Arylation of methyl acrylate

Equation 11.8 Arylation of methyl acrylate under phase-transfer conditions. (TBAB = tetrabutyl ammonium bromide)... 

Brown and coworkers [22] have studied the Pd-catalyzed Heck arylation of methyl acrylate via P and NMR (see Figure 1.7). Reaction of the aryl iodide complex 23 with AgOTf (THF, 195 K) gives the THF and aquo-complexes 24 and 25, respectively, which were detected via P NMR below 203 K. Addition of HjO to the sample shifts the equilibrium towards 25, pointing to an existing fast exchange between solvates 24 and 25. Reaction of 24/25 with 3- C labeled methyl acrylate (20-fold excess, 213 K) affords the insertion product 26. Warming to 233 K leads to the formation of 27, which is in turn converted into 29, stable to... 

Recently, arylation of methyl acrylate was intensively studied [15-21], Phenylation with Ph3BiX2 was largely affected by X, as shown in Scheme 6. PdCl2 as well as Pd2(dba)3 (dba = dibenzylideneacetone) are efficient catalysts, whereas the addition of phosphine ligands retards the phenylation e.g., PdCl PPh3 afforded no... 

H° =NeTf2N Me N "Bu Pd(OAc)2 Et3N 100 °C. Phosphine-free arylation of methyl acrylate with aryliodides presence of catalytic amounts of various halide ions were found to accelerate the reaction excellent recycling of the catalyst demonstrated product extracted with cyclohexane. [21] [79]... 

In recent years there have been a number of reports on the use of nonpalladium catalysts in the Heck-type reaction. An example of a Cu-catalyzed arylation of methyl acrylate is presented in entry 49. ... 

Brown, J.M. and Hii, K.K. (1996) Characterization of reactive intermediates in palladium-catalyzed arylation of methyl acrylate (Heck reaction). Angew. Chem., Int. Ed. Engl., 35, 657-9. 

Accordingly, catalytic and stoichiometric amounts of cuprous salts were employed for Mizoroki-Heck-type reactions of various conjugated alkenes [ 19]. Intermolecular catalytic arylations of methyl acrylate (1, not shown) and styrene (2) were accomplished under ligand-free conditions using CuBr (3) or Cul (4) as catalyst in A-methyl-2-pyrrolidinone (NMP) as solvent various aryl iodides could be employed (Scheme 10.2). On the contrary, aryl bromides and chlorides, as well as aliphatic halides, were found to be unsuitable substrates. The reactions employing an alkenyl bromide, methylmethacrolein or methyl methacrylate required stoichiometric amounts of copper salts. 

Scheme 10.17 Homogeneous platinum-catalysed arylation of methyl acrylate (1).

An organometallic reaction which shows a close similarity to the Mizoroki-Heck reaction is the cobalt-catalysed [46] reaction between alkenes and organic halides. The use of [CoCKPPhsls] (59) as catalyst for intermolecular arylations of methyl acrylate (1) and styrene (2) was reported by Iyer [47] (Scheme 10.20). The para-substituted aryl iodides could be employed with this homogeneous catalyst, but the more sterically hindered ortho-substituted iodoarenes failed to undergo the desired substitution reaction. Aryl bromides and chlorides, as well as alkyl-substituted halides, proved unreactive under these reaction conditions. 

When the carbopalladation of the bicyclopropylidene is performed in the presence of methyl acrylate, the reaction takes a different course (Scheme 8.34) [79]. The 1,3-diene intermediate 75 reacts in situ with the dienophile to give the spiro[2.5]octane derivative 76. An extension of this cascade Heck-Diels-Alder reaction involving l,3-dicyclopropyl-l,2-propadiene as the alkene partner, an alkenyl or aryl halide and a dienophile has been reported [80]. 

Waterlot, C., D. Couturier, and B. Rigo. 2000. Montmorillonite-palladium-copper catalyzed cross-coupling of methyl acrylate with aryl amines. Tetrahedron Lett. 41 317-319. 

Head-to-tail dimerisation of methyl acrylate to the dimethyl ester of 2-methylenepentane-dioic acid (126) occurred in 82-85% yield in the presence of catalytic amounts of P(RNCH2CH2)3N with R = PP, Bu or Bz but the less sterically hindered proazaphosphatrane with R = Me, gave oligomer or pol-ymer. The proazaphosphatrane, P(RNCH2CH2)3N with R = Bu also acts as an effective ligand for the palladium-catalyzed direct arylation of ethyl cyano-acetate (127) with aryl bromides (e.g. 128) to form (129) in high yield. ... 

As reported above, a literature survey shows that the hydroformylation of this class of alkene has been scarcely investigated. Indeed, these studies have been devoted exclusively to the hydroformylation of arylic esters such as methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethoxyethyl acrylate, and 2-ethylhexyl acrylate (Eq. 4) [18-21], Most attention has been focused on the hydroformylation of methyl acrylate to 2-formylpropanoate ester since the latter is used extensively for the synthesis of pharmaceuticals and may also be considered as a potential source of methyl methacrylate [18]. 

In contrast with the first class of functionalized alkenes, immobilization of the catalyst in aqueous phase results in an enhancement of the catalytic activity [19]. Indeed, it has been observed that the hydroformylation rates of arylic esters having high solubility in water were much higher in biphasic systems than those observed under comparable homogeneous conditions. Except for 2-ethylhexyl acrylate, the initial rate was increased by a factor of 2.4, 12, 2.8, and 14 for methyl, ethyl, butyl, and 2-ethoxyethyl acrylate, respectively (see Figure 1) [20]. One of the most intriguing features is that the hydroformylation rates for ethyl and butyl acrylates in biphasic medium were respectively higher than and comparable with those observed with methyl acrylate. Actually, the water-solubilities of ethyl and butyl acrylates (18.3 and 2.0 g L-1 at 20 °C, respectively) are lower than that of methyl acrylate (59.3 g L-1 at 20°C). 

Only a select group of 1,4-diaza-1,3-butadienes has been shown to function as 4w components of [4 + 2] cycloadditions. Dehydroindigo affords Diels-Alder products on reaction with styrene, vinyl aryls, acrylonitrile, methyl acrylate, and methyl propiolate under forcing conditions [Eq. 

The synthesis of those 2-bromomethyl-2-aryl-acrylic acids (84) that are not accessible by the above routes due to failure of the MBH reaction can be accomplished by methoxide-induced addition of methyl acrylate to aromatic and heteroaromatic aldehydes (Scheme 3.24). Thus, it may serve as an alternate method in cases where the MBH reaction is slow or fails altogether. 

A heterogeneous arylation of ethyl acrylates and styrene (2) was successfully catalysed by CU/AI2O3 (15). This catalytic system proved applicable to aryl iodides with both electron-withdrawing and -donating substituents [24]. Subsequently, a silica-supported poly-y-aminopropylsilane Cu(II) complex was used for Mizoroki-Heck-type reactions of three aryl iodides with methyl acrylate (1), acrylic acid (16) and styrene (2) [23, 25]. 

The use of pyridine (31) as additive allowed for more selective and efficient nickel-catalysed arylations of styrenes (Scheme 10.10) [32, 33]. Aryl and alkyl bromides gave good yields of isolated products. With respect to the latter, secondary alkyl bromides proved superior to primary ones. However, use of methyl acrylate (1) as substrate yielded predominantly products originating from conjugate additions, rather than Mizoroki-Heck-type reactions. 

In a comparative study, Wilkinson s catalyst (84) was employed in intermolecular ary-lation reactions of methyl acrylate (1) and styrene (2). Rhodium catalyst 84 was reported to be more efficient than a cobalt precursor. Note, however, that the reproducibility of these results was recently questioned [58]. Simple aryl iodides were efficiently converted at 110°C (Scheme 10.30), but crr/zo-substituted aryl iodides required a higher reaction temperature of 150 °C. Aryl bromides and chlorides, as well as aliphatic halides, could not be converted using rhodium catalyst 84 [47]. 

As part of comparative studies, Iyer [47] reported the use of Vaska s complex [IrCl(CO)(PPh3)2l (92) in intermolecular Mizoroki-Heck-type reactions of methyl acrylate (1) and styrene (2). Aryl iodides could be used as electrophiles, while bromobenzene, chlorobenzene and aliphatic halides gave no desired product. The catalytic activity was found to be lower than that observed when using Wilkinson s complex [RhCl(PPh3)3] (84). Thus, a higher reaction temperature of 150 °C was mostly required. In contrast to the corresponding cobalt-catalysed reaction, however, Vaska s complex (92) proved applicable to orf/io-substituted aryl iodides (Scheme 10.33). 

An alternative method for the classical Knoevenagel-type preparation of cinnamic acids has been reported this came to light during a study of the bromine-induced decarboxylation of substituted cinnamic acids. Cinnamic acid derivatives can also be prepared by the palladium-catalysed coupling of methyl acrylate with electron-rich aryl iodidessimilarly 5-arylpenta-2,4-dienoic acids (29) can be synthesized from penta-2,4-dienoic acid and bromo-aryls. A Stobbe-type condensation between aromatic aldehydes and methyl propylidenemalonate leads to the , -unsaturated acids (30), probably via a 5-lactone intermediate. ... 

Pd(II), and Pt(II) (Scheme 7.9) [18]. The pincer palladium complex 21 was air-stable and able to efficiently catalyze the Heck reaction of methyl acrylate with aryl haHdes. The catalyst could be recovered by fluorous soHd-phase extraction and reused for four times without significant loss of catalytic activity. 

Kochi (1956a, 1956b) and Dickerman et al. (1958, 1959) studied the kinetics of the Meerwein reaction of arenediazonium salts with acrylonitrile, styrene, and other alkenes, based on initial studies on the Sandmeyer reaction. The reactions were found to be first-order in diazonium ion and in cuprous ion. The relative rates of the addition to four alkenes (acrylonitrile, styrene, methyl acrylate, and methyl methacrylate) vary by a factor of only 1.55 (Dickerman et al., 1959). This result indicates that the aryl radical has a low selectivity. The kinetic data are consistent with the mechanism of Schemes 10-52 to 10-56, 10-58 and 10-59. This mechanism was strongly corroborated by Galli s work on the Sandmeyer reaction more than twenty years later (1981-89). 

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