Isomerization dienes

Using an oxidative cleavage reaction, explain how you would distinguish between the following two isomeric dienes ... 

The synthesis of chlorotrifluorobutadiene illustrates a general method that has been used to make tetrafluorobutadiene and substituted fluorodienes.3- 9 The same procedure can be used to transform fluorocyclobutenes and chlorofluorocyclobutenes to the isomeric dienes 2-methyl-1,1,4,4-tetrafluorobutadiene, 2-chloro-l,l,4,4-tetrafluorobutadiene, and l-chloro-l,4,4-trifluoro-2-phenylbutadiene have been made thus.3... 

In contrast LP-DE gives disappointing results for intramolecular imino Diels-Alder reactions, even in the presence of CSA. This is due to the fact that weak acids become strong acids in highly polar media such as 5.0m LP-DE and the protonation of diene, with concomitant diene isomerization, competes with cycloaddition [42]. This observation was supported by using trifluoroacetic acid (TEA). The imine 33 (Scheme 6.21) in LP-DE at room temperature in the presence of TEA gave a 1 1 mixture of cycloadduct 34 and the isomerized diene 35 within the unreacted imine 33. No Diels-Alder cycloadduct 36 was detected. 

In 15-58, we used the principle of conservation of orbital symmetry to explain why certain reactions take place readily and others do not. The orbital symmetry principle can also explain why certain molecules are stable though highly strained. For example, quadricyclane and hexamethylprismane are thermodynamically much less stable (because much more strained) than their corresponding isomeric dienes, norbomadiene and hexamethylbicyclo[2.2.0]hexadiene (108). Yet the... 

Alkoxyallenes turned out to be excellent starting materials also for the synthesis of highly functionalized 1,3-dienes, two examples being depicted in Schemes 8.61 and 8.62. As described by Kantlehner et al., 1,3-dienes such as 238 were obtained from methoxyallene derivative 50 by condensation with CH-acidic compounds 237 [135]. Hoppe and co-workers explored the stereochemical course of the allene Claisen rearrangement under Johnson s conditions, e.g. the reaction of 239 with trimethyl orthoacetate, which furnished intermediate 240 followed by rearrangement to the isomeric dienes 241a,b [136],... 

Only a trace of the corresponding cubane 167 is formed on irradiation of the tricy-clooctadiene 168 in pentane at ambient temperatures using a 125-watt mercury arc lamp. The principal product 169 is the result of rearrangement within a biradical intermediate79. A review of the synthetic approaches to cubane and to its reactions has been published77. The diene 170 photochemically converts on irradiation in pentane solution at 254 nm to yield a photostationary mixture of the cubane 171, the starting material 170 and the isomeric diene 17280. Other additions of this type have been used for synthesis of the propellaprismane 173, essentially a heavily substituted cubane, by the intramolecular (2 + 2)-photocycloaddition of the diene 17481. 

The fluoride ion, especially that of cesium fluoride, has been used effectively for the transformation of perfluorodienes into acetylenes or more stable isomeric dienes.4-5... 

An efficient synthesis of hexafluorobut-2-yne25,26 combined the knowledge that hexafluorocy-clobutene thermally rearranges to hexafluorobuta-1,3-diene (vide supra) and that cesium or potassium fluoride isomerize dienes to alkynes (see Section 5.1.2.3.). Thus, when hexafluoro-cyclobutene is passed over cesium or potassium fluoride at 590-600 C, hexafluorobut-2-yne is obtained in yields up to 90%, with 95% recovery of material. 

Christie and Breckenridge (42) describe the application of this column to the isolation and determination of FAs containing trans double bonds in samples of natural and industrial origin. A column (250 X 4.6-mm ID) of NUCLEOSIL 5SA was flushed with 1% ammonium nitrate solution at a flow rate of 0.5 ml/min for 1 h, then with distilled water at 1 ml/min for 1 h. Silver nitrate (0.2 g) in water (1 ml) was injected onto column via the Rheodyne valve in 50-yu.l aliquots at 1-min intervals silver began to elute from the column after about 10 min, and 20 min after the last injection the column was washed with methanol for 1 h, then with 1,2-dichloroethane-dichloromethane (1 1 v/v) for 1 h. For most of the analytical work, the column temperature was maintained at 30°C in a thermostatted oven. 1,2-Dichloroethane-dichloromethane (1 1) (mixture A) at a flow rate of 1.5 ml/min was the mobile phase (detector operated at 242 nm) for the separation of isomeric monoenes, and the same solvents with the addition of 0.5% acetonitrile (mixture B) at a flow rate of 0.75 ml/min were employed for isomeric dienes and trienes. 

The separation achieved with the isomeric dienes derived from oleic acid is shown in Fig. 14. Three peaks are apparent, the last of which is the natural 9-cis,12-cis isomer the first must be 9-trans,12-trans octadecadienoate, and the second peak is presumably a mixture of the 9-cis,12-trans and 9-trans,12-cis compounds. With the geometric isomers of linolenic acid six... 

It is interesting and of preparative value that although 1-bromo-2-methyl-l-propene and similar halides add to 1-hexene at both double-bond carbons, only one of the two 7r-allylic intermediates reacts with the amine. The result is that a mixture of six isomeric dienes is formed, but only one allylic amine is produced. Therefore the reaction is useful since the dienes and the amine are separated easily (2). 

Siegel carried out detailed studies with di-fert-butyl-substituted cyclohexadienes with the aim of clarifying their role as intermediates in the hydrogenation of di-tert-butylbenzenes on a 5% Rh-alumina catalyst291. The three isomeric dienes (34, 35, 36)... 

Opening of each cyclobutene ring can occur by either of two conrotatory routes to yield the isomeric dienes. Using B as an example ... 

Knox et al. (31) have also reported that cyclic 1,3-dienes react in a Diels-Alder fashion with the acetylene adduct, 4 (eq. 26). The Mo-Mo distance in 10 is 2.504(1)A, commensurate with a MosMo triple bond as required by the 18-electron rule. Acyclic dienes do not give 10, but with hexa-2,4-diene, 4 yields ethyne and the hexyne complex from the isomerized diene (eq. 27). 

Fry, in a search for an intermediate capable of undergoing stereospecific cyclization to 11/3-alkylbenzomorphans, studied the 2,3-cis and trans isomers of 2-benzyl-l,3,4-trimethyl-l,2,3,6-tetrahydropyridine (Scheme 4.11). These were prepared from the iminium dienes (80 and 81) isolated as crystalline perchlorates from benzyl Grignard attack on 1,3,4-trimethylpyridinium bromide. The isomeric dienes were differentiated through their cyano derivatives (82 and 83), which on borohydride reduction gave the isomeric tetrahy-dropyridines, 84 and 85. Elimination of HCN from 82 gave the iminium diene (86) isomeric with 81. Addition of nitrile to 81 followed by borohydride reduction resulted in the appropriate trans tetrahydropyridine (88) that cyclized to the 11/3-methylbenzomorphan (89). 

The mechanism follows initial fluorine ion attack on the silicon atom yielding an ion which transfers the trifluoroviiiyl anion to the alkene, leading to formation of fluorotrimethylsilane and a carbanion. Stabilization of this species by fluoride ion elimination may give a mixture of isomeric dienes which isomerize in the presence of cesium fluoride under the reaction conditions to the end product 3. ... 

It has also been reported that treatment of (233) with potassium acetate at 140 °C for 40 h gives the strained tricyclic diene (234) whereas treatment with potassium t-butoxide gives the isomeric diene (235)/ ... 

A 1,4-cyclohexadienic structure (46) was proposed for the octahydroparacyclophane formed in the hydrogenation (Pt02) of paracyclophane (47), whose unusual properties provided a degree of plausibility to the claim (equation 38).Actually, four isomeric dienes, none of which has the first postulated structure, are formed. The possible structures have one trisubstituted double bond in each six-carbon cycle, as in formula (48). Dienes are more reactive than the related arenes or cyclohexenes and apparently are more tightly bound to a catalytic site. - ... 

Reaction of isomeric dienes 120 with acetaldehyde in the presence of zinc chloride gave a mixture of C-4 epimeric enones 121, 122 (O Scheme 42) [224], which are convenient substrates for synthesis of all four racemic 3-amino-2,3,6-trideoxy pyranoses. 

Isomeric diene diester [64] has been studied by Bloomfield and Owsley (137). They obtained a crossed addition in the n=2 and straight addition in the n=3 derivatives. 

---