Regio- and Stereoselective Copper-Catalyzed Allylation of 1,3

9 hours ago - Simple ligand-free copper systems were found as efficient catalysts for the addition of 1,3-dicarbonyl compounds to N-allenyl derivative...
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Letter Cite This: Org. Lett. XXXX, XXX, XXX−XXX

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Regio- and Stereoselective Copper-Catalyzed Allylation of 1,3Dicarbonyl Compounds with Terminal Allenes Rémi Blieck,† Racha Abed Ali Abdine,† Marc Taillefer,*,† and Florian Monnier*,†,‡ †

Ecole Nationale Supérieure de Chimie de Montpellier, Institut Charles Gerhardt Montpellier UMR 5253 CNRS, AM2N, 8 rue de l’Ecole Normale, Montpellier 34296 Cedex 5, France ‡ Institut Universitaire de France, IUF, 1 rue Descartes, 75231 Paris cedex 5, France S Supporting Information *

ABSTRACT: Simple ligand-free copper systems were found as efficient catalysts for the addition of 1,3-dicarbonyl compounds to N-allenyl derivatives. This highly regio- and stereoselective reaction has been accomplished in the presence of malonates, 1,3-ketoesters, and 1,3-diketones with good to excellent yields under mild conditions. This methodology represents the first allylation of 1,3-dicarbonyl compounds with allenes catalyzed by copper.

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Scheme 1. State of the Art: Metal-Catalyzed Allylation of Carbon Pronucleophiles with Terminal Allenes

ecently, allene compounds have gained particular attention in the synthetic organic chemistry community.1 Among other studies on the reactivity of the latter, hydrofunctionnalization of allenes consists of the addition of simple nucleophiles to allenes and affords corresponding allylic compounds in a direct pathway with total atom economy.2 Recently, these selective methodologies have become a real alternative to the traditional allylic substitution, as they do not need the presence of a leaving group on the starting allylic substrate.3 For this purpose, transition-metal-catalyzed hydrofunctionalizations of allenes for the selective formation of the C−N bond have been reported recently.4 In parallel, few methodologies for the formation of the C−O bond by hydroalkoxylation or hydrocarboxylation of allenes were reported.5 The latter were also able to couple with carbon pronucleophiles to selectively provide the corresponding branched or linear allylic product with the formation of a novel C−C bond catalyzed by transition metals (Scheme 1).6 In 1994, Yamamoto’s group described for the first time this kind of reaction by using a catalyst based on Pd2(dba)3·CHCl3.7 The addition of activated methylene and methyne compounds occurred at the terminal carbon of the allene with complete regio- and stereoselectivity. Others groups also developed this reaction with different carbon pronucleophiles (Meldrum’s acids, malonates, and β-ketoesters) catalyzed by Pd8 or mediated by a stoichiometric amount of AgF.9 Later, Yamamoto’s group proved that electronic and steric effects of the allene have a strong influence on the observed regioselectivities.10 For example, different studies revealed that the reaction of alkoxyallenes with Meldrum’s acids or others 1,3-dicarbonyl compounds allowed the selective addition on the carbon bearing the alkoxy group (Scheme 1). On the other hand, Luo and co-workers developed an enantioselective terminal addition to allenes with α-branched β-ketocarbonyls thanks to a synergistic chiral amine/achiral palladium system.11 © XXXX American Chemical Society

Alternatively, Breit et al. used a chiral phosphine ligand combined with rhodium to catalyze the regio- and enantioselective addition of 1,3-dicarbonyl compounds to allenes.12b This catalytic system allowed the addition of the carbon nucleophiles to the carbon bearing the substitution of the allene.12 Recently, we focused our efforts on the development of regio- and stereoselective hydroamination of alkynes13 and allenes14 catalyzed by simple copper-based catalytic systems. To pursue our studies, we then explored the addition of carbon pronucleophiles on allenes via a hydrocarbonation-type reaction. To the best of our knowledge, copper-catalyzed addition of 1,3-dicarbonyls compounds to allenes has never been performed. In the literature,7−12 only palladium- and rhodium-based catalytic systems were described for the Received: February 16, 2018

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DOI: 10.1021/acs.orglett.8b00575 Org. Lett. XXXX, XXX, XXX−XXX

Letter

Organic Letters

desired γ,δ-unsaturated diester 1a in excellent yield. The formation of the latter proceeds under smooth conditions (2 mol % of CuI with 1 equiv of base at 100 °C during 18 h) with total control of regio- and stereoselectivities as we only observed one product with the addition of a on the terminal carbon of the allene with the E configuration of the double blond (confirmed by NMR analysis). With these optimized conditions in hand, we first explored the scope and limitations of this original catalytic system for the hydrocarbonation of allenamide 1 with different 1,3-dicarbonyl compounds and derivatives a−f (Scheme 2).

allylation of carbon pronucleophiles (methylene active compounds) with allenes (Scheme 1). Herein, we report the first copper-catalyzed allylation of carbon pronucleophiles with allenes. Inspired by our recent report on hydroamination of allenamides catalyzed by copper,14 we began to study the model reaction between N-allenyl-2pyrrolidinone 1 with diethyl malonate a under various catalytic conditions presented in Table 1. Table 1. Hydrocarbonation of N-Allenyl-2-pyrrolidinone 1 with Diethyl Malonate: Selected Data for Reaction Developmenta,b

Scheme 2. CuI-Catalyzed Allylation of Different 1,3Dicarbonyls Compounds a−f with Allene 1a

entry

solvent

base (y equiv)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

dioxane dioxane dioxane dioxane dioxane dioxane dioxane dioxane dioxane dioxane THF THF THF THF THF THF THF THF THF

− t-BuOK (2) t-BuOK (2) t-BuOK (2) t-BuOK (2) KOH (2) NaOH (2) K2CO3 (2) Na2CO3 (2) Cs2CO3 (2) Cs2CO3 (2) Cs2CO3 (2) Cs2CO3 (2) Cs2CO3 (2) Cs2CO3 (2) Cs2CO3 (1) K2CO3 (1) Na2CO3 (1) t-BuOK (1)

[Cu] (x mol %) Cu(CH3CN)4PF6 Cu(CH3CN)4PF6 Cu(CH3CN)4PF6 Cu(CH3CN)4PF6 − Cu(CH3CN)4PF6 Cu(CH3CN)4PF6 Cu(CH3CN)4PF6 Cu(CH3CN)4PF6 Cu(CH3CN)4PF6 Cu(CH3CN)4PF6 Cu(OTf)2 (20) Cu(acac)2 (20) CuI (20) CuI (2) CuI (2) CuI (2) CuI (2) CuI (2)

(20) (20) (20) (20) (20) (20) (20) (20) (20) (20)

yield (%)b 0 tracesc 10d 45 0 0 0 0 0 49 52 54 59 84 52 96 9 7 35

a

Reaction conditions: 1 (0.5 mmol), a−f (1 mmol), CuI (0.01−0.05 mmol), THF (1 mL), argon, 100 °C, 18 h. Isolated yields.

The reaction of both ethyl and methyl malonates with 1 gave the formation of 1a and 1b, respectively in 84% and 59% isolated yields with 2 mol % of CuI catalyst. On the other hand, β-ketoester c and 1,3-diketones d, f required a slightly higher loading of CuI (10 mol %) to obtain the corresponding desired γ,δ-unsaturated dicarbonyl compounds 1c−d and 1f in moderate to good isolated yields (respectively 73%, 61%, and 72%). Surprisingly after purification on silica, monocarbonyl compound 1e was obtained in 54% yield. It is noteworthy that malonitriles and derivatives do not react under these conditions. We then tested several types of terminal N-allenyl compounds 2−12 to show the tolerance of this reaction (Scheme 3). In this set of experiments, we first tested several cyclic Nallenamides 2−5 in reaction with ethyl malonate a. As previously observed with 1, N-allenyl-2-valerolactam 2 and Nallenyl-oxazolidinone 3 afforded the products 2a and 3a with 2 mol % and 5 mol % of CuI with good yields. The substituted Nallenyl-oxazolidinones 4 and 5 required 10 mol % of catalyst to react with a and then gave 4a and 5a in good isolated yields. As discussed in one of our reports,14b N-allenyl azoles were good candidates for the hydroamination reaction; then, we tested 1allenyl-1H-benzotriazole 6 and allenyl-triazole 7 under classical reaction conditions with various carbon pronucleophiles such as malonate a and β-ketoester c. Because of rapid decomposition of N-allenyl-azoles at 100 °C, decreasing the reaction temperature to 50 °C was needed to obtain desired products 6a, 6c, and 7a in moderate to good yields. We finally extended the scope of this reaction to many different protected Nphenyl-N-allenyls derivatives 8−13 with ditheyl malonate a, β-

a

Reaction conditions: 1 (0.5 mmol), a (1 mmol), base (0.5 to 1 mmol), and catalyst (0.01 to 0.1 mmol) were placed in a screw tube under argon in 1 mL of solvent for 18 h at 100 °C. bNMR yields using 1,3,5-trimethoxybenzene as internal standard. cAt 25 °C. dAt 50 °C.

Based on our previous report,14a we tested the reaction of 1 with a catalyzed by Cu(CH3CN)4PF6 as a precatalyst in dioxane at 25 °C (Table 1, entry 1). We rapidly found that a base is absolutely needed to obtain the desired product 1a (Table 1, entries 1−4). Compared to hydroamination conditions, the hydrocarbonation of 1 with a requires a thermic activation by heating the mixture at 100 °C with the formation of 1a in moderate yield (Table 1, entries 2−4). Different bases were tested, and Cs2CO3 allowed the best rate of formation of 1a (Table 1, entries 6−10). We then changed dioxane by THF as solvent and tested several sources of copper. These experiments revealed that CuI is much more efficient than Cu(CH3CN)4PF6, Cu(OTf)2, and Cu(acac)2 (Table 1, entries 11−14). Finally, we found that reducing both amounts of CuI (from 20 to 2 mol %) and of Cs2CO3 (from 2 to 1 equiv) permitted the best rate of formation of desired product 1a (Table 1, entries 14 and 16). Others base sources such as K2CO3, Na2CO3 and t-BuOK did not give 1a in better yield than Cs2CO3 (Table 1, entries 16−19). Thus, a copper catalytic system is able for the first time to perform the allylation of diethyl malonate a with allene 1 to allow the formation of the B

DOI: 10.1021/acs.orglett.8b00575 Org. Lett. XXXX, XXX, XXX−XXX

Letter

Organic Letters ORCID

Scheme 3. CuI-Catalyzed Allylation of Different 1,3Dicarbonyls Compounds with Various Allenesa

Florian Monnier: 0000-0002-9924-2012 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Financial support provided by Région Languedoc-Roussillon (PhD fellowship for R.B.), ENSCM (PhD fellowship for R.A.), IUF (Institut Universitaire de France to F.M.), ANR CD2I (Agence Nationale de la Recherche), and CNRS is warmly acknowledged with thanks.

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a

Reaction conditions: 1−12 (0.5 mmol), a-f (1 mmol), CuI (10 mol % unless otherwise notified), THF (1 mL), argon, 100 °C (unless otherwise notified), 18 h. Isolated yields. bCuI (2 mol %). cCuI (5 mol %). dAt 50 °C.

ketoester c, and 1,3-diketones d. Results shown in Scheme 3 related the formation of the desired products with good to excellent yields. Analysis of 1H NMR spectra clearly confirmed the E configuration of the double bond of all isolated products. To conclude, we developed the first allylation of carbon pronucleophiles catalyzed by copper. This novel methodology occurs without any additional ligand and allows the hydrocarbonation of a wide range of N-allenyl derivative substrates with total regio- and stereoselectivity. Highly valuable and unprecedented γ,δ-unsaturated dicarbonyl compounds were obtained with moderate to excellent yields. Further investigations on the potential of copper-catalyzed systems for hydrofunctionalization of allenes will be reported in due course.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.orglett.8b00575. Detailed experimental procedures and characterization data for all new compounds (PDF)

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REFERENCES

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*E-mail: fl[email protected]. *E-mail: [email protected]. C

DOI: 10.1021/acs.orglett.8b00575 Org. Lett. XXXX, XXX, XXX−XXX

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Organic Letters (13) (a) Bahri, J.; Blieck, R.; Jamoussi, B.; Taillefer, M.; Monnier, F. Chem. Commun. 2015, 51, 11210. (b) Bahri, J.; Jamoussi, B.; Van der Lee, A.; Taillefer, M.; Monnier, F. Org. Lett. 2015, 17, 1224. (14) (a) Perego, L.; Blieck, R.; Groué, A.; Monnier, F.; Taillefer, M.; Ciofini, I.; Grimaud, L. ACS Catal. 2017, 7, 4253. (b) Perego, L.; Blieck, R.; Michel, J.; Ciofini, I.; Grimaud, L.; Taillefer, M.; Monnier, F. Adv. Synth. Catal. 2017, 359, 4388. (c) Blieck, R.; Bahri, J.; Taillefer, M.; Monnier, F. Org. Lett. 2016, 18, 1482.

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DOI: 10.1021/acs.orglett.8b00575 Org. Lett. XXXX, XXX, XXX−XXX