3-methyl-1,5-hexadiene

Experimental kinetic isotope effects are for the 1-methyl and 3-methyl 1,5-hexadienes Gajewski JJ, Conrad ND (1979) J Am Chem Soc 101 6693... 

The pyrolysis conditions suggest a free energy of activation of —43 kcal/mol for the reaction at 370°C. For comparison the 3,3-shift of 3-methyl-1,5-hexadiene has a free energy of activation of 41 kcal/mol at 220 C, and the expected BDE of the C4-C5 bond in 1,3,7,9-decatetraene is approximately 42 kcal/mol. 

When groups of atoms migrate from one site to another, the O-bonded atom that leaves one site is different than the one that forms a O bond at the second site. In such reactions, both ends of a O bond migrate. For example, in the rearrangement of 3-methyl-1,5-hexadiene, atom 3 of the three-atom migrating group eventually bonds to atom 3 of the second part of the molecule. 

The A//° for the [3,3] sigmatropic rearrangement of 3-methyl-1,5-hexadiene is shghdy negative. The number and types of bonds in both reactant and product are the same. However, the double bonds in the reactant are monosubstituted, whereas the product has a monosubstituted and a disubstituted double bond. The more stable disubstituted double bond increases the stability of the product. The is approximately zero because the reactant and products are structurally similar and have the same d ree of conformational mobihty. 

Further, it is shown in Figure 6 that this methyl steric effect can be observed even when the methyls are placed alpha to the metathesizing olefin itself. Thus, 3,4-dimethyl-1,5-hexadiene does not polymerize, whereas 3-methyl-1,5-hexadiene dimerizes in the 5 position. These steric interactions are quite subtle, and by examining the ADMET polymerization cycle shown earlier, it becomes evident that the formation of a metallacyclobutane ring and its stability is influenced by simple steric interaction. 

Alkin-ole werden ebenfalls selektiv zu Alken-olen reduziert (s. a. Bd. V/lc, S. 467). So erhalt man z. B. aus 5-Hydroxy-5-methyl-hexin-(l)-en-(3) an einer Kupfer/Silber-Ka-thode in Athanol/Natriumcarbonat 80-90% d.Th. 5-Hydroxy-5-methyl-hexadien-(l,3)2. Dagegen tritt beim 2,7-Dihydroxy-2,7-dimethyl-octadiin-(3,5) an einer Kupfer-Kathode in Athanol/Natronlauge gleichzeitig Wasser-Abspaltung und Isomerisierung ein und man gewinnt 7-Hydroxy-2,7-dimethyl-octadien-(2,4) (39% d.Th. Kp2 70-720)3 ... 

Analog wie Pentadien-(1,4) und Hcxadicn-(1,5) verhaltensich 2-Methyl- und 2,4-Dimethyl-pentadien-(l,4) bzw. 2-Methyl-hexadien-(l,5)1. 

Their synthesis began with conversion of ethyl 3,3-dimethylacrylate to (2 , AE)-6-f-butoxycarbonylamino-3-methyl-hexadienal 1233 in six steps (Scheme 1.313). This unsaturated aldehyde was relatively labile and was immediately converted to 960 in four additional steps. The starting oxazole 957 was prepared in one step from ethyl a-formyldiazoacetate and bromoacetonitrile. Coupling 960 with 957 in the presence of activated zinc afforded the target E, )-oxazole-diene fragment 961 after Swem oxidation. ... 

Racemic mixtures of stereoisomers were prepared in an analogous manner, utilizing diazoacetic ester and 5-chloro-2-methyl-hexadien-2,4 [123] or a similar precursor 86 (Reaction scheme 49). 

Dimethyl- Propene Ethane, ethylene, propane, 1- butene, 2,3-dimethylbutane, 2- methyl-4-pentene, isobutane, 1,5-hexadiene... 

Irradiation of l,l,3,3-tetraphenyl-5-methyl-l,4-hexadiene gives the two products shown below. When the reaction is carried out by photosensitization, B is not formed. Suggest mechanisms for the formation of A and B. What other products might have been expected Can you rationalize their absence ... 

Perkin pointed out that open chain compounds, which are analogous in structure to a terpene, show a certain similarity in behaviour thus the addition of an ethyl group to 2-methyl 1 5-hexadiene by converting it into 2-methyl 3-ethyl 1 5-hexadiene changes the unpleasant acrid odour into a pleasant one reminding of lemon and peppermint. 

Dihydroxy-trans-buten-(2)i / -Hydroxy-cis-2-methyl-buten-(2) 4 5-Hydroxy-pemadien-(l, 3)5 1-Hydroxy-cis -buten-(2)6 5-Hydroxy-4-methyl-pentin-(l )7 / -Hydroxymethyl-cyclohepten8 1-Hydroxy-1-hexadien-(2,4)9... 

As we have indicated with our arrows, the mechanism of the uncatalyzed Cope rearrangement is a simple six-centered pericyclic process. Since the mechanism is so simple, it has been possible to study some rather subtle points, among them the question of whether the six-membered transition state is in the boat or the chair form. ° For the case of 3,4-dimethyl-l,5-hexadiene it was demonstrated conclusively that the transition state is in the chair form. This was shown by the stereospecific nature of the reaction The meso isomer gave the cis-trans product, while the ( ) compound gave the trans-trans diene. If the transition state is in the chair form (e.g., taking the meso isomer), one methyl must be axial and the other equatorial and the product must be the cis-trans alkene ... 

Bertrand and Santelli (89) have investigated the hydrolysis, under apparently heterogeneous conditions, of 4,5-hexadien-2-yl tosylate, 114, and 4-methyl4,5-hexadien-2-yl tosylate, 115. After 90 min at 80°, 114 upon steam distillation yields a mixture consisting of 3% hydrocarbon 67% of cis- and rrans-2-methylcyclopropyl methyl ketone, 116 and 30% of 4,5-hexadien-2-ol, 117. When optically active 114 was treated under similar conditions, the resulting rrans-2-methylcyclopropyl methyl ketone had an inverted configuration at the reaction center, whereas the dienol 117 was found to be racemic (90). This... 

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. -"... 

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