Arylation of adamantanamines: II. Palladium-catalyzed amination of dihalobenzenes with adamantylalkanamines

Palladium-catalyzed arylation of various (1-adamantyl)alkanamines with isomeric (ortho, meta, and para) bromochloro- and dibromobenzenes was studied. Optimal catalytic systems were found for the synthesis of mono- and diamination products, and the dependences of their yields on the nature of the initial amine and dihalobenzene and on the amount of base were examined. Side amination products were isolated, and paths of their formation were analyzed.     

Hypervalent Iodine in Synthesis. Part 86

N‐Arylation of uracil and its derivatives 2 with diaryliodonium salts 1 was investigated in order to explore a new synthetic methodology associated with N‐aryluracil derivatives. In the presence of K₂CO₃, the copper‐catalyzed arylation gave N¹,N³‐diarylation products with high selectivity and in good yields (Table 2). However, the use of NaOAc as the base in the copper‐catalyzed arylation of 6‐methyluracil ( 2a ) resulted in N³‐arylation products with high selectivity, and, in the copper‐catalyzed arylation of uracil ( 2b ) or 5‐methyluracil (=thymine; 2c ), N¹‐arylation products were the major products (Table 3).     

Regioselective alkynylation of 2-aryl-4-chloro-3-iodoquinolines and subsequent arylation or amination of the 2-aryl-3-(alkynyl)-4-chloroquinolines

Palladium-CuI catalyzed Sonogashira coupling of 2-aryl-4-chloro-3-iodoquinolines with terminal acetylenes (1 equiv) in triethylamine afforded the 2-aryl-3-(alkynyl)-4-chloroquinolines as sole products. The 2-aryl-4-chloro-3-iodoquinolines coupled with excess terminal acetylenes (2.5 equiv) in dioxane/water to yield the 2-aryl-3,4-bis(alkynyl)quinoline derivatives in a one-pot operation. The 2-aryl-3-(alkynyl)-4-chloroquinolines were, in turn, subjected to arylation via Suzuki cross-coupling with arylboronic acid derivatives or amination with methylamine, respectively. The structures of the products of successive Sonogashira and Suzuki cross-couplings were also confirmed by X-ray crystallography.     

Arylation of adamantanamines: IV. Palladium-catalyzed arylation of amines of adamantane series with isomeric chloroquinolines

Palladium-catalyzed arylation of diverse amines of the adamantane series with isomeric chloroquinolines was investigated. The 2-chloroquinoline is the most reactive, however the best yields of the N-arylation products are most frequently obtained in the reaction with the less reactive 6-chloroquinoline. The applicability of the reaction is limited by the size of the substituent at the amino group. In some instances the noncatalytic amination of chloroquinolines was possible.     

Palladium-catalyzed direct arylation using free NH2 substituted thiophene derivatives with inhibition of amination type reaction

The palladium-catalyzed direct arylation at C2 or C5 of free NH₂ substituted thiophene derivatives was found to proceed in moderate to high yields using a variety of aryl halides. The choice of potassium acetate as the base was found to be crucial to inhibit the amination reaction and to promote the direct arylation.     

Palladium-Catalyzed Benzylic C(sp3)−H Carbonylative Arylation with Aryl Bromides

A novel, selective and high-yielding palladium-catalyzed carbonylative arylation of a variety of weakly acidic (pK_a 25–35 in DMSO) benzylic and heterobenzylic C(sp³)−H bonds with aryl bromides has been achieved. This system is applicable to a range of pro-nucleophiles for access to sterically and electronically diverse α-aryl or α,α-diaryl ketones, which are ubiquitous substructures in biologically active compounds. The Josiphos SL-J001-1-based palladium catalyst was identified as the most efficient and selective, enabling carbonylative arylation with aryl bromides under 1 atm CO to provide the ketone products without the formation of direct coupling byproducts. Additionally, (Josiphos)Pd(CO)₂ was identified as the catalyst resting state. A kinetic study suggests that the oxidative addition of aryl bromides is the turnover-limiting step. Key catalytic intermediates were also isolated.     

Rapid access to diverse α-carbolines through sequential transition metal catalyzed amination and direct C–H arylation

An efficient sequence of Pd catalyzed amination and direct C–H arylation for a synthesis of pharmacologically important α-carbolines is described. The outstanding feature in the synthetic sequence is that a combination of DBU and 2-(dicyclohexylphosphino)biphenyl (DCHPB) plays a critical role to not only enhance the reactivity but also suppress hydrodehalogenation in the direct C–H arylation step. The reaction protocol provides α-carbolines with various substituents including base-sensitive ester and ketone moieties in moderate to excellent yields. Moreover, combination with Cu catalyzed amination further enhanced the versatility of the α-carboline synthesis.     

On the mechanism of the palladium-catalyzed β-arylation of ester enolates

The palladium‐catalyzed β‐arylation of ester enolates with aryl bromides was studied both experimentally and computationally. First, the effect of the ligand on the selectivity of the α/β‐arylation reactions of ortho‐ and meta‐fluorobromobenzene was described. Selective β‐arylation was observed for the reaction of o‐fluorobromobenzene with a range of biarylphosphine ligands, whereas α‐arylation was predominantly observed with m‐fluorobromobenzene for all ligands except DavePhos, which gave an approximate 1:1 mixture of α‐/β‐arylated products. Next, the effect of the substitution pattern of the aryl bromide reactant was studied with DavePhos as the ligand. We showed that electronic factors played a major role in the α/β‐arylation selectivity, with electron‐withdrawing substituents favoring β‐arylation. Kinetic and deuterium‐labeling experiments suggested that the rate‐limiting step of β‐arylation with DavePhos as the ligand was the palladium–enolate‐to‐homoenolate isomerization, which occurs by a β? H‐elimination, olefin‐rotation, and olefin‐insertion sequence. A dimeric oxidative‐addition complex, which was shown to be catalytically competent, was isolated and structurally characterized. A common mechanism for α‐ and β‐arylation was described by DFT calculations. With DavePhos as the ligand, the pathway leading to β‐arylation was kinetically favored over the pathway leading to α‐arylation, with the palladium–enolate‐to‐homoenolate isomerization being the rate‐limiting step of the β‐arylation pathway and the transition state for olefin insertion its highest point. The nature of the rate‐limiting step changed with PCy₃ and PtBu₃ ligands, and with the latter, α‐arylation became kinetically favored. The trend in selectivity observed experimentally with differently substituted aryl bromides agreed well with that observed from the calculations. The presence of electron‐withdrawing groups on these bromides mainly affected the α‐arylation pathway by disfavoring C? C reductive elimination. The higher activity of the ligands of the biaryldialkylphosphine ligands compared to their corresponding trialkylphosphines could be attributed to stabilizing interactions between the biaryl backbone of the ligands and the metal center, thereby preventing deactivation of the β‐arylation pathway.     

Amination of <Emphasis Type="Italic">meso</Emphasis>-bromophenyl(polyalkyl)porphyrins: Synthesis of porphyrins containing a hydroxypiperidine fragment

5,15-Bis(4-bromophenyl)-2,8,12,18-tetraethyl-3,7,13,17-tetramethylporphyrin and 5-(4-bromophenyl)-13,17-dibutyl-2,3,7,8,12,18-hexamethylporphyrin were synthesized, and their palladium-catalyzed amination with a number of cyclic secondary amines, including hydroxypiperidines, was studied [Pd(OAc)₂, ligand, THF or dioxane, t-BuONa, 80–100°C]. The reactions of the meso-bromophenylporphyrins with piperidine and morpholine gave the corresponding amination products in quantitative yield. The amination with hydroxypiperidines required excess amine (3 equiv per bromine atom) and excess base (6–8 equiv) and was accompanied by formation of hydrodebromination products; in the reactions with the bis(bromophenyl)derivative, mixed products resulting from amination at one phenyl group and reductive debromination at the other were also formed. The yields of the amination products varied from good {75–50% in the reactions with 4-hydroxypiperidine and trans-3-hydroxy-4-[4-(2-fluorophenyl)piperazin-1-yl]piperidine} to moderate (20–50%, 3-hydroxypiperidine) and poor [11–25%, trans-3,4-dihydroxypiperidine and trans-3-hydroxy-4-(4-hydroxypiperidin-1-yl)piperidine].     

Studies on the Synthesis and Bioactivities of 4‐Amino Derivatives of Tetramic Acid

In order to study the potential bioactivities of 4‐amino tetramic acid derivatives, the 4‐amination products of pyrrolidine‐2,4‐diones ( 5 ) and 4‐hydroxy‐2‐oxo‐2,5‐dihydro‐1H‐pyrrole‐3‐carboxylates ( 4 ) were prepared. The 4‐amination of 5 took place in high yield when catalyzed by acetic acid, whereas the 4‐amination of 4 was achieved through a 4‐ethoxy intermediate, which was prepared by acidic etherification. Their herbicidal, fungicidal, insecticidal, and antitumor activities were tested. The bioassays showed that two of the compounds exhibited good herbicidal activity against dicot Arabidopsis thaliana at a concentration of 10 µg/mL, and one compound gave instinct fungicidal activity against Pythium sp. at a concentration of 2 µg/mL.     

Heterogeneous Aromatic Amination of Aryl Halides with Arylamines in Water with PS‐PEG Resin‐Supported Palladium Complexes

Catalytic aromatic amination is achieved in water under heterogeneous conditions by the use of immobilized palladium complexes coordinated with the amphiphilic polystyrene‐poly(ethylene glycol) resin‐supported di(tert‐butyl)phosphine ligand. Aromatic amination of aryl halides with diphenylamine and N,N‐double arylation of anilines with bromobenzene were found to proceed in water with broad substrate tolerance to give the triarylamines in high yield with high recyclability of the polymeric catalyst beads. Very little palladium leached from the polymeric catalyst under the water‐based reaction conditions to provide a green and clean (metal‐uncontaminated) protocol for the preparation of triarylamines, including the optoelectronically active N,N,N′,N′‐tetraaryl‐1,1′‐biphenyl‐4,4′‐diamines (TPDs).     

Radical-anions in the vicarious C-amination reactions of N-substituted nitrotriazoles

The vicarious nucleophilic substitution of hydrogen in symmetrical and vicinal nitrotriazoles by 1,1,1-trimethylhydrazinium iodide in t-BuOK/DMSO was studied by ESR. In the ESR monitoring of the reactions the primary radical-anions of 4-nitro-2-phenyl-1,2,3-triazole and 1-methyl-3-nitro-1,2,4-triazole were detected and characterized. It was shown by NMR that the amination of 4-nitro-2-phenyl-1,2,3-triazole takes place exclusively in the triazole ring with the formation of 5-amino-4-nitro-2-phenyl-1,2,3-triazole. 1-Methyl-3-nitro-1,2,4-triazole, like 3-nitro-1,2,4-triazole, does not form amination products. A possible mechanism for the vicarious C-amination of nitrotriazoles and the formation of the radical-anions of the substrates is discussed. Dedicated to Academician M. G. Voronkov on his 85th birthday. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1662–1670, November, 2006.     

A transition metal-free approach to a regioselective total synthesis of the natural product derivative 6-methylellipticine,a potent anticancer agent

A transition metal-free and regioselective total synthesis of 6-methylellipticine, a potent anticancer agent, was developed. This synthetic approach mainly involved two key reactions: a direct amination of multi-functional phenol via an alkylation-Smiles rearrangement protocol, and an intramolecular C–H bond arylation reaction promoted by potassium tert-butoxide. These reactions resulted in the formation of two key intermediates, diarylamine and carbazole derivative, under transition metal-free conditions. The last cyclization afforded the target product 6-methylellipticine.     

Ligand-Enabled Auxiliary-Free meta-C−H Arylation of Phenylacetic Acids

The meta-C−H arylation of free phenylacetic acid was realized using 2-carbomethoxynorbornene (NBE-CO₂Me) as a transient mediator. Both the modified norbornene and the mono-protected 3-amino-2-hydroxypyridine type ligand are crucial for this auxiliary-free meta-C−H arylation reaction. A series of phenylacetic acids, including mandelic acid and phenylglycine, react smoothly with various aryl iodides to provide the meta-arylated products in high yields.     

Triazoles XXXVI. The arylation of 5-amino-3-methylthio-1H-1,2,4-triazole with activated aryl chlorides

The possibility of the arylation of 5-amino-3-methylthio-1H-1,2,4-triazole ( 1 ) with different chlorobenzenes activated by a nitro group was studied. The ratio of products obtained was determined by hplc using isolated products as standards. It was stated that from among the monoarylated products 8 , 9 and 10 obtained the main product is 8 . However, from the reaction mixtures diarylated derivatives 11 and 12 and different by products such as 15, 16, 22, 24, 25, 27, 28, 32, 36 , and 38 were also isolated.     

BippyPhos: A Single Ligand With Unprecedented Scope in the Buchwald–Hartwig Amination of (Hetero)aryl Chlorides

Over the past two decades, considerable attention has been given to the development of new ligands for the palladium‐catalyzed arylation of amines and related NH‐containing substrates (i.e., Buchwald–Hartwig amination). The generation of structurally diverse ligands, by research groups in both academia and industry, has facilitated the accommodation of sterically and electronically divergent substrates including ammonia, hydrazine, amines, amides, and NH heterocycles. Despite these achievements, problems with catalyst generality persist and access to multiple ligands is necessary to accommodate all of these NH‐containing substrates. In our quest to address this significant limitation we identified the BippyPhos/[Pd(cinnamyl)Cl]₂ catalyst system as being capable of catalyzing the amination of a variety of functionalized (hetero)aryl chlorides, as well as bromides and tosylates, at moderate to low catalyst loadings. The successful transformations described herein include primary and secondary amines, NH heterocycles, amides, ammonia and hydrazine, thus demonstrating the largest scope in the NH‐containing coupling partner reported for a single Pd/ligand catalyst system. We also established BippyPhos/[Pd(cinnamyl)Cl]₂ as exhibiting the broadest demonstrated substrate scope for metal‐catalyzed cross‐coupling of (hetero)aryl chlorides with NH indoles. Furthermore, the remarkable ability of BippyPhos/[Pd(cinnamyl)Cl]₂ to catalyze both the selective monoarylation of ammonia and the N‐arylation of indoles was exploited in the development of a new one‐pot, two‐step synthesis of N‐aryl heterocycles from ammonia, ortho‐alkynylhalo(hetero)arenes and (hetero) aryl halides through tandem N‐arylation/hydroamination reactions. Although the scope in the NH‐containing coupling partner is broad, BippyPhos/[Pd(cinnamyl)Cl]₂ also displays a marked selectivity profile that was exploited in the chemoselective monoarylation of substrates featuring two chemically distinct NH‐containing moieties.     

Synthesis of hybrid molecules containing fragments of sesquiterpene lactones and plant alkaloids

The Pd-catalyzed arylation of isoalantolactone by deoxyvasicinone and lappaconitine halides occurred with formation mainly of cross-coupling products with the (E)-configuration of the double bond. Another three compounds were isolated from the reaction of isoalantolactone with 6-bromodeoxyvasicinone. These were the lactone diarylation product, a compound with the (Z)-configuration of the double bond, and a product with a shift of the C(11,13) double bond and configuration inversion at C(8). The new compounds are interesting as potential biologically active agents.     

Ligand‐Enabled Auxiliary‐Free meta‐C−H Arylation of Phenylacetic Acids

The meta ‐C−H arylation of free phenylacetic acid was realized using 2‐carbomethoxynorbornene (NBE‐CO₂Me) as a transient mediator. Both the modified norbornene and the mono‐protected 3‐amino‐2‐hydroxypyridine type ligand are crucial for this auxiliary‐free meta ‐C−H arylation reaction. A series of phenylacetic acids, including mandelic acid and phenylglycine, react smoothly with various aryl iodides to provide the meta ‐arylated products in high yields.     

聚氯乙烯三乙撑四胺负载钯配合物的制备及对Heck反应的催化性能

以聚氯乙烯为原料, 通过胺化反应制得聚氯乙烯三乙撑四胺, 然后用较简单方法得到聚氯乙烯三乙撑四胺负载钯配合物(PVC-TETA-Pd), 利用XPS, TG, DTA和TEM等手段对其进行了表征. 热分析表明PVC-TETA-Pd在室温至250 ℃范围内有很好的热稳定性; TEM分析证实钯在PVC-TETA-Pd中分布比较均匀, 钯颗粒呈球形, 粒径在2～3 nm. PVC-TETA-Pd不需在惰性气体氛围中就能有效地催化丙烯酸、苯乙烯与芳基碘的Heck芳基化反应, 并且在较低的温度(40 ℃)或较少的催化剂用量(0.02%)下, 对Heck反应仍有较好的催化性能. PVC-TETA-Pd便于回收, 且有很好的重复使用性能, 对于碘苯与丙烯酸的反应, 重复使用十二次, 肉桂酸的产率仍达到80.1%.     

Highly regioselective synthesis of chiral diamines via a Buchwald–Hartwig amination from camphoric acid and their application in the Henry reaction

In this work the synthesis of new asymmetric diamine ligands from camphoric acid is described. The new diamines can be directly prepared in a regioselective arylation of the less hindered primary amine group of (+)‐cis‐1,2,2‐trimethylcyclopentane‐1,3‐diamine via a Buchwald–Hartwig amination in high yields. The resulting diamines incorporate a secondary and primary amine group and were successfully applied as ligands in a copper‐catalyzed Henry reaction. Copyright © 2014 John Wiley & Sons, Ltd.