Rh(III)-Catalyzed Cascade Reactions of Sulfoxonium Ylides with α

Letter Cite This: Org. Lett. XXXX, XXX, XXX−XXX

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Rh(III)-Catalyzed Cascade Reactions of Sulfoxonium Ylides with α‑Diazocarbonyl Compounds: An Access to Highly Functionalized Naphthalenones Xi Chen, Muhua Wang, Xinying Zhang,* and Xuesen Fan*

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Henan Key Laboratory of Organic Functional Molecules and Drug Innovation, Key Laboratory of Green Chemical Media and Reactions, Ministry of Education, Collaborative Innovation Center of Henan Province for Green Manufacturing of Fine Chemicals, School of Chemistry and Chemical Engineering, Henan Normal University, Xinxiang, Henan 453007, China S Supporting Information *

ABSTRACT: An unprecedented cascade reaction of benzoyl sulfoxonium ylides with α-diazocarbonyl compounds leading to the formation of highly functionalized naphthalenones containing a β-ketosulfoxonium ylide moiety is presented. Promisingly, the naphthalenone derivative thus obtained was found to be a versatile intermediate toward diversely functionalized naphthalene derivatives including substituted 1-naphthol, 2-hydroxynaphthalen-1(2H)-one, naphthalen-1,2-dione, and 2(methylsulfinyl)naphthalen-1-ol.

F

Scheme 1. Diverse Transformations of Benzoyl Sulfoxonium Ylide

unctionalized naphthalene derivatives such as naphthalenones are prevalent in natural products, optical/electronic materials, and pharmaceuticals.1,2 Due to their importance, several synthetic protocols for the preparation of naphthalenone derivatives have been developed.3 While these literature methods are generally efficient and reliable, new methods starting from easily accessible substrates and accomplished through short and simple synthetic procedures with improved atom-economy are still highly desirable. As reliable synthetic intermediates, sulfonium/sulfoxonium ylides have been routinely used in various transformations due to their easy accessibility, moisture/air-stability, and diverse reactivity.4−6 Meanwhile, directing group-assisted functionalization of inert C−H bonds represents one of the hottest topics in synthetic chemistry in past decades.6 In this aspect, Aϊssa and Li have independently disclosed Rh(III)-catalyzed C(sp2)−H acylmethylation of arenes by using β-ketosulfoxonium ylides as stable and safe carbene surrogates.7 Later, Li and others applied this strategy into the preparation of various carbocycles and heterocycles through initial alkylation with sulfoxonium ylides followed by an intramolecular condensation.8 Furthermore, Li et al. disclosed a Rh(III)-catalyzed C(sp2)−H functionalization on the phenyl ring of benzoyl sulfoxonium ylides with alkynes to afford naphthols (Scheme 1, (1)).9 More recently, Maulide et al. reported a Ru(II)-catalyzed crossolefination of sulfoxonium ylides with diazo compounds through exquisitely exploiting the intrinsic difference in the reactivity of diazo compounds and sulfoxonium ylides as carbene precursors and nucleophiles (Scheme 1, (2)).10 Inspired by these elegant pioneering studies and as a continuation of our own interest in the chemistry of sulfoxonium ylides11 and diazo compounds,12 we have explored the reaction of benzoyl sulfoxonium ylides with α-diazocarbonyl compounds under the catalysis of a © XXXX American Chemical Society

Rh(III) catalyst. From this study, we serendipitously found novel access toward highly functionalized naphthalenones containing a β-ketosulfoxonium ylide moiety (Scheme 1, (3)). Our study was initiated by treating benzoyl sulfoxonium ylide 1a with α-diazocarbonyl compound 2a in the presence of [RhCp*Cl2]2 and AgSbF6 in DCE. From this reaction, 3a was obtained along with its acylmethylation derivative 4a in yields of 17% and 23%, respectively (Table 1, entry 1). It is worthwhile to be noted herein that the unexpected formation of 3a and 4a is mechanistically interesting in that it reveals a different reaction pattern compared with either that of benzoyl sulfoxonium ylides with simple diazo compounds (Scheme 1, (2)) or that of benzoyl sulfoxonium ylides with alkynes (Scheme 1, (1)). In addition, this reaction is also synthetically fascinating as it discloses a novel approach toward unique naphthalenone derivatives bearing a β-ketosulfoxonium ylide unit. A literature Received: January 28, 2019

A

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Organic Letters Table 1. Optimization for the Formation of 3a or 4aa

temperature on this reaction was also explored (entries 15−18). As a result, the optimum temperature for the formation of 4a was determined as 80 °C, while that for 3a was found to be 100 °C. It was also observed that in the absence of AgSbF6, the formation of either 3a or 4a was not observed (entries 19−20). Finally, with toluene or TFE as the reaction medium, [RhCp*(MeCN)3](SbF6)2, [RhCp*(OAc)2]2, [Ir(cod)Cl2]2, or [Ru(cymene)2Cl2]2 was tried as possible catalyst to replace [RhCp*Cl2]2. However, they were found to be less efficient than [RhCp*Cl2]2 (see SI for the details). With the establishment of the optimum reaction conditions, the substrate scope for the synthesis of 3 was studied. First, the suitability of diversely substituted benzoyl sulfoxonium ylides 1 was investigated by using 2a as a model substrate. The results listed in Scheme 2 showed that 1 bearing either a methyl or methoxy unit on the para-position of the phenyl ring took part in this reaction smoothly to afford 3b and 3c. In addition, 1 bearing either an electron-donating group (EDG) such as methyl or methoxy or an electron-withdrawing group (EWG) such as

yieldb (%) entry

ratio of 1a/ 2a

catalyst

solvent

T (°C)

3a

4a

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19c 20c

1:1 1:1 1:1 1:1 1:1 1:1 1:1 1:1 1:2 1:2.2 1:2.5 1.2:1 1.5:1 2.0:1 1:2.2 1:2.2 1.2:1 1.2:1 1:2.2 1.2:1

[RhCp*Cl2]2 [RhCp*Cl2]2 [RhCp*Cl2]2 [RhCp*Cl2]2 [RhCp*Cl2]2 [RhCp*Cl2]2 [RhCp*Cl2]2 [RhCp*Cl2]2 [RhCp*Cl2]2 [RhCp*Cl2]2 [RhCp*Cl2]2 [RhCp*Cl2]2 [RhCp*Cl2]2 [RhCp*Cl2]2 [RhCp*Cl2]2 [RhCp*Cl2]2 [RhCp*Cl2]2 [RhCp*Cl2]2 [RhCp*Cl2]2 [RhCp*Cl2]2

DCE dioxane THF CH3CN TFE HFIP toluene PhCl toluene toluene toluene TFE TFE TFE toluene toluene TFE TFE TFE TFE

80 80 80 80 80 80 80 80 80 80 80 80 80 80 100 60 100 120 80 100

17 15 11 15 43 42 trace trace trace trace trace 45 46 41 trace trace 51 50 ND ND

23 8 14 10 trace trace 29 28 48 58 50 trace trace trace 53 43 trace trace ND ND

Scheme 2. Substrate Scope for the Synthesis of 3a,b

a

Conditions: 1a (0.5 mmol for entries 1−11, 15−16, 19), 2a (0.5 mmol for entries 12−14, 17−18, 20), catalyst (0.02 mmol, 4 mol %), AgSbF6 (0.08 mmol, 16 mol %), solvent (3 mL), N2, 24 h. bIsolated yield. cIn the absence of AgSbF6.

search revealed that, while bis-substituted sulfoxonium ylides are important synthetic intermediates with unique reactivity and applications, reliable methods for their preparation have only been sporadically reported,13 and some of these known methods usually suffer from drawbacks such as tedious synthetic steps, limited substrate scope, and expensive reagents. Very recently, Burtoloso et al. disclosed an elegant preparation of acylic α-aryl β-ketosulfoxonium ylides via the reactions of β-ketosulfoxonium ylides with the in situ generated aryne intermediates.14 However, to the best of our knowledge, the synthesis of αcycloalkenyl β-ketosulfoxonium ylides has not been previously reported. To develop this novel reaction into a reliable and practical approach toward bis-substituted β-ketosulfoxonium ylides, several parameters possibly affecting this reaction were screened. First, different solvents were tried. It was thus found that using dioxane, THF, or CH3CN as the reaction medium could not improve the efficiency or selectivity compared with that using DCE (entries 2−4 vs 1). In further screening, we were pleased to find that the reaction run in TFE (2,2,2-trifluoroethanol) or HFIP (hexafluoroisopropanol) could selectively give 3a as the predominant product in substantially improved yields (entries 5 and 6). However, when the reaction was run in toluene or PhCl, 4a could be formed as a major product (entries 7 and 8). Next, by using TFE or toluene as the optimum solvent, the effect of different molar ratio of 1a:2a on the efficiency for the formation of 3a or 4a was explored (entries 9−14). It was thus found that the best ratio for the formation of 4a is 1:2.2 (entry 10), while that for the formation of 3a is 1.2:1 (entry 12). Next, the effect of

a Conditions: 1 (0.6 mmol), 2 (0.5 mmol), [RhCp*Cl2]2 (0.02 mmol, 4 mol %), AgSbF6 (0.08 mmol, 16% mmol), TFE (3 mL), 100 °C, N2, 24 h. bIsolated yield.

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Organic Letters Scheme 3. Substrate Scope for the Synthesis of 4a,b

chloro or bromo on the meta-position of the phenyl ring are also suitable substrates for this reaction to give 3d−3g. Notably, the reactions of substrates bearing a meta-chloro or bromo unit gave a mixture of two regioisomers (3e and 3e′, 3f and 3f′). Promisingly, when 1 with an ortho-methyl, -chloro, or -bromo substituted phenyl unit were treated with 2a, the corresponding reactions proceeded equally well to give 3h−3j without showing obvious steric effect. Second, by using 1a as a model substrate, the generality of different α-diazocarbonyl compounds 2 for this reaction was studied. It was observed that 2-diazo-3-oxo-3phenylpropanoates bearing various functional groups including methyl, methoxy, chloro, bromo, or trifluoromethyl on the phenyl ring took part in this reaction efficiently to give 3k−3q. Meanwhile, it was noted that the electronic nature of the phenyl moiety rendered a slight effect on this reaction in that substrates bearing EDGs on the phenyl ring generally gave higher yields than those bearing EWGs (3l vs 3m). When alkyl substituted αdiazocarbonyl compounds were used, the reactions proceeded successfully to give 3r and 3s. Just like ethyl 2-diazo-3-oxo-3phenylpropanoate, the reactions of methyl 2-diazo-3-oxo-3phenylpropanoate and tert-butyl 2-diazo-3-oxobutanoate with 1a proceeded well to give 3t and 3u. We were delighted to find that 3-diazopentane-2,4-dione could also serve as the αdiazocarbonyl substrate to react with 1a to give 3v in 55% yield. Finally, benzoyl sulfoxonium ylides with strong EWGs (F and CF3) attached on the para-position of the phenyl ring were also tried. From the corresponding reactions, 3w and 3x were obtained. Meanwhile, it should be noted that the structure of 3b was unambiguously confirmed by its X-ray single crystal diffraction analysis. After establishing a novel synthesis of 3, we continued our study by exploring the substrate scope for the synthesis of 4, the acylmethylation derivative of 3. For this purpose, a series of benzoyl sulfoxonium ylides 1 were allowed to react with different α-diazocarbonyl compounds 2 such as ethyl/methyl 2diazo-3-oxo-3-phenylpropanoates bearing a diversely substituted phenyl unit, or ethyl 2-diazo-3-(furan-2-yl)-3-oxopropanoate, respectively. From these reactions, the corresponding products 4a−4t were obtained in yields ranging from 45% to 75%, thus resulting in a reliable and general synthetic protocol toward the structurally more complex naphthalenones containing a β-ketosulfoxonium ylide unit (Scheme 3). Notably, the structure of 4h was confirmed by its NMR data and X-ray single crystal diffraction analysis. Interestingly, when tert-butyl 2-diazo-3-oxobutanoate was used as the diazo substrate to react with 1a, the corresponding reaction afforded a benzo[de]chromene derivative 5, most likely with 4u as an intermediate (Scheme 4). As a further exploration of the scope, simple terminal diazo ester and ketone were allowed to react with 1a. It turned out that the reaction of 1a with ethyl 2-diazoacetate in TFE or toluene gave unidentifiable mixtures (Scheme 5, (1)). Meanwhile, the reaction of 1a with 2-diazo-1-phenylethan-1-one in TFE or toluene afforded 1-phenyl-2-(2,2,2-trifluoroethoxy)ethan-1-one (A) or 1,4-diphenylbut-2-ene-1,4-dione (B) (Scheme 5, (2)). To get some insight into the reaction mechanism accounting for the formation of 3a, the following experiments were conducted. First, 1a was treated with CD3OD in the presence of [RhCp*Cl2]2 and AgSbF6 in TFE at 100 °C for 30 min, from which deuterium incorporations at the ortho-position of the phenyl ring (6%) and the α-position of the carbonyl unit (27%) were observed (Scheme 6). These results indicate that the C−H bond cleavage process should be reversible.

a

Conditions: 1 (0.5 mmol), 2 (1.1 mmol), [RhCp*Cl2]2 (0.02 mmol, 4 mol %), AgSbF6 (0.08 mmol, 16 mol %), toluene (3 mL), 80 °C, N2, 24 h. bIsolated yield.

Scheme 4. Formation of 5 from an Alkyl Substituted αDiazocarbonyl Substrate

Scheme 5. Reaction of 1a with Terminal α-Diazoester and Ketone

Scheme 6. Reversibility of C−H Bond Cleavage

Second, a competitive reaction between 1a with 2a and 1a-d5 with 2a was carried out. From this reaction, an intermolecular kinetic isotopic effect value (KH/KD) of 3.5 was determined (Scheme 7). This result shows that the cleavage of the ortho-C− C

DOI: 10.1021/acs.orglett.9b00340 Org. Lett. XXXX, XXX, XXX−XXX

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Organic Letters H bond might be involved in the rate-limiting step of this cascade process.

Scheme 10. Gram-scale Synthesis of 3a

Scheme 7. Intermolecular Kinetic Isotope Effect Study

Scheme 11. Synthetic Applications of 3a Based on the above-described mechanistic studies and related reports,9,12 a plausible mechanism accounting for the formation of 3a from the reaction of 1a with 2a is proposed in Scheme 8. Scheme 8. Proposed Mechanism for the Formation of 3a

important 4-hydroxy-2-phenyl-1-naphthoate (6), 3-hydroxy-4oxo-2-phenyl-3,4-dihydronaphthalene-1-carboxylate (7), 4-hydroxy-3-(methylsulfinyl)-2-phenyl-1-naphthoate (8),15 and 3,4dioxo-2-phenyl-3,4-dihydronaphthalene-1-carboxylate (9)16 were obtained in moderate to excellent yields. In conclusion, we have developed a general, efficient, and sustainable synthesis of novel naphthalenone derivatives containing a β-ketosulfoxonium ylide moiety through direct C−H functionalization and subsequent annulations of benzoyl sulfoxonium ylides with α-diazocarbonyl compounds. To our knowledge, this is the first example in which α-cycloalkenyl βketosulfoxonium ylides are prepared. Moreover, the synthetic significance of the novel naphthalenone derivative thus obtained was showcased by its easy transformations into a series of synthetically and biologically interesting naphthalene derivatives. With notable features such as easily accessible substrates, convenient synthetic procedure, and good atom economy, the chemical transformations described in this Letter are expected to find broad applications in related areas.

Initially, coordination of the carbonyl oxygen of 1a with Rh(III) and subsequent cyclometalation through C−H bond cleavage gives rise to a five-membered rhodacycle I. I then reacts with 2a to afford a rhodium-carbene species II through releasing N2. Next, migratory insertion of carbene into the Rh−C bond affords a six-membered rhodacycle intermediate III. Protonolysis of III leads to the formation of intermediate IV and regenerates the Rh(III) catalyst. In the final stage of this cascade reaction, IV undergoes an intramolecular nucleophilic addition to form V, from which 3a is formed through β-elimination. As for the plausible mechanism accounting for the formation of 4a, it should first involve the formation of 3a from the cascade reaction of 1a with 2a as described in Scheme 8. Then, a Rh(III)catalyzed acylmethylation of 3a with 2a under the assistance of the naphthalenone carbonyl unit takes place to afford 4a. This proposal is confirmed by the following control experiment that treatment of 3a with 2a under standard reaction conditions could afford 4a in a yield of 83% (Scheme 9).

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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.9b00340. Copies of 1H and 13C NMR spectra of all products and the X-ray crystal structures and data of 3b, 4h, and 8 (PDF) Accession Codes

CCDC 1887533, 1887549, and 1887578 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/ cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

Scheme 9. Formation of 4a from the Reaction of 3a with 2a

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AUTHOR INFORMATION

Corresponding Authors

To see whether this newly developed synthesis of naphthalenone derivatives bearing a β-ketosulfoxonium ylide unit is suitable for larger scale application, the preparation of 3a was carried out in 5 mmol scale. Under these circumstances, 3a was obtained in a yield of 42% (Scheme 10). To showcase the synthetic potential of the naphthalenones bearing a β-ketosulfoxonium ylide unit obtained above, several structural elaborations of 3a were carried out (Scheme 11). From these transformations, the synthetically and biologically

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Xinying Zhang: 0000-0002-3416-4623 Xuesen Fan: 0000-0002-2040-6919 Notes

The authors declare no competing financial interest. D

DOI: 10.1021/acs.orglett.9b00340 Org. Lett. XXXX, XXX, XXX−XXX

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Organic Letters

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(11) Chen, G.; Zhang, X.; Jia, R.; Li, B.; Fan, X. Adv. Synth. Catal. 2018, 360, 3781. (12) (a) Li, B.; Zhang, B.; Zhang, X.; Fan, X. Chem. Commun. 2017, 53, 1297. (b) Zhang, B.; Li, B.; Zhang, X.; Fan, X. Org. Lett. 2017, 19, 2294. (13) (a) Dost, F.; Gosselck, J. Tetrahedron Lett. 1970, 11, 5091. (b) Niitsuma, S.; Sakamoto, T.; Yamanaka, H. Heterocycles 1978, 10, 171. (c) Yamanaka, H.; Konno, S.; Sakamoto, T.; Niitsuma, S.; Noji, S. Chem. Pharm. Bull. 1981, 29, 2837. (14) Talero, A. G.; Martins, B. S.; Burtoloso, A. C. B. Org. Lett. 2018, 20, 7206. (15) (a) Bernoud, E.; Le Duc, G.; Bantreil, X.; Prestat, G.; Madec, D.; Poli, G. Org. Lett. 2010, 12, 320. (b) Huang, X.; Maulide, N. J. Am. Chem. Soc. 2011, 133, 8510. (c) Li, Y.; Qiu, D.; Gu, R.; Wang, J.; Shi, J.; Li, Y. J. Am. Chem. Soc. 2016, 138, 10814. (d) Yamamoto, K.; Otsuka, S.; Nogi, K.; Yorimitsu, H. ACS Catal. 2017, 7, 7623. (16) (a) Das, A. K.; Goswami, S.; Dutta, G.; Maity, S.; Mandal, T. K.; Khanra, K.; Bhattacharyya, N. Org. Biomol. Chem. 2016, 14, 570. (b) Hatfield, M. J.; Chen, J.; Fratt, E. M.; Chi, L.; Bollinger, J. C.; Binder, R. J.; Bowling, J.; Hyatt, J. L.; Scarborough, J.; Jeffries, C.; Potter, P. M. J. Med. Chem. 2017, 60, 1568. (c) Ding, C.; Tian, Q.; Li, J.; Jiao, M.; Song, S.; Wang, Y.; Miao, Z.; Zhang, A. J. Med. Chem. 2018, 61, 760.

ACKNOWLEDGMENTS We are grateful to the National Natural Science Foundation of China (NSFC) (21572047), Plan for Scientific Innovation Talents of Henan Province (184200510012), and 111 Project (D17007) for financial support.

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