2.3- Butadienoates

Carbonylation of propargylic carbonates proceeds under mild neutral conditions (50 °C, I-10 atm) using Pd(OAc)2 and Ph ,P as a catalyst, yielding the 2,3-alkadienoates 18 in good yields[9,10]. The 2.3-alkadienoates isomerize to 2,4-dienoates during the reaction depending on the solvents and reaction time. 2-Decynyl methyl carbonate is converted into methyl 2-heptyl-2,3-butadienoate (19) in 82% yield. 

In the presence of triphenylphosphine as a catalyst, benzotriazole adds readily to activated allenes. Its reaction with ethyl 2,3-butadienoate produces a mixture of adducts 149 (54%) and 150 (20%). Both derivatives form exclusively as (Tyi-isomers <2006T3710>. In a reaction of benzotriazole with dibenzoylacetylene and... 

In 1952, Wotiz and co-workers reported the reaction of ethylmagnesium bromide with 2-butyl-2,3-butadienoic acid affording 3-alkenoic acid 474 via a 1,4-addition process [216, 217]. 

The 1,4-conjugate addition of dialkyl cuprate to 4-methoxycarbonyl-2,3-butadieno-ate 476 or 4-thioethyl-2,3-butadienoate 478 leads to the 3-( )-alkenoates 477 and 479 with high diastereoselectivity [218, 219]. 

Sodium salt of diethyl acetamidomalonate 480 reacts with ethyl 2,3-butadienoate in the presence of a catalytic amount of EtONa to afford /fy-unsaturated enoate 481, which can be easily decarboxylated leading to /3-methyleneglutamic acid hydrochloride 482 [220],... 

Dipolar cydoaddition of ethyl 2-(ethoxycarbonyl)-4,4-diphenyl-2,3-butadieno-ate 518 with CH2N2 or Ph2CN2 afforded bicyclic or monocyclic products 519 and 520, respectively. The possibility of extra cydopropanation depends on the steric effect of the diazo compound [234]. 

In 1954, Eglinton et al. [235] reported the reaction of ethyl 2,3-butadienoate with NaOEt in EtOH. It was observed that the product is ethyl 2-ethoxy-2-butenoate, showing that the C=C bond migrated from the /3,/-position to the a,/3-position under the basic conditions [235],... 

Methyl 2,3-butadienoate can undergo 1,3-dipolar cycloaddition with nitrones leading to the formation of 528, which would undergo homolytic cleavage of the N-O bond followed by radical rearrangement and coupling to afford benzazepinone 531 [239]. 

In 1985, Cristiau et al. reported that the reaction of methyl 2,3-butadienoate with PPh3 followed by the addition of Nal afforded phosphonium iodide 532, which makes the y-carbon prone to nucleophilic attack, leading to the formation of 4-meth-oxy-2-enonate 533 [197a]. 

In 1995, Lu et al. developed the PPh3-catalyzed reaction of 2,3-butadienoate with dimethyl malonate [240]. A similar catalytic reaction was also observed with PhOH and benzyl alcohol leading to the y-addition product 534 [241]. 

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]. 

A flask containing 5.0 gm (0.06 mole) of 3-butynoic acid and 200 ml of an 18 % aqueous potassium carbonate solution is heated at 40°C for 3 hr. After acidification the product is extracted with ether, dried, and concentrated to afford 4.6 gm (92 %) of 2,3-butadienoic acid, m.p. 65°-66°C (recrystallized from petroleum ether). 

Bromophenylazo)-2/-toluene, 309 (2-BromophenyI)-iVM7-azoxy (2-hydroxy-5-methylbenzene), 358 p-Bromophenylurea, 138-139 Bromopropadiene, 17 2,3-Butadienoic add, 16 iV-l-Butenylpiperazine, 92 Butter yellow, hazard of, 291 f-Butylamine, oxidation of, 323 -Butyl azide, 269 f-Butyl-OlW-azoxymethane, 349 t-Butyl p-Bromophenylazoformate, 328 t-Butyl 2-(p-bromophenyl)carbazate, 328 H-Butyl carbamate, 238-239 t-Butyl carbamate, 241-243... 

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... 

A study of the range of substrates revealed regioselectivity was usually high, in the range 94 6 to 100 0. This [3+2]-cydoaddition developed by the Zhang group is a powerful method for asymmetric synthesis of optically active cyclopentene products. A reaction mechanism has also been proposed. The initial step is formation of an adduct between the phosphine catalyst and the 2,3-butadienoate, followed by cydoaddition with the acrylate component as a key step. 

Phosphine-Catalyzed Reactions. This ligand has also been shown to be effective in the direct organocatalysis of asymmetric processes. For example, the phosphine-catalyzed [3 -1- 2] annula-tion reaction of ethyl 2,3-butadienoate and isobutyl acrylate produces two cyclopentene regioisomers (1 and 2) (eq 2). Isomer 1 generally predominates and enantiomeric excesses ranging from... 

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-... 

Occasionally, molecular mechanics calculations provide a rationale when FMO theory fails to account for a given regiochemical outcome.For example, cycloaddition of C-phenyl-Af-methyl nitrone to methyl 2-methyl-2,3-butadienoate leads exclusively to the S-exo-methylene cycloadduct, as one would expect based upon FMO theory. In contrast, C7-phenyl- -r-butyl nitrone affords only the 4-exomethylene isoxazolidine, a result which clearly cannot be in accord with the same principles (Scheme 12). Molecular mechanics calculations, carried out under the assumption that the relative energy differences between the products parallel the energy differences between transition states, were in accord with the experimental results, suggesting that the difference in behavim- between the two nitrones may have a steric rather than an electronic origin (Table 10). ... 

Dicarbonylation occurs mainly by the carbonylation of propargylic halides and alcohols carried out under a high pressure of carbon monoxide. The carbonylation of propargyl bromide (51) at 20 atm affords 2,3-butadienoate (52) as described in Section 11.3.2.2. On the other hand, carbonylation of propargyl chloride (77) in methanol at room temperature under high pressure (100 atm) catalyzed by PdClj or Pd/charcoal afforded dimethyl itaconate (79). The primary product seems to be 2,3-butadienoate (78), which is carbonylated further (Scheme 11-23) [10,11]. As supporting evidence, formation of diethyl itaconate (81) in 64% yield by the carbonylation of ethyl 2,3-butadienoate (80) at room temperature under high pressure was confiimed. 

Formation of these products can be understood by assuming that the carbonylation of propargyl alcohol under high pressure involves two different reaction pathways. One is the Pd(0)-catalyzed carbonylation and the other is the Pd(II)-catalyzed oxidative carbonylation 2,3-Butadienoate (80) is a primary product of the Pd(0)-catalyzed carbonylation, but further attack by carbon monoxide at the central sp carbon of 80 under high carbon monoxide pressure yields itaconate (81) as the dicarbonylation product. Formation of aconitate (83) is explained by the oxidative dicarbonylation of a triple bond with Pd(II) species, followed by Pd(0)-catalyzed allylic carbonylation. As a supporting evidence, methyl aconitate (83) was... 

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. ... 

Methyl-o-benzoquinone, 76, 251 N-Methylbenzylamine, 406,485 Methyl-N-benzylcarbamate, 343 B-Methyl-9-borabicydononane, 310 Methyl 2,3-butadienoate, 306-307... 

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