Octadienes, rearrangement

Studies of solvolysis of similar polyfluonnated polycyclic aromatic systems, such as 2,3-(tetrafluorobenzo)bicyclo[2 2 2]octadienes and related compounds, proved the ionic mechanism of this rearrangement [55, 36, 37] (equation 9) Possible nonclassical carbonium ion involvement has been discussed [5S, 39, 40, 41]... 

The cis-, 2-divinylcyclobutane in the reaction mixture rearranges rapidly under reflux to the higher-boiling 1,5-cyclo-octadiene. 

Base-induced rearrangement of bicyclo[2.2.2]octane oxide 67 gives predominantly bicyclo[2.2.2]octanone 68 (Scheme 5.15), which once again indicates that close proximity between the carbenoid center and the C-H bond into which it may insert is important if such an insertion is to occur [30]. In comparison, the sense of product distribution is reversed for the related substrate bicyclo[2.2.2]octadiene oxide 70 on treatment with LDA [15, 22], alcohol 72 being the favored product. 

It was pointed out earlier that a Cope rearrangement of 1,5-hexadiene gives 1,5-hexadiene. This is a degenerate Cope rearrangement (p. 1380). Another molecule that undergoes it is bicyclo[5.1.0]octadiene (105). At room temperature the NMR... 

A common example of Cope rearrangement involving [3, 3] sigmatropic rearrangement in a 1, 5 diene is the pyrolysis of meso 3, 4 dimethyl hexa-1, 5 diene giving exclusively cis, trans isomer of 2, 6 octadiene. The process involves a six electron transition state which has a chair like configuration and substituents occupy equatorial sites. 

Using this hetero-Claisen rearrangement, Saito and coworkers95 have recently shown that octadiene 144 can be converted to the rearranged product 145 with total retention of... 

The relatively easy rearrangement of cis-l,2-divinylcyclobutane was first reported by Vogel (1958) who found that at 120° ci5,cis-l,5-cyclo-octadiene was the only product. 

Derivatives of 1,2-dihydroazocine are potentially available by valence isomerization of the 7-azabicyclo[4.2.0]octadiene system. Sulfonyl derivatives (71) of the latter have been prepared, but the equilibria with dihydroazocines lie completely on the side of the bicyclic isomers (71JOC435). On heating, the bicyclooctadienes rearrange to the acyclic tetraenes (73), presumably via the unstable dihydroazocines (72). 

It has been suggested307 that the observed thermal rearrangement of the bicyclo[2.2.2]- to the bicyclo[3.2.1]-octadiene skeleton in tricyclic lactams, viz. (265)—>-(266), is consistent with an intramolecular Diels-Alder reaction in which a zwitterion is formed by the migration of one vinyl group from C(l) to C(5) of the lactam moiety (see Scheme 62). It has been shown308 that the 7r-facial selectivity of the Diels-Alder reaction of 1,3-dienes (267) having an attached stereogenic centre can be... 

The reaction is very slow in acetic acid alone, and accelerated as acetate by the addition of bases [59]. These two isomers undergo Pd-catalysed allylic rearrangement with each other. 3-Acetoxy-l,7-octadiene (139) is converted to the allylic alcohol 157 and to the enone 158, which is used as a bisannulation reagent [60], Thus Michael addition of 158 to 2-methylcyclopentanedione (159) and aldol condensation give 160. The terminal alkene is oxidized using PdCl2/CuCl/02 to the methyl ketone 161. After reduction of the double bond in 161, aldol condensation affords the tricyclic system 162. 

The conformationally rigid s-cis diene 123-(Sch. 28) yields, after triplet sensitized irradiation and distillation, the [4+4] adduct 127. Inspection of the dimeric products before distillation, however, found that the cyclo-octadiene 127 was not present, only two [2+2] adducts 124 and 125, and one [4+2] adduct 126. The cis divinylcyclobutane 124 rearranges during distillation [82]. 

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