Cyclooctatrienes rearrangement

The thermolysis of the bicyclodiene 109 at 225 °C gives rise to equilibrium mixture of cyclooctatriene and its transformation products (see below)54. More recently the influence of a methoxy group on the thermal behavior of the bicyclo[5.1.0]octa-2,4-diene system was studied56. Heating of 8-ewdo-methoxydiene 115 in cyclooctane at 95 °C gaves rise to methoxy substituted diene 117 and not to the product 116 of butadienylcyclopropane rearrangement (equation 41). The thermolysis of the 8-exo-isomer 118 has taken place as an equilibrium reaction to give 6-ewdo-methoxy diene 119 (equation 42)56. These two reaction partners were separated by TLC. 

Hoffmann and Pete [106] have irradiated D-alk- 3 -e n y I salicylates and obtained products which result from rearrangement reactions of primary ortho adducts (Scheme 31). The authors realized that the linear tricyclic dienes, formed by ring closure of the cyclooctatriene derivatives, are enol ethers which can be converted into acetals by acid-catalyzed addition of an alcohol. This shifts the... 

From 1987 onward, many examples of rearrangements of ortho photocycloadducts to derivatives of cyclooctatriene and subsequent reactions of these compounds have been reported. The same year marks the start of a series of investigations on intramolecular ortho photocycloadditions. This may not be a coincidence, because ortho adducts formed by intramolecular photoaddition seem especially prone to undergo rearrangement, although it has also frequently been observed in adducts arising from intermolecular addition. 

The first investigations by Bryce-Smith et al. [46,67,153] on ortho photocycloaddition of an alkene to hexafluorobenzene have revealed yet another secondary reaction of ortho photocycloadducts. Irradiation of a solution of hexafluorobenzene in r/.v-cyclooctene leads to the rapid formation of seven adducts of which six were identified (i) the exo-meta adduct, (ii) a product that can be formed from the meta adduct by a thermal 1,5 H-shift but which apparently is also a primary product, (iii) an ortho adduct of which the configuration could not be established, (iv) a cyclooctatriene derivative formed by thermal ring opening of the ortho adduct, and (v) and (vi) two stereoisomers of 2,3,4,5,6,7-hexaflu-orotetracyclo[6.6.0.02,7.03,6]tetradec-4-ene. The experiment was repeated 9 years later by Sket et al. [151] with the important difference that cyclohexane was used as a diluent. The meta adduct (i) and its formal rearrangement product (ii) were not found. One ortho adduct (iii), the cyclooctatriene (iv), and the two tetracyclic products (v) and (vi) could be identified and their stereochemistry determined. From their results, the authors concluded that a second ortho adduct with the alternative stereochemistry must also have been formed. They also performed experiments in which the influence of the solvent on the course of the reaction was studied and found that the difference between their results and those of Bryce-... 

When 18 is treated with acetone, boronic ester 20 with a cyclooctatriene structure is cleanly obtained indicating the valence tautomerism between 18 and 19. In fact, 19 appears to be the kinetic product in the borylation of lithium or potassium cyclononatetraenide with alkylboron dihalides which rearranges quickly to 18 due to the comparatively high thermodynamic stability of the latter.1819 Acetaldehyde,... 

The syntheses from [2+3] atom fragments are neither as general nor as important as those from [1+4] atom fragments. Wrackmeyer et at. have found thatm-2-boryl-l-stannylalkene 195 reacts with carbodiimides, isocyanates, and isothiocyanates as shown in Scheme 24 <2001CHE1396>. The reaction of 9-cyclopentyl-9-borabarbarlane 196 with acetone takes place with rearrangement to cyclooctatriene derivative 197 (Equation 33) <1998JOC3599>. 

Several bishomobenzene and trishomobenzene derivatives rearrange on thermolysis to yield cyclooctatriene and cyclononatriene derivatives, respectively. Thus, the c/s-oxabishomobenzene diester 14 exists in equilibrium with the corresponding oxacyclooctadiene diester 15 at 100 °C. ... 

Methylenation of 1,3,5-cyclooctatriene at low temperatures gives bicyclo[5.2.0]-nona-2,5-diene suggesting that the expected product, bicyclo[6.1.0]nona-2,6-diene, rearranges via a 3,3-shift under the reaction conditions (Scheme 10.43). " ... 

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