homoallylic alcohols, for which the resulting acyloxylated products are obtained selectively as E-isomers in fair to good yields.
Palladium(II)-catalyzed allylic oxidation of internal or cyclic olefins in acetic acid is an efficient process for the synthesis of allylic acetates.1 On the other hand, terminal olefins generally yield mixtures of allylic acetates, vinyl acetates, and ketones.2 Recently, two important progresses have been achieved toward more selective transformations. White et al. demonstrated that the association of Pd(OAc)2, benzoquinone (BQ), and DMSO or a bis(sulfoxide) ligand promoted the regio- and stereoselective allylic acetoxylation of terminal alkenes. In addition, either linear or branched (1) (a) Beccalli, E. M.; Broggini, G.; Martinelli, M.; Sottocornola, S. Chem. Rev. 2007, 107, 5318. (b) Frison, J.-C.; Legros, J.; Bolm, C. Copper- and Palladium-Catalyzed Allylic Acyloxylations; Wiley-VCH Verlag GmbH & Co: Weinheim, Germany, 2005; Vol. 2. (c) Grennberg, H.; B€ackvall, J.-E. Allylic oxidations: palladium-catalyzed allylic oxidation of olefins; Wiley-VCH Verlag GmbH & Co: Weinheim, Germany, 2004; Vol. 2. (d) Muzart, J. Bull. Soc. Chim. Fr. 1986, 65. (2) (a) Tsuji, J. Palladium Reagents and Catalysts: New Perspectives for the 21st Century; Wiley and Sons: New York, 2004. (b) Åkermark, B.; Larsson, E. M.; Oslob, J. D. J. Org. Chem. 1994, 59, 5729. (c) Kitching, W.; Rappoport, Z.; Winstein, S.; Yong, W. G. J. Am. Chem. Soc. 1966, 88, 2054. (3) (a) Covell, D. J.; White, M. C. Angew. Chem., Int. Ed. 2008, 47, 6448. (b) Fraunhoffer, K. J.; Prabagaran, N.; Sirois, L. E.; White, M. C. J. Am. Chem. Soc. 2006, 128, 9032. (c) Delcamp, J. H.; White, M. C. J. Am. Chem. Soc. 2006, 128, 15076. (d) Covell, D. J.; Vermeulen, N. A.; Labenz, N. A.; White, M. C. Angew. Chem., Int. Ed. 2006, 45, 8217. (e) Fraunhoffer, K. J.; Bachovchin, D. A.; White, M. C. Org. Lett. 2005, 7, 223. (f) Chen, M. S.; Prabagaran, N.; Labenz, N. A.; White, M. C. J. Am. Chem. Soc. 2005, 127, 6970. (g) Chen, M. S.; White, M. C. J. Am. Chem. Soc. 2004, 126, 1346.
DOI: 10.1021/jo902587u r 2010 American Chemical Society
Published on Web 02/09/2010
products were selectively obtained depending on the reaction conditions.3 This methodology has been applied in the total synthesis of 6-deoxyerythronolide B, through a C-H oxidative macrolactonization, increasing the overall efficiency of the synthesis and providing stereochemical control at a key lactone position.4 Kaneda and co-workers described a regioselective process leading to linear allylic acetates using N,N-dimethylacetamide (DMA) as solvent and molecular oxygen as the sole oxidant, high pressures of O2 (6 atm) being required, however.5 Bipyrimidines as ligands were also found to improve the allylic acetoxylation of olefins.6 The proposed mechanism of such transformations generally involves π-allyl-Pd(II) intermediates.3f,6,7 Surprisingly, the influence of additives, such as acetate salts, has not received so much attention for the oxidation of terminal olefins.8 Such compounds could act as bases to facilitate the formation of π-allyl complexes,9 and as nucleophiles on such complexes. Herein, we disclose our results on the use of bases for the Pd-catalyzed oxidation of terminal alkenes. The oxidation of allylbenzene (1a) in the presence of Pd(OAc)2 (0.05 equiv) and BQ (2.0 equiv) in AcOH at 40 °C for 24 h led to a high conversion, but as observed before,3g to a low yield of cinnamyl acetate (2a) (Table 1, entry 1). The use of DMSO or DMA as the cosolvent improved the selectivity of the reaction, but dropped the conversion (entries 2 and 3). Almost full conversion was observed with CH3CN as cosolvent, leading to 2a in 54% yield (entry 4). CH2Cl2 was not an efficient cosolvent (entry 5). In AcOH containing NaOAc as additive, 2a can be produced in high yields but the results were inconsistent (entry 6). In contrast, reproducible results were obtained in EtCO2H containing LiOH 3 H2O as a base,10 affording 3a in up to 75% yield, with high regioselectivity and good stereoselectivity (entries 7 and 8). The use of MnO2, MnO2/BQ, O2/Cu(OAc)2, or O2 as oxidizing agents led to lower conversions and yields, but in some cases to higher L/B and E/Z ratios (entries 9-12). The scope of the process was then examined, under the experimental conditions of entry 8 of Table 1 (namely afterward, method A). An electron donating group on the arene decreases the regioselectivity of the oxidation (Table 2, 3b and 3c), while an electron withdrawing group did not affect it (3d). The methodology was found to be particularly well adapted to homoallylic alcohols and their derivatives. A protected homoallylic alcohol, such as 1-phenylbut-3-enyl acetate (1e), was regio- and stereoselectively oxidized into (4) Stang, E. M.; White, M. C. Nat. Chem. 2009, 1, 547. (5) Mitsudome, T.; Umetani, T.; Nosaka, N.; Mori, K.; Mizugaki, T.; Ebitani, K.; Kaneda, K. Angew. Chem., Int. Ed. 2006, 45, 481. (6) Lin, B.-L.; Labinger, J. A.; Bercaw, J. E. Can. J. Chem. 2009, 87, 264. (7) Grennberg, H.; B€ ackvall, J.-E. Chem.;Eur. J. 1998, 4, 1083. (8) A noncoordinating base was recently used as additive, but its exact role is unclear, see ref 3d. AcO- anions accelerate the reaction of Pd(OAc)2 with alkenes in apolar solvents, due to better solubility of Pd(II) species in the presence of (R4N)þAcO-, see: Kozitsyna, N. Y.; Bukharkina, A. A.; Martens, M. V.; Vargaftik, M. N.; Moiseev, I. I. J. Organomet. Chem. 2001, 636, 69. (9) Trost, B. M; Strege, P. E.; Weber, L.; Fullerton, T. J.; Dietsche, T. J. J. Am. Chem. Soc. 1978, 100, 3407. (10) NaOH and LiOH 3 H2O afforded similar results, but the latter which is less hygroscopic was used for easier handling.
J. Org. Chem. 2010, 75, 1771–1774
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JOC Note TABLE 1.
Thiery et al.
Optimization of the Oxidation of Allylbenzene (1a)a
entry
RCO2H/cosolvent
Pd(OAc)2, %
Ox (equiv)
base
1 2 3 4 5 6 7 8 9 10 11 12
AcOH AcOH/DMSO, 1:1 AcOH/DMA, 1:1 AcOH/CH3CN, 1:1 AcOH/CH2Cl2, 1:1 AcOH EtCO2H EtCO2H EtCO2H EtCO2H EtCO2H EtCO2H
5 5 5 5 5 5 5 10 10 10 10 10
BQ (2.0) BQ (2.0) BQ (2.0) BQ (2.0) BQ (2.0) BQ (2.0) BQ (2.0) BQ (2.0) MnO2 (2.0) BQ (0.05), MnO2 (2.0) Cu(OAc)2 (0.5), O2e O2e
NaOAc LiOH 3 H2O LiOH 3 H2O LiOH 3 H2O LiOH 3 H2O LiOH 3 H2O LiOH 3 H2O
conv.,b % 70 38 29 97 50 80-100 78 100 80 92 85 45
yield,c % (12) (25) (18) (54) ( 99.9; 1H NMR (250 MHz, CDCl3) δ 1.00 (t, 3H, J = 7.6 Hz), 2.20 (q, 2H, J = 7.5 Hz), 3.05 (br s, 1H), 4.43 (d, 2H, J = 5.0 Hz), 5.05 (d, 1H, J = 5.2 Hz), 5.65-5.85 (m, 2H), 7.21 (m, 5H); 13C NMR (63 MHz, CDCl3) δ
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9.1, 27.5, 64.1, 74.0, 124.7, 126.3, 127.7, 128.5, 136.2, 142.6, 174.4; IR (film) 3445, 2982, 2942, 1738, 1454, 1382, 1349, 1276, 1186, 1083, 1009, 974, 759, 701. Anal. Calcd for C13H16O3: C, 70.89; H, 7.32. Found: C, 70.63; H, 7.45. (E)-4-Hydroxy-4-phenylbut-2-enyl pivalate (5f): colorless oil, 78%, L/B and E/Z > 99.9; 1H NMR (250 MHz, CDCl3) δ 1.11 (s, 9H), 2.72 (br s, 1H), 4.46 (d, 2H, J = 4.6 Hz), 5.10 (d, 1H, J = 4.9 Hz), 5.80 (m, 2H), 7.21 (m, 5H); 13C NMR (63 MHz, CDCl3) δ 27.6, 39.2, 64.5, 74.6, 125.5, 126.8, 128.2, 129.0, 136.2, 143.0, 178.8; IR (film) 3455, 2975, 1728, 1480, 1373, 1283, 1156, 1045, 971, 701; ESHRMS calcd for C15H20O3Na 271.1310, found 271.1304. (E)-4-(4-Chlorophenyl)-4-hydroxybut-2-enyl propionate (3h): pale yellow oil, 78%, L/B and E/Z > 99.9; 1H NMR (250 MHz, CDCl3) δ 1.09 (t, 3H, J = 7.3 Hz), 2.30 (q, 2H, J = 7.3 Hz), 3.19 (br s, 1H), 4.53 (d, 2H, J = 4.0 Hz), 5.12 (d, 1H, J = 4.1 Hz), 5.84 (m, 2H), 7.25 (m, 4H); 13C NMR (63 MHz, CDCl3) δ 8.9, 27.3, 63.8, 73.2, 125.0, 127.6, 128.5, 133.2, 135.6, 140.8, 174.2; IR (film) 3417, 2979, 1731, 1491, 1383, 1187, 1090, 1014, 911, 735; ESHRMS calcd for C13H15O3NaCl 277.0607, found 277.0614. (E)-4-(2-Bromophenyl)-4-hydroxybut-2-enyl propionate (3j): pale yellow oil, 74%, L/B and E/Z > 99.9; 1H NMR (250 MHz, CDCl3) δ 0.88 (t, 3H, J = 7.6 Hz), 2.08 (q, 2H, J = 7.5 Hz), 3.11 (br, 1H), 4.31 (m, 2H), 5.35 (s, 1H), 5.66 (m, 2H), 6.89 (dt, 1H, J = 1.5 Hz, J = 7.9 Hz), 7.08 (dd, 1H, J = 4.6 Hz, J = 9.6 Hz), 7.28 (m, 2H); 13C NMR (63 MHz, CDCl3) δ 8.9, 27.3, 64.0, 72.1, 122.1, 125.0, 127.6, 127.7, 128.9, 132.5, 134.0, 141.3, 174.2; IR (film) 3436, 2980, 1729, 1465, 1349, 1190, 1084, 1016, 910, 733; ESHRMS calcd for C13H15O3NaBr 321.0102, found 321.0095. (E)-4-Hydroxy-4-p-tolylbut-2-enyl pivalate (5k): colorless oil, 80%, L/B and E/Z > 99.9; 1H NMR (250 MHz, CDCl3) δ 1.08 (s, 9H), 2.21 (s, 3H), 3.23 (br s, 1H), 4.41 (d, 2H, J = 4.8 Hz), 5.00 (d, 1H, J = 4.4 Hz), 5.71 (td, 1H, J = 4.9 Hz, J = 15.6 Hz), 5.79 (dd, 1H, J = 5.2 Hz, J = 15.7 Hz), 7.01 (d, 2H, J = 7.6 Hz), 7.10 (d, 2H, J = 7.8 Hz); 13C NMR (63 MHz, CDCl3) δ 20.8, 27.0, 38.5, 64.0, 73.5, 124.3, 126.0, 128.9, 135.8, 137.0, 139.5, 178.1; IR (film) 3439, 2973, 1728, 1480, 1397, 1283, 1156, 1088, 970, 819; ESHRMS calcd for C16H22O3Na 285.1467, found 285.1457. (E)-4-(4-Chlorophenyl)-4-methoxybut-2-enyl pivalate (5q): colorless oil, 64%, L/B and E/Z > 99.9; 1H NMR (250 MHz, CDCl3) δ 1.13 (s, 9H), 3.23 (s, 3H), 4.53 (m, 3H), 5.74 (m, 2H), 7.21 (m, 4H); 13C NMR (63 MHz, CDCl3) δ 27.0, 38.5, 56.2, 63.6, 82.5, 126.6, 128.0, 128.5, 133.2, 133.5, 139.0, 177.8; IR (film) 2976, 1729, 1482, 1462, 1282, 1152, 1090, 1015, 968, 824; ESHRMS calcd for C16H21O3NaCl 319.1077, found 319.1082.
Acknowledgment. We are indebted to “Ville de Reims” for a Ph.D. studentship to E.T. and to the CNRS for financial support through the program “CPDD, Chimie et Developpement Durables”. Supporting Information Available: General information, analytical data of compounds 3a-3e, 3g, 3i, 3m-3p, 5a, 5c, 5e, 5g, 5l, and 5r-5v, ESI/MS(þ) spectra (Figures S1-S6), and the copies of 1H NMR and 13C NMR. This material is available free of charge via the Internet at http://pubs.acs.org.
