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Butadienes, substituted

Butadienes substituted with alkoxy groups in the 2-position, e.g., 2-ethoxy-1,3-butadiene,6 have been prepared from methyl vinyl ketone, but they required several conversions and a tedious spinning-band distillation to purify the product. This slight modification of the House procedure has been used to conveniently prepare 2-trimethylsilyloxy-l,3-butadiene from the readily available methyl vinyl ketone. This one-step procedure has provided large amounts of a new and reactive diene for Diels-Alder reactions, as illustrated in Table I. [Pg.167]

Conlin and coworkers photolyzed vinyltris(trimethylsilyl)silane 188 in the presence of a variety of trapping reagents such as butadiene, substituted butadienes or silanes and observed products derived from intermediate silenes 189 (formed by rearrangement) or from silylenes 190 resulting from elimination of hexamethyldisilane93. In some cases complex mixtures of products which could have been derived from intermediate silyl radicals were also observed. The reaction products formed from the silene and the silylene in the presence of butadiene, 191 and 192 respectively, are shown in Scheme 32. [Pg.1266]

Recently, the reaction of masked ortho-benzoquinone [92] with C60 was tested [93]. The [4+2] cycloaddition reaction of such electron-deficient dienes with fullerenes resulted in the formation of highly functionalized bicyclo [2.2.2] octenone-fused fullerenes. The reactants were generated in situ by the oxidation of the readily available 2-methoxy phenols with hypervalent iodine agents. For the several different masked ortho-benzoquinones that were tested, it was found that the yield of the cycloadducts depends on the nature of the starting materials and the reaction conditions. Other Diels-Alder reactions of such electron-deficient dienes with electron-poor fullerenes involved tropones [94], 1,3-butadienes substituted with electron-withdrawing groups [95], and 2-pyrone [96]. [Pg.9]

Conversion of —Si (013)3 to —OH. Searle chemists have used this transformation in a synthesis of 4-demethoxydaunomycinone (6). Thus aryl-trimethylsilanes were known to be converted into aryl trifluoroacetates by lead tetrakistrifluoroacetate (4, 282-283) the Searle chemists found that this trifluoroacetoxylation was also applicable to benzyltrimethylsilane. With this information and knowing that 1,3-butadienes substituted by trimethylsilyl groups show selectivity in Diels-Alder reactions, they then devised the route shown in the formulation. The first step involved a Diels-Alder reaction to give 3. This product... [Pg.439]

I-Oxa-12-butadienes Substituted with C-3, C-4 Electron-donating Substituents... [Pg.451]

A select group of 1,4-diaza-1,3-butadienes have been demonstrated to participate as 4ir components of Diels-Alder reactions (Table 12). Perhaps the most successful system described to date is the LUMOdiene-controlled [4 + 2] cycloaddition reaction of diiminosuccinonitrile, a 1,4-diaza-1,3-butadiene substituted with C-2 and C-3 electron-withdrawing groups, with electron-rich dienophiles (equation 15). A common and competitive reaction of the a-diimines is [2 + 2] cycloaddition to afford azetidine cycloaddition products and many of the early reports of the [4 + 2] cycloaddition reactions are incorrect. [Pg.486]

The recent development of dienes incorporating latent has greatly expanded the utility of Diels Alder approaches of complex molecules. Butadiene substituted by silicon at is available from l,4-dichloro-2-butyne by H2PtCl2catalyzed reaction with Et3SiH followed by dehydrohalogenation (Zn). The product reacts readily with dlenophiles. ... [Pg.275]

Butadienylsulphonium salts (140) undergo condensation with stabilized carbanions to give vinylcyclopropanes in good yields (37—65%) by two routes (paths a and b Scheme 16). The operation of both pathways has been established by using butadienes substituted at C-3 which result in two distinct vinylcyclopropane products. The... [Pg.35]

Butadienes substituted in the 1 position can exist as either cis or trans isomers. In all reported cases, the trans compound gives much higher yields... [Pg.105]

SUBSTITUTED BUTADIENES. The consequences of p-type orbitals rotations, become apparent when substituents are added. Many structural isomers of butadiene can be foiined (Structures VIII-XI), and the electrocylic ring-closure reaction to form cyclobutene can be phase inverting or preserving if the motion is conrotatory or disrotatory, respectively. The four cyclobutene structures XII-XV of cyclobutene may be formed by cyclization. Table I shows the different possibilities for the cyclization of the four isomers VIII-XI. These structmes are shown in Figure 35. [Pg.369]

THE cvcLOBUTADENE-TETRAHEDRANE SYSTEM. A related reaction is the photoisomerization of cyclobutadiene (CBD). It was found that unsubstituted CBD does not react in an argon matrix upon irradiation, while the tri-butyl substituted derivative forms the corresponding tetrahedrane [86,87]. These results may be understood on the basis of a conical intersection enclosed by the loop shown in Figure 37. The analogy with the butadiene loop (Fig. 13) is obvious. The two CBDs and the biradical shown in the figure are the three anchors in this system. With small substituents, the two lobes containing the lone electrons can be far... [Pg.370]

Thus, to name just a few examples, a nucleophilic aliphatic substitution such as the reaction of the bromide 3.5 with sodium iodide (Figure 3-21a) can lead to a range of stereochemical products, from a l l mbrture of 3.6 and 3.7 (racemization) to only 3.7 (inversion) depending on the groups a, b, and c that are bonded to the central carbon atom. The ring closure of the 1,3-butadiene, 3.8, to cyclobutene... [Pg.196]

Insertion of one of two double bonds of butadiene into Pd—X forms substituted a 7r-allylpalladium complex 24 (see Chapter 3, Section 4). [Pg.14]

When butadiene is treated with PdCU the l-chloromethyl-7r-allylpalladium complex 336 (X = Cl) is formed by the chloropalladation. In the presence of nucleophiles, the substituted 7r-methallylpalladium complex 336 (X = nucleophile) is formed(296-299]. In this way, the nucleophile can be introduced at the terminal carbon of conjugated diene systems. For example, a methoxy group is introduced at the terminal carbon of 3,7-dimethyl-I,3,6-octatriene to give 337 as expected, whereas myrcene (338) is converted into the tr-allyl complex 339 after the cyclization[288]. [Pg.66]

An active catalytic species in the dimerization reaction is Pd(0) complex, which forms the bis-7r-allylpalladium complex 3, The formation of 1,3,7-octa-triene (7) is understood by the elimination of/5-hydrogen from the intermediate complex 1 to give 4 and its reductive elimination. In telomer formation, a nucleophile reacts with butadiene to form the dimeric telomers in which the nucleophile is introduced mainly at the terminal position to form the 1-substituted 2,7-octadiene 5. As a minor product, the isomeric 3-substituted 1,7-octadiene 6 is formed[13,14]. The dimerization carried out in MeOD produces l-methoxy-6-deuterio-2,7-octadiene (10) as a main product 15]. This result suggests that the telomers are formed by the 1,6- and 3,6-additions of MeO and D to the intermediate complexes I and 2. [Pg.424]

Formic acid behaves differently. The expected octadienyl formate is not formed. The reaction of butadiene carried out in formic acid and triethylamine affords 1,7-octadiene (41) as the major product and 1,6-octadiene as a minor product[41-43], Formic acid is a hydride source. It is known that the Pd hydride formed from palladium formate attacks the substituted side of tt-allylpalladium to form the terminal alkene[44] (see Section 2.8). The reductive dimerization of isoprene in formic acid in the presence of Et3N using tri(i)-tolyl)phosphine at room temperature afforded a mixture of dimers in 87% yield, which contained 71% of the head-to-tail dimers 42a and 42b. The mixture was treated with concentrated HCl to give an easily separable chloro derivative 43. By this means, a- and d-citronellol (44 and 45) were pre-pared[45]. [Pg.430]

Active methylene or methine compounds, to which two EWGs such as carbonyl, alko.xycarbonyl, formyl, cyano, nitro, and sulfonyl groups are attached, react with butadiene smoothly and their acidic hydrogens are displaced with the 2,7-octadienyl group to give mono- and disubstituted compounds[59]. 3-Substituted 1,7-octadienes are obtained as minor products. The reaction is earned out with a /3-keto ester, /9-diketone, malonate, Q-formyl ketones, a-cyano and Q-nitro esters, cya noacetamide, and phenylsulfonylacetate. Di(octadienyl)malonate (61) obtained by this reaction is converted into an... [Pg.432]

Simple ketones and esters are inert. On the other hand, nitroalkanes react smoothly in r-butyl alcohol as a solvent with butadiene, and their acidic hydrogens are displaced with the octadienyl group. From nitromethane, three products, 64, 65, and 66, are formed, accompanied by 3-substituted 1,7-octadiene as a minor product. Hydrogenation of 65 affords a fatty amine 67 which has a primary amino function at the center of the long linear chain[46,61]. [Pg.433]

Like butadiene, allene undergoes dimerization and addition of nucleophiles to give 1-substituted 3-methyl-2-methylene-3-butenyl compounds. Dimerization-hydration of allene is catalyzed by Pd(0) in the presence of CO2 to give 3-methyl-2-methylene-3-buten-l-ol (1). An addition reaction with. MleOH proceeds without CO2 to give 2-methyl-4-methoxy-3-inethylene-1-butene (2)[1]. Similarly, piperidine reacts with allene to give the dimeric amine 3, and the reaction of malonate affords 4 in good yields. Pd(0) coordinated by maleic anhydride (MA) IS used as a catalyst[2]. [Pg.450]

Several Diels-Alder reactions in which acrolein participates as the dienophile are of industrial significance. These reactions involve butadiene or substituted butadienes and yield the corresponding 1,2,5,6-tetrahydroben2aldehyde derivative (THBA) examples are given in Table 9 (90). These products have found use in the epoxy and perfume/fragrance industries. [Pg.127]

A process has been disclosed in which the mixture of naphthoquinones is reacted with a diene such as butadiene. Owing to the fact that the undesked product is an unsubstituted naphthoquinone, this dieneophile readily reacts to form a Diels-Alder adduct. By appropriate control of reaction parameters, Htde reaction is observed with the substituted naphthoquinone. Differential solubiUty of the adduct and vitamin allows for a facile separation (57,58). [Pg.154]

Addition Reactions. 1,3-Butadiene reacts readily via 1,2- and 1,4-free radical or electrophilic addition reactions (31) to produce 1-butene or 2-butene substituted products, respectively. [Pg.341]

The dienoplules for reaction with butadiene can be alkenes, allenes, and alkynes. Simple alkenes like ethylene are poor dienoplules resulting in sluggish reactions. Substituted olefins, X—C=C—X, are more reactive when X and/or X are C=C, Ar, COOR, COOH, COH, COR, COCl, CN,... [Pg.343]

Between the 1920s when the initial commercial development of mbbery elastomers based on 1,3-dienes began (5—7), and 1955 when transition metal catalysts were fkst used to prepare synthetic polyisoprene, researchers in the U.S. and Europe developed emulsion polybutadiene and styrene—butadiene copolymers as substitutes for natural mbber. However, the tire properties of these polymers were inferior to natural mbber compounds. In seeking to improve the synthetic material properties, research was conducted in many laboratories worldwide, especially in the U.S. under the Rubber Reserve Program. [Pg.530]


See other pages where Butadienes, substituted is mentioned: [Pg.305]    [Pg.296]    [Pg.51]    [Pg.305]    [Pg.296]    [Pg.51]    [Pg.71]    [Pg.254]    [Pg.251]    [Pg.209]    [Pg.426]    [Pg.438]    [Pg.521]    [Pg.465]    [Pg.110]    [Pg.493]    [Pg.306]    [Pg.342]    [Pg.345]    [Pg.37]    [Pg.171]   
See also in sourсe #XX -- [ Pg.85 ]




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1,3-Butadiene with substituted 1,3-dienes

1,3-Butadienes, 4-alkyl-2-amino-4-(substituted

1.3- Butadienes substituted acyclic

Butadiene and 2-Substituted 1,3-Butadienes

Butadienes substituted, cycloadditions

Butadienes terminally substituted

Homopolymerization and Copolymerization of Substituted Butadienes (other than Isoprene)

Styrene-butadiene rubbers vinyl-substituted

Substituted 1,3-Butadienes and Non-conjugated Polyenes

Substituted and 1,4-Disubstituted 1,3-Butadienes

Substitutions electrophilic, - 1,3-butadiene

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