Ethylene, aryl iodide reaction

Over 35 years ago, Richard F. Heck found that olefins can insert into the metal-carbon bond of arylpalladium species generated from organomercury compounds [1], The carbopalladation of olefins, stoichiometric at first, was made catalytic by Tsutomu Mizoroki, who coupled aryl iodides with ethylene under high pressure, in the presence of palladium chloride and sodium carbonate to neutralize the hydroiodic acid formed (Scheme 1) [2], Shortly thereafter, Heck disclosed a more general and practical procedure for this transformation, using palladium acetate as the catalyst and tri-w-butyl amine as the base [3], After investigations on stoichiometric reactions by Fitton et al. [4], it was also Heck who introduced palladium phosphine complexes as catalysts, enabling the decisive extension of the ole-fination reaction to inexpensive aryl bromides [5],... 

The copper-catalyzed reactions of aryl bromides were more effectively conducted with the hindered phenols 2,6-dimethylphenol (64) and 2-phenylphenol (65) as additive than with ethylene glycol. These reactions were conducted at 100 °C instead of 80 °C, as for the reactions of aryl iodides. Moreover, amine in large excess as solvent was required (equation 63). 

Another resin-capture approach has been pubhshed in relation to the synthesis of tetrasubstituted ethylenes via Suzuki coupling reactions (Scheme 20) [42, 53]. A 25-member hbrary was synthesized using five alkynes, five aryl halides, and a polymer-bound aryl iodide. The alkynes 55 were converted into bis(boryl)alkenes 56 in solution, and the crude intermediates were used in Suzuki reactions with an excess of aryl halide. When all of the bis(boryl)alkene 56 had been consumed, the aryl iodide resin 59 was added to the reaction mixture and the reaction continued on the solid support. Side products such as 58, arising from a double Suzuki reaction, remained in solution and could be washed away. Compounds 60 were cleaved from the polymer using trifluoroacetic acid and products 61 were obtained in > 90% purity. 

When the surfactant was sodium dodecyl sulfate, some butanol had to be present to achieve the microemulsion. A typical run used 2 mmol aryl iodide, 0.5 g surfactant, 1 mL butanol, 10 mL water, and 2 mmol base. The butanol was unnecessary with nonionic surfactants, such as the one derived from 1-dodecanol with 23 eq of ethylene oxide. The advantages of such a system include the following (a) No organic solvent is needed. The substrate is the oil phase, (b) The microemulsions form without the need for vigorous agitation, (c) No excess base is needed, in contrast with some reactions in which phase-transfer catalysis is used, (d) The surfactants can be recovered and recycled. They are inexpensive and biodegradable. 

Zhang and Wang reported the use of Pd nanopartides (5nm) stabUised by poly(ethylene glycol) (PEG) as an efficient and recyclable catalyst for the Heck reaction of aryl iodide and bromides with ethyl acrylate or styrene [31]. Leaching of Pd species in solution was evidenced by ICP-AES analyses. The authors concluded from a filtration experiment made on a cold reaction mixture that the activity was due to heterogeneous systems. However, the method used allows the dissolved Pd species to redeposit on the support. That is, more probably, the activity observed with these catalysts was due to (temporarily) leached Pd spedes. 

Recently, Beletskaya and coworkers reported the use of Pd colloids stabilised by block-copolymer micelles formed by polystyrene-co-poly(ethylene oxide) and cetyl-pyridinium chloride as surfactant [37]. The material exhibited moderate to high activities and high recyclability for the Heck reaction between aryl iodides and acrylates. 

In 2002, Venkataraman published the synthesis of bisaryl- and arylalkyl-thioethers catalyzed by the Cul/neocuproine system [74]. At the same time, using excess ethylene glycol as a ligand, Cul-catalyzed coupUng of aryl iodides with thiols was found to take place at 80 °C [75]. Soon after, N,N-dimethylglycine (L2) (Table 9.15, entry 1) [76] and L-proline (LI) (entry 2) [77] were revealed to be effective for the same transformation. Recently, CuBr/ 3-keto ester (L19) was reported to be able to promote this cross-coupling reaction to afford the corresponding diaryl thioethers at 60-75 °C (entry 3) [27]. 

Reaction of ethylene with aryl iodide can be carried out under pressure. The vinylpyridone was prepared in 80% yield from the 3-iodopyridone 112 under pressure (7 atm) [67]. 

Method E is based on the tetrakis(dimethylamino)ethylene (TDAE) as a soluble and very mild organic reductant with Pd(PhCN)2Cl2 as the catalyst in the coupling reactions of aryl iodides and bromides [18]. Excellent yields of biaryls were obtained under mild reaction conditions, at 50 C in DMF as the solvent. The latter method is the most efficient homogeneous palladium-based catalytic system for the coupling of aryl iodides and bromides to biaryls. 

After the first works on the copper-catalyzed aiylation of alkyl amines in the presence of ethylene glycol (2 equiv.) L15 [134] or diethylsalicylamide (5-20 mol%) L16 [135] as ligands, Buchwald reported in 2006 a room-temperature procedure for this type of reaction (Scheme 4). The condensation of primary or secondary alkyl amines [136, 137], and amino alcohols (selective N- versus O-arylation) with aryl iodides was performed at 25°C, thanks to the help of cheap 1,3-diket(Mie ligands L17 associated with Cul (5%). Harsher cmiditions (90°C) had to be applied from aryl bromides (Scheme 4). 

Tributylstannyl)-3-cyclobutene-1,2-diones and 4-methyl-3-(tributylstan-nyl)-3-cyclobutene-l,2-dione 2-ethylene acetals undergo the palladium/copper-catalyzed cross coupling with acyl halides, and palladium-catalyzed carbon-ylative cross coupling with aryl/heteroaryl iodides [45]. The coupling reaction of alkenyl (phenyl )iodonium triflates is also performed by a palladium/copper catalyst [46],... 

Lipshutz and colleagues presented recently palladium-catalyzed direct coupling reactions of alkyl iodides and vinyl bromides or iodides catalyzed by 1 mol% Pd(amphos)Cl2 in the presence of zinc and TMEDA in a biphasic aqueous/poly-(ethylene glycol tocopheryl sebacate) reaction medium [198], Internal olefins were obtained in 51-95% yield. For aryl-substituted (Aj-vinyl bromides, retention of double bond geometry was observed, while different degrees of isomerization occurred for (Z)-isomers, which may indicate the intervention of a radical addition process in the course of the coupling process. Alkyl-substituted (Z)-vinyl halides were transformed in contrast with retention of alkene geometry. Aryl halides also reacted [199],... 

---