Diastereoselective Nickel-Catalyzed Carboiodination Generating Six

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

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Diastereoselective Nickel-Catalyzed Carboiodination Generating Six-Membered Nitrogen-Based Heterocycles Austin D. Marchese, Louise Kersting, and Mark Lautens* Davenport Research Laboratories, Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario, Canada M5S 3H6

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ABSTRACT: A scalable, diastereoselective nickel-catalyzed carboiodination reaction is reported that avoids metal-based reducing agents. Novel anti-dihydroquinolones and previously unreported tetrahydroquinolines are now readily prepared. The generation of anti-dihydroquinolones is noteworthy, as this selectivity is opposite to that of the Pd variant. Mechanistic insight into the nature of the nickel-catalyzed carboiodination reaction was derived experimentally, suggesting a catalyst-controlled cyclization and stereoretentive reductive elimination.

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Scheme 1. Ni-Catalyzed Carboiodination Cyclizations

ver the past decade, carboiodination has emerged as a new strategy to build complex heterocyclic scaffolds containing a reactive C−I bond.1−3 Typically, palladium has been used to perform this reaction, but the use of air-sensitive catalysts as well as high-molecular-weight and expensive ligands is often required.2 Among the various reactions we have reported, palladium was shown to form iodinated dihydroisoquinolones (DHIQs) with high selectivity for the syn diastereomer.3e Recently we discovered a nickel-catalyzed carboiodination reaction that employs simple phosphines or phosphites as ligands (Scheme 1).2a,c To date this methodology has been applied to make five-membered heterocycles and shown promise in generating enantioenriched products. During our investigations of the diastereoselectivity of nickel-catalyzed carboiodination reactions, we observed an interesting phenomenon: Ni and Pd form opposite diastereomers of the DHIQ scaffold, each with moderate to high selectivity. Utilizing a Ni−phosphite catalyst generated in the absence of a metal reductant, we can selectively obtain the anti diastereomer of DHIQs in moderate to excellent yields. These conditions also enabled the synthesis of iodotetrahydroquinolines (iodo-THQs), a scaffold that has not been reported in carboiodination chemistry. Again, high yields and excellent diastereoselectivity favoring the anti isomers were observed. We also identified a method for the synthesis of enantioenriched products via enantioenriched starting materials as well as key mechanistic insight for the general nickel-catalyzed carboiodination reaction. 2-Substituted THQs are an interesting scaffold in their own right, as they are known to be AMPK activators4 as well as to © XXXX American Chemical Society

make up the core of known EP1 receptor ligands.5 The iodide handle provides a simple route to study the structure−activity relationship of some analogues that cannot be easily prepared under the previously reported route of synthesis. The optimized conditions leading to efficient carboiodination were NiI2 (10 mol %) and P(OiPr)3 (40 mol %) in Received: August 7, 2019

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DOI: 10.1021/acs.orglett.9b02797 Org. Lett. XXXX, XXX, XXX−XXX

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Organic Letters toluene (1 mL) at 80 °C for 18 h, which provided the product 2a in 85% isolated yield as a single diastereomer (88:12 d.r. for the crude reaction). Changing the ligand to P(OEt)3 gave the product in 78% yield with 83.5:16.5 d.r. (Table 1). Other

Scheme 2. Ni-Catalyzed Carboiodination Generating Dihydroisoquinolones

Table 1. Optimization of Ni-Catalyzed Carboiodination

entry

variation from standard conditions

yield (%)a

d.r.

1 2 3 4 5 6 7 8 9

P(OEt)3 instead of P(OiPr)3 at 100 °C 30 mol % ligand 50 mol % ligand 100 °C instead of 80 °C 120 °C instead of 80 °C 60 °C instead of 80 °C 0.4 M instead of 0.1 M 0.2 M instead of 0.1 M 0.4 equiv of NEt3 added

78 88 88 88 83 25 88 88 88

83.5:16.5 88:12 88:12 88:12 83.5:16.5 88:12 88:12 88:12 88:12

a

Yields of the major diastereomer as determined by 1H NMR analysis using 1,3,5-trimethoxybenzene as an internal standard.

phosphites were studied but yielded only trace amounts, or less, of product.6 The use of phosphines in this reaction showed no reactivity whatsoever.7 Changing the amount of ligand to 30 or 50 mol % led to no further improvement, and incomplete conversion was observed at 99:1 e.r. This starting material showed reduced reactivity and required double the catalyst loading to achieve complete conversion. Employing a substrate with two dioxolane moieties severely decreased the reactivity and required double the catalyst loading. The d.r. was 1:1, giving the anti diastereomer in 40% isolated yield (2i). The decrease in d.r. is likely due to a combination of the electron-donating para-dioxolane as well as the steric hindrance of the ortho substitution. In 2014, our group published the formal synthesis of (+)-corynoline featuring the Pd-catalyzed carboiodination reaction, starting from compound 1i. Although there is no diastereoselectivity, the ability to isolate product 2i as a single diastereomer in moderate yield is noteworthy, as it represents a precursor to the natural product epi-corynoline, which was unattainable using the palladium methodology. The nature of the protecting group was examined and found to have a strong impact. A benzyl moiety gave the product in a combined yield of 91% with 1.5:1 d.r. (2j). A substrate lacking B


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impacted the reaction, providing the product 2p in 82% yield as a single diastereomer. Substituting the pendent aromatic ring at the para position with Me and F substituents gave the products 2q and 2f in excellent yields as single diastereomers. Having a 2,4dichlorophenyl ring hindered the reactivity of the starting material, giving the product 2s in only 48% isolated yield even when 20 mol % catalyst was used at 120 °C. This result is likely due to increased steric hindrance at the ortho position. A PMBprotected alcohol on the α-carbon of the acetyl group required elevated temperatures of 120 °C but was otherwise welltolerated, giving the product 2t in 70% yield as a single diastereomer. To probe the influence of the ligand versus the substrate, cyclization of a racemic mixture of 1a was explored with a chiral nickel catalyst (Scheme 4). When an (R)-BINOL-

the pendent aromatic ring was also reactive, and the unsubstituted dihydroisoquinoline 2k was formed in 98% yield. Next, we wanted to explore the viability of using the carboiodination reaction to generate iodo-THQs (Scheme 3). Scheme 3. Ni-Catalyzed Carboiodination Generating Tetrahydroquinolines

Scheme 4. Catalyst-Controlled Enantioselective Migratory Insertion

derived N,N-diisopropyl phosphoramidite ligand was mixed with NiI2 in toluene in the presence of manganese, the product was obtained in ∼70:30 d.r. Each diastereomer was enantiomerically enriched with the opposite stereochemistry of the pendent Ph group. This suggests that each enantiomer of the starting material reacted on the same face of the olefin in a parallel resolution process. In both cases, the R stereocenter was obtained at the newly formed quaternary carbon, suggesting a catalyst-controlled migratory insertion. This result supports a classic two-electron migratory insertion cyclization rather than a radical pathway and is consistent with our previous findings with phosphines.2c It also aligns with what has been reported on the palladium-catalyzed carboiodination reaction employing aryl halides.3j To investigate the nature of the carbon−iodine bondforming step, we undertook a deuterium labeling study (Table 2). Both phosphines and phosphites promote the Ni-catalyzed carboiodination reaction to form THQs, oxindoles, and indolines.2c The N-Ts starting material 1u is more readily prepared than the N-Ac analogue. Additionally, the Ni− phosphite system failed to catalyze the reaction of substrate 1u, so PPh3 was used as the ligand in this study. At 10 h, the reaction showed high diastereoselectivity, giving indoline 2u with a diasteromeric ratio of 29.5:1. This result is indicative of a stereoretentive reductive elimination, analogous to what was reported by Tong in 2011, who employed palladium as a catalyst.3j This result along with the aforementioned observed parallel resolution further support a catalyst-controlled migratory insertion over single-electron alternatives.3j Over time, there is a slight degradation in the diasteroselectivity (to ∼6:1). It is possible that nickel may be able to reversibly oxidatively add

The reaction was run at 120 °C. b20 mol % catalyst was employed.

a

We investigated both Ni and Pd9 catalysis and observed that both catalysts generated the same diastereomer of product 2l. Because of the simplicity, cost benefit, superior reactivity, and diastereoselectivity of the Ni-catalyzed system, we focused on using this catalyst. Under similar reaction conditions, Nacylated tetrahydroquinolines were generated from the corresponding alkylated 2-iodoaniline derivatives.10 Using NiI2 (10 mol %) and P(OiPr)3 (40 mol %) in toluene (0.133 M) at 100 °C afforded product 2l in 95% isolated yield as a single diastereomer. The reaction also worked with NiI2 (10 mol %), PPh3 (20 mol %), and Mn (60 mol %) in toluene (0.133 M) at 100 °C, giving product 2l in identical yield and selectivity. This observation is noteworthy because the phosphine system has been shown to be advantageous with certain substituents2a and may be superior for different THQ scaffolds than the ones explored in this study. The simplicity of employing a phosphite lies in negating the need for substoichiometric Mn, so all subsequent studies were conducted using P(OiPr)3. A crystal structure of 2l was obtained, confirming the anti configuration of the pendent aryl group and the CH2I functionality. A Me or Cl moiety para to the aryl iodide resulted in a slightly reduced yield, with products 2m and 2n formed in 90% and 81% yield, respectively, as single diastereomers. An electron-withdrawing Cl atom meta to the aryl iodide had no effect on the reaction, giving 2n in 98% yield as a single diastereomer. Changing the halogen to a more electron-withdrawing fluorine modestly C


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Organic Letters Table 2. Deuterium Incorporation Study Indicative of a Stereoretentive Reductive Elimination

time (h)

X (%D)

Y (%D)

total (% D)

d.r.

yield of 2u (%)

10 12 14 24

59 60 56 55

2 2 8 11

61 62 64 66

29.5:1 30:1 8:1 5.5:1

40a 36b 52a 68a

Scheme 6. Derivatization of the C−I Bond

a

Yield determined by 1H NMR analysis using 1,3,5-trimethoxybenzene as an internal standard. bIsolated yield of product 2u.

into the alkyl iodide bond, either through an SN2 pathway or a single electron pathway, the former of which has been reported in the palladium-catalyzed carboiodination methodology.3j On the basis of these results, we propose the following mechanism for the Ni-catalyzed carboiodination reaction (Scheme 5). NiI2 is reduced to Ni0 by use of the alkyl

cyanation reaction is noteworthy, as it is the first step in the previously reported synthesis of corynoline from epi-2i. The softer nucleophile NaSPh gave the thiolated product 2x in 80% yield. Utilizing Pd catalysis,13 we were able to reduce the C−I bond in 79% yield (2y). This reaction is noteworthy, as it shows the ability of Pd to oxidatively add into the C−I bond and perform subsequent cross-coupling transformations. In conclusion, we have identified a novel approach to generate anti six-membered heterocycles via a simple metalreducing-agent-free Ni-catalyzed carboiodination reaction. This report is complementary to the Pd methodology, as we now have a way to generate each diastereomer of the DHIQ products with high selectivity as well as a method to obtain products with excellent e.r. The generation of these THQs is also of interest, as these novel iodinated scaffolds closely resemble important medicinally relevant compounds, with the added alkyl iodide handle for further functionalization. We have also conducted preliminary mechanistic experiments suggesting that this reaction proceeds through an oxidative addition−migratory insertion−reductive elimination pathway. We are currently examining DFT to investigate the origin of the change in diastereoselectivity for Ni and Pd variants of the DHIQ synthesis. This methodology shows that nickel not only can perform the carboiodination reaction on diverse scaffolds but also offers unique selectivity compared with palladium. Its advantages over palladium go beyond the basic economic and accessibility arguments, as nickel can provide access to previously unattainable scaffolds and isomers of medicinally relevant heterocycles. Expanding on these fronts represents steps toward solidifying carboiodination as a valuable synthetic tool.

Scheme 5. Potential Mechanism for the Ni-Catalyzed Carboiodination Reaction

phosphite,11 (or in the cases with phosphines, Mn is the reducing agent) followed by oxidative addition into the aryl iodide bond. Subsequent alkene co-ordination is followed by migratory insertion of the tethered alkene into the Ar−Ni bond, and finally, the cycle is completed by a stereoretentive reductive elimination of the C−I bond to regenerate the Ni(0) catalyst. Oxidation states are not specified, as Ni is known to have access to the (I), (II), and (III) oxidation states.1c,12 We postulate that the necessity of the carbonyl in all of the nickel-catalyzed carboiodination reactions may be related to the ortho effect, a known phenomenon where Lewis basic ortho substituents chelate to the oxidative addition complex and stabilize it in the (II) oxidation state.12 We have also explored the divergent reactivity of the C−I bond (Scheme 6). 2a in the presence of nucleophiles such as NaN3 or NaCN in DMF at 100 °C with 15-crown-5 yields the SN2-displaced products in good yields. The cyano (2v) and azido (2w) products were obtained in 65% and 74% isolated yield, respectively, as single diastereomers. The success of the

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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.9b02797. Experimental procedures, optimization, characterization and X-ray data (PDF) NMR spectra (PDF) Accession Codes

CCDC 1946885−1946886 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 e-mailing [email protected], or by contacting The D


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1780. (o) Phapale, V. B.; Cárdenas, D. J. Nickel-catalysed Negishi cross-coupling reactions: scope and mechanisms. Chem. Soc. Rev. 2009, 38, 1598. (2) For examples of Ni-catalyzed carboiodination, see: (a) Marchese, A. D.; Lind, F.; Mahon, Á .; Yoon, H.; Lautens, M. Forming Benzylic Iodides via a Nickel Catalyzed Diastereoselective Dearomative Carboiodination Reaction of Indoles. Angew. Chem., Int. Ed. 2019, 58, 5095. (b) Takahashi, T.; Kuroda, D.; Kuwano, T.; Yoshida, Y.; Kurahashi, T.; Matsubara, S. Nickel-catalyzed intermolecular carboiodination of alkynes with aryl iodides. Chem. Commun. 2018, 54, 12750. (c) Yoon, H.; Marchese, A. D.; Lautens, M. Carboiodination Catalyzed by Nickel. J. Am. Chem. Soc. 2018, 140, 10950. (3) For examples of Pd-catalyzed carboiodination, see: (a) Zhang, Z.-M.; Xu, B.; Wu, L.; Zhou, L.; Ji, D.; Liu, Y.; Li, Z.; Zhang, J. Palladium/XuPhos-Catalyzed Enantioselective Carboiodination of Olefin-Tethered Aryl Iodides. J. Am. Chem. Soc. 2019, 141, 8110. (b) Lee, Y. H.; Morandi, B. Palladium-Catalyzed Intermolecular Aryliodination of Internal Alkynes. Angew. Chem., Int. Ed. 2019, 58, 6444. (c) Sun, Y.-L.; Wang, X.-B.; Sun, F.-N.; Chen, Q.-Q.; Cao, J.; Xu, Z.; Xu, L.-W. Enantioselective Cross-Exchange between C−I and C−C σ-Bonds. Angew. Chem., Int. Ed. 2019, 58, 6747. (d) Hou, L.; Zhou, Z. Z.; Wang, D.; Zhang, Y.; Chen, X.; Zhou, L.; Hong, Y.; Liu, W.; Hou, Y.; Tong, X. DPPF-Catalyzed Atom-Transfer Radical Cyclization via Allylic Radical. Org. Lett. 2017, 19, 6328. (e) Petrone, D. A.; Yoon, H.; Weinstabl, H.; Lautens, M. Additive effects in the palladium-catalyzed carboiodination of chiral N-allyl carboxamides. Angew. Chem., Int. Ed. 2014, 53, 7908. (f) Petrone, D. A.; Lischka, M.; Lautens, M. Harnessing Reversible Oxidative Addition: Application of Diiodinated Aromatic Compounds in the Carboiodination Process. Angew. Chem., Int. Ed. 2013, 52, 10635. (g) Jia, X.; Petrone, D. A.; Lautens, M. A conjunctive carboiodination: indenes by a double carbopalladation-reductive elimination domino process. Angew. Chem., Int. Ed. 2012, 51, 9870. (h) Petrone, D. A.; Malik, H. A.; Clemenceau, A.; Lautens, M. Functionalized Chromans and Isochromans via a Diastereoselective Pd (0)-Catalyzed Carboiodination. Org. Lett. 2012, 14, 4806. (i) Newman, S. G.; Lautens, M. Palladiumcatalyzed carboiodination of alkenes: carbon-carbon bond formation with retention of reactive functionality. J. Am. Chem. Soc. 2011, 133, 1778. (j) Liu, H.; Li, C.; Qiu, D.; Tong, X. Palladium-Catalyzed Cycloisomerizations of (Z)-1-Iodo-1,6-dienes: Iodine Atom Transfer and Mechanistic Insight to Alkyl Iodide Reductive Elimination. J. Am. Chem. Soc. 2011, 133, 6187. (k) Newman, S. G.; Howell, J. K.; Nicolaus, N.; Lautens, M. Palladium-catalyzed carbohalogenation: bromide to iodide exchange and domino processes. J. Am. Chem. Soc. 2011, 133, 14916. (l) Liu, H.; Chen, C.; Wang, L.; Tong, X. Pd(0)Catalyzed Iodoalkynation of Norbornene Scaffolds: The Remarkable Solvent Effect on Reaction Pathway. Org. Lett. 2011, 13, 5072. (4) Chen, L.; Feng, L.; He, Y.; Huang, M.; Liu, M.; Zhou, M. Novel Tetrahydroquinoline Derivatives. WO 2012/001020 A1, Jan 5, 2012. (5) Aguilar, N.; Fernandez, J. C.; Terricabras, E.; Carceller Gonzalez, E.; Salas Solana, J. Substituted Tricyclic Compounds with Activity towards EP1 Receptors. WO 2013/149997 A1, Oct 10, 2013. (6) Other phosphites examined included P(OPh)3, P(OtBu)3, and tris(2-ethylhexyl)phosphite, but little to no conversion was observed. Additionally, combinations of P(OiPr)3 and these aforementioned ligands were tried but were again unsuccessful. Di-tert-butyl-N,Ndiethyl phosphoramidite was also employed but failed in the reaction. (7) Triphenylphosphine and ethoxydiphenylphosphine in the presence of Mn (0.6 equiv) were employed but failed to show any reactivity. (8) A concentration of 0.1 M was chosen, as many of the substrates were saplike liquids and it was necessary to have enough solvent to dissolve them. Adding an amine such as triethylamine did not improve the d.r. of the reaction, as shown in the palladium methodology. (9) The best conditions achieved with Pd afforded product 2l in 79% NMR yield, with >90:10 d.r. The conditions used were

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Austin D. Marchese: 0000-0002-3090-2748 Mark Lautens: 0000-0002-0179-2914 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank the University of Toronto, the Natural Science and Engineering Research Council (NSERC), Alphora Research Inc., and Kennarshore Inc. for financial support. A.D.M. thanks OGS and NSERC for an NSERC Vanier Fellowship. We thank Alan Lough (University of Toronto) for X-ray analysis of 2b and 2l, Dr. Darcy Burns and Dr. Jack Sheng (University of Toronto) for their assistance with NMR experiments, and Dr. Hyung Yoon and Dr. Dave Petrone for the synthesis of substrates 1b and 1d−i.

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REFERENCES

(1) For work outlining metal-catalyzed C−X bond formation, see: (a) Garrison Kinney, R.; Tjutrins, J.; Torres, G. M.; Liu, N. J.; Kulkarni; Arndtsen, B. A. A General Approach, to Intermolecular Carbonylation of Arene C-H Bonds to Ketones Through Catalytic Aroyl Triflate Formation. Nat. Chem. 2018, 10, 193. (b) Shen, Y.; Cornella, J.; Julia-Hernandez, F.; Martin, R. Visible Light-Promoted Atom Transfer Radical Cyclization of Unactivated Alkyl Iodides. ACS Catal. 2017, 7 (1), 409. (c) Petrone, D. A.; Ye, J.; Lautens, M. Modern Transition-Metal-Catalyzed Carbon-Halogen Bond Formation. Chem. Rev. 2016, 116, 8003. (d) Roy, A. H.; Hartwig, J. F. Reductive Elimination of Aryl Halides upon Addition of Hindered Alkylphosphines to Dimeric Arylpalladium(II) Halide Complexes. Organometallics 2004, 23, 1533. For work related to Ni-catalyzed cross-coupling reactions, see: (e) Clark, J. S. K.; Ferguson, M. J.; McDonald, R.; Stradiotto, M. PAd2-DalPhos Enables the NickelCatalyzed C−N Cross-Coupling of Primary Heteroarylamines and (Hetero)aryl Chlorides. Angew. Chem., Int. Ed. 2019, 58, 6391. (f) Sun, S.-Z.; Börjesson, M.; Martin-Montero, R.; Martin, R. SiteSelective Ni-Catalyzed Reductive Coupling of α-Haloboranes with Unactivated Olefins. J. Am. Chem. Soc. 2018, 140, 12765. (g) Yu, P.; Morandi, B. Nickel Catalyzed Cyanation of Aryl Chlorides and Triflates Using Butyronitrile: Merging Retro-Hydrocyanation with Cross Coupling. Angew. Chem., Int. Ed. 2017, 56, 15693. (h) Schley, N.; Fu, G. C. Nickel-Catalyzed Negishi Arylations of Propargylic Bromides: A Mechanistic Investigation. J. Am. Chem. Soc. 2014, 136, 16588. (i) Tasker, S. Z.; Standley, E. A.; Jamison, T. F. Recent advances in homogeneous nickel catalysis. Nature 2014, 509, 299. (j) Cherney, A. H.; Reisman, S. E. Nickel-catalyzed asymmetric reductive cross-coupling between vinyl and benzyl electrophiles. J. Am. Chem. Soc. 2014, 136, 14365. (k) Han, F. − S. Transition-metalcatalyzed Suzuki−Miyaura cross-coupling reactions: a remarkable advance from palladium to nickel catalysts. Chem. Soc. Rev. 2013, 42, 5270. (l) Davis, J. L.; Arndtsen, B. A. Comparison of Imine to Olefin Insertion Reactions: Generation of Five- and Six-Membered Lactams via a Nickel-Mediated CO, Olefin, CO, Imine Insertion Cascade. Organometallics 2011, 30, 1896. (m) Watson, M. P.; Jacobsen, E. N. Arylcyanation of Unactivated Olefins via C-CN Bond Activation. J. Am. Chem. Soc. 2008, 130, 12594. For mechanistic insight on Nicatalyzed cross-couplings, see: (n) Liu, C.; Zhang, H.; Shi, W.; Lei, A. Bond Formations between Two Nucleophiles: Transition Metal Catalyzed Oxidative Cross-Coupling Reactions. Chem. Rev. 2011, 111, E


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Organic Letters Pd[P(tBu)3]2 (5 mol %) and Et3N (100 mol %) in PhMe (0.2 M) at 110 °C for 24 h. (10) A substate where the N-acetyl group was replaced by an Nbenzyl moiety showed no reaction. (11) For literature pertaining to the reduction of NiX2 species to Ni(0), see: (a) Villemin, D.; Elbilali, A.; Siméon, F.; Jaffrés, P.-A.; Maheut, G.; Mosaddak, M.; Hakiki, A. Nickel and palladium catalysed reaction of triethyl phosphite with aryl halides under microwave irradiation. J. Chem. Res. 2003, 2003, 436. Vinal, R. S.; Reynolds, L. T. The Reduction of Nickel(II) Halides by Trialkyl Phosphites. Inorg. Chem. 1964, 3 (7), 1062. (12) (a) Bajo, S.; Laidlaw, G.; Kennedy, A.; Sproules, S.; Nelson, D. J. Oxidative Addition of Aryl Electrophiles to a Prototypical Nickel(0) Complex: Mechanism and Structure/Reactivity Relationships. Organometallics 2017, 36, 1662. (b) Mohadjer Beromi, M.; Nova, A.; Balcells, D.; Brasacchio, A. M.; Brudvig, G. W.; Guard, L. M.; Hazari, N.; Vinyard, D. J. Mechanistic Study of an Improved Ni Precatalyst for Suzuki−Miyaura Reactions of Aryl Sulfamates: Understanding the Role of Ni(I) Species. J. Am. Chem. Soc. 2017, 139, 922. (c) Wada, M.; Kusabe, K.; Oguro, K. Ary 1(pentachlorophenyl) nickel(II) Complexes. Lack of Free Rotation about Toly 1-Nickel Bonds and Lack of “Ortho Effect” in Carbonylation. Inorg. Chem. 1977, 16 (2), 446. (13) Petrone, D. A.; Franzoni, I.; Ye, J.; Rodriguez, J. F.; PobladorBahamonde, A. L.; Lautens, M. Palladium-Catalyzed Hydrohalogenation of 1,6-Enynes: Hydrogen Halide Salts and Alkyl Halides as Convenient HX Surrogates. J. Am. Chem. Soc. 2017, 139 (9), 3546− 3557.

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Diastereoselective Nickel-Catalyzed Carboiodination Generating Six

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