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DOI: 10.1055/s-0036-1590869
Enantioselective Palladium-Catalyzed Decarboxylative Allylation of β-Keto Esters Assisted by a Thiourea
We are grateful for a start-up fund from the South University of Science and Technology of China (to X. Zhang), and the National Natural Science Foundation of China (21672096) (to L. W. Chung) and the Shenzhen Science and Technology Innovation Committee (KQTD20150717103157174) (to X. Zhang and L. W. Chung) for financial support.
Publication History
Received: 16 June 2017
Accepted after revision: 18 July 2017
Publication Date:
22 August 2017 (online)
‡ These two authors contributed equally to this work
Abstract
Enantioselective intramolecular decarboxylative allylation of β-keto esters catalyzed by a palladium bis(phosphine)-thiourea complex is reported. This procedure is not only effective for β-keto esters, but also effective for β-keto amides. An intermolecular variant of the asymmetric decarboxylative allylation is also established. DFT calculations indicate that an outer-sphere mechanism is viable for the decarboxylative allylation of β-keto esters.
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Key words
asymmetric synthesis - β-keto esters - decarboxylative allylation - thioureas - palladium catalysisThe enantioselective formation of all-carbon quaternary stereocenters remains an interesting but challenging topic in synthetic organic chemistry.[1] For the past two decades, transition-metal-catalyzed decarboxylative asymmetric allylation of prochiral enolates (the Tsuji allylation reaction) has emerged as a powerful tool for the synthesis of enantioenriched quaternary stereocenters.[2]
Although tremendous efforts have been devoted to the development of the Tsuji allylation reaction,[3] [4] [5] [6] [7] [8] the intramolecular decarboxylative asymmetric allylation of β-keto esters remains problematic.[9] For example, the Stoltz group reported an elegant example of a palladium-catalyzed protocol for the asymmetric Tsuji allylation;[9a] however, this allylation reaction was primarily effective for the allylation of unstabilized ketone enolates. For the allylation of stabilized allyl enol carbonates such as 1a, the ee of the allylation product 2a was only 24% (Scheme [1]). Later, the ee of 2a was improved to 70% through high-throughput screening of ligands and solvents.[9c] Nevertheless, new methods are still needed for enantioselective intramolecular decarboxylative allylation of β-keto esters.[10]
The combination of a transition-metal catalyst and an organocatalyst through a covalent bond into one bifunctional molecule provides unprecedented opportunities to achieve challenging transformations.[11] Recently, we have discovered that bis(phosphine)-thiourea (ZhaoPhos) ligated metal complexes efficiently catalyzed the asymmetric hydrogenation of imines and pyridines,[12] nitroalkenes,[13] α,β-unsaturated compounds,[14] and maleic acid derivatives.[15] The hydrogen bonding between the substrate and the thiourea moiety of the ligand was believed to be crucial for achieving high enantioselectivity. As part of our continued effort to extend the application of ZhaoPhos, we propose that this bis(phosphine)-thiourea ligand can also promote the enantioselective allylation of β-keto esters (Figure [1]). Herein, we report the enantioselective allylation of β-keto esters catalyzed by a palladium(0) bis(phosphine)-thiourea complex.
We commenced our study by examining substrate 1a as a model substrate catalyzed by a 1:2.5 mixture of Pd2(dba)3 (2.5 mol %) and ZhaoPhos in various solvents at room temperature. Substrates 1a–l can be synthesized by deprotonation of β-keto esters with potassium tert-butoxide in tetrahydrofuran (THF) at room temperature followed by nucleophilic substitution with allyl chloroformate. Initially, ethereal solvents and halogenated solvents were tested, but no or trace amount of product 2a was formed. Full conversion was achieved by using nonpolar solvent n-hexane as the solvent, whereas the ee of 2a turned out to be negligible (Table [1], entry 1). Addition of one equivalent of K2CO3 to the reaction solution proved to be beneficial to the enantioselectivity (32% ee; entry 2). Subsequently, different solvents were screened for the allylation of 1a. Ethereal solvents such as THF and 1,2-dimethoxyethane (DME) provided 2a with 83% ee (entries 3 and 4). Diethyl ether, methyl tert-butyl ether (MTBE) and 1,4-dioxane gave 2a with low enantioselectivity (25–73% ee; entries 5–7). Use of toluene as the solvent formed the desired product 2a in 44% ee (entry 8). Halogenated solvents were also tested and CH2Cl2 turned out to be the choice of solvent, providing 2a with 89% ee (entry 9). Polar solvents such as ethanol, acetonitrile, and ethyl acetate gave 2a with low ee (15–66%; entries 13–15). Among the bases examined, K3PO4 gave an ee comparable to that with K2CO3 (entry 16). Triethylamine and BSA did not promote the reaction at all (entries 18 and 19). The addition of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) or 1,4-diazabicyclo[2.2.2]octane (DABCO) as base gave 2a with 84% ee (entries 20 and 21). Overall, these experiments demonstrated that the use of CH2Cl2 as the solvent and K2CO3 as the base provided the best results (92% yield, 89% ee; entry 9).
a Reaction conditions: substrate 0.30 mmol, Pd2(dba)3 (0.0075 mmol), ZhaoPhos (0.019 mmol), solvent (5 mL), base (0.30 mmol), r.t., 24 h. TBD = 1,5,7-Triazabicyclo-[4.4.0]dec-5-ene. BSA = N,O-Bis(trimethylsilyl)acetamide. DBU = 1,8-Diazabicyclo[5.4.0]undec-7-ene. DABCO = 1,4-Diazobicyclo(2.2.2)octane. N.R. = no reaction. N.A.= not available.
b Isolated yield.
c The ee was determined by HPLC using a chiral stationary phase.
With the optimized conditions in hand, we sought to study the substrate scope.[16] As summarized in Scheme [2], substrates containing a six-membered ring with ester functionality such as ethyl (2a), methyl (2b), benzyl (2c), and isopropyl (2d) esters provided the products in good yield with high enantioselectivity (88–89% ee). When the ester functionality was changed to phenyl ester, 82% ee was achieved for the desired allylation product (2f). However, when the ester group was switched to tert-butyl ester, the ee of the desired product (2e) turned out to be negligible. In addition, β-keto esters containing a five-membered ring (2g) or a seven-membered ring (2h) provided the allylation product with low enantioselectivity. Meanwhile, the incorporation of a heteroatom such as nitrogen (2i) and sulfur (2j) into the cyclohexanone ring had a detrimental effect on the ee of the allylation product. Substrate containing a tetralone moiety (2k) provided the desired product with diminished ee (57%) under the optimized conditions. Finally, β-keto amide worked well for the asymmetric decarboxylative allylation reaction, rendering the allylation product 2l in 57% yield and 88% ee.
We also sought to study the intermolecular decarboxylative asymmetric allylation of β-keto esters.[17] [18] To this end, treatment of ethyl 2-cyclohexanonecarboxylate (3; 1.2 equiv) and cinnamyl methyl carbonate (4a; 1 equiv) with a catalytic amount of Pd2(dba)3 (2.5 mol%) and ZhaoPhos (6.25 mol%) in the presence of a stoichiometric amount of K2CO3 (1.2 equiv) in CH2Cl2 at 40 °C for 24 h provided the desired allylation product 5 in 83% isolated yield and 76% ee (5a; Scheme [3]).[19] As summarized in Scheme [3, a] variety of cinnamyl methyl carbonates were tested and moderate to good enantioselectivities were observed. Substrates with electron-donating substituents (4b and 4d) furnished the products with good ee values. Electron-withdrawing (4c) and sterically demanding (4e) substituents on the aromatic ring led to a decrease of the enantioselectivity for the corresponding products.
To gain insight into the mechanism of the intramolecular asymmetric allylation reaction, a control experiment was conducted (Scheme [4]). Subjecting 1a to a catalytic 1:2.5 mixture of Pd2(dba)3 and ZhaoPhos-Me2 (L1) in CH2Cl2 at r.t. for 24 h led to the formation of allylated product 2a in 96% isolated yield with 15% ee. This result highlights the key role of the hydrogen bonding donor in the catalyst to achieve high enantioselectivity.
According to previous computational studies,[2b] [20] the enantioselectivity should be determined by the reductive elimination step. A mechanistic study on the enantioselectivity of this Pd-catalyzed allylation was performed by DFT (M06) calculations. Three mechanisms were considered: inner-sphere, outer-sphere, and three-membered-ring reductive elimination pathways (see the Supporting Information for details). TS-RE-O2-Si is the most favorable transition state for the Si-face of the enolate, which is lower in free energy than that for the Re-face manifold via TS-RE-O1-Re by 2.3 kcal/mol (Figure [2], and Figure X1 in the Supporting Information). These computational results are in good agreement with the experimental observations. Both transition states can be regarded as following the outer-sphere pathway.[21] TS-RE-O2-Si is an earlier transition state than TS-RE-O1-Re , due to the longer C–C bond forming in the former case (2.36 Å). Furthermore, the enolate substrate forms stronger interactions with the catalyst, and strong stacking between the thiourea part and one phenyl on the P ligand were found in TS-RE-O2-Si . Our distortion/interaction analysis[22] further supports the conclusion that larger interaction stabilization between the substrate and catalyst (18.3 kcal/mol) in TS-RE-O2-Si is a major factor in the observed enantioselectivity.
In summary, we have developed a new protocol for the asymmetric allylation of β-keto esters catalyzed by a palladium bis(phosphine)-thiourea complex. This protocol works well with both β-keto esters and amides that contain six-membered rings. An intermolecular variant of this decarboxylative allylation is also reported. DFT calculations indicate that an outer-sphere mechanism is operative for the allylation of β-keto esters. Further studies to explain the role of K2CO3 on enantioselectivity, as well as improving the enantioselectivity and expanding the substrate scope of the enantioselective decarboxylative allylation, is under way in our laboratory.
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Supporting Information
- Supporting information for this article is available online at https://doi-org.accesdistant.sorbonne-universite.fr/10.1055/s-0036-1590869.
- Supporting Information
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References and Notes
- 1a Fuji K. Chem. Rev. 1993; 93: 2037
- 1b Corey EJ. Guzman-Perez A. Angew. Chem. Int. Ed. 1998; 37: 388
- 1c Christoffers J. Mann A. Angew. Chem. Int. Ed. 2001; 40: 4591
- 1d Douglas CJ. Overman LE. Proc. Natl. Acad. Sci. U. S. A. 2004; 101: 5363
- 1e Baro A. Christoffers J. Adv. Synth. Catal. 2005; 347: 1473
- 1f Trost BM. Jiang C. Synthesis 2006; 369
- 1g Bella M. Gasperi T. Synthesis 2009; 1583
- 1h Das JP. Marek I. Chem. Commun. 2011; 4593
- 1i Quasdorf KW. Overman LE. Nature 2014; 516: 181
- 2a Weaver JD. Recio III A. Grenning AJ. Tunge JA. Chem. Rev. 2011; 111: 1846
- 2b Mohr JT. Stoltz BM. Chem. Asian J. 2007; 2: 1476
- 3a Trost BM. Xu J. J. Am. Chem. Soc. 2005; 127: 2846
- 3b Trost BM. Xu J. J. Am. Chem. Soc. 2005; 127: 17180
- 3c Trost BM. Xu J. Schmidt T. J. Am. Chem. Soc. 2009; 131: 18343
- 3d Trost BM. Schäffner B. Osipov M. Wilton DA. A. Angew. Chem. Int. Ed. 2011; 50: 3548
- 4a Zheng W.-H. Zheng B.-H. Zhang Y. Hou X.-L. J. Am. Chem. Soc. 2007; 129: 7718
- 4b Lei B.-L. Ding C.-H. Yang X.-F. Wan X.-L. Hou X.-L. J. Am. Chem. Soc. 2009; 131: 18250
- 5a Liu W.-B. Reeves CM. Virgil S. Stoltz BM. J. Am. Chem. Soc. 2013; 135: 10626
- 5b Liu W.-B. Reeves CM. Stoltz BM. J. Am. Chem. Soc. 2013; 135: 17298
- 5c Hethcox JC. Shockley SE. Stoltz BM. Angew. Chem. Int. Ed. 2016; 55: 16092
- 6 Burger EC. Tunge JA. Org. Lett. 2004; 6: 4113
- 7 Pupo G. Properzi R. List B. Angew. Chem. Int. Ed. 2016; 55: 6099
- 8a Trost BM. Radinov R. Grenzer EM. J. Am. Chem. Soc. 1997; 119: 7879
- 8b Yoshida M. Yano S. Hara S. Synthesis 2017; 49: 1295
- 8c Hayashi T. Kanehira K. Hagihara T. Kumada M. J. Org. Chem. 1988; 53: 113
- 9a Behenna DC. Stoltz BM. J. Am. Chem. Soc. 2004; 126: 15044
- 9b Keith JA. Behenna DC. Mohr JT. Ma S. Marinescu SC. Oxgaard J. Stoltz BM. Goddard III WA. J. Am. Chem. Soc. 2007; 129: 11876
- 9c McDougal NT. Virgil SC. Stoltz BM. Synlett 2010; 1712
- 9d Keith JA. Behenna DC. Sherden N. Mohr JT. Ma S. Marinescu SC. Nielsen RJ. Oxgaard J. Stoltz BM. Goddard WA. J. Am. Chem. Soc. 2012; 134: 19050
- 9e Behenna DC. Mohr JT. Sherden NH. Marinescu SC. Harned AM. Tani K. Seto M. Ma S. Novák Z. Krout MR. McFadden RM. Roizen JL. Enquist JA. White DE. Levine SR. Petrova KV. Iwashita A. Virgil SC. Stoltz BM. Chem. Eur. J. 2011; 17: 14199
- 9f Reeves CM. Eidamshaus C. Kim J. Stoltz BM. Angew. Chem. Int. Ed. 2013; 52: 6718
- 9g Reeves CM. Behenna DC. Stoltz BM. Org. Lett. 2014; 16: 2314
- 9h Craig II R. A. Loskot SA. Mohr JT. Behenna DC. Harned AM. Stoltz BM. Org. Lett. 2015; 17: 5160
- 10 An enantioselective Claisen rearrangement of O-allyl β-keto esters catalyzed by thiourea has been reported, see: Uyeda C. Rötheli AR. Jacobsen EN. Angew. Chem. Int. Ed. 2010; 49: 9753
- 11 Dong X.-Q. Zhao Q. Li P. Chen C. Zhang X. Org. Chem. Front. 2015; 2: 1425
- 12a Zhao Q. Wen J. Tan R. Huang K. Metola P. Wang R. Anslyn EV. Zhang X. Angew. Chem. Int. Ed. 2014; 53: 8467
- 12b Wen J. Tan R. Liu S. Zhao Q. Zhang X. Chem. Sci. 2016; 7: 3047
- 13a Zhao Q. Li S. Huang K. Wang R. Zhang X. Org. Lett. 2013; 15: 4014
- 13b Li P. Zhou M. Zhao Q. Wu W. Hu X. Dong X.-Q. Zhang X. Org. Lett. 2016; 18: 40
- 14a Li P. Hu X. Dong X.-Q. Zhang X. Chem. Commun. 2016; 11677
- 14b Wen J. Jiang J. Zhang X. Org. Lett. 2016; 18: 4451
- 15a Han Z. Li P. Zhang Z. Chen C. Wang Q. Dong X.-Q. Zhang X. ACS Catal. 2016; 6: 6214
- 15b Han Z. Wang R. Gu G. Dong X.-Q. Zhang X. Chem. Commun. 2017; 4226
- 16 General procedure for decarboxylative allylation of β-keto esters: A Schlenk tube containing Pd2(dba)3 (7 mg, 0.0076 mol), ZhaoPhos (16 mg, 0.0184 mmol) and K2CO3 (42 mg, 0.30 mmol) in degassed anhyd CH2Cl2 (5 mL) was stirred for 15 min under Ar. Substrate (0.30 mmol) was added last. The resulting mixture was stirred at r.t. under Ar for 24 h and was concentrated under vacuum. The residue was then purified by chromatography with petroleum ether/EtOAc to afford enantioenriched product. For 2a: Yield: 58 mg (92%); colorless oil; 89% ee. 1H NMR: δ = 5.83–5.67 (m, 1 H), 5.04 (d, J = 13.3 Hz, 2 H), 4.19 (q, J = 7.1 Hz, 2 H), 2.61 (dd, J = 14.0, 6.9 Hz, 1 H), 2.47 (dt, J = 14.9, 4.3 Hz, 3 H), 2.34 (dd, J = 14.0, 7.8 Hz, 1 H), 2.07–1.97 (m, 1 H), 1.82–1.71 (m, 3 H), 1.50–1.43 (m, 1 H), 1.26 (t, J = 7.1 Hz, 3 H). 13C{1H} NMR: δ = 207.5, 171.4, 133.3, 118.2, 61.2, 60.8, 41.1, 39.3, 35.7, 27.5, 22.4, 14.1. HPLC (Daicel Chiralpak) AD-H column; hexanes/i-PrOH = 99.5:0.5; flow rate = 0.5 mL/min; UV detection at 210 nm): t R = 10.512 (t minor), 12.371 (t major) min.
- 17a Gavrilov KN. Zheglov SV. Novikov IM. Lugovsky VV. Zimarev VS. Mikhel I. Tetrahedron: Asymmetry 2016; 27: 1260
- 17b Savoia D. Alvaro G. Fabio RD. Fiorelli C. Gualandi A. Monari M. Piccinelli F. Adv. Synth. Catal. 2006; 348: 1883
- 17c Gavrilov KN. Shiryaev AA. Zheglov SV. Bochelyuk MS. Chuchelkin IV. Tafeenko VA. Chernyshev VV. Zamilatskov IA. Mikhel IS. Tetrahedron Lett. 2015; 56: 4756
- 17d Nemoto T. Masuda T. Matsumoto T. Hamada Y. J. Org. Chem. 2005; 70: 7172
- 18a Zhou H. Zhang L. Xu C. Luo S. Angew. Chem. Int. Ed. 2015; 54: 12645
- 18b Kita Y. Kavthe RD. Oda H. Mashima K. Angew. Chem. Int. Ed. 2016; 55: 1098
- 19 Cinnamyl methyl carbonates were the limiting reagents in the intermolecular asymmetric allylation reaction.
- 20a Bai D.-C. Yu F.-L. Wang W.-Y. Chen D. Li H. Liu Q.-R. Ding C.-H. Chen B. Hou X.-L. Nat. Commun. 2016; 7: 11806
- 20b Huo X. Yang G. Liu D. Liu Y. Gridnev ID. Zhang W. Angew. Chem. Int. Ed. 2014; 53: 6776
- 20c Patil M. Thiel W. Chem. Eur. J. 2012; 18: 10408
- 20d Chen J.-P. Peng Q. Lei B.-L. Hou X.-L. Wu Y.-D. J. Am. Chem. Soc. 2011; 133: 14180
- 20e Meletis P. Patil M. Thiel W. Frank W. Braun M. Chem. Eur. J. 2011; 17: 11243
- 21 Considering the Pd-O distance of 2.602 Å, TS-RE-O2-Si can be classified as a quasi-outer-sphere pathway (with some inner-sphere character).
For examples of asymmetric intermolecular allylation of β-keto esters with allyl acetate, see:
For selected examples on asymmetric allylation of β-keto esters with cinnamyl acetate or cinnamyl carbonates, see:
For asymmetric allylation of β-keto esters with cinnamyl alcohols, see:
-
References and Notes
- 1a Fuji K. Chem. Rev. 1993; 93: 2037
- 1b Corey EJ. Guzman-Perez A. Angew. Chem. Int. Ed. 1998; 37: 388
- 1c Christoffers J. Mann A. Angew. Chem. Int. Ed. 2001; 40: 4591
- 1d Douglas CJ. Overman LE. Proc. Natl. Acad. Sci. U. S. A. 2004; 101: 5363
- 1e Baro A. Christoffers J. Adv. Synth. Catal. 2005; 347: 1473
- 1f Trost BM. Jiang C. Synthesis 2006; 369
- 1g Bella M. Gasperi T. Synthesis 2009; 1583
- 1h Das JP. Marek I. Chem. Commun. 2011; 4593
- 1i Quasdorf KW. Overman LE. Nature 2014; 516: 181
- 2a Weaver JD. Recio III A. Grenning AJ. Tunge JA. Chem. Rev. 2011; 111: 1846
- 2b Mohr JT. Stoltz BM. Chem. Asian J. 2007; 2: 1476
- 3a Trost BM. Xu J. J. Am. Chem. Soc. 2005; 127: 2846
- 3b Trost BM. Xu J. J. Am. Chem. Soc. 2005; 127: 17180
- 3c Trost BM. Xu J. Schmidt T. J. Am. Chem. Soc. 2009; 131: 18343
- 3d Trost BM. Schäffner B. Osipov M. Wilton DA. A. Angew. Chem. Int. Ed. 2011; 50: 3548
- 4a Zheng W.-H. Zheng B.-H. Zhang Y. Hou X.-L. J. Am. Chem. Soc. 2007; 129: 7718
- 4b Lei B.-L. Ding C.-H. Yang X.-F. Wan X.-L. Hou X.-L. J. Am. Chem. Soc. 2009; 131: 18250
- 5a Liu W.-B. Reeves CM. Virgil S. Stoltz BM. J. Am. Chem. Soc. 2013; 135: 10626
- 5b Liu W.-B. Reeves CM. Stoltz BM. J. Am. Chem. Soc. 2013; 135: 17298
- 5c Hethcox JC. Shockley SE. Stoltz BM. Angew. Chem. Int. Ed. 2016; 55: 16092
- 6 Burger EC. Tunge JA. Org. Lett. 2004; 6: 4113
- 7 Pupo G. Properzi R. List B. Angew. Chem. Int. Ed. 2016; 55: 6099
- 8a Trost BM. Radinov R. Grenzer EM. J. Am. Chem. Soc. 1997; 119: 7879
- 8b Yoshida M. Yano S. Hara S. Synthesis 2017; 49: 1295
- 8c Hayashi T. Kanehira K. Hagihara T. Kumada M. J. Org. Chem. 1988; 53: 113
- 9a Behenna DC. Stoltz BM. J. Am. Chem. Soc. 2004; 126: 15044
- 9b Keith JA. Behenna DC. Mohr JT. Ma S. Marinescu SC. Oxgaard J. Stoltz BM. Goddard III WA. J. Am. Chem. Soc. 2007; 129: 11876
- 9c McDougal NT. Virgil SC. Stoltz BM. Synlett 2010; 1712
- 9d Keith JA. Behenna DC. Sherden N. Mohr JT. Ma S. Marinescu SC. Nielsen RJ. Oxgaard J. Stoltz BM. Goddard WA. J. Am. Chem. Soc. 2012; 134: 19050
- 9e Behenna DC. Mohr JT. Sherden NH. Marinescu SC. Harned AM. Tani K. Seto M. Ma S. Novák Z. Krout MR. McFadden RM. Roizen JL. Enquist JA. White DE. Levine SR. Petrova KV. Iwashita A. Virgil SC. Stoltz BM. Chem. Eur. J. 2011; 17: 14199
- 9f Reeves CM. Eidamshaus C. Kim J. Stoltz BM. Angew. Chem. Int. Ed. 2013; 52: 6718
- 9g Reeves CM. Behenna DC. Stoltz BM. Org. Lett. 2014; 16: 2314
- 9h Craig II R. A. Loskot SA. Mohr JT. Behenna DC. Harned AM. Stoltz BM. Org. Lett. 2015; 17: 5160
- 10 An enantioselective Claisen rearrangement of O-allyl β-keto esters catalyzed by thiourea has been reported, see: Uyeda C. Rötheli AR. Jacobsen EN. Angew. Chem. Int. Ed. 2010; 49: 9753
- 11 Dong X.-Q. Zhao Q. Li P. Chen C. Zhang X. Org. Chem. Front. 2015; 2: 1425
- 12a Zhao Q. Wen J. Tan R. Huang K. Metola P. Wang R. Anslyn EV. Zhang X. Angew. Chem. Int. Ed. 2014; 53: 8467
- 12b Wen J. Tan R. Liu S. Zhao Q. Zhang X. Chem. Sci. 2016; 7: 3047
- 13a Zhao Q. Li S. Huang K. Wang R. Zhang X. Org. Lett. 2013; 15: 4014
- 13b Li P. Zhou M. Zhao Q. Wu W. Hu X. Dong X.-Q. Zhang X. Org. Lett. 2016; 18: 40
- 14a Li P. Hu X. Dong X.-Q. Zhang X. Chem. Commun. 2016; 11677
- 14b Wen J. Jiang J. Zhang X. Org. Lett. 2016; 18: 4451
- 15a Han Z. Li P. Zhang Z. Chen C. Wang Q. Dong X.-Q. Zhang X. ACS Catal. 2016; 6: 6214
- 15b Han Z. Wang R. Gu G. Dong X.-Q. Zhang X. Chem. Commun. 2017; 4226
- 16 General procedure for decarboxylative allylation of β-keto esters: A Schlenk tube containing Pd2(dba)3 (7 mg, 0.0076 mol), ZhaoPhos (16 mg, 0.0184 mmol) and K2CO3 (42 mg, 0.30 mmol) in degassed anhyd CH2Cl2 (5 mL) was stirred for 15 min under Ar. Substrate (0.30 mmol) was added last. The resulting mixture was stirred at r.t. under Ar for 24 h and was concentrated under vacuum. The residue was then purified by chromatography with petroleum ether/EtOAc to afford enantioenriched product. For 2a: Yield: 58 mg (92%); colorless oil; 89% ee. 1H NMR: δ = 5.83–5.67 (m, 1 H), 5.04 (d, J = 13.3 Hz, 2 H), 4.19 (q, J = 7.1 Hz, 2 H), 2.61 (dd, J = 14.0, 6.9 Hz, 1 H), 2.47 (dt, J = 14.9, 4.3 Hz, 3 H), 2.34 (dd, J = 14.0, 7.8 Hz, 1 H), 2.07–1.97 (m, 1 H), 1.82–1.71 (m, 3 H), 1.50–1.43 (m, 1 H), 1.26 (t, J = 7.1 Hz, 3 H). 13C{1H} NMR: δ = 207.5, 171.4, 133.3, 118.2, 61.2, 60.8, 41.1, 39.3, 35.7, 27.5, 22.4, 14.1. HPLC (Daicel Chiralpak) AD-H column; hexanes/i-PrOH = 99.5:0.5; flow rate = 0.5 mL/min; UV detection at 210 nm): t R = 10.512 (t minor), 12.371 (t major) min.
- 17a Gavrilov KN. Zheglov SV. Novikov IM. Lugovsky VV. Zimarev VS. Mikhel I. Tetrahedron: Asymmetry 2016; 27: 1260
- 17b Savoia D. Alvaro G. Fabio RD. Fiorelli C. Gualandi A. Monari M. Piccinelli F. Adv. Synth. Catal. 2006; 348: 1883
- 17c Gavrilov KN. Shiryaev AA. Zheglov SV. Bochelyuk MS. Chuchelkin IV. Tafeenko VA. Chernyshev VV. Zamilatskov IA. Mikhel IS. Tetrahedron Lett. 2015; 56: 4756
- 17d Nemoto T. Masuda T. Matsumoto T. Hamada Y. J. Org. Chem. 2005; 70: 7172
- 18a Zhou H. Zhang L. Xu C. Luo S. Angew. Chem. Int. Ed. 2015; 54: 12645
- 18b Kita Y. Kavthe RD. Oda H. Mashima K. Angew. Chem. Int. Ed. 2016; 55: 1098
- 19 Cinnamyl methyl carbonates were the limiting reagents in the intermolecular asymmetric allylation reaction.
- 20a Bai D.-C. Yu F.-L. Wang W.-Y. Chen D. Li H. Liu Q.-R. Ding C.-H. Chen B. Hou X.-L. Nat. Commun. 2016; 7: 11806
- 20b Huo X. Yang G. Liu D. Liu Y. Gridnev ID. Zhang W. Angew. Chem. Int. Ed. 2014; 53: 6776
- 20c Patil M. Thiel W. Chem. Eur. J. 2012; 18: 10408
- 20d Chen J.-P. Peng Q. Lei B.-L. Hou X.-L. Wu Y.-D. J. Am. Chem. Soc. 2011; 133: 14180
- 20e Meletis P. Patil M. Thiel W. Frank W. Braun M. Chem. Eur. J. 2011; 17: 11243
- 21 Considering the Pd-O distance of 2.602 Å, TS-RE-O2-Si can be classified as a quasi-outer-sphere pathway (with some inner-sphere character).
For examples of asymmetric intermolecular allylation of β-keto esters with allyl acetate, see:
For selected examples on asymmetric allylation of β-keto esters with cinnamyl acetate or cinnamyl carbonates, see:
For asymmetric allylation of β-keto esters with cinnamyl alcohols, see:
