Bicyclic triene

The formation of the bridged product 191 was investigated using the cyclopentadiene system as a model. Thus, the salt of the tosylhydrazone 198 was prepared and thermolyzed in order to examine three possible variants of rearrangements (equation 62)75. Analysis of the reaction products 200-202 and their transformations [e.g. the pyrolysis of bicyclic triene 202 to cA-8,9-dihydroindene 203 (equation 63) rather than to product 200 or 201] allows one to conclude that the mechanism involves a transformation of carbene 188 into diradical 204 which can be the precursor of all the products observed (equation 64)75. An analogous conversion takes place via radical 205 in the case of carbene 199 (equation 65). 

Interesting examples of a tandem Cope-Cope rearrangement are represented by the transformation of Cookson s diester 499, which proceeds thermally to afford its ring-degenerate isomer 500 (330-350 °C, as a melt) (equation 188)246, and by thermal isomerization of bicyclic triene 501 into hexahydro-1-vinylnaphthalene 502 upon heating in chlorobenzene at 220 °C for 20 h (equation 189)247. 

Rhodium-catalyzed, silane-initiated cascade cyclization of 1,6,11-triynes 83 was proposed to occur via a silane-initiated cascade carbocyclization to form the silylated bicyclic triene (Z,Z)-In. / -Migratory insertion of the silylated G=G bond into the Rh-G bond of (Z,Z)-In followed by / -hydride elimination from frans-lln could then form 84a. Alternatively, cisitrans isomerization of (Z,Z)-In followed by / -migratory insertion of the silylated G=G bond into the Rh-G bond of resulting isomer ( ,Z)-In could form cis-Wn. Subsequent / -silyl elimination from m-IIn would form unsilylated tricycle 84b (Scheme 21). 

Isomerization of bicyclic triene 81 proceeds fast even at low temperature in the presence of a catalytic amount of SbF5 an attempt to observe the corresponding intermediate carbocation by NMR spectroscopy was unsuccessful [167] ... 

In analogy to the preparation of bicyclic triene 37 from bisacetylene J449, the diethynyloxiranes 35 and thiiranes 36 (both cis and trans isomers can be employed tram- 36 leads to desulfurized product only) were subjected to gas phase flow-pyrolyses to effect clean, though low yielding, rearrangement to furo- and thienocyclobutadiene J S50 and 39sl respectively, systems that are isoelectronic with anion 33. Both 38 and 39 are planar Sir-systems and as such exhibit typical... 

The trons-cycloalkenes 37a, 67, and trans-cyclononene 227 react with diironnonacarbonyl 228 to form the tetracarbonyliron(O) complexes 229-231 with the frans-cyclooctene complex 229 being significantly more stable than that of trons-cyclodecene 231 (177). The bicyclic triene 232 reacts with 228 preferentially at one of the trans double bonds of the trans, trans- cy-clodecadiene substructure. In line with the expected stability, the trans, cis-cycloocta-1,5-diene 234 and trans, ris-cycloocta-1,3-diene 236 react with 228 exclusively at the trans double bond to give the complexes 235 and 237. In the complex 238, tetracarbonyliron(O) is bonded to the bridgehead double bond of bicyclo[4.3.2]deca-7,9-diene (184b) (177). 

The starting material in our synthesis was cyclododecyne whose oligomerization with two moles of butadiene gave the bicyclic triene 44, which in turn was converted into the cis doubly bridged ethylene 46 by partial catalytic hydrogenation with Raney nickel. Irradiation of 46 with a low-pressure mercury lamp in cyclohexane led to a 1 2 cis-trans mature, from which the trans isomer48, m.p. 37-38°C, was isolated after removal of the unchanged cis isomer as a dichlo-rocarbene adduct. 

Actually it is true that under the catalysis of a Pd(0) species, i.e., Pd(dba)2, the czs-cyclohexyl carboxylate-allene 101 afforded the bicyclic trienes 102 and 103 via the oxidative addition of the allylic carboxylate moiety forming a 7i-allylic Pd intermediate, which underwent intramolecular carbopalladation and P-H elimination to afford the cis fused bicyclic products 102 and 103 (Scheme 47)... 

In the presence of benzoquinone (2 equiv), the allene-l,3-cyclohexdiene 115 afforded the czs-fused bicyclic triene 116 under the catalysis of Pd(OAc)2... 

Its decomposition product appears to be a bicyclic triene, which is dehydrogenated by chloranil to give a methylindene ... 

There are interesting pressure effects on the product distribution from the trans isomer. At 247°C and 100 Torr, only the bicyclic triene is formed, but at 0.1 Torr, 20% of fulvenallene and 9.6% of ethynylcyclopentadiene are formed in addition to the bicyclic triene. Since the latter two materials are the products from high temperature pyrolysis of the bicyclic triene, the suggestion was made that... 

Spiro[2,4]hepta-l,4,6-triene undergoes a 1,5-carbon shift to bicydo[3.2.0]hepta-1,3,6-triene with log k= 12 — 24100/23RT in chloroform solution. The reaction is not irreversible, but rapid dimerization of the bicyclic triene to 2 + 2 and 4 + 4 cycloaddition products apparently drives the reaction (Scheme 8.4). 

Calculations at various levels suggest that the relative energy difference between the two isomers is small. Also calculated was the relative energy of the 1,3-carbon shift product from the spirotriene, namely norbornatriene, but it was 50 kcal/mol higher in energy than the spirotriene The bicyclic triene has also been subjected to theoretical scrutiny and has a low-lying triplet state which may be responsible for the dimerization. 

Octamethylbicyclo[4,2,0]octatriene (285) has been prepared by elimination of nitrogen at low temperature from (286). The bicyclic triene reverts to its monocyclic isomer, = 322 min at 5 °C, and the equilibrium mixture at 35 °C contains over 95 % of the monocyclic isomer (286). The diene reacts readily at 0° with dienophiles such as maleic anhydride to give the expected adducts (287). 

Palladium-catalyzed seven-membered ring formation ofVCP 45 was developed (Scheme 2.40) [58]. The reaction was accompanied by elimination of diethyl phosphate to provide bicyclic triene 46. 

Palladium-catalysed cyclisation of olefinic propargylic diethyl phosphate (73) afforded bicyclic trienes (74) (Scheme 24). ... 

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