Cyclooctatetraene derivatives

Dimethyl acetylenedicarboxylate (DMAD) (125) is a very special alkyne and undergoes interesting cyclotrimerization and co-cyclization reactions of its own using the poorly soluble polymeric palladacyclopentadiene complex (TCPC) 75 and its diazadiene stabilized complex 123 as precursors of Pd(0) catalysts, Cyclotrimerization of DMAD is catalyzed by 123[60], In addition to the hexa-substituted benzene 126, the cyclooctatetraene derivative 127 was obtained by the co-cyclization of trimethylsilylpropargyl alcohol with an excess of DMAD (125)[6l], Co-cyclization is possible with various alkenes. The naphthalene-tetracarboxylate 129 was obtained by the reaction of methoxyallene (128) with an excess of DMAD using the catalyst 123[62],... 

Cyclization with various nickel complex catalysts gives up to 97% selectivity to a mixture of cyclooctatetraene derivatives, with only 3% of benzene derivatives. The principal isomer is the symmetrical l,3,5,7-cyclooctatetraene-l,3,5,7-tetramethanol (29). 

Table 5. Bicyclo[4.2.0]ocla-2,4-dienes by Valence Isomerization of Cyclooctatetraene Derivatives...

Some preliminary work on the oligomerization of acetylenes, particularly ethylpropiolate and phenylacetylene, using supported nickel(O) catalysts has been reported (4, 15, 30). The initial products appear to be benzene derivatives (4, 30), although one group (30) reports that reuse of the catalyst yielded some cyclooctatetraene derivatives on the second... 

Cyclotetramerization to form cyclooctatetraene occurs only with nickel.46,63 68 The best catalysts are octahedral Ni(II) complexes, such as bis(cyclooctatetraene) dinickel.46 Internal alkynes do not form cyclooctatetraene derivatives but participate in cooligomerization with acetylene. Of the possible mechanistic pathways, results with [l-13C]-acetylene81 favor a stepwise insertion process or a concerted reaction, and exclude any symmetric intermediate (cyclobutadiene, benzene). The involvement of dinuclear species are in agreement with most observations.46,82-84... 

Access to homotropenylium ions can be achieved by two general routes. The first involves the addition of an electrophile to a cyclooctatetraene or cyclooctatetraene derivative, an approach which can be considered to correspond to a homoallyl route (Scheme 4). In this route the electrophile is generally attached stereoselectively to the endo position on C(8)18 7,1 74. The second approach involves the ionization of a bicyclo[5.1.0]octadienyl derivative. This is the cyclopropylcarbinyl approach (Scheme 4). This route has the potential of generating a wide range of differently substituted cations however, the starting materials can be difficult to access75 . 

Irradiation of complex 52 and a small excess of internal alkynes 55 gave [6ji+2ji] cycloadducts in 42-78% yield (Scheme 5) <1997TL2049>. A second irradiation (vycor filter) of the cycloadducts 56 afforded cyclooctatetraene derivatives 57 in 85-95% yield, via cheleotropic extrusion of sulfur dioxide. 

Rearrangements of semibullvalenes to cyclooctatetraene derivatives as illustrated in equation 179 lead to compounds not easily available otherwise ... 

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)). 

Optically active polyacetylene derivatives 97 were synthesized through ring-opening polymerization of the corresponding cyclooctatetraene derivatives.25 A twisted conformation of the main chain was proposed on the basis of CD and UV absorptions. Various optically active polyacetylenes have also been prepared from chiral monomers.24,25,263,177-183 The examples include a phenylacetylene derivative (98),26a alkylacetylenes 99,24 propionic esters such as 100,177,178 a Si-containing monomer (101),179 and disubstituted monomers such as 102.180 Poly-(A)-98 synthesized using a [RhCl(norbornadiene)]2 catalyst shows intense CD bands in the UV—vis region, probably based on a predominant helical sense of the main chain.263 This polymer effectively resolves several racemic... 

In the case of quadricyclan-3-ones 21, the cycloadducts 22 immediately extrude carbon monoxide and rearrange to cyclooctatetraene derivatives 23. ... 

Cyclotrimerization and cyclotetramerization of alkynes to form benzene and cyclooctatetraene derivatives was first achieved with various nickel catalysts26. Several other metal systems are also active and numerous applications have been reported3 5. Various concerted or stepwise reaction paths have been suggested3,5,2 -29. 

Transition-metal compounds catalyze the cyclooiigomerization of aikynes, giving rise to benzene and cyclooctatetraene derivatives. ... 

The utilization of pericyclic reactions of thermolabile intermediates has been extended to 7-methylcyclooctatetraene, a pheromone from the brown alga Cutleria multifida. Boland and Pohnert have reported the electrolytic ring closure of l,3Z,5Z,7E-nonatriene to afford the cyclooctatetraene derivative [52]. The biomimetic synthesis of this pheromone lends additional support to the suggested use of pericyclic reactions in the biosynthesis of the algal gynogametes. 

The reactions of the strained benzene derivative 25 with DCA were originally studied with the aim of synthesizing planar cyclooctatetraene derivatives which are interesting compounds with respect to the question of their antiaromaticity [56]. The cyclooctatetraene derivative, 29 (Scheme 2.9) synthesized by photolysis of the barrelene derivative 26, however, turned out to be non-planar [57]. But the synthesis and the reactions of barrelene derivative 26 are interesting with respect to the utility of high pressure to control the course of reaction. The reaction of 25 with DCA at 1 bar and 127 °C produces the (1 1) Diels-Alder adduct 26 (yield, 49 %) and the unexpected dark blue (2 1) adduct 27 (yield, 14 %). At high pressure (9 kbar, 83 °C) 27 is the major product even after the low conversion of 36 % of the... 

This reaction has general application in the preparation of cyclooctatetraene derivatives. 

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