Acrylates codimerization

As in the case of dimerizations, MCP derivatives are known to undergo metal-catalysed [2 + 2] codimerizations with other alkenes in a few cases [2]. The examples are limited to strained olefins, such as norbornadiene (572) (Scheme 79) [152] and cyclobutene (574) (Scheme 80) [153], and to alkyl acrylates (Table 46) [154] and always compete with the alternative [3 + 2] addition of TMM species. 

Some of these derivatives are useful catalysts for the codimerization of dienes with acrylic esters (82, 138, 140, 143). The reaction between cobalt vapor and butadiene is complex, and the nature of the products remains to be elucidated. However, there is a report of the synthesis of the yellow complex HCo(C4H6)2 from the condensation of a mixture of C4H and Me3CH with cobalt vapor (104, 110). 

Nickel(0)-catalyzed codimerization of methylenecyclopropanes with electron-deficient olefines are highly regiospedfic, but show a rather poor stereoselectivity. Thus the asymmetric nickel(0)-catalyzed codimerization of methylenecyclopropanes with the chiral bomane derivatives of acrylic acid leads to the optically active 3-methylenecyclopen-... 

Functionalized dienes can be obtained by C-C bond formation between 1,3-dienes and alkenes via oxidative coupling with electron-rich ruthenium catalysts but also via insertion into Ru-H and then Ru-C bonds. For example, Ru(COD)(COT) catalyzed the selective codimerization of 1,3-dienes with acrylic compounds to give 3,5-dienoic acid derivatives [18] (Eq. 13). -coordination of 1,3-diene to a hydridoruthenium leads to a 7r-allylruthenium species to selectively give, after coupling with the C=C bond and isomerization, the functionalized conjugated 1,3-dienes. 

One of the most reported pathways for C=C and C=C bonds coupling involves the oxidative coupling and the ruthenacyde intermediate formation. The first ruthenium-catalyzed Unear codimerization of disubstituted alkynes and alkenes involved acrylates or acrylamides and selectively produced 1,3-dienes [33] (Eq. 23). The proposed mechanism involves a ruthenacyclopentene via oxidative coupUng on the Ru(0) catalyst Ru(COD)(COT). The formation of 1,3-di-ene results from intracyclic /1-hydride eUmination, this process taking place only when a favored exocyclic /1-elimination is not possible. 

The nickel(0)-catalyzed codimerizations of methylenecyclopropane (26) or 2,2-dimethylmethylene-cyclopropane with the chiral derivatives of acrylic acid lead to optically active 3-methylenecyclopen-tanecarboxylic esters or amides (39 equation 16) in good yields (Table 3). When (-)-camphorsultam acrylate is used, 3-methylenecyclopentanecarboxylic amides are obtained in up to 98% de. °... 

In a large number of carbene and carbenoid addition reactions to alkenes the thermodynamically less favored syn-isomers are formed 63). The finding that in the above cyclopropanation reaction the anti-isomer is the only product strongly indicates that the intermediates are organonickel species rather than carbenes or carbenoids. Introduction of alkyl groups in the 3-position of the electron-deficient alkene hampers the codimerization and favors isomerization and/or cyclodimerization of the cyclopropenes. Thus, with methyl crotylate and 3,3-diphenylcyclopropene only 16% of the corresponding vinylcyclopropane derivative has been obtained. 2,2-Dimethyl acrylate does not react at all with 3,3-dimethylcyclopropene to afford frons-chrysanthemic add methyl ester. This is in accordance with chemical expectations 69) since in most cases the tendency of alkenes to coordinate to Ni(0) decreases in the order un-, mono-< di- < tri- < tetrasubstituted olefines. 

In the presence of naked nickel , methylenecyclopropane can be codimerized with alkyl acrylates, alkyl crotonates and alkyl maleates 175-186-187) giving Type B cycloadducts in moderate to excellent yields (Eq. 80). 

Therefore, in the presence of phosphane-free or phosphane-modified Ni(0) catalysts, alkyl acrylates and alkyl crotonates codimerize with 2-methyl- and 2,2-dimethyl-methylenecyclopropanes to give Type B cycloadducts. The reactions turn out to be regio- but not stereoselective. The methyl group(s) bonded at the three-membered ring are always found at C-2 of the resulting methylenecyclopentanes, whereas the electron withdrawing group is bonded to C-4 (Eqs. 86 and 87) 27). 

A suitable approach to the synthesis of spiro[2.3]hexanes is the [2-1-2] cycloaddition of alkenes to the double bond of methylenecyclopropanes. This reaction is often described as a codimerization and usually requires catalysis by a nickel(O) complex such as bis(cycloocta-l,5-diene)nickel. l,l-Dimethyl-2-methylenecyclopropane reacts with alkyl acrylates to give a mixture of alkyl cis- and tranj-l,l-dimethylspiro[2.3]hexane-5-carboxylates 1 (19-40%) and alkyl 3,3-dimethyl-4-methylenecyclopentanecarboxylate 2 (60-81 %). The proportion of spiro [2.3]hexane derivative was highest when rer/-butyl acrylate was used as the activated alkene. 

Codimerizations with the acyclic acrylate esters derived from glyceraldehyde have also been investigated44. Methylenecyclopropane itself reacts with the -ester to form almost exclusively the trans-substituted methylenecyclopropane with modest diastereoselectivity, [palladium(O)-mediated]. The Z-ester, however, provides predominantly the cw-substituted product with improved diastereoselectivity. These results follow the pattern of results observed with analogous additions of the TMM-Pd unit53. 

The nickel(0)-mediated codimerization of methylenecyclopropane, as well as 2,2-disubstituted derivatives with electron-deficient olefins, has proven to be an excellent system for auxiliary controlled selectivity. As described in Section 1.6.1.2.3.1, the combination of methylenecyclopropane with alkyl acrylates and Ni(cod)2 catalysis results in the clean formation of typeB cycloadducts under mild conditions. These systems allow facile chiral modification in the form of acrylate esters or amides involving nonracemic residues and employment of the chiral camphorsultam7n as the auxiliary leads to impressive diastereoselectivity 1. The stereoselectiv-... 

Finally, the influence of chiral phosphanes in the phosphane-modified nickel(0)-mediated codimerization process has been investigated with reasonable success63. The enantioselectivity of the addition of methylenecyclopropane to methyl acrylate in toluene has been shown to be dependent on the phosphane employed. Reduction of the ester functionality to the corresponding alcohol enables determination of the enantiomeric excess75. 

Metal-catalyzed [2-i-2]-codimerizations of methylenecyclopropanes with other alkenes are limited to a few cases. Again the formation of the formal [3-f2]-cyclo-adducts is competing. As cosubstrates, strained alkenes (Eqs. 71 and 72) and alkyl acrylates could be applied successfully, the latter being of more interest from a synthetic point of view. 

The following alkenes have been found to give high yields of codimerization products with methylenecyclopropane acrylates, fumarates, maleates cyclopenten-3-one 2,3-dimethoxycarbonylnorbornene, 2j3-dimethoxycarbonylnorborna-diene and some a,p-unsaturated sulfones The reactions proceed in a temperature range of 100 to 140 °C. It has been found that pumping a solution of educts into a preheated solution of the catalyst increases the yield... 

Vinyl carbanions derived from acrylic esters and their jS-phenyl derivatives react with several carbon electrophiles to give a-substituted and a,/8-disub-stituted derivatives. While /8>alkyl substituted acrylates have been shown to dimerize in the presence of potassium catalyst at 110 C. Three simple unsaturated esters undergo palladium(0)-catalysed codimerization with methylenecyc-lopropane to furnish methylenecyclopentanecarboxylic esters in reasonable yield. An efficient procedure for the oxidation of isatins to anthranilic acid esters has appeared. Methyl 2,4,6-tri-isopropylbenzoate forms a dipole-stabilized carbanion on reaction with Bu Li, which then reacts with carbon electrophiles [e.g. E = Bui, (CH3)2C0, or CH3CHO] to give a range of ester derivatives in good yield (Scheme 52). ... 

The codimerization of acrylonitrile and methyl acrylate is catalyzed by ruthenium complexes under an atmosphere of hydrogen. Besides the hydrodimerization products of each monomer, up to 50% of the head-to-head codimerization products are formed [65] (Equation 47). 

Barlow reported some examples of codimerization using the catalyst dichlorobis(benzonitrile)palladium [49]. The reaction of styrene and methyl acrylate yielded the straight-chain isomer methyl lrans-5-phenyl-4-pentenoate (Equation 48). 

The codimerization of a functional olefin with a non-functional olefin is an interesting possibility for the synthesis of longer-chain monofunctional products. One example is the rhodium or rutheniixm chloride catalyzed codimerization of methyl acrylate with ethylene yielding linear monounsat-urated acids [48]. The main product is methyl-3-pentenoate (47%), but also esters of acids containing seven and nine carbon atoms were isolated in yields of 12 and 9%, respectively (Equation 49). 

Codimerization of Methyl Acrylate and Ethylene with [Ni(CgHi3)PR3(S03CF3)] ... 

The codimerization of acrylates and butadiene with cobalt catalysts can be used to produce the 4,6-heptadienic-l-ester (Equation 57) [66, 67]. This reaction proceeds under very mild conditions, for instance at 40—60 °C. 

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