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Palladium- and Nickel-Catalyzed Amination of Aryl Fluorosulfonates Patrick S. Hanley, Thomas P Clark, Arkady Krasovskiy, Matthias S. Ober, John Patrick O'Brien, and Tina S. Staton ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.6b00865 • Publication Date (Web): 27 Apr 2016 Downloaded from http://pubs.acs.org on May 7, 2016
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ACS Catalysis
Palladium- and Nickel-Catalyzed Amination of Aryl Fluorosulfonates Patrick S. Hanley*; Thomas P. Clark; Arkady L. Krasovskiy; Matthias S. Ober; John P. O’Brien; and Tina S. Staton. The Dow Chemical Company, Core R&D, Midland, MI 48674, United States
ABSTRACT: The first examples of the palladium and nickel catalyzed amination of aryl fluorosulfonates with aromatic and alkyl amines are described. Aniline is coupled to a diverse series of aryl fluorosulfonates catalyzed by the combination of CpPd(cinammyl) and Xantphos, and the relative reactivity of aryl fluorosulfonates to undergo Pd-catalyzed amination was compared with other common aryl electrophiles. In addition, we report the direct amination of a phenol by in situ formation of an aryl fluorosulfonate by reaction with sulfuryl fluoride and base followed by subsequent amination to form a new C-N bond. Finally, we report examples of the nickel-catalyzed amination of aryl fluorosulfonates catalyzed by the combination of Ni(COD)2 and DPPF in the presence of MeCN. The high reactivity of the aryl fluorosulfonate electrophile with generic palladium and nickel catalyst systems, combined with its simple preparation from sulfuryl fluoride will enable commercial amination reactions of abundant phenolic raw materials. Keywords: Buchwald-Hartwig amination, sulfuryl fluoride, fluorosulfonate, nickel catalysis, phenol
Transition-metal-catalyzed Buchwald-Hartwig amination methodologies are well-established reactions to form new carbon (sp2)-nitrogen bonds.1 Over the past two decades, palladium catalysts have been developed for the selective, mild amination of aryl halides and triflates.2 Aryl electrophiles derived from phenolic raw materials offer a more sustainable alternative to aryl halides.3 Recently, highly active palladium catalysts that aminate less activated sulfonate electrophiles such as mesylates and tosylates have been developed.4 Likewise, new nickel-catalyzed amination methodologies that couple aryl chloride, pivalate, sulfonate, sulfamate, and carbamate electrophiles have been reported,5,6 albeit these reactions typically occur under more forcing conditions and are limited in scope compared to those aminations catalyzed by palladium. Despite the abundance of functionalized phenolic raw materials, the implementation of transition metal catalyzed amination reactions of phenolic derived electrophiles into the manufacturing processes for pharmaceutical, agrochemical, and specialty chemicals has remained limited. These existing amination methods still require complex catalysts, expensive activating groups, or additional process steps. Aryl fluorosulfonates offer an inexpensive alternative to aryl halides and other aryl sulfonates.7,8,9 Aryl fluorosulfonates can be prepared in quantitative yield from the reaction of a phenol and the economical fumigant insecticide sulfuryl fluoride (Scheme 1).10 Researchers at Dow Chemical11 and the groups of Sharpless and Jiang12 have independently reported the Suzuki coupling of aryl fluorosulfonates with boronic acids (Scheme 2). These reports demonstrate the remarkable activity of the aryl fluorosulfonate electrophile towards cross coupling with simple palladium and nickel catalysts.13 This “triflate-like” activity combined with the abundant supply of
sulfuryl fluoride, make the aryl fluorosulfonate the unmatched phenolic based electrophile for commercial Suzuki-Miyaura coupling operations. To this end, we desired to develop the corresponding amination of aryl fluorosulfonates. Generally, transition-metalcatalyzed amination methodologies occur under strongly basic conditions at higher temperatures than the corresponding Suzuki coupling, and previous work indicates that the S-F bond of the fluorosulfonate is susceptible to nucleophilic substitution by amines. Kelly and co-workers have recently described the selective reaction of an aryl fluorosulfonate with a Lys residue of transthyretin (TTR) to form a sulfamate,14 and Johnson has described the preparation of the bis(fluorosulfonyl)amide salt from the reaction of SO2F2 and NH3 in the presence of NEt3.15 Scheme 1. Preparation of Aryl Fluorosulfonates
Scheme 2. Suzuki Coupling of Phenols Enabled by Sulfuryl Fluoride
Here, we report the first examples of a C-N bond-forming amination of aryl fluorosulfonates catalyzed by homogenous palladium and nickel catalysts. An optimized method for the
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coupling of aryl fluorosulfonates and aniline by the combination of CpPd(cinnamyl) and Xantphos is reported. In addition, we report the one-pot amination of a phenol by in situ formation of the aryl fluorosulfonate followed by C-N coupling to form aminated product in high yield. Finally, the first nickel catalyzed amination of aryl fluorosulfonates is reported, and shown to tolerate a diverse array of functionalized aryl fluorosulfonates. Because aryl fluorosulfonates have been shown to undergo sulfamation in the presence of amines, we postulated that mild conditions would be necessary for productive C-N bondforming amination. An initial reaction screen explored the coupling of p-tolylfluorosulfonate (1a) with aniline in the presence of Cs2CO3 with the palladium precatalyst CpPd(cinnamyl) and one of four ligands (t-BuBrettPhos, Xantphos, BINAP, and Josiphos) (Table 1). CpPd(cinnamyl) was selected as a precatalyst because it is known to rapidly form phosphine ligated Pd0 complexes under mild conditions.16 The combination of CpPd(cinnamyl) and Xantphos catalyzed the amination of 1a to form 4-methyl-Nphenylaniline (2a) in 90% yield over 15 h. We subsequently found that less expensive K2CO3 could be substituted for Cs2CO3. Table 1. Pd-catalyzed Amination of p-tolylfluorosulfonate with aniline
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and iodides are known to undergo rapid oxidative addition to palladium; however, under these mild conditions (K2CO3 base), transmetallation is likely the turnover limiting step. These data suggest that the identity of the resulting X-ligand in the LnPd(p-tolyl)X following oxidative addition of the aryl electrophile to palladium greatly affects the rate and productivity of these mild aminations.17 The aryl fluorosulfonate appears to offer the optimal combination of activity towards oxidative addition and the ability to promote facile transmetallation in the presence of K2CO3. Table 2. Palladium-Catalyzed Amination of Aryl Fluorosulfonatesa,b
H N N 2f, 95%
Entry 1 2 3 4 a
Ligand t-BuBrettPhos Xantphos BINAP Josiphosa
Yield (%) 30 90 0 57
(R)-1-[(SP)-2-(Dicyclohexylphosphino)ferrocenyl]ethyldi-tertbutylphosphine
These optimized conditions were explored for the amination of a diverse set of functionalized aryl fluorosulfonates (Table 2). In most examples, excellent yields of aminated product were obtained. Fluorosulfonates containing esters, amides, chlorides, ethers, and nitrogen-containing heterocycles were well-tolerated. Higher yields of aminated product were obtained from reactions with aryl fluorosulfonates containing electron-withdrawing functionalities than from reactions with aryl fluorosulfonates containing electron-donating groups. For example, the amination of 1c (R = p-CF3), 1e (R = p-COOEt), and 1h (R = p-CN) occurred in almost quantitative yield. Conversely, amination of the electron-rich aryl fluorosulfonate 1b (R = p-OMe) occurred in only 66% isolated yield. Sterically encumbered aryl fluorosulfonates were also coupled in excellent yields with the aminated thymol derivative 2j isolated in 97% yield. To compare the amination of aryl fluorosulfonates to the amination of other common aryl electrophiles under these mild reaction conditions, we measured the conversion and yield of the arylation of aniline with a variety of aryl electrophiles (Table 3). Notably, the fluorosulfonate was the most reactive and selective electrophile, giving rise to 96% yield of the amination product after 24 h (entry 1). The amination of the aryl triflate was slower and formed 2a in 84% yield. Surprisingly, amination of the aryl bromide and aryl iodide only formed trace amounts of product, while the aryl chloride slowly underwent productive amination in 13% yield. Aryl bromides
a General conditions: arylfluorosulfonate (2.5 mmol); aniline (3.0 mmol); potassium carbonate (5.0 mmol); Xantphos (0.030 mmol); CpPd(cinnamyl) (0.025 mmol); 1,4-dioxane (5.0 mL) bIsolated yields. c 24 h, d18 h, eControl reaction lacking added precatalyst and ligand.
Table 3. Pd-catalyzed Amination of Aryl Electrophiles under Mild Conditionsa
Entry
X
1 2 3 4 5 6 7
OFs OTf Cl Br I OMs OTs a
Conversion Ar-X (%) 7 h 95 20 10 2 0 0 0
Conversion Ar-X (%) 24 h 100 92 27 16 2 0 0
Yieldb (%) (24 h) 96 84 13 6
