Cyclohexene 1,3-butadiene

Certain A-acetyl-a-amino acids may also be prepared from diolefins, including dicyclopentadiene, 4-vinyl-l-cyclohexene, 1,3-butadiene and 1,7-octadiene (Table 1). Monoamido acids are the predominant products obtained from unsym-metrical dienes, such as dicylopentadiene and 4-vinyl-l-cyclohexene diamido acids are formed from symmetrical dienes. A number of these polyamido acids have potential as chelating agents. 

Unsaturated cyclic hydrocarbons (e.g., vinyl-cyclohexene) Butadienes... 

The primary decompositions occurring by parallel first-order processes yield cyclohexene, butadiene plus ethylene, and four cyclopropyl-propenes. The cyclopropylpropenes formed initially decompose to yield various Ce dienes at rates comparable with those of the primary reactions, and this leads to a complex reaction mixture that contains at least seventeen products. 

XII. Tricyclic Systems Containing a Cyclobxttane Ring The only system of this kind which appears to have been investigated kinetically in detail is tricyclo[3,3,0,0 ]octane (Srinivasan and Levi, 1964). At temperatures in the range 327 to 366° C the isomerization is a homogeneous first-order reaction. The observed products were 4-vinyl-cyclohexene, butadiene and 1,5-cyclo-octadiene. However, from separate studies on the cyclo-octadiene, it is concluded that the tricyclo-octane first isomerizes to the cyclo-octadiene which then undergoes secondary reactions to yield the other observed products. The observed rate is then the rate of this primaiy reaction, viz. ... 

Figure 4. Conversions and selectivities of cyclohexane oxidation. Up to 70% selectivity to total olefins are observed with cyclohexene, butadiene, and ethylene as the major products. At high O2 and higher temperatures ethylene and butadiene dominate, while at lower O2 and lower temperature, cyclohexene dominates. Much more cyclohexene is obtained than benzene, and much more ethylene and butadiene are produced than propylene.

The best olefin yields were observed over Pt-coated monoliths. In the case of ethane/02 mixtures, selectivities to ethylene up to 65% at 70% ethane conversion and complete O2 conversion were reported." The oxidative dehydrogenation of propane and -butane produced total olefin select vies of about 60% (mixtures of ethylene and propylene) with high paraffin conversions." " Mixtures of ethylene, propylene and 1-butene were observed by the partial oxidation of -pentane and n-hexane ethylene, cyclohexene, butadiene and propylene were the most abundant products of the partial oxidation of cyclohexane." ... 

It is possible to prepare 1-acetoxy-4-chloro-2-alkenes from conjugated dienes with high selectivity. In the presence of stoichiometric amounts of LiOAc and LiCl, l-acetoxy-4-chloro-2-hutene (358) is obtained from butadiene[307], and cw-l-acetoxy-4-chloro-2-cyclohexene (360) is obtained from 1.3-cyclohexa-diene with 99% selectivity[308]. Neither the 1.4-dichloride nor 1.4-diacetate is formed. Good stereocontrol is also observed with acyclic diene.s[309]. The chloride and acetoxy groups have different reactivities. The Pd-catalyzed selective displacement of the chloride in 358 with diethylamine gives 359 without attacking allylic acetate, and the chloride in 360 is displaced with malonate with retention of the stereochemistry to give 361, while the uncatalyzed reaction affords the inversion product 362. 

Diels-Alder Reactions. The important dimerization between 1,3-dienes and a wide variety of dienoplules to produce cyclohexene derivatives was discovered in 1928 by Otto Diels and Kurt Alder. In 1950 they won the Nobel prize for their pioneering work. Butadiene has to be in the j -cis form in order to participate in these concerted reactions. Typical examples of reaction products from the reaction between butadiene and maleic anhydride (1), or cyclopentadiene (2), or itself (3), are <7 -1,2,3,6-tetrahydrophthaHc anhydride [27813-21 -4] 5-vinyl-2-norbomene [3048-64-4], and 4-vinyl-1-cyclohexene [100-40-3], respectively. 

Other methods for the preparation of cyclohexanecarboxaldehyde include the catalytic hydrogenation of 3-cyclohexene-1-carboxaldehyde, available from the Diels-Alder reaction of butadiene and acrolein, the reduction of cyclohexanecarbonyl chloride by lithium tri-tcrt-butoxy-aluminum hydride,the reduction of iV,A -dimethylcyclohexane-carboxamide with lithium diethoxyaluminum hydride, and the oxidation of the methane-sulfonate of cyclohexylmethanol with dimethyl sulfoxide. The hydrolysis, with simultaneous decarboxylation and rearrangement, of glycidic esters derived from cyclohexanone gives cyclohexanecarboxaldehyde. 

Cycloaddition involves the combination of two molecules in such a way that a new ring is formed. The principles of conservation of orbital symmetry also apply to concerted cycloaddition reactions and to the reverse, concerted fragmentation of one molecule into two or more smaller components (cycloreversion). The most important cycloaddition reaction from the point of view of synthesis is the Diels-Alder reaction. This reaction has been the object of extensive theoretical and mechanistic study, as well as synthetic application. The Diels-Alder reaction is the addition of an alkene to a diene to form a cyclohexene. It is called a [47t + 27c]-cycloaddition reaction because four tc electrons from the diene and the two n electrons from the alkene (which is called the dienophile) are directly involved in the bonding change. For most systems, the reactivity pattern, regioselectivity, and stereoselectivity are consistent with describing the reaction as a concerted process. In particular, the reaction is a stereospecific syn (suprafacial) addition with respect to both the alkene and the diene. This stereospecificity has been demonstrated with many substituted dienes and alkenes and also holds for the simplest possible example of the reaction, that of ethylene with butadiene ... 

How do orbital symmetry requirements relate to [4tc - - 2tc] and other cycloaddition reactions Let us constmct a correlation diagram for the addition of butadiene and ethylene to give cyclohexene. For concerted addition to occur, the diene must adopt an s-cis conformation. Because the electrons that are involved are the n electrons in both the diene and dienophile, it is expected that the reaction must occur via a face-to-face rather than edge-to-edge orientation. When this orientation of the reacting complex and transition state is adopted, it can be seen that a plane of symmetry perpendicular to the planes of the... 

An orbital correlation diagram can be constructed by examining the symmetry of the reactant and product orbitals with respect to this plane. The orbitals are classified by symmetry with respect to this plane in Fig. 11.9. For the reactants ethylene and butadiene, the classifications are the same as for the consideration of electrocyclic reactions on p. 610. An additional feature must be taken into account in the case of cyclohexene. The cyclohexene orbitals tr, t72. < i> and are called symmetry-adapted orbitals. We might be inclined to think of the a and a orbitals as localized between specific pairs of carbon... 

Fig. 11.9. Symmetry properties of ethylene, butadiene, and cyclohexene orbitals with respect to cycloaddition.

Step through the sequence of structures corresponding to the combination of c/s -1,3-butadiene and ethene to give cyclohexene (Diels-Alder reaction). 

Table 12.1 Diels-Alder reaction of butadiene and ethylene to form cyclohexene...

Reaction with Acrylonitrile (9) As in the preceding case, a mixture of 61 g (0.45 mole) of aluminum chloride in 300 ml of benzene is heated to 60°, and a solution of 26.6 g (0.5 mole) of acrylonitrile in 100 ml of benzene is added. Butadiene (0.9 mole) is bubbled into the stirred and heated solution over a period of 4 hours, and the reaction mixture is worked up as above. Distillation gives 3-cyclohexene-1-carbonitrile, bp 80-87°/20 mm, nj,° 1.4742, in about 85% yield. 

The cyclodimerization of 1,3-butadiene was carried out in [BMIM][BF4] and [BMIM][PF(3] with an in situ iron catalyst system. The catalyst was prepared by reduction of [Fe2(NO)4Cl2] with metallic zinc in the ionic liquid. At 50 °C, the reaction proceeded in [BMIM][BF4] to give full conversion of 1,3-butadiene, and 4-vinyl-cyclohexene was formed with 100 % selectivity. The observed catalytic activity corresponded to a turnover frequency of at least 1440 h (Scheme 5.2-24). 

In the Monsanto/Lummus Crest process (Figure 10-3), fresh ethylbenzene with recycled unconverted ethylbenzene are mixed with superheated steam. The steam acts as a heating medium and as a diluent. The endothermic reaction is carried out in multiple radial bed reactors filled with proprietary catalysts. Radial beds minimize pressure drops across the reactor. A simulation and optimization of styrene plant based on the Lummus Monsanto process has been done by Sundaram et al. Yields could be predicted, and with the help of an optimizer, the best operating conditions can be found. Figure 10-4 shows the effect of steam-to-EB ratio, temperature, and pressure on the equilibrium conversion of ethylbenzene. Alternative routes for producing styrene have been sought. One approach is to dimerize butadiene to 4-vinyl-1-cyclohexene, followed by catalytic dehydrogenation to styrene ... 

Perhaps the most striking difference between conjugated and nonconjugated dienes is that conjugated dienes undergo an addition reaction with alkenes to yield substituted cyclohexene products. For example, 1,3-butadiene and 3-buten-2-one give 3-cycIohexenyl methyl ketone. 

The Diels-Alder cycloaddition reaction (Section 14.4) is a pericvclic process that takes place between a diene (four tt electrons) and a dienophile (two tr electrons) to yield a cyclohexene product. Many thousands of examples of Diels-Alder reactions are known. They often take place easily at room temperature or slightly above, and they are stereospecific with respect to substituents. For example, room-temperature reaction between 1,3-butadiene and diethyl maleate (cis) yields exclusively the cis-disubstituted cyclohexene product. A similar reaction between 1,3-butadiene and diethyl fumarate (trans) yields exclusively the trans-disubstituted product. 

Deeatriene may, of course, react further to 1,5,9,13-tetradeca-tetraene, 1,5,9,13,17-octadecapentaene, etc. (18). Even the conjugated system 1,3-butadiene participates in metathesis reactions (14). An example of an intramolecular process is the reaction of 1,7-octadiene, which gives cyclohexene and ethene (13, 15) ... 

Methyl-buten-(3)-in-(l) liefert mit Dicyclohexyl-boran und Deuterolyse 3-Methyl-1 -deutero-butadien-(trans-1,3) (92% d.Th.) bzw. 1-Athinyl-cyclohexen trans-2-Deute-ro-1 -[cyclohexen-(l)-yl]-athylen (87% d.Th.)3. Die Reduktionen sind auch mit [2,3-Di-methyl-butyl-(2)]-boran durchfiihrbar. 

Highly functionalized cyclohexenes have been prepared by Diels-Alder reactions of butadienes 1 (Scheme 2.1) and chiral butadienes 2 (Scheme 2.2) with... 

A study [19] of the cycloaddition between substituted (E)-l-phenyl-1,3-butadienes 55 and substituted 1,1-dicyanoethylenes 56 leading to cis- and trans-cyclohexenes 57 and 58 (Equation 5.8) has shown that diastereoselectivity is markedly dependent on pressure. 

Butadiene with an electron donating group at the 2-position has the largest HOMO amplitude on C, (Scheme 15). A bond forms between Cj of the dienes and Cp of the dienophiles (Scheme 17b). This is in agreement with the exclusive formation of 1,4-disubstituted cyclohexene in the reaction of 2-ethoxybutadiene with methyl acrylate (Scheme 13b) [13, 14]. 

List B contains all compounds that form peroxides which become dangerous when they reach a critical concentration. The danger will often become apparent during distillation operations. For hydrocarbons, this is the case for deca- and tetrahydronaphthalene, cyclohexene, dicyclopentadiene, propyne and butadiene. S ondary alcohols such as 2-butanol also form part of this list. Finally, for ethers there are diethyl ethers, ethyl and vinyl ethers, tetrahydrofuran, 1,4-dioxan, ethylene glycol diethers and monoethers. 

---