Butadiene allenes

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]. 

Methane Propane w-Hexane w-Octane Ethylene Propene trawx-2-Butene Isobutylene 1,3-Butadiene Allene Acetylene Methyl-acetylene Dimethyl-acetylene... 

Compounds (c) are called allenes an example is 3, named 1,2-butadiene. Allene 3 is an example of a cumulative 7i-system. Benzene (Chapter 5, Section 5.10 Chapter 21) is a conjugated system, but the conjugated 7i-bonds in a six-membered ring lead to the aromatic stability of benzene (see Chapter 21, Section 21.1). For consistency with the chemistry presented throughout the book, this chapter will ignore allenes and focus attention on conjugated dienes. 

Example [49] Preparation of muscone from butadiene, allene and CO. 

Oxidative cleavage of the complex 549 with CuCri affords 2,3-bis(chloro-methyl)-1,3-butadiene (550) and regenerates PdCri. Thus the preparation of this interesting dimerization product 550 can be carried out with a catalytic amount of PdCl2 and two equivalents of CuCb in MeCN[495], Similarly, treatment of allene with PdBr2 affords the dimeric complex 551. Treatment of this complex with 2 equiv, of bromine yields the dibromide 552. The tetra-bromide 553 is obtained by the reaction of an excess of bromine[496]. Similarly,... 

Aryl or alkenyl halides attack the central carbon of the allene system in the 2,3-butadien-l-ol 120 to form the 7r-allyl intermediate 121, which undergoes elimination reaction to afford the o,/3-unsaturated ketone 122 or aldehyde. The reaction proceeds smoothly in DMSO using dppe as a ligandflOl]. 

Chloro 1 3 butadiene (chloroprene) is the monomer from which the elastomer neoprene IS prepared 2 Chloro 1 3 butadiene is the thermodynamically controlled product formed by addi tion of hydrogen chloride to vinylacetylene (H2C=CHC=CH) The principal product under conditions of kinetic control is the allenic chlonde 4 chloro 1 2 butadiene Suggest a mechanism to account for the formation of each product... 

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,... 

The polymerization filling was effected by the ion-coordination mechanism [17-19]. The monomers were ethylene, propylene, allene, os-butylene, butadiene. The fillers were mineral materials such as ash, graphite, silica gel, glass fibers. The ultimate aim of filler conditioning prior to polymerization is to secure, on its surface, metal complex or organometallic catalysts by either physical or chemical methods [17-19],... 

Allene lassen sich mit Trimethyl-zinnhydrid zu Vinyl- und Allyl-zinn-Derivaten um-setzen, die mit Trifluoressigsaure die entsprechenden Olefine ergeben7 z.B. Buten-(2) ausgehend von Butadien-(1,2) ... 

Allene decomposes at pressures starting at 29 bar. Butadiene decomposes explosively at a higher pressure. 

Reaction of the nitrone 4-184 with allenic esters 4-185 as described by Ishar and coworkers led to the benzo[b]indolizines 4-186, together with small quantities of 4-187 (<5%) (Scheme 4.40) [63]. The first transformation is a 1,3-dipolar cycloaddition this is followed by four further steps, including a [4+2] cycloaddition of an intermediate 1-aza-l,3-butadiene. 

Instead of alkynes, allenes can also be used as substrates in this type of approach. Finally, one can also apply carbon-nucleophiles such as butadienes in this domino process. Thus, Lu and Xie [145] have treated the alkyne 6/1-303 with an aryl halide 6/1-304 and an amine 6/1-305 to give the substituted pyrrolidinone 6/1-308 via the proposed intermediates 6/1-306 and 6/1-307. As a side product, 6/1-309 is found to have been formed by a cycloaddition of 6/1-303 (Scheme 6/1.81). 

A carbon-iron bond is also formed by the reaction of the cyclopropenium salt 185 with dicarbonyl(i/5-cyclopentadienyl)(trimethylsilyl)iron [92], (Scheme 69) In the reaction with benzocyclobutenylidene- 5-cyclopentadienyliron(II) hexafluorophosphate 186, CpFe(CO)2R (R=cyelo-C3H5, CH2-cyclo-C3H5) is converted to the allene and butadiene complexes, 187 and 188, respectively [93]. (Scheme 70)... 

Atkinson, R., Pitts, J.N., Jr. (1977b) Absolute rate constants for the reaction of oxygen (3P) atoms with allene, 1,3-butadiene and vinyl methyl ether over temperature range 297 -39 K. J. Phys. Chem. 67, 2492-2495. 

Cooligomerization of butadiene with some olefinic compounds has been carried out. Two moles of allene reacted at 120°C with butadiene by the catalysis of Pd(PPh3)2 (maleic anhydride) to give cis- and trans-2-methyl-3-methylene-l,5,7-octatriene (119) in 39% yield (104) ... 

A study of the reactions of butadiene, isoprene, or allene coordinated to nickel in a metallacycle, with carbonylic compounds, has been reported by Baker (example 11, Table IV). In the presence of phosphines, these metallacycles adopt a cr-allyl structure on one end and a ir-allyl structure on the other, as mentioned in Section II,A,1. The former is mainly attacked by aldehydes or electrophilic reagents in general, the latter by nucleophiles (C—H acids, see Table I, or amines, see Table IX). 

Let us start with 1,2-butadiene. A particularly simple analysis is the comparison of allene and 1,2-butadiene using the formal methylation reaction 10... 

Takemura and Shida54 prepared the allene radical ion by /-radiolysis of halocarbon solid solution of allene at low temperatures and showed that the radical cation has a lower D2 structure than the precursor with a skew angle of 30-40°. Kubonzo and coworkers55 56 produced by /-radiolysis in a low-temperature halocarbon matrix several derivatives of the allene radical cation, i.e. the radical cations of 1,2-butadiene, 3-methyl-1,2-butadiene,... 

A single example of allene formation was reported for a reaction of 2-iodo-3-phe-nyl-1,3-butadiene (98) with MeMgBr (Scheme 3.48). The reaction, however, proceeded with poor selectivity and the terminal allene 99 was obtained in 36% yield together with 36% of a conjugated diene 100 [92]. 

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