Nickle Catalysis Enables Access to Thiazolidines from Thioureas via

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Nickle Catalysis Enables Access to Thiazolidines from Thioureas via Oxidative Double Isocyanide Insertion Reactions Wen-Kui Yuan,† Yan Fang Liu,*,‡ Zhenggang Lan,‡ Li-Rong Wen,*,† and Ming Li*,† †

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State Key Laboratory Base of Eco-Chemical Engineering, College of Chemistry and Molecular Engineering, Qingdao University of Science and Technology, Qingdao 266042, P. R. China ‡ Shandong Provincial Key Laboratory of Synthetic Biology, Laboratory of Biofuels, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, 266061, China S Supporting Information *

ABSTRACT: An efficient synthesis of thiazolidine-2,4,5-triimine derivatives was developed via Ni-catalyzed oxidative double isocyanide insertion to thioureas under air conditions, in which thioureas play three roles as a substrate, a ligand, and overcoming isocyanide polymerization. The reaction is featured by employing a low-cost and low loading Ni(acac)2 catalyst, without any additives, and high atom economy. This is the first example to directly apply a Ni(II) catalyst in oxidative double isocyanide insertion reactions.

T

on the oxidative single isocyanide insertions (Scheme 1, eq 1),7 only a few scattered examples of Pd-catalyzed oxidative double

he thiazolidine core is a structural motif of particular interest in the fields of agriculture and industry. For example, flubenzimines as general structures I have been applied as a mite growth regulating acaricide (Figure 1).1

Scheme 1. Transition Metal Catalyzed Oxidative Isocyanide Insertion Reactions

Figure 1. Selected thiazolidines with biological activities and industrial application.

Compounds II can be used as corrosion inhibitors of C-steel,2 and compound III is a dye for hair fibers.3 However, the methods for obtaining thiazolidine derivatives are still limited thus far, which may be due to these reported approaches’ lack of generality and requirement in some cases of inaccessible substrates.4 Therefore, the development of a novel and general approach would be desirable and valuable. Isocyanides are important active reactants containing stable divalent carbon atoms and have been widely used in the construction of nitrogen-containing compounds.5 In particular, transition-metal-catalyzed isocyanide insertion has served as a powerful tool in the strategy of organic synthesis.6 However, most oxidative isocyanide insertion reactions mainly focused © 2018 American Chemical Society

isocyanide insertion reactions were reported.8 In sharp contrast, given Ni’s position directly above palladium, Nienabled oxidative double isocyanide insertion is virtually rare, which may be due to easy polymerization of isocyanides in the presence of a transition metal.9 Therefore, the development of a double isocyanide insertion by the use of Ni catalysts would be a highly desirable goal of the utmost synthetic importance. Received: September 27, 2018 Published: November 6, 2018 7158

DOI: 10.1021/acs.orglett.8b03098 Org. Lett. 2018, 20, 7158−7162

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Organic Letters

amount of the catalyst was tested. Gratifyingly, decreasing the loading of Ni(acac)2 to 0.03 equiv still gave a 91% yield of 3a after 4 h (entry 17). However, further decreasing the loading of Ni(acac)2 to 0.01 equiv showed a loss of reaction efficiency (entry 18). Therefore, the optimal reaction conditions were determined to include 0.03 equiv of Ni(acac)2 as the catalyst and acetone as the solvent at 50 °C for 4 h. With the optimized reaction conditions in hand, the substrate scope of thioureas (1) and isocyanides (2) was explored. First, various alkyl and aromatic isocyanides were used to insert symmetrical dialkylthioureas. As shown in Scheme 2, in all cases, the reactions took place smoothly and

In continuation of our research on the development of isocyanide as a building block,10 herein, we report the first example of low-cost Ni(acac)2-catalyzed oxidative double isocyanide insertion to thioureas for the synthesis of thiazolidine derivatives (Scheme 1, eq 2). Significantly, in this transformation thioureas served as not only a substrate but also a ligand that in situ generated an active Ni(II)−thiourea complex, avoiding polymerization of isocyanides. This transformation represents the first example of applying Ni(II) in oxidative double isocyanide insertion reactions that resulted in the formation of thiazolidines. Our study commenced with the reaction between 1,3diphenylthiourea 1a and isocyanocyclohexane 2a in 1,4dioxane at 50 °C. A survey of reaction parameters was shown in Table 1. After unsuccessful trials by using other

Scheme 2. Substrate Scope of Symmetric Thioureasa,b

Table 1. Optimization of Reaction Conditions for 3aa

entry

catalyst (equiv)

solvent

temp (°C)

time (h)

yield (%)b

1 2 3 4 5 6 7 8

Pd(OAc)2 (0.3) Co(acac)2 (0.3) Cu(OTf)2 (0.3) Ni(acac)2 (0.1) Ni(acac)2 (0.05) Ni(OAc)2 (0.05) Ni(PPh3)2Cl2 (0.05) NiCl2·6H2O (0.05) Ni(acac)2 (0.05) Ni(acac)2 (0.05) Ni(acac)2 (0.05) Ni(acac)2 (0.05) Ni(acac)2 (0.05) Ni(acac)2 (0.05) Ni(acac)2 (0.05) Ni(acac)2 (0.03) Ni(acac)2 (0.01)

1,4-dioxane 1,4-dioxane 1,4-dioxane 1,4-dioxane 1,4-dioxane 1,4-dioxane 1,4-dioxane 1,4-dioxane

50 50 50 50 50 50 50 50

20 20 20 4 4 4 10 4

trace 16 15 83 NR 81 72 27

1,4-dioxane toluene 2-MeTHF EtOH acetone acetone acetone acetone acetone acetone

50 50 50 50 50 rt 40 60 50 50

4 23 4 6 4 4 4 4 4 4

20 70 85 79 92 67 81 85 91 85

9 10 11 12 13 14 15 16 17 18

a

Reaction conditions: 1 (0.60 mmol), 2 (1.32 mmol), Ni(acac)2 (0.018 mmol), acetone (2.0 mL), 50 °C, 4 h. bIsolated yields (the residues in mother liquor are not included). Cy = cyclohexyl, nBu = nbutyl, tBu = tert-butyl, 1-Ad = 1-Adamantane, PMP = paramethoxyphenyl, 1-Naph = 1-naphthyl, p-Toly = p-methylphenyl.

gave the corresponding thiazolidines in good to excellent yields. Notably, diarylthioureas with electron-donating substituents at the para-position achieved good yields of 80−85% (3k and 3l). However, diarylthioureas with electron-withdrawing groups such as Br, Cl, F, and CF3 at para-position showed slightly low reactivity to provide 40−80% yields (3m− 3p). Next, a series of unsymmetrical thioureas 1 were utilized to react with isocyanocyclohexane 2a for identifying the regioselectivity of the double insertion reactions (Scheme 3). As shown in Scheme 3, the 1,3-unsymmetrical thioureas with one aromatic and one aliphatic group can be transformed efficiently affording the desired products as a single isomer in moderate to excellent yields (4a−4k). Notably, the regioselectivity profile of this method was nicely illustrated in the functional groups such as alkynyl (4l), OH (4m), and ester (4n), which allowed further synthetic utilities, while the substrate with a carboxyl group showed low reactivity (4o). Additionally, the 1,3-unsymmetrical thioureas with one 2pyridine and an aromatic group also worked well (4q and 4r). However, the unsymmetrical diarylthioureas gave a mixture of two regioisomers (4s−4y).

a

Reaction conditions: 1a (0.60 mmol), 2a (1.32 mmol), solvent (2.0 mL). bIsolated yield (the residue in mother liquor is not included).

transition-metal catalysts (Table 1, entries 1−3), we found that 0.1 equiv of Ni(acac)2 led to the desired transformation, product 3a was isolated in 83% yield after 4 h (entry 4). A control experiment revealed that the reaction could not be initiated in the absence of the catalyst (entry 5). Then 0.05 equiv of Ni(acac)2 was employed, and an 81% yield of 3a was obtained (entry 6). Encouraged by these results, a screening of Ni(II) sources such as Ni(OAc)2, Ni(PPh3)2Cl2, and NiCl2· 6H2O was carried out. The results reveal that they were ineffective for this transformation (entries 7−9). Next, other solvents such as toluene, 2-MeTHF, EtOH, and acetone were also screened with 0.05 equiv Ni(acac)2 as the catalyst at 50 °C, and the results indicated acetone was best, as 3a could precipitate directly to provide an excellent yield of 92% (entries 10−13). The reaction temperature was also investigated, and it was found that increasing or decreasing the temperature was unfavorable (entries 14−16). Finally, the 7159

DOI: 10.1021/acs.orglett.8b03098 Org. Lett. 2018, 20, 7158−7162

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Organic Letters Scheme 3. Substrate Scope of Unsymmetrical Thioureasa,b

Scheme 5. Reactions of KTAs 6 with 2a

Thus, we speculated the above double isocyanide insertion reactions could be a step-by-step insertion mode. Scheme 6. Reactions of Diarylthioureas with α-Acidic Isocyanides

In order to demonstrate the synthetic utility of this method, the model reaction was performed on 5 mmol scale under the standard conditions, and the desired product 3a was provided in 85% yield (Scheme 7). Scheme 7. Gram-Scale Experiment

a

Reaction conditions: 1 (0.60 mmol), 2a (1.32 mmol), Ni(acac)2 (0.018 mmol), acetone (2.0 mL), 50 °C, 4 h. bIsolated yields (The residues in mother liquor are not included). cIsomer ratio was determined by 1H NMR. dIsomer ratio was determined after separation. PMP = para-methoxyphenyl. 1-Naph = 1-naphthyl. Th = 2-thienyl.

Notably, when unsubstituted thiourea was employed to react with 2a, 1H-imidazole-2(5H)-thione (5) in 40% yield rather than a thiazolidine compound was obtained (Scheme 4).

To understand the reaction mechanism, we carried out the following control experiments (Scheme 6). The reaction of 1,3-diphenylthiourea (1a) with 2a by 0.10 equiv Ni(acac)2 as the catalyst in degassed acetone at 50 °C under N2 provided 3a in 36% yield (Scheme 8, eq 1). The result suggests that O2 was very important for this oxidative double isocyanide insertion reaction. To further illustrate the catalytic cycle process, a complex A was synthesized using 1,3-diphenylthiourea (1a) and Ni(acac)2 at room temperature (the structure of complex A was confirmed by the single crystal X-ray diffraction analysis; see the Supporting Information) (Scheme 8, eq 2). Significantly, only 1 mol % complex A could catalyze effectively the model reaction to give 3a in 93% yield within 1 h (Scheme 8, eq 3). These results suggest that complex A was likely involved in the catalytic cycle as the active catalyst. On the basis of the above observation, a plausible reaction mechanism has been depicted in Scheme 9. The catalytic cycle is initiated by in situ generated thioureas−Ni(II) complex A from Ni(II) catalyst precursor Ni(acac)2 and thioureas 1. Next, two molecules of isocyanides 2 participate via coordination to form a new four coordination complex B, meanwhile releasing one molecule of thioureas 1. Then isocyanides insert to the Ni−S bond of B to give six-membered Ni(II) intermediate C.

Scheme 4. Reaction of Thiourea with 2a

β-Ketothioamides (KTAs)11 have proven to be fascinating and versatile synthons in the construction of heterocyclic systems. Our protocol could be applied successfully to synthesize 2-methylenethiazolidine-4,5-diimines (7) from KTAs (6) and 2a under similar conditions (Scheme 5). Interestingly, when α-acidic isocyanides such as isocyanoacetate, BnNC (isocyanomethylbenzene), or TosMIC (tosylmethyl isocyanide) were applied to this process under the optimized conditions, the reactions gave the single isocyanide insertion products 1,3-thiazetidine-2,4-diimines (8) (Scheme 6). These results may be subjected to the steric hindrance. 7160

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Scheme 8. Control Experiments

CCDC 1441175, 1447519, 1469948, 1490148, 1503923, and 1547710 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 data_ [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Authors

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

Yan Fang Liu: 0000-0002-9086-9599 Li-Rong Wen: 0000-0001-7976-0878 Ming Li: 0000-0003-4906-936X Notes

Scheme 9. Proposed Catalytic Cycle for the Ni(II)Catalyzed Oxidative Double Isocyanide Insertion Reaction

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by the National Natural Science Foundation of China (21572110, 21372137, 21607164, and 21801152).

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(1) Hans-Joachim, S.; Erich, K. 1972. DE2210882(A1). (2) Al-Sarawy, A. A.; Fouda, A. S.; El-Dein, W. A. S. Desalination 2008, 229, 279. (3) Alain, L.; Boris, L. 2014. FR3024356(A1). (4) (a) Mackenzie, P. B.; Moody, L. S.; Moore, K. C.; Lavoie, G. G. 2003, US6660677 (B1). (b) Mackenzie, P. B.; Moody, L. S.; Killian, C. M.; Lavoie, G. G. 1999, WO9962968 (A1). (5) For selected examples of isocyanides chemistry, see: (a) Giustiniano, M.; Basso, A.; Mercalli, V.; Massarotti, A.; Novellino, E.; Tron, G. C.; Zhu, J. P. Chem. Soc. Rev. 2017, 46, 1295. (b) Yang, Q.; Li, C.; Cheng, M.-X.; Yang, S.-D. ACS Catal. 2016, 6, 4715. (c) Gao, Q.; Zhou, P.; Liu, F.; Hao, W.-J.; Yao, C.; Jiang, B.; Tu, S.-J. Chem. Commun. 2015, 51, 9519. (d) Boyarskiy, V. P.; Bokach, N. A.; Luzyanin, K. V.; Kukushkin, V. Y. Chem. Rev. 2015, 115, 2698. (e) Xiao, P.; Yuan, H. Y.; Liu, J. Q.; Zheng, Y. Y.; Bi, X. H.; Zhang, J. P. ACS Catal. 2015, 5, 6177. (f) Chakrabarty, S.; Choudhary, S.; Doshi, A.; Liu, F. Q.; Mohan, R.; Ravindra, M. P.; Shah, D.; Yang, X.; Fleming, F. F. Adv. Synth. Catal. 2014, 356, 2135. (g) Estévez, V.; Van Baelen, G.; Lentferink, B. H.; Vlaar, T.; Janssen, E.; Maes, B. U. W.; Orru, R. V. A.; Ruijter, E. ACS Catal. 2014, 4, 40. (h) Lang, S. Chem. Soc. Rev. 2013, 42, 4867. (i) Vlaar, T.; Ruijter, E.; Maes, B. U. W.; Orru, R. V. A. Angew. Chem., Int. Ed. 2013, 52, 7084. (j) Qiu, G. S.; Ding, Q. P.; Wu, J. Chem. Soc. Rev. 2013, 42, 5257. (6) (a) Song, B. R.; Xu, B. Chem. Soc. Rev. 2017, 46, 1103. (b) Senadi, G. C.; Lu, T. Y.; Dhandabani, G. K.; Wang, J. Org. Lett. 2017, 19, 1172. (c) Tian, Y. M.; Tian, L. M.; Li, C. J.; Jia, X. S.; Li, J. Org. Lett. 2016, 18, 840. (d) Wang, J.; Tang, S.; Zhu, Q. Org. Lett. 2016, 18, 3074. (e) Qiu, G. Y. S.; Mamboury, M.; Wang, Q.; Zhu, J. P. Angew. Chem., Int. Ed. 2016, 55, 15377. (f) Tian, Y. M.; Tian, L. M.; Li, C. J.; Jia, X. S.; Li, J. Org. Lett. 2016, 18, 840. (g) Kobiki, Y.; Kawaguchi, S.; Ogawa, A. Org. Lett. 2015, 17, 3490. (h) Pan, Y. Y.; Wu, Y. N.; Chen, Z. Z.; Hao, W. J.; Li, G. G.; Tu, S. J.; Jiang, B. J. Org. Chem. 2015, 80, 5764. (i) Gu, Z. Y.; Zhu, T. H.; Cao, J. J.; Xu, X. P.; Wang, S. Y.; Ji, S. J. ACS Catal. 2014, 4, 49. (j) Wang, Y.; Wang, H. G.; Peng, J. L.; Zhu, Q. Org. Lett. 2011, 13, 4604. (7) For selected examples of oxidative single isocyanide insertion, see: Pd catalysis: (a) Jiang, H. F.; Gao, H. L.; Liu, B. F.; Wu, W. Q.

Finally, reductive elimination of C affords products 3 (or 4) along with Ni(0) species, which is immediately oxidized to Ni(II) by oxygen for next catalytic cycle. In summary, we have developed a Ni(II)-catalyzed oxidative double isocyanide insertion reaction to thioureas for the synthesis of thiazolidine-2,4,5-triimines. The reaction is featured by employing low-cost and low loading Ni(acac)2 catalyst under air conditions, without any additives, and high atom economy. The cleverness of this approach is that thioureas not only are used as a raw material but also can in situ form a new catalytically active complex instead of anion acac in Ni(acac)2, which prevents the polymerization of isocyanides. Such a “single stone for three birds” strategy is a versatile tool in organic synthesis.

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REFERENCES

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.orglett.8b03098. Experimental procedures, characterization and spectral data (PDF) 7161

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