Trienes 1,3,5-hexa

Azabicyclo[2.2.0]hexa-1,3,5-triene reactions, 7, 360 2-Azabicyclo[2.2.0]hex-5-ene reactivity, 7, 342 synthesis, 2, 371 2-Azabi cyclop. 1.0]hexene synthesis, 2, 371 2-Azabi cyclop. 1.0]hex-2-ene synthesis, 7, 67 2-Azabicyclo[k 1.0]hex-3-ene synthesis, 4, 258 6-Azabicyclo[k 1.0]hex-2-ene synthesis, 2, 305 Azabi cyclohexenes formation from azirines, 7, 58... 

The Woodward-Hoffmann rules for pericyclic reactions require an analysis of all reactant and product molecular orbitals, but Kenichi Fukui at Kyoto Imperial University in Japan introduced a simplified version. According to Fukui, we need to consider only two molecular orbitals, called the frontier orbitals. These frontier orbitals are the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). In ground-state 1,3,5-hexa-triene, for example, 1//3 is the HOMO and excited-stale 1,3,5-hexatriene, however, 5 is the LUMO. 

FIGURE 5. Representative graphs Q for an independent electron model based on Unear combinations of two-centre ir-orbitals nIL. Examples 1,3-butadiene 2, f3 )-hexa-1,3,5-triene 161, heptafulvene and... 

To demonstrate the quality of this simple approach we show in Figures 6 and 7 the PE spectra of 1,3-butadiene 2, (3 )-hexa-l,3,5-triene 161, (3E, 5 )-ocla-1,3,5,7-tetraene 234, [3]radialene 173, 3,4-dimethylidenecyclobutene 174 and fulvene 175. The observed positions I j1 of the tt-bands are collected in the third column of Table 2, and the eigenvalues xj obtained from standard HMO models in the fourth. A least-squares calculation yields the linear regression... 

The equilibration of a hexa-1,3,5 triene with a cyclohexa-1,3 diene differs in some respects from the electrocyclic processes discussed above. 

Hexa-1,3,5 triene gives on irradiation benzene, hydrogen and hexa 1,2,4-triene. The process is conrotatory in both the directions. 

The other possible linear vinylallene vinylog, 1,2,4,6-heptatetraene (22), has been prepared by the DMS route from the mono dibromocarbene adduct to 1,3,5-hexa-triene, 210 [78], practically simultaneously with the methyl derivative 211 [79] and several higher alkylated derivatives of 22, 214 (Scheme 5.31) [80],... 

Unlike the well-known chemistry of the vinylcyclopropane-cyclopentene rearrangement, there is no general method for the rearrangement of alkynyl-cyclopropane to cyclopentene derivatives. One specific example is the pyrolysis of l-ethynyl-2-methylcyclopropane to methylenecyclopentene and other compounds [5]. At 530°C, l-ethynyl-2-methylcyclopropane (1) undergoes a [1,5]-hydrogen shift to give hexa-l,2,5-triene (2), which further isomerizes to methy-lenecyclopentenes 3 and 4 in 38 and 29% yield, respectively (Scheme 1). 

Fig. 5 a and b. Schematic representation of a highest occupied MO, b lowest unoccupied MO in hexa-triene... 

Orbital mapping analysis of thermal isomerization of aza- and diaza-bicyclo[2.2.0]hexa-dienes has been carried out (80MI51205). Molecular orbital calculations (MNDO) of a series of bisdehydropyridines showed that the 2-azabicyclo[2.2.0]hexa-l,3,5-triene (125) is the least stable form having a calculated heat of formation of 728.4 kJ mol-1 (77CC539). 

Chelate complexes of the type [PdX2(diene)] (X = Cl, Br) are readily formed by the dienes hexa-1,5-diene (124), bicyclo 2,2,lJhepta-2,5-diene (1, 7) tricyclo[4,2,2,0]-deca-triene and -diene derivatives (10), cyclo-octa-1,5-diene and dicyclopentadiene, but not dipentene (43). These may be converted to complexes of the types [Pd2X2(dieneOR)2] and [PdCl(dieneOR)-(amine)] (R = alkyl) (43), and their properties indicate that they have similar structures to the platinum complexes (XXXI) and (XXXIII). 

A solution of sodium hydroxide (106 g., 2.7 moles) in 535 ml. of water is placed in a 2-1. flask equipped with a sealed mechanical stirrer and an outlet arranged for downward distillation into an ice-cooled receiver. The aqueous solution of the quaternary bromide is added dropwise to the boiling solution of sodium hydroxide during a period of 2.5-4 hours (Note 9). The hexa-triene and dimethylbenzylamine which form are distilled with the water. Distillation is continued for 10-15 minutes after the final addition of quaternary bromide solution. The clear upper layer of the distillate is separated, cooled to 5-10°, washed with three 170-ml. portions each of cold 2N hydrochloric acid and water, and dried over anhydrous sodium sulfate. The oil is then distilled,... 

Figure 14.6. (ia) Orbital correlation diagram for the photochemical electrocyclic reaction of butadienes. (b) Orbital correlation diagram for for the photochemical electrocyclic reaction of hexa-trienes. Solid lines and S, A denote correlation for conrotatory motion dashed lines and S, A denote correlation for disrotatory motion. 

Acetone, methyl ethyl ketone (2-butanone) and methyl isobutyl ketone (4-methyl-pentan-2-one) (6.8 mmol/kg bw for 3 days) increased the hepatotoxicity of carbon tetrachloride to Sprague-Dawley rats (Raymond Plaa, 1995a) this enhancement of toxicity was coincident with increased microsomal aniline hydroxylase activity (Raymond Plaa, 1995b). In addition to the effect on cytochrome P450, acetone, but not the other ketones, increased basal canalicular membrane fluidity, as measured by fluorescence polarization of 1,6-diphenyl-1,3,5 -hexatriene or 1 - [4-(trimethylammoniumphenyl)-6-phenyl] -1,3,5 -hexa-triene (Raymond Plaa, 1996). 

Triazines are generally more reactive in [2 + 4] cycloaddition in comparison with 1,2,3-tria-zines. The wide variety of dienophiles can be employed enamines, enaminones, vinyl silyl ethers, vinyl thioethers, cyclic ketene jV,O-acetals, /V-phenylmaleimide, 6-dimethylaminopentafulvene, 2-alkylidene-imidazolidines (cychc ketene aminals), cyclic vinyl ethers, arynes, benzocyclopropene, acetylenes, and alkenes like ethylene, (Z)-but-2-ene, cyclopentene, cyclooctene and bicyclo[2.2.1]hept-2-ene, hexa-1,5-diene, cycloocta-1,5-diene, diallyl ether, cyclododeca-l,5,9-triene,... 

The benzene cluster 114 can also be prepared from hexa-l,3,5-triene.83 Reaction of 2 with hexa-l,3,5-triene (a mixture of cis and trans isomers) in a sealed system in heptane at 155°C for 21 h results in the formation of the two isomers Ru6C(CO)i4 U-CH2(CH)4CH2 149 and 150 in 3 and 19% yield, respectively, together with the benzene derivative 114 in 22% yield (Scheme 25). 

Although one can envisage dehydrogenation and rearrangement of the coordinated trienes in 149 and 150 to yield 114, no such process has actually been observed to take place. Because both triene complexes are derived from the trans ligand, and not the cis isomer, it is possible that it is the ds-hexa-l,3,5-triene ligand that produces the benzene ring in cluster... 

Whereas the hexa-1,3,5-triene/cyclohexa-l,3-diene rearrangement serves as a model reaction in the hydrocarbon series, the perfluoro analog behaves differently, as presented in Section 5.3.2.1. Photolysis of perfluorohexa-l,3,5-triene (8) in the gas phase yields per-fluorobicyclo[2.2.0]hex-2-ene (10) as the major product, presumably via perfluorocyclohexa-1,3-diene (9).4 Perfluoro(3-vinylcyclobutene) is formed as the minor product. Thermolysis of hexa-tricnc 8 gives cyclohexadiene 9.4 Photolysis of 9 provides bicyclohexene 10, which reverts to 9 thermally.5... 

Dolbier and co-workers have studied the thermolysis of the fluorinated hexa-1,3,5-triene system using l,2-bis(trifluorovinyl)naphthalene and 9,10-bis(trifluorovinyl)phenanthrene as models. These compounds form a mixture of products thermally, of which cyclopentane derivatives... 

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