Monosubstituted cyclooctatetraenes

Ring-opened polymers have been made from monomers having various substituents R Br (Klavetter 1988), Me, i-Pr, Bu, s-Bu, r-Bu, neopentyl, 2-ethylhexyl, octyl, octadecyl, cyclopropyl, cyclopentyl, phenyl, methoxy, and t-butoxy (Gorman 1989, 1990, 1991a,b, 1993), SiMes (Ginsburg 1989 Sailor 1990), and the chiral substituents CHMeCHMe(OMe), CHMeCHMe(OSiMe2CMe3), and 

The possible application of these materials to form surface barrier solar cells and to make conductor/insulator/conductor sandwiches by sequential polymerization of different monomers has been explored (Sailor 1990 Jozefiak 1991 Gorman 1991b). 

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In cyclooctatetraenyl(dipropyl)borane 5 the dipropylboryl group occupies a vinylic position, and its orbital interaction with the adjacent double bond is very strong. This is one of the reasons why no borotropic rearrangements for 5 were found. The only dynamic process taking place in 5 is the reversible fluctuation of the double bonds (AH = 14.0 0.2 kcalmoF1 AS = -7.6 1.2 cal moF1 K 1) common to all monosubstituted cyclooctatetraenes (Eq. 5).7... 

By applying the indirect procedure to certain monosubstituted cyclooctatetraenes the triazole-dione adducts 13-15 are obtained in low yield and are not formed by the direct cycloaddition. On the other hand, the same adduct is obtained by both procedures when fluorocyclooctatc-traene is used. When the acetoxymethyl-, cyano-, chloro-. or phenylcyclooctatetraenes are used, mixtures of adducts are produced. The separated adducts are then converted to 9,10-diazabas-ketane and -snoutanes26. 

Gorman, C.B., Ginsburg, E.J., Grubbs, R.H., 1993. Soluble, highly conjugated derivatives of polyacetylene from the ring-opening metathesis polymerization of monosubstituted cyclooctatetraenes synthesis and the relationship between polymer structure and physical properties. I. Am. Chem. Soc. 115, 1397-1409. 

For both 104 and 105, values of AG (RI) 17 kcal/mol and AG (BS) 18 kcal/mol have been determined from NMR measurements (180). Analogous processes have been studied extensively in cyclooctatetraenes bearing other substituents (181). By way of comparison, ethoxycyclooctatetraene has AG (RI) = 12.5 kcal/mol and AGf(BS) = 16.0 kcal/mol (182). Values for other monosubstituted derivatives (118) differ by +2 kcal/mol and more heavily substituted compounds have substantially higher barriers for both processes, due to steric buttressing effects in the planar intermediate (181). Thus, while the transition metal substituent in 104 or 105 does increase the barriers for RI and BS relative to smaller substituents, this effect is not large enough to prevent observation of both these processes on the NMR time scale (180). Prior to our work, the effect of polyfluorination on the energetics of these isodynamic processes had not been evaluated. 

R denotes any monosubstituted COT, R = polymer tail or f-Bu Figure 2. Cycloextrusion in dilute solution polymerization of cyclooctatetraenes. 

The cobalt(I)-catalysed 6 + 2-cycloadditions of cyclooctatetraene with monosubsti-tuted alkynes produced monosubstituted bicyclo[4.2.2]deca-2,4,7,8-tetraenes in good yields.185 The 6 + 3-cycloaddition of fulvenes (145) with 3-oxidopyrylium betaines (144) formed 5-8 fused oxa-bridged cyclooctanoids (146,147), which can be manipulated by cycloaddition reactions to produce key intermediates (148,149) for the synthesis of fused cyclooctanoid natural products e.g. lancifodilactones (Scheme 38).186,187... 

Reppe and co-workers reported in 1948 the Ni-catalyzed cyclotetramerization of acetylene to give cyclooctatetraene (106) [58]. After this discovery, the reaction was expanded to monosubstituted alkynes. Monosubstituted alkyne 138 is cyclized smoothly to give tetrasubstituted cyclooctatetraene 139 [59]. Internal alkynes are... 

Monosubstituted alkynes may be included in this cyclization giving 1,2,4,7-, 1,2,4,6-, and 1,3,5,7-tetrasubstituted cyclooctatetraene derivatives [86]. A special case is the cyclotetramerization of 1 -phenylpropyne giving the octasubstituted C product besides the hexasubstituted benzene derivative [87] (eq. (30)). 

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