A mechanistic study on multifunctional Fei-Phos ligand-controlled asymmetric palladium-catalyzed allylic substitutions

Abstract

To shield light on the mechanism of palladium-catalyzed allylic substitutions with structurally diverse nucleophiles (up to 99% ee) in the presence of Fei-Phos ligand (chiral trans-1,2-diaminocyclohexane-derived biphosphine, CycloN2P2-Phos) as an effective chiral P-ligand, mechanistic studies were performed for clarification of the role of multifunctional Fei-Phos in this reaction. The cooperative action of nitrogen and phosphorous atoms in the present Pd-catalyzed allylic alkylation is proved to be a diphosphine-based catalyst system but not a nitrogen-controlled or monophosphine-involved transition state.

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Introduction

Transition-metal-catalyzed allylic substitutions have been proved to be one of the most practical approaches for the construction of allyl- or alkene-substituted compounds in the past few decades.¹ Accordingly, the catalytic asymmetric allylic alkylation reaction has become a powerful carbon–carbon or carbon–heteroatom bond forming reaction for enantioselective synthesis of structurally and stereochemically rich molecular frameworks in recent decades.² In this respect, transition-metal-catalyzed asymmetric allylic substitutions with structurally diverse allylic acetates has attracted much attention. In such approaches, the catalytic asymmetric allylic substitution reaction usually relies on the molecular design of chiral ligands bearing phosphorous, nitrogen, and other heteroatoms.³ Especially, numerous phosphine ligands have been developed as extremely useful in asymmetric palladium-catalyzed allylic alkylation reaction.⁴ However, although numerous chiral P-ligands has been applied in the catalytic asymmetric allylic substitution reaction of various nucleophiles in the past years,^1–5 the development of highly efficient chiral P-ligand for practically useful allylic substitutions is still highly desirable.

Recently, we have ever developed a new multifunctional and multidentate ligand bearing multiple stereogenic centers,⁶ and it is a structurally novel cyclic tertiary diamine-based biphosphine having two nitrogen atoms (CycloN2P2-Phos) derived from chiral trans-1,2-diaminocyclohexane, also called as Fei-Phos in the previous work (Scheme 1).^6,7

Scheme 1 Pd/Fei-Phos catalyzed asymmetric allylic substitution of structurally diverse nucleophiles with allylic acetate.

It was found that the asymmetric palladium-catalysed alkylation of structurally diverse hard/soft nucleophiles, including allylic etherification of alcohols, silanols, allylic alkylation of activated methylene compounds, indoles, and aromatic amines, resulted in good to excellent yields and excellent enantioselectivities (up to 99% ee). However, the full and detailed mechanism with possible transition state, as well as the role of phosphorous centers and nitrogen atoms of Fei-Phos in this reaction remains unclear. In addition, a true palladium catalyst that heretofore has not been determined in the previous work, thus we also became intrigued by the possibility of generating coordinated palladium complex (Pd/Fei-Phos) with nitrogen atoms or phosphorous centers. Meanwhile, the clarification of related reaction results and catalysis chemistry is an interesting task in this work. Herein, to shield light on the mechanism of the palladium-catalyzed allylic substitutions with structurally diverse nucleophiles (up to 99% ee) in the presence of the multifunctional Fei-Phos ligand (chiral trans-1,2-diaminocyclohexane-derived diphosphine, CycloN2P2-Phos) as an effective chiral P-ligand, the mechanistic studies were performed for the clarification of the role of Fei-Phos in this reaction.

Results and discussion

Possible Pd/Fei-Phos complex or intermediates in the palladium catalyst system

Although the Fei-Phos has been introduced successfully as chiral P-ligand in palladium – catalyzed allylic substitutions of various nucleophiles, previous work only focused on the experimental investigation of catalytic asymmetric allylic reaction. As a preliminary study/task, it is interesting to clarify the role of phosphorous and nitrogen atoms in the multifunctional Fei-Phos – controlled palladium-catalyzed allylic alkylation reaction under the optimized reaction conditions.^6,7 In addition, it is unclear that how to induce the stereoselective allylic substitutions by the complicated Fei-Phos bearing two nitrogen and two phosphorous centers on this ligand. Therefore it is necessary to investigate the possible transition state of Fei-Phos in these allylic substitutions for clarification of its possible stereoselective induction. Initially, to obtain useful information for the reasonable understanding of the observed activity and stereoselective induction of Fei-Phos ligand in the palladium-catalyzed allylic etherification reaction of benzyl alcohols and silanols (Scheme 2), we tried to perform the theoretical calculations using Gaussian 09 software package.⁸

Scheme 2 Proposed transition-state model in the catalytic asymmetric allylic etherification: diphosphine-involved model of allylic etherification of alcohols with biphosphine ligand (Fei-Phos)?

Initially, we performed the ESI(+)-MS analysis of the mixture of [Pd(η³-C₃H₃)Cl]₂ and Fei-Phos. Fig. 1 shows that the ESI(+)-MS collected the chiral palladium/Fei-Phos intermediate of m/z 835.3. Therefore the Pd/Fei-Phos complex could be possibly by the detection of these key ions. On the basis of the schematic drawing of three possible Pd/Fei-Phos complexes (Fig. 1, or S1 of ESI†), the relative energy of three possible palladium/Fei-Phos complex (I–III) derived from different coordination model is varied from 0 to 21.9 kcal mol⁻¹.⁸ As shown in the schematic drawing of Fig. 2, the coordination of Fei-Phos with palladium probably led to the formation of more stable complex I formed by one palladium linked with two phosphorous atoms in comparison to that of other type of palladium/Fei-Phos complex II or III. Therefore, it looks reasonable that the Brønsted basic nitrogen-center on the biphosphine ligand (Fei-Phos) would be a control element for the discrimination of the reactivity of various alcohols and thus lead to different performance of substrate activation (Scheme 2). However, the outcomes of calculated relative energy could not provide direct evidence and information for the supporting of the mechanism of palladium-catalyzed allylic alkylation with alcohols with superior catalytic activity of Fei-Phos ligand in this reaction. Furthermore, it is not so easy because the true palladium/Fei-Phos should be clarified in this work as well as the expanding of palladium/Fei-Phos – catalyzed allylic alkylation with various nucleophiles.

Fig. 1 ESI(+)-MS analysis for the Pd/Fei-Phos complex.

Fig. 2 What's the true role of nitrogen and phosphorous atoms on Fei-Phos in the palladium catalysis? Potential energy for coordination of Fei-Phos with palladium center calculated at B3LYP/6-31G(d,p) level of theory.⁸

To understand the role of phosphorous atoms in the Pd/Fei-Phos catalysis and the true structure of the palladium catalyst with ligand Fei-Phos, we fortunately obtained the complex Pd/Fei-Phos through the coordination of Fei-Phos ligand with [Pd(η³-C₃H₃)Cl]₂ in dichloromethane and toluene at room temperature for several days. Unexpectedly and interestingly, the crystal structure of the palladium/Fei-Phos complex was shown in Fig. 3. As seen from Fig. 3, the Fei-Phos ligand coordinated to palladium atom with phosphorous atom and benzyl ring via a conformationally restricted eight-membered palladium-containing heterometal ring. To the best of our knowledge, it is the first example of a new class of isolable and enantiomerically pure eight-membered-palladium complex. The only one related example of X-ray crystallographic studies on π–allylpalladium complexes coordinated with a chiral phosphine–olefin ligand was reported by Hayashi in 2005.⁹ It is a bicyclo[2.2.1]heptane-derived five-membered palladium-containing heterometal ring system combined with eight-membered ring. These characteristics of bonding structure showed in Fig. 3 might attribute to rigid diphenylpiperazine backbone of the ligand and the large chelate ring formed by the dephosphorous Fei-Phos ligand. Therefore, this structure character of Pd/Fei-Phos complex directly interprets its high enantioselectivity and activity in the palladium-catalyzed asymmetric allylic etherification of alcohols because of its capable of formation of conformationally restricted eight-membered P–Pd–C bond-involving heterometal ring.

Fig. 3 ORTEP illustration of the palladium/Fei-Phos complex (CCDC 1446415). All hydrogen atoms are omitted for clarity. Selected bond lengths [Å] and angles [°]: Pd(1)–C(1) 2.009(8), Pd(1)–P(1) 2.234(2), P(1)–C(29) 1.797(9), P(1)–C(23) 1.822(9), P(1)–C(22) 1.835(7), C(17)–C(22) 1.371(10), C(16)–C(17) 1.522(10), C(7)–C(16) 1.503(10), C(6)–C(7) 1.511(9), C(1)–C(6) 1.392(10); C(1)–Pd(1)–P(1) 86.3(2), C(29)–P(1)–C(23) 105.6(4), C(29)–P(1)–C(22) 107.1(4), C(23)–P(1)–C(22) 98.4(4), C(17)–C(22)–P(1) 121.8(6), C(22)–C(17)–C(16) 123.3(6), C(7)–C(16)–C(17) 106.5(6), C(16)–C(7)–C(6) 113.7(6), C(1)–C(6)–C(7) 123.2(6), C(6)–C(1)–Pd(1) 128.0(6).

Inspired by this finding that the carbon–phosphorous bond cleavage occurs in the formation of novel palladium complex in the presence of Fei-Phos, we then investigated the effect of the phenylboronic acid on the synthesis of palladium/Fei-Phos complex. As expected, the addition of phenylboronic acid or iodobenzene led to the formation of triphenylphosphine (PPh₃) in the presence of base (Scheme 3),¹⁰ which gave indirect evidence to support the structure of palladium/Fei-Phos complex in Fig. 3.

Scheme 3 The direct detection of triphenylphosphine by GC-MS: the C–P bond cleavage of Fei-Phos and new C–P bond-forming in the presence of palladium catalyst.

Furthermore, the addition of a catalytic amount of phenylboronic acid also led to improved yield of 2a (90% yield), and the enantioselectivity remained excellent (96% ee) in comparison to that of phenylboronic acid-free reaction conditions (Scheme 4). Notably, we observed that the use of the novel palladium complex in Fig. 3 as catalyst also resulted in the same level of enantioselectivity in this reaction. We also examined the reaction of phenylboronic acid with ligand L1, the analogues of Fei-Phos, in the presence of palladium and base. Under identical conditions, the carbon–phosphorous bond cleavage did not occur, suggesting that the structure of palladium/Fei-Phos is significantly influenced by the multistereogenic diphenylpiperazine and diphenylphosphine backbone. For example, no dicyclohexyl(phenyl)phosphine was detected in the reaction of ligand L1 and phenylboronic acid in the presence of [Pd(η³-C₃H₃)Cl]₂ (Scheme 5). Overall, this study led to the conclusion that the palladium-catalyzed allylic etherification reaction might be promoted by the novel eight-membered palladium/Fei-Phos complex (Fig. 3), which is possibly different from that of the preliminary hypothesis in Scheme 2 and Fig. 2. However, the reaction mechanism of such Fei-Phos – involved palladium-catalyzed allylic substitution reaction is quite complicated than that of our speculation because the eight-membered-Pd/Fei-Phos complex provided in this work are still insufficient for supporting the true palladium catalyst in these allylic alkylation reactions. Alternative pathway with cooperative activation is not completely ruled out because of the use of multifunctional Fei-Phos ligand bearing structural specifically backbone in this reaction.

Scheme 4 The effect of phenylboronic acid on the Pd/Fei-Phos – catalyzed allylic etherification.

Scheme 5 The possible reaction of ligand L1 and phenylboronic acid in the presence of palladium and base: no desired dicyclohexyl(phenyl)phosphine.

Mechanistic studies in palladium-catalyzed allylic etherification with Fei-Phos

Except the clarification of true structure of palladium/Fei-Phos complex in this reaction, it is important to focus on the role of nitrogen atoms of Fei-Phos in the Pd-catalyzed asymmetric allylic etherification and the corresponding issues of stereoselectivity and reactivity in this reaction. Thus we selected 1,3-diphenyl-2-propenyl acetate (1) as a substrate to probe the difference of alkyl alcohols in this reaction, which would be useful for the understanding the mechanism of palladium/Fei-Phos – catalyzed allylic alkylation reaction. Owing to the structural similarity of benzyl alcohols and silanols, we first attempted the catalytic asymmetric allylic alkylation of simple alkyl alcohols, such as methanol, or ethanol, with Pd/Fei-Phos under the reported reaction conditions, in which it was found that the Pd/Fei-Phos was really sensitive to the structure of alcohols.⁶ To our delight, the catalytic asymmetric allylic alkylation of methanol with 1,3-diphenyl-2-propenyl acetate (1) led to the desired product in excellent yield (95% yield) and high enantioselectivity (97% ee). Unexpectedly, the catalytic asymmetric allylic alkylation reaction of other alkyl alcohols, such as ethanol, iso-propanol, tert-butanol, and other butanol, gave quite low yields and even with almost no reaction in the presence of Pd/Fei-Phos. Although the trifluoroethanol was effective substrate in this reaction, low enantioselectivity was achieved in this case. Meanwhile, it was found that the hydrolysis of racemic 1,3-diphenyl-2-propenyl acetate with water was not possible under the optimized reaction conditions (Scheme 6).

Scheme 6 Comparison of activity of various alkyl alcohols in the Pd/Fei-Phos – catalyzed asymmetric allylic alkylation reaction under the optimized reaction conditions.

It is well-known that pK_a is arguably one of the most important physical constants for alcohols, which provided useful information in this reaction in term of the reactivity of these alcohols. Traditionally, for palladium-catalyzed allylic alkylation reactions, “soft” and “hard” nucleophiles have been identified by their pK_a. In generally, hard nucleophiles (pK_a > 25) is less acidic than soft nucleophiles (pK_a < 25).¹¹ Of course, for most pronucleophiles, such functional compounds with a resonance-stabilizing group could increase the polarizability of the molecular orbitals and would lower the pK_a value, in which it is difficult to discriminate classic hard/soft reactivity trends.¹² Thus, the interpretation of the unexpected results in this allylic etherification reaction should take into account the acidities of alcohols that should match for structure of palladium/Fei-Phos complex. On the basis of the experimental results and the systematic data of pK_a for the various alcohols evaluated in this reaction,¹³ we can concluded that our Pd/Fei-Phos catalyst system exhibited extraordinarily selectivity for methanol and benzyl alcohols that the pK_a (in H₂O) would be in a certain range of about 12.5 to 15.5 (or pK_a = 23.5 to 27.9 in DMSO), owing to high yield and promising enantioselectivity of catalytic asymmetric allylic alkylation reactions with methanol, trifluoroethanol, and benzyl alcohols or its analogues. Thus the equilibrium acidities (pK_a) provided a fundamental data base for assessment of the reactivity of structurally diverse alcohols brought from the electronic and steric effects,^13b which inspired us to deduce the importance of nitrogen atoms in the Pd/Fei-Phos – catalyzed asymmetric allylic alkylation with 1,3-diphenyl-2-propenyl acetate because of possibly matchable interaction between nitrogen-centered Brønsted base and Brønsted acidic alcohol.

At last, to provide indirect evidence for the mechanism of the palladium-catalyzed allylic etherification, we carried out the comparable investigation on the catalytic activity and stereocontrol of the analogues of Fei-Phos ligand, which further support the privileged role of phosphorous and nitrogen atoms on the Fei-Phos ligand. Chiral ligands L1 were then used in the palladium-catalyzed allylic etherification of benzyl alcohol with 1,3-diphenyl-2-propenyl acetate (1). In sharp contrast to the results for Fei-Phos-promoted allylic etherification with excellent enantioselectivity, the ligand L1 gave poor enantioselectivities (only 2% ee).⁷ The low enantioselectivity of L1 might be aroused from the strong coordination of electron-rich biphosphine and palladium center. Significantly, this observation is consistent with the evidence that Fei-Phos – derived palladium–monophosphine complex is better than biphosphine on the backbone of trans-1,2-diaminocyclohexane (for example, L1). These results also allowed us to conclude that the utility of present palladium/Fei-Phos was one of a privileged palladium complex in this reaction.

It should be noted that, on the basis of Kagan's nonlinear stereochemical effect,¹⁴ we hypothesized that the enantioselective induction arose from the formation of possible Pd/Fei-Phos complex with one Fei-Phos ligand. According to the previous report,¹⁴ the nonlinear effect would be an important diagnostic tool in mechanistic studies of stereochemistry and asymmetric reactions. And our results of this nonlinear study with catalyst enantiopurity (ee_cat) on product enantiomeric excess (ee_prod), graphically depicted in Fig. 4, demonstrated the linear curve without nonlinear effect might be attributed to the single-metal center with one Fei-Phos. Fortunately, it is easily to distinguish the similar mechanistic process between asymmetric allylic alkylation of alcohols and activated methylene compounds.

Fig. 4 Relationship between enantioselectivity of the reaction product (ee_prod) and enantiomeric excess of the chiral catalyst (ee_cat).

The generally accepted mechanism for palladium-catalyzed allylic alkylation could be abbreviated as two key steps,¹⁵ the initially oxidative addition of low valent palladium species (Pd(0)L₂) to allylic acetate (electrophile) and nucleophilic attack on the corresponding allylic Pd(II) cation, to resulted into the regeneration of Pd(0) complex when simultaneously liberated the product. Thus based on our scenario for the catalytic asymmetric allylic etherification of alcohols with 1,3-diphenyl-2-propenyl acetate (1), the results of palladium-catalyzed allylic alkylation and the related reaction information obtained in this work, we proposed a major and simplified mechanistic procedure and corresponding transition-state model (II) in Scheme 7. In fact, more profitable evidence with NMR analysis (Fig. 5 and S4 in ESI†) also showed that this chiral Pd/Fei-Phos complex (II) – catalyzed allylic alkylation reaction was not completely relied on the pathway of the Pd(II)/Pd(III) catalysis because of the conformationally restricted eight-membered palladium-based catalyst system (Fig. 3).¹⁶ As shown in Fig. 5, the ³¹P-NMR analysis of the Pd/Fei-Phos catalyst system and its mixture with two substrates respectively supported the formation of diphosphine-based Pd complex as major component in this reaction. And the Pd/Fei-Phos complex was enough stable in allylic alkylation of indole with allylic acetate. On the basis of experimental data and spectroscopic analysis, therefore we suggested that diphosphine-based palladium/Fei-Phos complex was possibly acted as more reasonable catalyst system (intermediate II in Scheme 7). In addition, the experimental results as well as the preliminary findings in the mechanistic study revealed that the distinctive activation showed in Scheme 7 is reasonable because of the multifunctional structure of Fei-Phos ligand in the palladium catalysis, which also provide a good example that the mechanistic study based on X-ray analysis but without other evidences was not completely true.

Scheme 7 Proposed model of the palladium-catalyzed allylic alkylation: a possibly major model of general allylic alkylation of structurally diverse nucleophiles by diphosphine-based Pd/Fei-Phos catalyst system but not with nitrogen-controlled or monophosphine-involved transition state.

Fig. 5 Original ³¹P-NMR spectra of the mixture of Pd/Fei-Phos with two substrates.

Conclusions

In summary, although a conformationally restricted eight-membered crystal structure of a Pd/Fei-Phos complex has been clarified by X-ray analysis, the detailed mechanistic study on the possible Pd(III) catalysis in this reaction is insufficient in this allylic substation reaction. In this work, extensive elucidation of the role of Fei-Phos on the stereoselectivity and reactivity has been studied on the basis of Pd/Fei-Phos complex as well as an equilibrium acidities (pK_a) of these nucleophiles, which provided unexpected and interesting information for the mechanistic model of asymmetric palladium-catalyzed allylic alkylation in this work. A particularly appealing feature of the relationship of alcoholic substrate and reaction activity we outline here is that it is based on an equilibrium acidities (pK_a), which provided interesting and important information for the comparably mechanistic model of palladium-catalyzed asymmetric allylic alkylation of alcohols, activated methylene compounds, or indoles. The experimental results as well as the preliminary findings with relative energy analysis, ESI-MS, and NMR analysis, revealed that it is a diphosphine-controlled mechanistic pathway.

Acknowledgements

The authors gratefully thank the financial support of the National Natural Science Foundation of China (No. 21173064, 51303043, 21472031, and 21503060), and Zhejiang Provincial Natural Science Foundation of China (LR14B030001) is appreciated. The authors also thank Prof. Z. R. Qu, Dr K. Z. Jiang, Dr C. Q. Sheng, and Dr Y. Deng (all at HZNU) for their technical and analytical support.

Notes and references

1. (a) B. M. Trost and P. E. Strege, J. Am. Chem. Soc., 1977, 99, 1649–1651; (b) B. M. Trost, Acc. Chem. Res., 1980, 13, 385–393; (c) J. Tsuji, I. Minami and I. Shimizu, Chem. Lett., 1983, 1325–1326; (d) B. M. Trost and T. R. Verhoeven, in Comprehensive Organometallic Chemistry, ed. W. Bartmann and K. B. Sharpless, Pergamon Press, Oxford, 1982, vol. 8, ch. 57; (e) D. Caine, in Comprehensive Organic Synthesis, ed. B. M. Trost and I. Fleming, Pergamon, Oxford, 1991, vol. 3, pp. 1–63.
2. For representative reviews, see: (a) B. M. Trost and M. L. Crawley, Chem. Rev., 2003, 103, 2921–2943; (b) Z. Lu and S. Ma, Angew. Chem., Int. Ed., 2008, 47, 258–297. for selected examples, see: (c) B. L. Lei, C. H. Ding, X. X. Yang, X. L. Wan and X. L. Hou, J. Am. Chem. Soc., 2009, 131, 18250–18251; (d) B. M. Trost, J. Xu and T. Schmidt, J. Am. Chem. Soc., 2009, 131, 18343–18357; (e) B. M. Trost, K. Lehr, D. J. Michaelis, J. Xu and A. K. Buckl, J. Am. Chem. Soc., 2010, 132, 8915–8917; (f) B. M. Trost, D. A. Thaisrivongs and J. Hartwig, J. Am. Chem. Soc., 2011, 133, 12439–12441; (g) X. M. Wang, F. Y. Meng, Y. Wang, Z. B. Han, Y. J. Chen, L. Liu, Z. Wang and K. L. Ding, Angew. Chem., Int. Ed., 2012, 51, 9276–9282; (h) B. M. Trost, R. Koller and B. Schäffner, Angew. Chem., Int. Ed., 2012, 51, 8290–8293; (i) B. M. Trost, D. J. Michaelis, J. Charpentier and J. Xu, Angew. Chem., Int. Ed., 2012, 51, 204–208; (j) K. Ohmatsu, M. Ito, T. Kunieda and T. Ooi, J. Am. Chem. Soc., 2013, 135, 590–593; (k) F. Nahra, Y. Macé, D. Lambin and O. Riant, Angew. Chem., Int. Ed., 2013, 52, 3208–3212; (l) B. M. Trost, J. T. Masters and A. C. Burns, Angew. Chem., Int. Ed., 2013, 52, 2260–2264; (m) J. Fournier, O. Lozano, C. Menozzi, S. Arseniyadis and J. Cossy, Angew. Chem., Int. Ed., 2013, 52, 1257–1261; (n) T. Hellmuth, W. Frey and R. Peters, Angew. Chem., Int. Ed., 2015, 54, 2788–2791; (o) R. M. Maksymowicz, A. J. Bissette and S. P. Fletcher, Chem.–Eur. J., 2015, 21, 5668–5678; (p) A. N. Marziale, D. C. Duquette, R. A. Craig, K. E. Kim, M. Liniger, Y. Numajiri and B. M. Stoltz, Adv. Synth. Catal., 2015, 357, 2238–2245; (q) H. Zhou, L. Zhang, C. M. Xu and S. Z. Luo, Angew. Chem., Int. Ed., 2015, 54, 12645–12648; (r) M. Sidera and S. P. Fletcher, Nat. Chem., 2015, 7, 935–939; (s) T. Sandmeier, S. Krautwald, H. F. Zipfel and E. M. Carreira, Angew. Chem., Int. Ed., 2015, 54, 14363–14367; (t) J. Kim, S. Park, J. Park and S. H. Cho, Angew. Chem., Int. Ed., 2015, 55, 1498–1501.
3. For recent reviews or books: (a) W. Tang and X. Zhang, Chem. Rev., 2003, 103, 3029–3069; (b) Privileged Chiral Ligands and Catalysts, ed. Q. L. Zhou, Wiley-VCH, Singapore, 2011; (c) M. P. Carroll and P. J. Guiry, Chem. Soc. Rev., 2014, 43, 819–833. For recent examples, see: (d) C. C. Pattillo, J. I. Strambeanu, P. Calleja, N. A. Vermeulen, T. Mizuno and M. C. White, J. Am. Chem. Soc., 2016, 138, 1265–1272; (e) S. C. Sha, H. Jiang, J. Y. Mao, A. Bellomo, S. A. Jeong and P. J. Walsh, Angew. Chem., Int. Ed., 2016, 55, 1070–1074; (f) S. T. Madrahimov, Q. Li, A. Sharma and J. F. Hartwig, J. Am. Chem. Soc., 2015, 137, 14968–14981; (g) M. V. Jimenez, J. Fernandez-Tornos, F. J. Modrego, J. J. Perez-Torrente and L. A. Oro, Chem.–Eur. J., 2015, 21, 17877–17889; (h) F. Gerhards, N. Griebel, J. Runsink, G. Raabe and H. J. Gais, Chem.–Eur. J., 2015, 21, 17904–17920; (i) M. Weiss and R. Peters, ACS Catal., 2015, 5, 310–316; (j) W. H. Deng, F. Ye, X. F. Bai, Z. J. Zheng, Y. M. Cui and L. W. Xu, ChemCatChem, 2015, 7, 75–79.
4. (a) F. L. Lam, T. T. L. Au-Yeung, F. Y. Kwong, Z. Zhou, K. Y. Wong and A. S. C. Chan, Angew. Chem., Int. Ed., 2008, 47, 1280–1283; (b) M. Coll, O. Pàmies and M. Diéguez, Org. Lett., 2014, 16, 1892–1895; (c) B. Feng, H. G. Cheng, J. R. Chen, Q. H. Deng, L. Q. Lu and W. J. Xiao, Chem. Commun., 2014, 50, 9550–9553; (d) U. Uria, C. Vila, M. Y. Lin and M. Rueping, Chem.–Eur. J., 2014, 20, 13913–13917; (e) M. Fananas-Mastral, R. Vitale, M. Perez and B. L. Feringa, Chem.–Eur. J., 2015, 21, 4209–4212; (f) M. Majdecki, J. Jurczak and T. Bauer, ChemCatChem, 2015, 7, 799–807.
5. For recent reviews, see: (a) I. G. Rios, A. Rosas-Hernandez and E. Martin, Molecules, 2011, 16, 970–1010; (b) H. Fernández-Pérez, P. Etayo, A. Panossian and A. Vidal-Ferran, Chem. Rev., 2011, 111, 2119–2176.
6. F. Ye, Z. J. Zheng, L. Li, K. F. Yang, C. G. Xia and L. W. Xu, Chem.–Eur. J., 2013, 19, 15452–15457.
7. J. X. Xu, F. Ye, X. F. Bai, J. Zhang, Z. Xu, Z. J. Zheng and L. W. Xu, RSC Adv., 2016, 6, 45495–45502.
8. M. J. Frisch, et al., J. Gaussian 09, Revision C. 01, Gaussian, Wallingford, 2010.
9. (a) R. Shintani, W. L. Duan, K. Okamoto and T. Hayashi, Tetrahedron: Asymmetry, 2005, 16, 3400–3405; (b) R. Shintani, W. L. Duan, T. Nagano, A. Okada and T. Hayashi, Angew. Chem., Int. Ed., 2005, 44, 4611–4614.
10. The elimination of a PPh₂ group from a chiral ligand is known in the literature, see: (a) T. J. Geldbach, D. Drago and P. S. Pregosin, Chem. Commun., 2000, 1629–1630; (b) T. J. Geldbach and P. S. Pregosin, Organometallics, 2001, 20, 1932–1938; (c) T. J. Geldbach, P. S. Pregosin and M. Bassetti, Organometallics, 2001, 20, 2990–2997.
11. (a) M. H. Yang, D. L. Orsi and R. A. Altman, Angew. Chem., Int. Ed., 2015, 54, 2361–2365; (b) B. M. Trost and D. A. Thaisrivongs, J. Am. Chem. Soc., 2008, 130, 14092–14093; (c) B. M. Trost and D. L. V. Vranken, Chem. Rev., 1996, 96, 395–422.
12. J. D. Weaver, A. Recio III, A. J. Grenning and J. A. Tunge, Chem. Rev., 2011, 111, 1846–1913.
13. The equilibrium acidities of simple alcohols in DMSO or water were cited from the reported references: (a) W. N. Olmstead, Z. Margolin and F. G. Bordwell, J. Org. Chem., 1980, 45, 3295–3299; (b) F. G. Bordwell, Acc. Chem. Res., 1988, 21, 456–463; (c) P. Ballinger and F. A. Long, J. Am. Chem. Soc., 1960, 82, 795–798.
14. (a) C. Puchot, O. Samuel, E. Duñach, S. Zhao, C. Agami and H. B. Kagan, J. Am. Chem. Soc., 1986, 108, 2353–2357; (b) D. Guillaneux, S. H. Zhao, O. Samuel, D. Rainford and H. B. Kagan, J. Am. Chem. Soc., 1994, 116, 9430–9439; (c) C. Girard and H. B. Kagan, Angew. Chem., Int. Ed., 1998, 37, 2922–2959; (d) T. Satyanarayana, S. Abraham and H. B. Kagan, Angew. Chem., Int. Ed., 2009, 48, 456–494. And our recent work regarding nonlinear stereochemical effect, see: (e) T. Song, L. S. Zheng, F. Ye, W. H. Deng, Y. L. Wei, K. Z. Jiang and L. W. Xu, Adv. Synth. Catal., 2014, 356, 1708–1718.
15. (a) L. A. Evans, N. Fey, J. N. Harvey, D. Hose, G. C. Lloyd-Jones, P. Murray, A. G. Orpen, R. Osborne, G. J. J. Owen-Smith and M. Purdie, J. Am. Chem. Soc., 2008, 130, 14471–14473; (b) C. P. Butts, E. Filali, G. C. Lloyd-Jones, P.-O. Norrby, D. A. Sale and Y. Schramm, J. Am. Chem. Soc., 2009, 131, 9945–9957; (c) M. H. Katcher, P.-O. Norrby and A. G. Doyle, Organometallics, 2014, 33, 2121–2133; (d) M. Magre, M. Biosca, P. O. Norrby, O. Pamies and M. Dieguez, ChemCatChem, 2015, 7, 4091–4107; (e) A. J. DeAngelis, P. G. Gildner, R. Chow and T. J. Colacot, J. Org. Chem., 2015, 80, 6794–6813.
16. It is unexpectedly and unbelievable that Pd(III) complex could be used in catalytic asymmetric allylic alkylation. In fact, there are few reports on the Pd(III) catalysis in the past decades, see: (a) D. C. Powers and T. Ritter, Top. Organomet. Chem., 2011, 35, 129–156. For high-valent palladium complexes, see: (b) K. J. Bonney and F. Schoenebeck, Chem. Soc. Rev., 2014, 43, 6609–6638.

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Footnote

† Electronic supplementary information (ESI) available. CCDC 1446415. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c6ra15665g

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