Cyclo-hexadiene

Alkenes in (alkene)dicarbonyl(T -cyclopentadienyl)iron(l+) cations react with carbon nucleophiles to form new C —C bonds (M. Rosenblum, 1974 A.J. Pearson, 1987). Tricarbon-yi(ri -cycIohexadienyI)iron(l-h) cations, prepared from the T] -l,3-cyclohexadiene complexes by hydride abstraction with tritylium cations, react similarly to give 5-substituted 1,3-cyclo-hexadienes, and neutral tricarbonyl(n -l,3-cyciohexadiene)iron complexes can be coupled with olefins by hydrogen transfer at > 140°C. These reactions proceed regio- and stereospecifically in the successive cyanide addition and spirocyclization at an optically pure N-allyl-N-phenyl-1,3-cyclohexadiene-l-carboxamide iron complex (A.J. Pearson, 1989). 

The reaction of the exo-methylenefuranone 216 with cyclopentadiene and cyclo-hexadiene was conducted in dichloromethane as a solvent at temperatures ranging from 60 to 160°C (90T4371). The tricyclic stereoisomeric adducts 218a,b and 219a,b, respectively, were obtained (Scheme 60) (90T4371). It was found that the ratios of the isomers a/b are temperature-dependent the proportion of b is increasing moderate at higher reaction temperatures. 

Figure 15.2 A comparison of the heats of hydrogenation for cyclohexene, 1,3-cyclo-hexadiene, and benzene. Benzene is 150 kJ/mol (36 keal/mol) more stable than might be expected for "cyclohexatriene."...

The most striking feature of electrocyclic reactions is their stereochemistry. For example, (2 ,4Z,6 )-2,4,6-octatriene yields only c/s-5,6-dimethyl-l,3-cyclo-hexadiene when heated, and (2 ,4Z,6Z)-2,4,6-octatriene yields only trnns-5,6-dimethyl-l,3-cyclohexadiene. Remarkably, however, the stereochemical results change completely when the reactions are carried out under what are called photochemical, rather than thermal, conditions. Irradiation, or photolysis,... 

Cathode material Electroactive substance Reaction potential — E (V) Electrical yield (%) benzene (molar yield) (%) aniline (molar yield) (%) 1,4-cyclo-hexadiene (molar yield ) (%)... 

Benzoquinone, 2,5-dwm-butyl- [2,5-Cyclo-hexadiene-1,4-dione, 2,5-bis(l,l-di-methylethyl)-], 55, 32, 34... 

A one-pot procedure [9] based on the cycloaddition of 4-aryl-2-silyloxybuta-dienes 7 and bisdiene 8 with alkynes, followed by oxidative aromatization of the cycloadducts, opened a route to polycyclic phenols without isolating the cyclo-hexadiene derivative intermediates (Scheme 2.5). 

Fast Green FCF (FD C Green No. 3, Cl Food Green 3) is a triarylmethane dye related to Brilliant Blue, the disodinm 3-[N-ethyl-N-[4-[[4-[N-ethyl-N-(3-snl-fonatobenzyl)amino] -phenyl] (4-hydroxy-2-snlfonatophenyl)methylene] -2,5-cyclo-hexadien-l-ylidene]ammonio-methyl]-benzenesnlfonate. Fast green is a red to brown-violet powder or crystals, solnble in water, sparingly solnble in ethanol, with a maximnm absorption in water at 625 nm. It is not permitted as food colorant in the EU. -"... 

Patent Blue V (E 131, Cl Food Blue 5, Patent Blue 5) is a triarylmethane dye, the calcium or sodium salt of 2-[(4-diethylaminophenyl)(4-diethylimino-2,5-cyclo-hexadien-l-ylidene)methyl]-4-hydroxy-l,5-benzenedisulfonate. It is a dark-blue powder, soluble in water, slightly soluble in ethanol. The absorption maximum is 638 nm in water, pH 5, with = 2000. Patent blue is not permitted for use as... 

Reiner AM, GD Hegeman (1971) Metabolism of benzoic acid by bacteria. Accumulation of (-)-3,5-cyclo-hexadiene-l,2-diol-l-carboxylic acid by a mutant strain of Alcaligenes eutrophus. Biochemistry 10 2530-2536. 

Figure 7.22 (a) 50A x 50A STM image showing the structure formed by 1,4-cyclo-hexadiene on Pt(l 1 1) at 1 x 10 5Torr and 300 K. Lines in the [1 1 0]-type directions of the underlying platinum lattice are drawn. The surface species form hexagonal units in domains containing a few unit cells and in... 

The coordinated ligand is called rj6-boratabenzene by Chemical Abstracts however, as ligands in sandwich-type complexes should be named as neutral entities according to the IUPAC rules, Tj6-bora-3,5-cyclo-hexadien-2-yl would be the correct name. For the sake of simplicity we prefer boratabenzene in the following. 

Nitrile oxides are oxidized by tertiary amine N-oxides, for example, N-methylmorpholine N-oxide, in various solvents at room temperature to unstable nitrosocarbonyl compounds. In the presence of dienes, such as 1,3-cyclo-hexadiene, they afford Diels-Alder adducts, e.g., 372 fromPhCNO, in fair yields. The mild conditions used in oxidizing a variety of nitrile oxides promise a wide application of this method in synthetic processes (420). 

Chemical catalysts for transfer hydrogenation have been known for many decades [2e]. The most commonly used are heterogeneous catalysts such as Pd/C, or Raney Ni, which are able to mediate for example the reduction of alkenes by dehydrogenation of an alkane present in high concentration. Cyclohexene, cyclo-hexadiene and dihydronaphthalene are commonly used as hydrogen donors since the byproducts are aromatic and therefore more difficult to reduce. The heterogeneous reaction is useful for simple non-chiral reductions, but attempts at the enantioselective reaction have failed because the mechanism seems to occur via a radical (two-proton and two-electron) mechanism that makes it unsuitable for enantioselective reactions [2 c]. 

Generating 6 from 6,6-dibromobicydo[3.1.0]hexane (35) with methyllithium in the presence of styrene, Moore and Moser [55] observed the first [2 + 2]-cycloaddi-tions of 6. Bottini et al. extended the variety of compounds able to trap 6 to 1,3-cyclo-hexadiene [54, 60], furan, 2-methyl furan, 1,3-cyclopentadiene and methyl-substituted 1,3-butadienes [54], In all these reactions, the dimer 38 of 6 is a byproduct or, as in the case of the less reactive trapping agents, even the main product. Hence it is advisable to use a reaction partner of 6, if it is a liquid, as the solvent. 

Scheme 6.19 Relative rate constants (Icrei) forthe reactions of 1,2-cyclo-hexadiene (6), generated from 35, with conjugated dienes and styrene.

Scheme 6.21 Steric course of the [4 + 2]-cycloaddition of 1,2-cyclo-hexadiene (6) to (Z,Z)-1,4-dideutero-l, 3-butadiene.

Scheme 6.39 Generation ofl62 by -elimination from 1 -bromo-1,4-cyclo-hexadiene (174), trapping of162 by furan and 2,5-dimethyl-furan and deprotonation of162 by KOtBu.

Scheme 6.82 Treatment of 6,6-dibromo-3-thiabicyclo[3.1.0]hexane (398) with methyllithium, trapping ofthe resulting l-thia-3,4-cyclo-hexadiene (399) by styrene, 1,3-butadiene and furan and the structure ofthe dimer404 of 399.

The student is recommended to carry out the Diels and Alder diene synthesis when making preparations from the original literature. For example, he should condense cyclo-hexadiene with quinone (Annalen. 1933, 507, 288) or furane with maleic anhydride (Ber., 1929, 62, 554). 

The hydrogenation of simple alkenes, such as hexene, cyclohexene, cyclo-hexadiene and benzene, has been extensively studied using biphasic, alternative solvent protocols. These hydrocarbon substrates are more difficult to hydrogenate compared to substrates with electron withdrawing groups. Benzene and alkyl substituted aromatic compounds are considerably more difficult to hydrogenate... 

Malachit Green N-[4-[[4-(Dimethylamino)phenyl]phenyl-methylene]-2,5-cyclo-hexadien -l-ylident]-N-methyl-methanaminium chloride... 

The photochemistry of vitamin D and its various isomers has been reviewed comprehensively many times129,171,172,207,226, but as it lies at the very heart of hexatriene/cyclo-hexadiene photochemistry, it seems fitting to provide a very brief overview of the salient features here. 

Stepwise Cg dehydrocyclization (aromatization) involving the gradual loss of hydrogen atoms from an alkane followed by a triene - cyclo-hexadiene ring closure step 20, 21). This can be ... 

Hexane Hexenes Cyclohexane Cyclohexene Hexa- dienes 1,3-Cyclo- hexadiene Trans-, 5,S- hexatriene Benzene... 

No. of pulse < C Hexane Hexenes Hexa- dienes Cyclo- hexane Cyclo- hexene 1,3-Cyclo- hexadiene 1,3,5-Hexatriene Benzene... 

Benzene and its homologs can be converted to the corresponding cyclo-hexadienes and cyclohexenes, and even cyclohexanes, by treatment with dissolving metals lithium, sodium, potassium or calcium in liquid ammonia or amines. Conversions are not complete, and the ratio of cyclohexadienes to cyclohexenes depends on the metal used, on the solvent, and on the presence of hydrogen donors (alcohols) added to the ammonia or amine [392, 393, 394]. 

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