2.3- Butadienoic esters

Butadienoate esters undergo AICI3 and EtAlCh catalyzed stereospecific [2 + 2] cycloadditions with a wide variety of alkenes to give alkyl cyclobutylideneacetates in good yield. The stereospecificity and ratios of ( )- and (Z)-isomers suggest a [ 2 + v2a] cycloaddition of the ester-Lewis acid complex to the alkene analogous to the cycloaddition of ketenes with alkenes. Similar results are obtained with methyl 2,3-pentadienoate, methyl 4-methyl-2,3-pentadienoate and methyl 2-methyl-2,3-butadi-... 

Cycloaddition. Zwitterionic adducts from PhiP and allenyl ketones or 2,3-butadienoic esters are dipolarophiles toward tropone. 

I,S-Additions. The umpolung mode of addition to 2,3-butadienoic esters is made possible in the presence of Ph P. Zwitterionic intermediates formed by conjugate addition of the phosphine are poised to perform proton abstraction from the true nucleophiles, and the subsequent combination of the ensuing ion pairs follows a course favored by the formation of ylides. 

Since 3-methylenecyclobutane-l,2-dicarboxylic anhydride is easily converted to 3-methyl-2-cydobutene-l,2-dicarboxylic acid, it is an intermediate to a variety of cyclobutenes. The dimethyl ester of 3-methylenecyclobutane-l,2-dicarboxylic acid is also a versatile compound on pyrolysis it gives the substituted allene, methyl butadienoate, and on treatment with amines it gives a cyclobutene, dimethyl 3-methyl-2-cyclobutene-l,2-di-carboxylate. ... 

METHYL BUTADIENOATE (Butadienoic acid, methyl ester)... 

The method used is described by Drysdale, Stevenson, and Sharkey.4 The methyl ester of butadienoic acid has not been described previously, but the free acid contaminated by 2-bu-tynoic acid has been prepared by Wotiz, Matthews, and Lieb 5 by carbonation of propargylmagncsium bromide. Ethyl butadienoate has been prepared by Eglinton, Jones, Mansfield, and Whiting by alkali-catalyzed isomerization of ethyl 3-butynoate prepared from 3-butynol by chromic acid oxidation and esterification. 

Hydride-promoted reactions are also well known, such as the acrylic and vinylacrylic syntheses (examples 7-10, Table VII). Some less-known compounds, which form in the presence of halide ions added to tetracar-bonylnickel, have been described by Foa and Cassar (example 11, Table VII). Reaction of allene to form methacrylates, and of propargyl chloride to give itaconic acid (via butadienoic acid), have been reported (examples 13 and 14, Table VII). 1,5-Hexadiene has been shown to be a very good substrate to obtain cyclic ketones in the presence of hydrogen chloride and tetracarbonylnickel (example 15, Table VII). The latter has also been used to form esters from olefins (example 16, Table VII). In the presence of an organic acid branched esters form regioselectivity (193). 

Cydoaddition reactions of electron-deficient allenes are also known. In the presence of A1C13, ethyl 2,3-butadienoate (32) reacts with alkenes to give cyclobutyl-ideneacetic esters at room temperature [28]. 

A fundamentally different approach to the synthesis of 3-pyrrolines is evidenced in the annulation in Eq. 13.50 [58]. Ethyl 2,3-butadienoate 150 reacts with N-sulfony-limine 151 in the presence of triphenylphosphine under very mild conditions to give JV-protected 3-pyrroline 152 in 90% yield. The mechanism that has been postulated is related to that of the Baylis-Hillman reaction. Michael addition of triphenylphosphine to the allenyl ester generates a zwitterion that combines with the imine to give 153 in a non-concerted process. This is followed by ring closure, proton exchange and expulsion of triphenylphosphine to give 152. This annulation is successful only for aromatic or cinnamyl imines [59]. 

Cycloaddition. In the presence of either C2H5AICI21 or AICI3,2 esters of 2,3-butadienoic acid (1) undergo [2 + 2] cycloadditions at the 3,4-double bond with acyclic or cyclic alkenes to give cyclobutylideneacetic esters. The reaction is considered to involve the vinyl cation H2C— CH - C(OR)OAlCl,. A mixture of... 

Butadiene, 1,4-diphenyl-, 40, 36 Butadienoic acid, methyl ester, 43, 71... 

Reaction of ethyl 2,5-butadienoate with aldehydes.1 This ester (1) reacts with propionaldehyde in ether at 23° in the presence of DABCO to provide 2 in 42% yield, formed by replacement of the a-proton of 1. This condensation can also be effected with butyllithium, but then 2 is accompanied by 3, formed via a dianion of 1. 

Nitrone cycloaddition reactions promoted by dichlorotitanium TADDOLate can be improved by using A(-(2-alkenyl)succinimides as the dipolarophiles. Regioselective and enantioselective formation of cyclopentenecarboxylic esters is observed using 8 to catalyze the [3+2]cycloaddition of 2,3-butadienoates with electron-deficient alkenes. ... 

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