1-alkoxy-1-alkene formate ester

Modeling the Formate Ester Formation. Formate esters up to 4% of the total products are side products mainly in the unmodified cobalt-catalyzed alkene hydroformylation. Their formation has been explained in analogy to the Heck and Breslow mechanism of olefin hydroformylation (203). By the addition of HCo(CO)4 to the aldehyde carbonyl group, either an a-hydroxyaUgrl- or an alkoxy-cobalt carbonyl is formed. The latter complex converts with carbon monoxide into an (alkoxycarbonyl)cobalt carbonyl. Reduction of this complex gives the formate product (Scheme 15). 

The first report of oxidative carbonylation is the reaction of alkenes with CO in benzene in the presence of PdCh to afford the /3-chloroacyl chloride 224[12,206]. The oxidative carbonylation of alkene in alcohol gives the q, f3-unsaturated ester 225 and /3-alkoxy ester 226 by monocarbonylation, and succinate 111 by dicarbonylation depending on the reaction conditions[207-209]. The scope of the reaction has been studied[210]. Succinate formation takes... 

The oxycarbonylation of propene under the same conditions results in the formation of crotonic acid as the major product instead of the more valuable methacrylic acid.439 When the oxycarbonylation of ethylene or terminal alkenes is carried out in anhydrous alcoholic solvents instead of acetic acid, dialkyl succinates and /3-alkoxy esters are the major products (equation 173).441,442... 

The /f-alkoxy ester 111 is formed by nucleophilic substitution of 114 with alkoxide. Formation of 109, the esters 111, and 112 can be regarded as the nucleophilic addition to alkenes promoted by Pd(II). 

The frontier orbital picture for a simple nitrone is shown in Fig. 6.38, where we can see that the easy reactions will be dipole-LU-controlled with X-substituted alkenes and dipole-HO-controlled with Z-substituted alkenes. In practice, phenyl, alkoxy, and methoxycarbonyl substituents speed up the cycloadditions. Any substituent on the carbon atom of the dipole introduces a steric element in favour of the formation of the 5-substituted isoxazolidines 6.238. The selectivity with monosubstituted alkenes is in favour of this regioisomer, decisively so with C- and X-substituents, but delicately balanced with Z-substituents, since the HOMO of the dipole is not strongly polarised. With methyl crotonate, both adducts have the methyl group on the 5-position and the ester group on the 4-position. 

Oxidative carbonylation of alkenes is a unique reaction of Pd(II). Three types of oxidative carbonylation to give -substituted acid derivatives 130, a, -unsaturated esters 132 and succinate derivatives 134 are known, which can be understood by the following mechanism. Palladation of alkenes with PdX2, followed by CO insertion, generates the acylpalladium intermediate 129 whose reductive elimination affords -substituted carboxylic acid derivatives 130 (path a). Reaction in alcohol in the presence of a base starts by the formation of the alkoxycarbonylpalladium 128. Carbopalladation of alkene with 128 generates 131. Then y3-H elimination of the intermediate 131 yields the a-unsaturated ester 132 (path b). Further CO insertion to 131 gives the acylpalladium intermediate 133 and its alcoholysis yields the succinate derivative 134 (path c). Formation of the jS-alkoxy ester 130 (X-OR) is regarded as nucleophilic substitution of Pd-X in 131 with alcohols. 

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