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Allylic Arylation of 1,3-Dienes via Hydroboration/ Migrative Suzuki-Miyaura Cross-Coupling Reactions Xiao-Ming Zhang, Jie Yang, Qing-Bo Zhuang, Yong-Qiang Tu, Zongyuan Chen, Hui Shao, Shao-Hua Wang, and Fu-Min Zhang ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.8b01823 • Publication Date (Web): 04 Jun 2018 Downloaded from http://pubs.acs.org on June 5, 2018
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ACS Catalysis
Allylic Arylation of 1,3-Dienes via Hydroboration/Migrative SuzukiMiyaura Cross-Coupling Reactions Xiao‐Ming Zhang,*,† Jie Yang,† Qing‐Bo Zhuang,† Yong‐Qiang Tu,†,‡ Zongyuan Chen,§ Hui Shao,‡ Shao‐Hua Wang,†,¶ and Fu‐Min Zhang† †State Key Laboratory of Applied Organic Chemistry and Department of Chemistry, Lanzhou
University, Lanzhou 730000, P. R. China ‡School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai 200240, P. R. China §Radiochemistry Laboratory, School of Nuclear Science and Technology, Lanzhou University, Lanzhou 730000, P. R. China ¶School of Pharmacy, Lanzhou University, Lanzhou 730000, P. R. China ABSTRACT: The hydroboration/Pd‐catalyzed migrative Suzuki‐Miyaura cross‐coupling of 1,3‐dienes with electron‐deficient aryl halides has been developed, which enables the synthesis of branched allylarenes directly from primary homoallylic alkyl boranes. A ligand‐tuned linear‐ or branch‐selective coupling for these aryl halides has also been achieved. KEYWORDS: palladium catalysis, Suzuki‐Miyaura reaction, migrative cross‐coupling, allylic compounds, regioselectivity
Transition‐metal‐catalyzed alkyl Suzuki˗Miyaura cross‐ coupling reactions have served as powerful tools in the construction of C(sp3)‐C bonds and a multitude of applications have been found in organic synthesis.1 These reactions have been frequently employed for the synthesis of linear coupling products starting from terminal alkenes, since the primary alkyl boranes can be easily prepared via highly regioselective hydroboration and used directly for cross‐coupling in a one‐pot approach.1a‐d In comparison, the synthesis of branched coupling products often requires the initial preparation of a secondary or tertiary boron species, which increases the number of synthetic steps required for the overall reaction sequence.1f,g,2 In particular, recent advances of allylic Suzuki˗Miyaura cross‐coupling for the synthesis of branched allylarenes3 have relied on access to corresponding secondary allylic boronic esters.4 As an alternative strategy, the use of readily accessible homoallylic alkyl boranes (generated from the hydroboration of 1,3‐dienes)5 as coupling partners in such allylic couplings, depite being synthetically more straightforward, has received little study. Such an approach would allow direct allylic arylation from 1,3‐dienes6 and would be possible if a migrative type cross‐coupling of the primary alkyl boranes could be achieved. Pd‐catalyzed cross‐coupling reactions that involve a palladium migration step have recently been developed and utilized in β‐ or long‐range arylation of carboxylic derivatives and N‐Boc amines,7 alkene difunctionalization,8 and certain types of migrative couplings.9 In these reactions, the migration of a palladium species along the alkyl chain takes place via β‐hydride elimination/alkene insertion sequences prior to the C‒C bond‐forming event and is controlled by either the substrates,7a certain ligands, or both.7b‐f,8,9 Since the coupling sites in these cases have been
Figure 1. Palladium catalyzed migrative allylic cross‐cou‐ pling reactions. diverted from the initial nucleophilic or electrophilic carbon center, a formal functionalization of the adjacent or remote C‒H bond is often involved in such migrative cross‐coupling reactions.10 In 2012, Sigman and coworkers developed an elegant allylic arylation and vinylation methodology via the migrative cross‐coupling of homoallylic electrophiles with aryl or vinyl boronic acids (Figure 1a)9a,b. Mechanistically, the oxidative addition of a Pd(0)‐catalyst into the alkyl tosylate formed a homoallylic Pd(II)‐species, which would rearrange to a л‐allyl Pd species preceding the transmetalation and reductive elimination. Herein, via extension of hydroboration/Suzuki‐Miyaura reactions of 1,3‐dienes (Figure 1b),11 a migrative cross‐coupling of
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homoallylic nucleophiles has been achieved with Pd‐ migration sequences ocurring after the transmetalation step. Both the substrate and the ligand were found to play essential roles in the regioselection of such reactions, and a ligand‐tuned coupling to selectively generate either linear or branched product has also been demonstrated. This study was initiated when we attempted a hydroboration/Suzuki‐Miyaura cross‐coupling reaction between 1,3‐diene 1a and 2‐methoxycarbonyl bromobenzene 2a under standard Suzuki‐Miyaura conditions (Table 1, entry 1). Surprisingly, the branched coupling product 3a was obtained, instead of the linear product 3a', in good yield and good selectivity (branched:linear = 11:1). Given the unprecedented branch‐ selective coupling result11 and its potential utility for the synthesis of allylarenes, optimization studies on this reaction were performed. Lowering the reaction temperature from 65 °C to 25 °C can slightly enhance the branched‐to‐linear (B:L) selectivity without any influence on the product yield except for the reaction conducted at room temperature, which experienced a decrease of yield from 82% to 64% (entry 1‐4). Bases and solvents were found to have a noticeable impact on both the yield and selectivity of this reaction, and although the branch‐ selective coupling was observed in all cases, inferior results were generally obtained (entry 5, 6). Next, the effect of ligands was examined. The palladium catalysts with R,S‐ Josiphos, dppe, dppp, dppb or monodentate PPh3 were also capable of providing the branched coupling products (entry 7‐11), albeit in diminished yields or regioselectivities. Notably, the use of monodentate PtBu2Ph or triaryl substituted bidentate phosphine ligands, such as rac‐binap, R‐Segphos, or xantphos, was observed to thoroughly reverse the regioselectivity of the reaction, resulting in the generation of linear coupling product 3a′ (entry 12‐16). These results showed the equal importance of the chosen ligand in affecting the reaction selectivity, and the more electron‐rich bidentate ligand with a larger bite angle12 (i.e. dppb) might favor the branch‐selective coupling. Finally, when we reduced the catalyst loading of Pd(dppf)Cl2 to 5 mol% (entry 17, 18), a further increase in branched selectivity was observed. With the optimal conditions in hand, the scope of the aryl halides was examined. We initially hypothesized that the use of an aryl halide bearing an ortho‐electron‐withdrawing group (e.g. a methoxycarbonyl group) presumably led to a migrative cross‐coupling in light of Baudoin’s pioneering work on the β‐arylation of carboxylic esters.7a Therefore, a wide range of such aryl halides were investigated (Table 2). Both 2‐methoxycarbonyl bromobenzene and 2‐ methoxycarbonyl iodobenzene generated the same branched coupling product 3a in similar yields and selectivities, indicating negligible effect of the halide on the reaction selectivity. Different ortho‐ester groups affected the reaction selectivity slightly (3a‐3d), and consistent with our expectations, the reaction of the phenyl bromide with a more electronegative ortho‐ester group resulted in a relatively higher B:L selectivity. Additionally, substitutions on C4, C5 or C6 positions of the 2‐methoxycarbonyl bromobenzene were well‐tolerated (3f‐3k), with all the reactions providing the allylic coupling products in good
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yields with good to excellent selectivities. In comparison, however, the reaction with 3‐methyl‐2‐methoxycarbonyl bromobenzene 2e produced 3e with moderate selectivity, Table 1. Optimization of the hydroboration/migrative Suzuki‐Miyaura cross‐coupling reactiona
entry
Pd (mol %)
base/solvent
temp (°C)
yield (%)b
3a/3a′c
1
Pd(dppf)Cl2 (10)
3 M NaOH
65
82
11:1
2
Pd(dppf)Cl2 (10)
3 M NaOH
50
81
12:1
3
Pd(dppf)Cl2 (10)
3 M NaOH
40
82
12.5:1
4
Pd(dppf)Cl2 (10)
3 M NaOH
25
64
12.5:1
5
Pd(dppf)Cl2 (10)
K3PO4/DMF
40
79
8:1
6
Pd(dppf)Cl2 (10)
K2CO3/DMF
65
31
6:1
7
Pd(R,S‐Josi‐ phos)Cl2 (10)
3 M NaOH
40
7
5:1
8
Pd(dppe)Cl2 (10)
3 M NaOH
40
21
11:1
9
Pd(dppp)Cl2 (10)
3 M NaOH
40
24
15:1
10
Pd(dppb)Cl2 (10)
3 M NaOH
40
37
>20:1
11
Pd(PPh3)2Cl2 (10)
3 M NaOH
40
68
12:1
12
Pd(PtBu2Ph)2Cl2 (10)
3 M NaOH
40
39
1:5
13
Pd(rac‐binap)Cl2 (10)
3 M NaOH
40
11
20:1)
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3v' 79% (16:1)d
3r' 53% (>20:1) O
O
n-Bu n-Bu 4c', 51% (>20:1)
Ph 4k' 52% (18:1)e
aUnless otherwise noted, reaction conditions: 1 (0.3 mmol in 0.2 mL THF), 9‐BBN (0.5 M in THF, 0.66 mL, 0.33 mmol), 25 °C; then 3 M NaOH (0.4 mL), 2a or 2l or 2r (0.2 mmol), Pd(rac‐ binap)Cl2 (0.01 mmol), 40 °C. Yields of the isolated linear prod‐ ucts. L:B selectivities were determined by 1H NMR spectro‐ scopic analysis of the isolated mixtures of linear and branched products. b2 M NaOH (0.4 mL) was used. cPd(rac‐binap)Cl2 (0.02 mmol, 10 mol%) was used. dWhen Pd(dppf)Cl2 was used, 3v′ was obtained in 66% yield (L:B = 3:1). eThe reaction was conducted at 65 °C.
We next probed the mechanism of this reaction by first performing the cross‐coupling of Z‐diene 1e with 2l (Figure 2). Formation of both E and Z isomers in a ratio of 1.6:1 (eq. 1) suggested the existence of an intermediate allyl palladium species in this reaction. The observation that the cross‐coupling of a 3‐deuterated diene 6 produced 7 with deuterium incorporation into the distal methyl group was also indicative of a β‐hydride elimination/alkene insertion event in the reaction process (eq. 2), and a kinetic isotope effect probably existed in the β‐hydride elimination. Additionally, when another diene 1i was added to the coupling reaction of 2l with the borane derivative of 1a (eq. 3), the crossover product 4k was obtained along with the normal coupling product 3l.14 The ratio of 3l:4k was shown to decrease and approach a fixed value as the amount of 1i (from 1 equiv to 16 equiv) used in the coupling reaction was increased. These outcomes signify that a dissociation/association process of the 1,3‐diene from and to the Pd‐hydride intermediate was involved as a major but not exclusive pathway in the Pd migration event. Although the exact roles of different ligands in tuning the regioselectivity have not been understood yet, the presence of electron‐withdrawing groups on arene can increase the barrier of the direct reductive elimination,7c thus favoring
Figure 2. Mechanistic studies. On the basis of the above experimental results, a proposed reaction mechanism for the migrative coupling is depicted in Figure 3. Oxidative addition of the Pd(0) catalyst to bromide 2 followed by transmetalation with the primary borane B would generate a Pd(II) intermediate C. Subsequently, β‐hydride elimination would then take place to form a Pd hydride D. The ensuing hydride insertion event could proceed either directly to form the σ‐allyl Pd species F, which is in equilibrium with its л‐allyl form, or through a dissociation/association process by first releasing the 1,3‐ diene 1 and the Pd hydride E. Final reductive elimination of F would generate the allylic coupling product 3 or 4.
Figure 3. Proposed mechanism.
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In summary, we have developed a novel type of Pd‐ catalyzed migrative Suzuki‐Miyaura cross‐coupling reactions for the allylic arylation of 1,3‐dienes using electron‐deficient aryl halides. This method is synthetically useful in the preparation of branched allylarenes and shows a wide substrate scope in terms of both aryl halides and 1,3‐ dienes. A ligand‐tuned linear‐ and branch‐selective coupling for these substrates was also achieved. Preliminary mechanistic studies revealed a palladium migration process in the formation of allyl palladium species via the β‐hydride elimination/alkene insertion sequence, and an alkene dissociation/association process was partially involved in the reinsertion step.
ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website. Experimental procedures and spectral data for new com‐ pounds (PDF)
AUTHOR INFORMATION Corresponding Author *E‐mail:
[email protected] ORCID
Lloyd‐Jones, G. C. Selection of Boron Reagents for Suzuki‐Miyaura Coupling. Chem. Soc. Rev. 2014, 43, 412‐443. (i) Maluenda, I.; Na‐ varro, O. Recent Developments in the Suzuki‐Miyaura Reaction: 2010‐2014. Molecules 2015, 20, 7528‐7557. 2. (a) Crudden, C. M.; Glasspoole, B. W.; Lata, C. J. Expanding the Scope of Transformations of Organoboron Species: Carbon‐Carbon Bond Formation with Retention of Configuration. Chem. Commun., 2009, 6704‐6716. (b) Leonori, D.; Aggarwal, V. K. Stereospecific Couplings of Secondary and Tertiary Boronic Esters. Angew. Chem., Int. Ed. 2015, 54, 1082‐1096. (c) Collins, B. S. L.; Wilson, C. M.; My‐ ers, E. L.; Aggarwal, V. K. Asymmetric Synthesis of Secondary and Tertiary Boronic Esters. Angew. Chem., Int. Ed. 2017, 56, 11700‐ 11733. (d) Sandford, C.; Aggarwal, V. K. Stereospecific Functionali‐ zations and Transformations of Secondary and Tertiary Boronic Esters. Chem. Commun. 2017, 53, 5481‐5494. (e) Rygus, J. P. G.; Crudden, C. M. Enantiospecific and Iterative Suzuki–Miyaura Cross‐Couplings. J. Am. Chem. Soc. 2017, 139, 18124‐18137. 3. (a) Glasspoole, B. W.; Ghozati, K.; Moir, J. W.; Crudden, C. M. Su‐ zuki‐Miyaura Cross‐Couplings of Secondary Allylic Boronic Esters. Chem. Commun. 2012, 48, 1230‐1232. (b) Farmer, J. L.; Hunter, H. N.; Organ, M. G. Regioselective Cross‐Coupling of Allylboronic Acid Pinacol Ester Derivatives with Aryl Halides via Pd‐PEPPSI‐IPent. J. Am. Chem. Soc. 2012, 134, 17470‐17473. (c) Chausset‐Boissarie, L.; Ghozati, K.; LaBine, E.; Chen, J. L. Y.; Aggarwal, V. K.; Crudden, C. M. Enantiospecific, Regioselective Cross‐Coupling Reactions of Sec‐ ondary Allylic Boronic Esters. Chem. Eur. J. 2013, 19, 17698‐17701. (d) Yang, Y.; Buchwald, S. L. Ligand‐controlled palladium‐catalyzed regiodivergent Suzuki–Miyaura Cross‐Coupling of Allylboronates and Aryl Halides. J. Am. Chem. Soc. 2013, 135, 10642‐10645. 4. For a recent review, see: Diner, C.; Szabό, K. J. Recent Advances in the Preparation and Application of Allylboron Species in Organic Synthesis. J. Am. Chem. Soc. 2017, 139, 2‐14.
Xiao‐Ming Zhang: 0000‐0002‐9294‐9672; Yong‐Qiang Tu: 0000‐0002‐9784‐4052 Shao‐Hua Wang: 0000‐0002‐4347‐8245 Fu‐Min Zhang: 0000‐0001‐5578‐1148
Notes The authors declare no competing financial interests.
ACKNOWLEDGMENT We would like to thank the Natural Science Foundation of China (No. 21502080, 21772071, 21290180, 21772076, 21372104, and 21472077), the fundamental research funds for the central universities (lzujbky‐2017‐116), and the “111” Program of MOE for their financial support.
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Isomerization and C–H Activation: Regioselective Hydroheteroary‐ lation of Allylarenes. Org. Lett. 2013, 15, 5358‐5361. (f) Yamakawa, T.; Yoshikai, N. Alkene Isomerization–Hydroarylation Tandem Ca‐ talysis: Indole C2‐Alkylation with Aryl‐Substituted Alkenes Lead‐ ing to 1,1‐Diarylalkanes. Chem. Asian J. 2014, 9, 1242‐1246. (g) Bair, J. S.; Schramm, Y.; Sergeev, A. G.; Clot, E.; Eisenstein, O.; Hart‐ wig, J. F. Linear‐Selective Hydroarylation of Unactivated Terminal and Internal Olefins with Trifluoromethyl‐Substituted Arenes. J. Am. Chem. Soc. 2014, 136, 13098‐13101. (h) Hamasaki, T.; Aoyama, Y.; Kawasaki, J.; Kakiuchi, F.; Kochi, T. Chain Walking as a Strategy for Carbon–Carbon Bond Formation at Unreactive Sites in Organic Synthesis: Catalytic Cycloisomerization of Various 1,n‐Dienes. J. Am. Chem. Soc. 2015, 137, 16163‐16171. (i) Vasseur, A.; Perrin, L.; Ei‐ senstein, O.; Marek, I. Remote Functionalization of Hydrocarbons with Reversibility Enhanced Stereocontrol. Chem. Sci. 2015, 6, 2770‐2776. (j) Palmer, W. N.; Diao, T.; Pappas, I.; Chirik, P. J. High‐ activity Cobalt Catalysts for Alkene Hydroboration with Electroni‐ cally Responsive Terpyridine and α‐Diimine Ligands. ACS Catalysis 2015, 5, 622‐626. (k) Scheuermann, M. L.; Johnson, E. J.; Chirik, P. J. Alkene Isomerization–Hydroboration Promoted by Phosphine‐ Ligated Cobalt Catalysts. Org. Lett. 2015, 17, 2716‐2719. (l) Buslov, I.; Becouse, J.; Mazza, S.; Montandon‐Clerc, M.; Hu, X. Chemoselec‐ tive Alkene Hydrosilylation Catalyzed by Nickel Pincer Complexes. Angew. Chem., Int. Ed. 2015, 54, 14523‐14526. (m) Buslov, I.; Song, F.; Hu, X. An Easily Accessed Nickel Nanoparticle Catalyst for Al‐ kene Hydrosilylation with Tertiary Silanes. Angew. Chem., Int. Ed. 2016, 55, 12295‐12299. (n) He, Y.; Cai, Y.; Zhu, S. Mild and Regiose‐ lective Benzylic C–H Functionalization: Ni‐Catalyzed Reductive Ar‐ ylation of Remote and Proximal Olefins. J. Am. Chem. Soc. 2017, 139, 1061‐1064. 11. The hydroboration/Suzuki‐Miyaura cross‐coupling reactions of 1,3‐dienes with aryl halides have been used only in the synthesis of linear coupling products. For selected recent examples, see: (a) Lange, H.; Fröhlich, R.; Hoppe, D. Cu(I)‐Catalyzed Stereospecific Coupling Reactions of Enantioenriched α‐Stannylated Benzyl Car‐ bamates and Their Application. Tetrahedron 2008, 64, 9123‐9135. (b) Rosen, B. R.; Werner, E. W.; O’Brien, A. G.; Baran, P. S. Total Syn‐ thesis of Dixiamycin B by Electrochemical Oxidation. J. Am. Chem. Soc. 2014, 136, 5571‐5574. (c) Lin, H.‐C.; Wang, P.‐S.; Tao, Z.‐L.; Chen, Y.‐G.; Han, Z.‐Y.; Gong, L.‐Z. Highly Enantioselective Allylic C– H Alkylation of Terminal Olefins with Pyrazol‐5‐ones Enabled by Cooperative Catalysis of Palladium Complex and Brønsted Acid. J. Am. Chem. Soc. 2016, 138, 14354‐14361. 12. Birkholz, M.‐N.; Freixa, Z.; van Leeuwen, P. W. N. M. Bite Angle Effects of Diphosphines in C‐C and C‐X Bond Forming Cross Cou‐ pling Reactions. Chem. Soc. Rev. 2009, 38, 1099‐1118. 13. The secondary homoallylic boranes generated from internal dienes failed to participate in the coupling reaction probably due to a slow transmetalation step, please see: (a) Littke, A. F.; Dai, C.; Fu, G. C. Versatile Catalysts for the Suzuki Cross‐Coupling of Aryl‐ boronic Acids with Aryl and Vinyl Halides and Triflates under Mild Conditions. J. Am. Chem. Soc. 2000, 122, 4020‐4028. (b) Dreher, S. D.; Dormer, P. G.; Sandrock, D. L.; Molander, G. A. Efficient Cross‐ Coupling of Secondary Alkyltrifluoroborates with Aryl Chlorides‐ Reaction Discovery Using Parallel Microscale Experimentation. J. Am. Chem. Soc. 2008, 130, 9257‐9259. (c) van den Hoogenband, A.; Lange, J. H. M.; Terpstra, J. W.; Koch, M.; Visser, G. M.; Visser, M.; Korstanje, T. J.; Jastrzebski, J. T. B. H. Ruphos‐Mediated Suzuki Cross‐Coupling of Secondary Alkyl Trifluoroborates. Tetrahedron Lett. 2008, 49, 4122‐4124. 14. We did not isolate any side products related to a possible Heck reaction.
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