2.2- Dimethyl-4-pentenoic esters

Cleavage of 2,2-dimethyl-4-pentenoic esters. Hydroboration delivers a primary... 

The Sagami-synthesis, starting with a meta-phenoxyphenyl ester of 3,3-dimethyl-pentenoic ester (Reaction scheme 263) gives permethrin 372, without having to go through the step of free permethric acid [181]. 

Dimethyl-4-pentenoic acid, methyl ester EINECS 264-431-8 Methyl 3,3-dimethyl-4-pentenoate Methyl 3,3-dimethylpent-4-enoate 4-Pentenoic acid, 3,3-dimethyl-, methyl ester Penten-4-oic acid, 3,3-dimethyl, methyl ester,... 

The first example of a heterogeneous catalyst able to metathesize olefinic esters was recently reported (92). The combination of Re207/ (CH3)4Sn at an olefin/Re/Sn molar ratio of 219/6/1 converted methyl 4-pentenoate at 50°C in 51% conversion to ethylene and the corresponding dimethyl ester of 4-octene-l,8-dioic acid. This reaction exhibited a high degree of selectivity (>99%), and in the absence of (CH3)4Sn the rhenium catalyst was inactive (90). 

Carboxylation of dienes and trienes, which takes place in a stepwise fashion, affords mono- or dicarboxylated products.146 Cobalt carbonyl,147 palladium chloride,148 149 and palladium complexes150 were used. 1,4 Addition to 1,3-butadiene gives the corresponding unsaturated tram ester (methyl trans-3-pentenoate) in the presence of [Co(CO)4]2 and a pyridine base.147 The second carboxylation step requires higher temperature than the first one to yield dimethyl adipate. In a direct synthesis (110°C, 500 atm, then 200°C, 530 atm) 51% selectivity was achieved.147... 

Michael addition-alkylation pathway has to be considered because simple methylene active compounds such as dimethyl malonate or methylcyanoac-etate were found to be good Michael donors with /1-substituted unsaturated esters such as 5-phenyl-2-pentenoate in the reaction conditions. However, when the reaction was quenched before completion, a substantial amount of product resulting from attack onto the zr-allylPd complex was isolated, bringing an evidence for the alkylation/Michael addition pathway. 

In the second step, the concentration of pyridine as ligand must be low because it has an inhibitory effect on the hydroalkoxycarbonylation. In situ isomerization to the 4-pentenoic acid ester is a prerequisite for the subsequent carbonylation which provides dimethyl adipate. To ensure internal double-bond rearrangement, the temperature of the reaction is increased to 160-200 °C to give dimethyl adipate with 80 % selectivity. After hydrolysis of the ester, adipic acid is obtained with an overall selectivity of about 70% [1]. So far, this process has been performed on pilot-plant scale. 

Butadiene, which is bound in a n -manner to iron, reacts stoichio-metrically with carbon dioxide to form an allyl carboxylato complex in yields up to 75 % [38]. This allyl complex shows a dynamic behaviour Presumably three isomeric structures exist in solution, two of them with a n"-allyl bonding (Figure 16). Subsequent reactions of the allyl carboxylato complexes yield carboxylic acids. Acidic hydrolysis in methanol at -30°C gives methyl-3-pentenoate and methyl-4-pentenoate in a ratio of 10 1. If the iron allyl complex reacts with further carbon dioxide at 90 C, a second insertion of CO2 into the Fe-C-bond occurs after hydrolysis with hydrochloric acid in methanol the Z- and E-dimethyl esters of 3-hexenedioic acid are formed. 

Brucein A (49a), B (50) and C (51), isolated in 1967 from Brucea amarissima, were the first C-15 esters of bruceolide (48) to have their structures determined 82). These quassinoids differ in the nature of the ester group at C-15. They are esters of isovaleric, acetic and 3,4-dimethyl-4-hydroxy-2-pentenoic acid, respectively. 

This reaction sequence could be applied to the synthesis of the quassinoid analogs 15-0-P-octanoylglaucarubolone (98) and 15-0-P-3, 4 -dimethyl-2 -pentenoylglaucarubolone (99) (5). The latter, which has the bruceantin (53) ester side chain, was obtained by esterification of the hydroxylactone (95) with 3,4-dimethyl-2-pentenoic anhydride prepared by treatment of the corresponding acid with chlorosulfonyl isocyanate (35). 

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