Octa-2,7-diene, 2,6-dimethyl

Two classes of diene have been copolymerized successfully with ethylene/propene, in both of which one double bond is deactivated such that the monomer behaves as a mono-olefin. These are unconjugated diolefins, such as cis and trans 1,4-hexadiene or 3,7-dimethyl 1,6-octa-diene, and compounds containing the 2-norbornene structure... 

As a typical example, Fig. 1 shows the H NMR NOE difference spectra of the monomer 3, 1-phenyl-7,7-dihexyl-8,8-dimethyl-7,8-disilabicyclo[2.2.2]octa-2,5-diene. Irradiation of the methyl peak on silicon of the major isomer enhanced the peak intensities of the methyne (H and two vinylic hydrogens (Hb). The fact clearly indicates that the major isomer has the structure 3a. The isomer ration (7.8/1) was calculated from the relative area of methyl peaks. In a similar way, structures and isomer ratios were determined for all the monomers. Table 1 lists the results. Apparently, the ratio of the isomers a/b increased with increasing steric bulkiness of the alkyl substituents on the dichlorodisilanes, reaching to 96/4 for the di(2-methylpropyl)dimethyl-substituted derivative 5. 

Scheme 6.30 Structure ofthe trapping products of bicyclo[3.2.1]-octa-2,3-diene (123) with 1,3-cyclopentadiene, (Z)-l, 3-pentadiene and 2,3-dimethyl-l, 3-butadiene and ofthe dimers of123.

Scheme 26 Synthesis of (3R,5 )-2,6-dimethyl-2,3-epoxy-octa-5,7-diene, isolated from male Amblypelta nitida [121]...

The major product is l,4-dimethyl-4-vinylcyclohexene together with smaller amounts of 1,6-dimethylcyclo-octa-l,5-diene, isoprene and 4-isopropenyl-1 -methylcyclohexene. 

Octan-l-ol acetate Rh Oct-trans-2-en-l-al Rh Octa-2-6-diene-l-8-diol, 2-6-dimethyl Rh Octa-3-7-diene-l-6-diol, 2-6-dimethyl Rh Octa-3-cis-6-dien-l-al, 3-7-dimethyl Rh Octa-d-tram-h dien-l-al, 3-7-dimethyl Rh Octa-traTiS 2 CiS 6 dien l ol, 3-7 dimethyl 8-hydroxy, P-D-glucopyranoside Rh 5.2 °... 

Tetramethyl 3,7-dihydroxy-1,5-dimethylbicyclo-[3.3.0]octa-2,6-diene-2,4,6,8-tetracarboxylate 1,3,4,6-Pentalenetetracarboxylic acid, 1,3a,4,6a-tetrahydro-2,5-dihydroxy-3a,6a-dimethyl-, tetramethyl ester (11) (79150-94-0) Biacetyl 2,3-Butanedione (8,9) (431-03-8)... 

In the formation of tetraenes from bicyclo[4.2.0]octa-2,4-dienes, two bonds are broken. This may occur in one concerted reaction which can be regarded as a retro [2 + 2] cycloaddition. It is also possible that the central bond, being part of a cyclohexadiene system, is the first one to break in a thermal, concerted disrota-tory process that leads to a 1,3,5-cyclooctatriene derivative. Ring opening of the cyclooctatriene then might take place photochemically, again disrotatory, to produce a tetraene. This two-step sequence was first observed by Mirbach et al. [114] in their study of the photocycloaddition of the two parent molecules benzene and ethene. The same explanation for the formation of a tetraene was given by Nuss et al. [160] in their report on the intramolecular ortho photocycloaddition of ( )-6-(2-methoxyphenyl)-5,5-dimethyl-2-hexenenitrile (see Scheme 40). 

Only four transient disilenes have been studied to date by fast time-resolved spectroscopic techniques l,l,2-trimethyl-2-phenyldisilene (103), ( )- and (Z)-l,2-dimethyl-l,2-diphenyldisilene (104) and tetrakis(trimethylsilyl)disilene (35). The first three compounds were generated by photolysis of the 7,8-disilabicyclo[2.2.2]octa-2,5-diene derivatives 101 and 102 (equation 76)148 while 35 was generated, together with 106, by photolysis of the 1,2-disilacyclobutane derivative 33 (equation 77)68. 

Dimethoxy-3,6-dimethylpyrazine (182) gave 6,8-dimethoxy-l,4-dimethyl-2,3-dioxa-5,7-diazabicyclo[2.2.2]octa-5,7-diene (183) (hv, 02 J, CH2C12, methylene blue, h %), and thence methyl 5-methoxy-2,4-dimethyl-l-imidazolecarboxylate (184) or its isomer (Ph3P, THF—H20, 20°C, 5 days 47% mechanism suggested).165... 

Azocin 3,8-Dimethyl-2-methoxy-V/ld, 448 E9d, 512 (8-OR-1.6-R2—7-aza-bicyclo[4.2.0]octa-3,7-dien/NBS NaOR)... 

Benzo-2-aza-bicy clo 3.3.0]octa-1,7-dien 3,3-Dimethyl-5-hydroxy- -2-oxid E14b, 1474 (aus Nitro-keton)... 

The bicyclic 8,8-dimethyl-8-silyl-bicyclo[3.2.1]octa-2,6-diene is the only product isolated from the Barbier reaction of cylohepta-2,4,6-triene with dimethyldichlorosilane [104]. 

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