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DOI: 10.1055/a-1892-4134
Rhodium-Catalyzed Regio- and Enantioselective Direct Allylation of Methyl Ketones
This work was supported by the National Natural Science Foundation of China (NSFC) (Grant 21602130).
Abstract
We report a highly branch-selective and enantioselective allylic alkylation of simple ketones with racemic aliphatic allylic carbonates under mild conditions. By using a Rh–bisoxazolinephosphine system and catalytic amounts of a base in THF, a series of chiral β-branched γ,δ-unsaturated ketones were obtained with excellent regio- and enantioselectivities. An outer-sphere nucleophilic substitution C–C bond-formation process is proposed on the basis of mechanistic studies.
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Key words
rhodium catalysis - bisoxazolinephosphines - ketones - allylic substitution - asymmetric catalysisTransition-metal-catalyzed regio- and enantioselective allylic substitution reactions of monosubstituted allylic precursors form one of the most powerful methods for constructing C–C bonds and synthesizing chiral molecules with alkene functions.[1] A variety of soft nucleophiles, such as more-acidic activated methylene compounds, have been widely used in asymmetric allylation reactions because of the higher stabilities of their carbon anions.[2] The direct asymmetric allylation of less-acidic methyl ketones[3] is much more challenging, probably due to the relatively hard nature of ketone enolates. Several ketone surrogates have been used in syntheses of β-chiral γ,δ-unsaturated ketones (Scheme [1a]). Evans and Leahy reported that stoichiometric amounts of a strong base and a Cu(I) salt are necessary to soften the ketone enolates in Rh-catalyzed stereospecific allylations.[4] The groups of Hartwig, Onitsuka, and Yang reported that enol silyl ethers and enamines are suitable ketone surrogates in Ir- or Ru-catalyzed asymmetric allylations.[5] Recently, Yang and co-workers realized an asymmetric allylation of aryl enamides with racemic allylic alcohols by using Carreira’s ligands and an acidic promoter.[6] The direct asymmetric allylation of simple ketones represents an ideal process with better atom- and step-economic advantages. However, such a branched and enantioselective direct allylation of simple ketones has not been reported.[7] [8] [9]
Our group has developed a robust branched and enantioselective allylation system based on rhodium and a bisoxazolinephosphine (NPN*) ligand.[10] The formation of a zwitterionic species containing a cationic Rh(III)Cl/allyl/NPN* intermediate and an alkoxide anion was proposed. Various acidic pronucleophiles, such as phenols, amides, indoles, terminal alkynes, pyridinium salts, and others, have been selectively allylated under neutral conditions. We surmised that the alkoxide anion might be basic enough to deprotonate the α-hydrogen of simple ketones and that the monocationic Rh(III) intermediate might stabilize the ketone enolate. Here, we report that this desired reaction of allylic tert-butyl carbonates and simple methyl ketones can be realized with only a catalytic amount of a base initiator (Scheme [1b]).
We started our study with the allylic propyl carbonate rac-1a (1.0 equiv) and p-methoxyacetophenone (2a; 1.5 equiv) as model substrates (Table [1]). Product 3aa was not detected in the presence of 2.5 mol% of [Rh(cod)Cl]2 and 5 mol% of NPN Ph,i–Pr (L1) at 80 °C in THF for 12 hours (Table [1], entry 1). An equilibrium between the tert-butoxide anion and the ketone enolate might have existed so that the amount of the latter was limited. We speculated that a catalytic amount of the enolate nucleophile prepared in advance might initiate this α-allylation reaction. To verify our hypothesis, several bases such as t-BuONa, t-BuOK, t-BuOLi, and LiHMDS (10 mol%) were tested (entries 2–5). The desired product 3aa was isolated in yields of 63% and 83% with a >10:1 branched/linear (b/l) ratio and 95% ee when the bases containing a lithium ion were used (entries 4 and 5). The stronger Li–O bond might stabilize the ketone enolate. Decreasing the catalyst loading led to an even higher 96% yield of 3aa without any erosion of the b/l ratio or the ee (entry 6). With the same amount of base and less Rh complex, the ratio of the nucleophile Rh/allyl intermediate increased and the formation of β-hydride-elimination product was inhibited. Ligands L2 to L6 with various groups at R1 and R2 positions did not further improve the reaction (entries 7–11).
a Reaction conditions: 1a (0.2 mmol, 1.0 equiv), 2a (0.3 mmol, 1.5 equiv), THF (1.0 mL), 80 °C, 12 h.
b Isolated yield.
c Determined by 1H NMR.
d Determined by HPLC with a chiral column.
e [Rh(cod)Cl]2 (1.25 mol%), ligand (3.0 mol%), additive (10.0 mol%), THF (1.0 mL).
With the optimized reaction conditions in hand (Table [1], entry 6), we next examined the scope of methyl ketone (Scheme [2]). Electron-donating groups at the o-, m-, or p-positions of the phenyl ring were all tolerated (3aa–ac). The ortho-substituent on Celestolide had little influence on the yield or ee (3ad). Ketones with halo or other electron-withdrawing groups on the phenyl ring reacted at a lower rate, and a longer reaction time was needed to give the allylation products 3ae–ah in high yields and ee. Other aromatic rings such as neutral phenyl or 2-naphthyl could also be introduced onto the chiral β-branched γ,δ-unsaturated ketones (3ai and 3aj). In addition, 3ak and 3al with indole and styryl groups. respectively, were synthesized in yields of 78% and 57%.
The scope of the allylic carbonate in the rhodium-catalyzed regioselective allylation reaction was next examined with p-methoxyacetophenone (2a) as a model substrate (Scheme [3]). Simple methyl- and ethyl-substituted β-chiral ketones 3ba and 3ca, respectively, were readily synthesized under the standard conditions. Sterically more-hindered β-branched allylic carbonates with isopropyl, isopentyl, cyclopropyl, or cyclohexyl groups reacted smoothly to afford the corresponding products 3da–ga in high yields and high selectivity when the reaction time was extended to 48 hours. In addition, an allylic carbonate with a styryl group underwent this transformation at 100 °C for 48 hours to give an excellent yield of ketone 3ha with two olefin groups. The phenyl-substituted allylic carbonate 1i also participated in this reaction in the presence of 10 mol% t-BuOLi to give 3ia in 85% yield and 92% ee.
To demonstrate the synthetic utility of our protocol, we prepared the γ,δ-unsaturated ketone 3ag in 80% yield and 95% ee on a 10 mmol scale with 0.5 mol% catalyst for 24 hours (Scheme [4]; eq 1). The absolute configuration of 3gh [Scheme [4], eq 2; 1.0 mmol scale; yield: 221 mg (80%), 98% ee, >20:1 b/l] was assigned as R by a single-crystal X-ray diffraction analysis.[11]
Some stoichiometric experiments were conducted to explore the reaction mechanism (Scheme [5]). [L1-Rh(MeC3H4Cl)]OTf[8b] reacted with ketone 2k in the presence of 1.0 equivalents of LiHMDS in THF to afford 3ca in 62% yield and 96% ee (Scheme [5], eq 1). This complex can also serve as a catalyst to give 3ca in a comparable yield and ee, which supports the view that a Rh(III)/allyl/NPN* intermediate might be involved in the reaction (Scheme [5], eq 2). The R-configuration of 3ca is consistent with the idea that other soft nucleophiles and a lithium enolate might also attack the carbon of [L1-Rh(MeC3H4Cl)]OTf in an outer-sphere mechanism.
In conclusion, we have developed a highly branched-selective and enantioselective direct allylic alkylation of simple ketones with racemic allylic carbonates in the presence of Rh/NPN* and a catalytic amount of a base. Chiral β-branched γ,δ-unsaturated ketones were obtained with up to a 20:1 b/l ratio and 97% ee.[12] Mechanistic studies supported an outer-sphere nucleophilic attack of the enolate on a Rh(III)/allyl/NPN* intermediate.
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Conflict of Interest
The authors declare no conflict of interest.
Supporting Information
- Supporting information for this article is available online at https://doi-org.accesdistant.sorbonne-universite.fr/10.1055/a-1892-4134.
- Supporting Information
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References and Notes
- 1a Trost BM, Van Vranken DL. Chem. Rev. 1996; 96: 395
- 1b Lu Z, Ma S. Angew. Chem. Int. Ed. 2008; 47: 258
- 1c Hartwig JF, Stanley LM. Acc. Chem. Res. 2010; 43: 1461
- 1d Qu J, Helmchen G. Acc. Chem. Res. 2017; 50: 2539
- 1e Turnbull BW. H, Evans PA. J. Org. Chem. 2018; 83: 11463
- 1f Thoke MB, Kang Q. Synthesis 2019; 51: 2585
- 1g Cheng Q, Tu H.-F, Zheng C, Qu J.-P, Helmchen G, You S.-L. Chem. Rev. 2019; 119: 1855
- 1h Rössler SL, Petrone DA, Carreira EM. Acc. Chem. Res. 2019; 52: 2657
- 2a Helmchen G, Janssen JP. Tetrahedron Lett. 1997; 38: 8025
- 2b Trost BM, Hildbrand S, Dogra K. J. Am. Chem. Soc. 1999; 121: 10416
- 2c You S.-L, Zhu X.-Z, Luo Y.-M, Hou X.-L, Dai L.-X. J. Am. Chem. Soc. 2001; 123: 7471
- 2d Trost BM, Dogra K, Hachiya I, Emura T, Hughes DL, Krska S, Reamer RA, Palucki M, Yasuda N, Reider PJ. Angew. Chem. Int. Ed. 2002; 41: 1929
- 2e Kanayama T, Yoshida K, Miyabe H, Takemoto Y. Angew. Chem. Int. Ed. 2003; 42: 2054
- 2f Schelwies M, Dübon P, Helmchen G. Angew. Chem. Int. Ed. 2006; 45: 2466
- 2g Gnamm C, Förster S, Miller N, Brödner K, Helmchen G. Synlett 2007; 790
- 2h He H, Zheng X.-J, Li Y, Dai L.-X, You S.-L. Org. Lett. 2007; 9: 4339
- 2i Dübon P, Schelwies M, Helmchen G. Chem. Eur. J. 2008; 14: 6722
- 2j Trost BM, Miller JR, Hoffman CM. Jr. J. Am. Chem. Soc. 2011; 133: 8165
- 2k Liu W.-B, Reeves CM, Virgil SC, Stoltz BM. J. Am. Chem. Soc. 2013; 135: 10626
- 2l Liu W.-B, Reeves CM, Stoltz BM. J. Am. Chem. Soc. 2013; 135: 17298
- 2m Stanley LM, Bai C, Ueda M, Hartwig JF.
- 2n He Z.-T, Jiang X, Hartwig JF. J. Am. Chem. Soc. 2019; 141: 13066
- 2o Huo X, He R, Zhang X, Zhang W. J. Am. Chem. Soc. 2016; 138: 11093
- 2p Huo X, Zhang J, Fu J, He R, Zhang W. J. Am. Chem. Soc. 2018; 140: 2080
- 3a Bordwell FG. Acc. Chem. Res. 1988; 21: 456
- 3b Bordwell FG, Cornforth FJ. J. Org. Chem. 1978; 43: 1763
- 4 Evans PA, Leahy DK. J. Am. Chem. Soc. 2003; 125: 8974
- 5a Graening T, Hartwig JF. J. Am. Chem. Soc. 2005; 127: 17192
- 5b Weix DJ, Hartwig JF. J. Am. Chem. Soc. 2007; 129: 7720
- 5c Liang X, Wei K, Yang Y.-R. Chem. Commun. 2015; 51: 17471
- 5d Kanbayashi N, Yamazawa A, Takii K, Okamura T, Onitsuka K. Adv. Synth. Catal. 2016; 358: 555
- 6 Yue B.-B, Deng Y, Zheng Y, Wei K, Yang Y.-R. Org. Lett. 2019; 21: 2449
- 7 Tsuji J, Shimizu I, Minami I, Ohashi Y, Sugiura T, Takahashi K. J. Org. Chem. 1985; 50: 1523
- 8a Chen T, Yang H, Yang Y, Dong G, Xing D. ACS Catal. 2020; 10: 4238
- 8b Cheng L, Li M.-M, Xiao L.-J, Xie J.-H, Zhou Q.-L. J. Am. Chem. Soc. 2018; 140: 11627
- 9a Trost BM, Schroeder GM. J. Am. Chem. Soc. 1999; 121: 6759
- 9b Trost BM, Schroeder GM, Kristensen J. Angew. Chem. Int. Ed. 2002; 41: 3492
- 9c You S.-L, Hou X.-L, Dai L.-X, Zhu X.-Z. Org. Lett. 2001; 3: 149
- 9d Yan X.-X, Liang C.-G, Zhang Y, Hong W, Cao B.-X, Dai L.-X, Hou X.-L. Angew. Chem. Int. Ed. 2005; 44: 6544
- 9e Zheng W.-H, Zheng B.-H, Zhang Y, Hou X.-L. J. Am. Chem. Soc. 2007; 129: 7718
- 10a Xu W.-B, Ghorai S, Huang W, Li C. ACS Catal. 2020; 10: 4491
- 10b Huang W.-Y, Lu C, Ghorai S, Li B, Li C. J. Am. Chem. Soc. 2020; 142: 15276
- 10c Li K, Li C. Org. Lett. 2020; 22: 9456
- 10d Liu M, Zhao H, Li C. Chin. Chem. Lett. 2021; 32: 385
- 10e Sun M, Liu M, Li C. Chem. Eur. J. 2021; 27: 3457
- 10f Xu W.-B, Sun M, Shu M, Li C. J. Am. Chem. Soc. 2021; 143: 8255
- 10g Li B, Liu M, Ur Rehman S, Li C. J. Am. Chem. Soc. 2022; 144: 2893
- 11 CCDC 2142005 contains the supplementary crystallographic data for compound 3gh. The data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/structures.
- 12 Chiral β-Branched γ,δ-Unsaturated Ketones 3; General ProcedureIn a N2-filled glovebox, a pressure tube equipped with a magnetic stirrer bar was charged with [Rh(cod)Cl]2 (1.3 mg, 1.25 mol%), NPNPh, iPr (3.0 mg, 3.0 mol%), and THF (1.0 mL), and the mixture was stirred at rt for 15 min. rac-1 (0.2 mmol, 1.0 equiv), 2 (0.3 mmol, 1.5 equiv), and a 1.0 M solution of LiHMDS in THF (20 μL; 10.0 mol%) were added to the solution and the tube was tightly capped, transferred out of the glovebox, and heated at 80 °C for 12 h. The mixture was then cooled, filtered through a short pad of silica gel (with elution by EtOAc), and concentrated under reduced pressure. The residue was purified by column chromatography.(3S)-1-(4-Methoxyphenyl)-3-propylpent-4-en-1-one (3aa)Synthesized from 1a and 2a by following the general procedure on a 0.2 mmol scale as a colorless viscous oil; yield: 44.1 mg, (96%; 95% ee, b/l = 15:1), [α]D 25 –14.0 (c = 0.8, CHCl3).HPLC [Shimadzu LC-2030; Chiralpak IG, i PrOH–hexane (1.0:99.0), 1.0 mL/min, 40 °C, λ = 254 nm]: t R = 22.660 min (major), 26.555 min (minor). 1H NMR (400 MHz, CDCl3): δ = 7.85 (d, J = 8.9 Hz, 2 H), 6.85 (d, J = 8.9 Hz, 2 H), 5.60 (ddd, J = 17.2, 10.3, 8.3 Hz, 1 H), 4.95–4.85 (m, 2 H), 3.79 (s, 3 H), 2.84 (d, J = 7.1 Hz, 2 H), 2.72–2.62 (m, 1 H), 1.38–1.19 (m, 4 H), 0.82 (t, J = 8.0 Hz, 3 H). 13C NMR (101 MHz, CDCl3): δ = 198.1, 163.4, 141.7, 130.5, 130.4, 114.6, 113.7, 55.4, 43.6, 39.8, 36.9, 20.2, 14.1. HRMS (ESI): m/z [M + H]+ calcd for C15H21O2: 233.1536; found: 233.1532.
For selected reviews, see:
For selected examples, see:
For direct allylation of ketones from 1,3-dienes, see:
For selected examples of the chirality control at ketones, see:
For selected examples of Rh(I)/bisoxazolinephosphine catalyst systems, see:
Corresponding Author
Publication History
Received: 05 May 2022
Accepted after revision: 05 July 2022
Accepted Manuscript online:
05 July 2022
Article published online:
30 September 2022
© 2022. Thieme. All rights reserved
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References and Notes
- 1a Trost BM, Van Vranken DL. Chem. Rev. 1996; 96: 395
- 1b Lu Z, Ma S. Angew. Chem. Int. Ed. 2008; 47: 258
- 1c Hartwig JF, Stanley LM. Acc. Chem. Res. 2010; 43: 1461
- 1d Qu J, Helmchen G. Acc. Chem. Res. 2017; 50: 2539
- 1e Turnbull BW. H, Evans PA. J. Org. Chem. 2018; 83: 11463
- 1f Thoke MB, Kang Q. Synthesis 2019; 51: 2585
- 1g Cheng Q, Tu H.-F, Zheng C, Qu J.-P, Helmchen G, You S.-L. Chem. Rev. 2019; 119: 1855
- 1h Rössler SL, Petrone DA, Carreira EM. Acc. Chem. Res. 2019; 52: 2657
- 2a Helmchen G, Janssen JP. Tetrahedron Lett. 1997; 38: 8025
- 2b Trost BM, Hildbrand S, Dogra K. J. Am. Chem. Soc. 1999; 121: 10416
- 2c You S.-L, Zhu X.-Z, Luo Y.-M, Hou X.-L, Dai L.-X. J. Am. Chem. Soc. 2001; 123: 7471
- 2d Trost BM, Dogra K, Hachiya I, Emura T, Hughes DL, Krska S, Reamer RA, Palucki M, Yasuda N, Reider PJ. Angew. Chem. Int. Ed. 2002; 41: 1929
- 2e Kanayama T, Yoshida K, Miyabe H, Takemoto Y. Angew. Chem. Int. Ed. 2003; 42: 2054
- 2f Schelwies M, Dübon P, Helmchen G. Angew. Chem. Int. Ed. 2006; 45: 2466
- 2g Gnamm C, Förster S, Miller N, Brödner K, Helmchen G. Synlett 2007; 790
- 2h He H, Zheng X.-J, Li Y, Dai L.-X, You S.-L. Org. Lett. 2007; 9: 4339
- 2i Dübon P, Schelwies M, Helmchen G. Chem. Eur. J. 2008; 14: 6722
- 2j Trost BM, Miller JR, Hoffman CM. Jr. J. Am. Chem. Soc. 2011; 133: 8165
- 2k Liu W.-B, Reeves CM, Virgil SC, Stoltz BM. J. Am. Chem. Soc. 2013; 135: 10626
- 2l Liu W.-B, Reeves CM, Stoltz BM. J. Am. Chem. Soc. 2013; 135: 17298
- 2m Stanley LM, Bai C, Ueda M, Hartwig JF.
- 2n He Z.-T, Jiang X, Hartwig JF. J. Am. Chem. Soc. 2019; 141: 13066
- 2o Huo X, He R, Zhang X, Zhang W. J. Am. Chem. Soc. 2016; 138: 11093
- 2p Huo X, Zhang J, Fu J, He R, Zhang W. J. Am. Chem. Soc. 2018; 140: 2080
- 3a Bordwell FG. Acc. Chem. Res. 1988; 21: 456
- 3b Bordwell FG, Cornforth FJ. J. Org. Chem. 1978; 43: 1763
- 4 Evans PA, Leahy DK. J. Am. Chem. Soc. 2003; 125: 8974
- 5a Graening T, Hartwig JF. J. Am. Chem. Soc. 2005; 127: 17192
- 5b Weix DJ, Hartwig JF. J. Am. Chem. Soc. 2007; 129: 7720
- 5c Liang X, Wei K, Yang Y.-R. Chem. Commun. 2015; 51: 17471
- 5d Kanbayashi N, Yamazawa A, Takii K, Okamura T, Onitsuka K. Adv. Synth. Catal. 2016; 358: 555
- 6 Yue B.-B, Deng Y, Zheng Y, Wei K, Yang Y.-R. Org. Lett. 2019; 21: 2449
- 7 Tsuji J, Shimizu I, Minami I, Ohashi Y, Sugiura T, Takahashi K. J. Org. Chem. 1985; 50: 1523
- 8a Chen T, Yang H, Yang Y, Dong G, Xing D. ACS Catal. 2020; 10: 4238
- 8b Cheng L, Li M.-M, Xiao L.-J, Xie J.-H, Zhou Q.-L. J. Am. Chem. Soc. 2018; 140: 11627
- 9a Trost BM, Schroeder GM. J. Am. Chem. Soc. 1999; 121: 6759
- 9b Trost BM, Schroeder GM, Kristensen J. Angew. Chem. Int. Ed. 2002; 41: 3492
- 9c You S.-L, Hou X.-L, Dai L.-X, Zhu X.-Z. Org. Lett. 2001; 3: 149
- 9d Yan X.-X, Liang C.-G, Zhang Y, Hong W, Cao B.-X, Dai L.-X, Hou X.-L. Angew. Chem. Int. Ed. 2005; 44: 6544
- 9e Zheng W.-H, Zheng B.-H, Zhang Y, Hou X.-L. J. Am. Chem. Soc. 2007; 129: 7718
- 10a Xu W.-B, Ghorai S, Huang W, Li C. ACS Catal. 2020; 10: 4491
- 10b Huang W.-Y, Lu C, Ghorai S, Li B, Li C. J. Am. Chem. Soc. 2020; 142: 15276
- 10c Li K, Li C. Org. Lett. 2020; 22: 9456
- 10d Liu M, Zhao H, Li C. Chin. Chem. Lett. 2021; 32: 385
- 10e Sun M, Liu M, Li C. Chem. Eur. J. 2021; 27: 3457
- 10f Xu W.-B, Sun M, Shu M, Li C. J. Am. Chem. Soc. 2021; 143: 8255
- 10g Li B, Liu M, Ur Rehman S, Li C. J. Am. Chem. Soc. 2022; 144: 2893
- 11 CCDC 2142005 contains the supplementary crystallographic data for compound 3gh. The data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/structures.
- 12 Chiral β-Branched γ,δ-Unsaturated Ketones 3; General ProcedureIn a N2-filled glovebox, a pressure tube equipped with a magnetic stirrer bar was charged with [Rh(cod)Cl]2 (1.3 mg, 1.25 mol%), NPNPh, iPr (3.0 mg, 3.0 mol%), and THF (1.0 mL), and the mixture was stirred at rt for 15 min. rac-1 (0.2 mmol, 1.0 equiv), 2 (0.3 mmol, 1.5 equiv), and a 1.0 M solution of LiHMDS in THF (20 μL; 10.0 mol%) were added to the solution and the tube was tightly capped, transferred out of the glovebox, and heated at 80 °C for 12 h. The mixture was then cooled, filtered through a short pad of silica gel (with elution by EtOAc), and concentrated under reduced pressure. The residue was purified by column chromatography.(3S)-1-(4-Methoxyphenyl)-3-propylpent-4-en-1-one (3aa)Synthesized from 1a and 2a by following the general procedure on a 0.2 mmol scale as a colorless viscous oil; yield: 44.1 mg, (96%; 95% ee, b/l = 15:1), [α]D 25 –14.0 (c = 0.8, CHCl3).HPLC [Shimadzu LC-2030; Chiralpak IG, i PrOH–hexane (1.0:99.0), 1.0 mL/min, 40 °C, λ = 254 nm]: t R = 22.660 min (major), 26.555 min (minor). 1H NMR (400 MHz, CDCl3): δ = 7.85 (d, J = 8.9 Hz, 2 H), 6.85 (d, J = 8.9 Hz, 2 H), 5.60 (ddd, J = 17.2, 10.3, 8.3 Hz, 1 H), 4.95–4.85 (m, 2 H), 3.79 (s, 3 H), 2.84 (d, J = 7.1 Hz, 2 H), 2.72–2.62 (m, 1 H), 1.38–1.19 (m, 4 H), 0.82 (t, J = 8.0 Hz, 3 H). 13C NMR (101 MHz, CDCl3): δ = 198.1, 163.4, 141.7, 130.5, 130.4, 114.6, 113.7, 55.4, 43.6, 39.8, 36.9, 20.2, 14.1. HRMS (ESI): m/z [M + H]+ calcd for C15H21O2: 233.1536; found: 233.1532.
For selected reviews, see:
For selected examples, see:
For direct allylation of ketones from 1,3-dienes, see:
For selected examples of the chirality control at ketones, see:
For selected examples of Rh(I)/bisoxazolinephosphine catalyst systems, see:
