Buta-l,2-diene

Diels-Alder reaction is the 1,4-addition of an alkene or alkyne (dienophile) across a conjugated diene. An example is the addition of pro-penal to buta-l,3-diene to give A -tetrahy-... 

Figure 6.44 Torsional vibrations in (a) toluene, (b) phenol, (c) ethylene, (d) methyl alcohol, (e) s-lraws-buta-l,3-diene and (1) s-cis-buta-l,3-diene...

The methiodide of 2,5-dihydrothiophene (239) is transformed in high yield to Z)-l-(methylthio)buta-l,3-diene (240) on treatment with alkali (81AJC1017). The thermal cheletropic extrusion of sulfur dioxide from both cis and trans isomers of 2,5-dihy-drothiophene 1,1-dioxides is highly stereospecific. For example, c/5-2,5-dimethyl-2,5-dihydrothiophene 1,1-dioxide (241) yields ( , )-hexa-2,4-diene (242) and sulfur dioxide (75JA3666, 75JA3673). 

Recently, the research groups of Enders (Eq. 8.38)61 and Barluenga (Eq. 8.39)62 reported on the cycloaddition of chiral 2-aminobutadiene and described elegant solutions to the stereochemistry problems (regio-, diastereo-, and enantioselectivity). The reaction of 2-[(5)-2-methoxymethyl]pyrrolidin-l-yl]buta-l,3-diene with various 2-aryl-1-nitroethenes produces after hydrolysis 5-aryl-2-methyl-substituted 4-nitrocyclohexanones in excellent enantiomeric purity (ee = 75-95%) and with high diastereoselectivity (ds = 75-95%).61... 

The scope and efficiency of [4+2] cycloaddition reactions used for the synthesis of pyridines continue to improve. Recently, the collection of dienes participating in aza-Diels Alder reactions has expanded to include 3-phosphinyl-l-aza-l,3-butadienes, 3-azatrienes, and l,3-bis(trimethylsiloxy)buta-l, 3-dienes (1,3-bis silyl enol ethers), which form phosphorylated, vinyl-substituted, and 2-(arylsulfonyl)-4-hydroxypyridines, respectively <06T1095 06T7661 06S2551>. In addition, efforts to improve the synthetic efficiency have been notable, as illustrated with the use of microwave technology. As shown below, a synthesis of highly functionalized pyridine 14 from 3-siloxy-l-aza-1,3-butadiene 15 (conveniently prepared from p-keto oxime 16) and electron-deficient acetylenes utilizes microwave irradiation to reduce reaction times and improve yields <06T5454>. 

The reactions of 4-nitrobenzodifuroxan 242 with a series of common dienes, such as cyclopentadiene, cyclohexa-diene, isoprene, 2,3-dimethylbutadiene, and 1-acetoxybutadiene, with ethoxymethyleneacetylacetone were found to proceed very readily to afford stable cycloadducts, which are the result of highly stereoselective normal electron-demand (NED) Diels-Alder reactions. Due to the additional activation provided by the two adjacent furoxan rings, the nitroalkene double bond of compound 242 is also prone to undergo NED reactions with less reactive dienic structures, such as the enol form of ethoxymethyleneacetylacetone and the in situ generated 2-ethoxy-4-(2-furfur-yl)buta-l,3-diene <2004TL1037, 2005T8167>. 

The reaction of a-mercaptocarbonyl compounds [e.g. (148)] with buta-l,3-dien-l-yltriphenylphosphonium salts unexpectedly leads to 3-vinylthiophens,138 whereas reaction with vinylphosphonium salts results in the formation of c/ -2,5-dialkyl-2,5-dihydrothiophens (149).139... 

Ab initio calculations on aza-Diels-Alder reactions of electron-deficient imines with buta-l,3-diene show that these reactions are HOMO (diene)-LUMO(dienophile)-controlled and that electron-deficient imines should be more reactive than alkyl-or aryl-imines. The Diels-Alder reaction of r-butyl 2//-azirine-3-carboxylate (80) proceeds with high diastereoselectivity with electron-rich dienes (81) (Scheme 28). The hetero-Diels-Alder additions of imines with sterically demanding dienes yield perhydroquinolines bearing an angular methyl group. The asymmetric hetero-Diels-Alder reaction between alkenyloxazolines and isocyanates produces diastereometri-cally pure oxazolo[3,2-c]pyrimidines. °... 

Note Locants are placed immediately before that part of the name to which they relate, e.g. ethane-l,2 2,l-tetrayl (not l,2 2,l-ethanetetrayl) or buta-l,3-diene-l,4 3,2-tetrayl (not 1,3 -butadiene-1,4 3,2-tetrayl) [7]. 

A diblock copolymer consisting of a block derived from the 1,4 and 1,2 polymerization of buta-l,3-diene and a block of polystyrene ... 

E5 poly(styrene-stot-buta-l,3-diene)-Z)/oc -polystyrene-Z)/oc -l,2-polybutadiene... 

E6 deca(buta-l,3-diene)-Z)/ocA -(methylsilanetriyl-grq// -polystyrene)-Z)/ocA -pentadeca(buta-1,3 -diene)... 

Generie source-based name polyaIkylene buta-l,3-diene Source-based name poly(buta-1,3-diene)... 

J. Jnrczalc, A. Gotfbiowski, and J. Raczko, Influence of the N-protecting group on the stereochemical course of [4+2]cycloaddition of l-ethoxy-3-[(trimethylsilyl)oxy] buta-l,3-diene to... 

The Lewis acid-catalyzed reaction of the endoperoxide of 1-methoxycarbonylpyrrole with enol ethers presents an interesting route to 2-alkylpyrroles (Scheme 30) (79TL3477, 80H(14)102>. In the case of the reaction with l-(trimethylsilyloxy)buta-l,3-diene, the reaction provides a viable route to indole, which, with only slight modification, can also be employed in the synthesis of 4-substituted indoles <8lH(l6)959>. The endoperoxide reacts with 1-methylpyrrole to produce the l,l -disubstituted 2,2 -bipyrrole in low yield. 

Thermal cyclization of l-(l-methyl-2-pyrrolyl)buta-l,3-diene yields l-methyl-4,5-dihy-droindole (77TL151) and several examples of the cyclization of substituted vinyl derivatives have been reported, e.g. (395) -> (396) <74JCS(Pl)153l), (397) -> (398) <80JCR(S)233>, whilst the 2-(2-indolyl)propenoic ester (399) cyclizes under Vilsmeier-Haack conditions to produce (400) (80T2125). 

The chalcogene heterocycles have been used as stable precursors for sulfur-and selenium-containing hetero-l,3-dienes in cycloaddition reactions 3//-1,2,4-Thiaselenazoles are a convenient source of 4,4-bis(trifluoromethyl)-l-thia-3-aza-buta-l,3-dienes, and 3H-diselenazoles are a convenient source of 4,4-bis(trifluoromethyl)-l-selena-3-azabuta-l,3-dienes as well as bis(tnfluoro-methyl)-subsbtuted mtnle ylides [137]... 

The Me3Si group in ( )-l,3-bis(trimethylsilyloxy)buta-l,3-diene (177) provides the necessary steric requirement to react with 10-amino-9-hydroxy-l,4-anthraquinone derivatives 176 in a regio- and stereospecific manner (equation 74)230. Thus a single anthracyclinone derivative (178) is obtained in an excellent yield through the Diels-Alder process. 

Molander and Siedem have reported the reaction of l-methoxy-l,3-bis(trimethylsilylo-xy)-buta-l,3-diene, the bis(trimethylsilyl) enol ether of methyl acetoacetate, with 1,4- and 1,5-dicarbonyl species under the influence of trimethylsilyl triflate. Two regioisomeric oxabicyclo[3.2.1]octane products are formed (Scheme 83)194. Use of 4- or 5-ketoacyl silanes as the dicarbonyl species can result in a reversal of the sense of regioselectivity. 

P. Celani, F. Bernardi, M. Olivucci, and M. A. Robb,/. Cbem. Pbys., 102, 5733 (1995). Excited-State Reaction Pathways for s-eis-Buta-l,3-diene. 

I )ithijzolc[4.5-r/]thiazinc. Y-oxidc 150 is formed in low yield by the reaction of trithiazyl trichloride ((NSC1)3>, which is in thermal equilibration with its monomer (N=S-C1), with l,4-diphenyl-l,3-buta-l,3-diene followed by oxidation with air (Scheme 28) <1998CC1207>. The structure of product 150 was confirmed by X-ray crystallography. The mechanism of this transformation involves an initial 1,4-cycloaddition process. 

Figure 4.4 Inversion centre, i, in (a). v-/ram-buta-l, 3-diene and (b) sulphur hexafluoride...

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