Hepta-1,2,6-trienes

The cyclic diradical, 2-methylene-1,4-cyclohexadiyl (18), can be formed from the hepta-1,2,6-triene 1722,23. Thermolysis of 17 gives 3-methylene-l,5-hexadiene 19 as a Cope rearrangement product, while the same treatment (155 °C, benzene) in the presence of SO2 leads to sulfones 20 and 21 instead of 19 (equation 6). It was shown that sulfone 20 is obtained by reaction of SO2 with the rearrangement product 19, while sulfone 21 originates directly from the diradical 18. 

Related Reagents. Tricarbonyl[(2,3,4,5,6,7-j))-cyclo-hepta-triene]chromium(0) Tricarbonyl[(2,3,4,5,6,7-7 )-thiepin-1,1-dio-xide]molybdenum(0) Tricarbonyl[(2,3,4,5,6,7- ))-thiepin-I,l-dioxide]tungsten(0) Tricarbonyl[(2,3,4,5,6,7- ))-thiepin]-iron(O) Tricarbonyl[(2,3,4,5,6,7-7 )methyl-l//-azepine-l-carboxylate]chromium Thiepin-1,1-dioxide Trisaceto-nitrile-tricarbonyl-chromium(0). ... 

Benzoxepin, 55, 89 Benzoyl chloride, 55, 123 BICYCLO[4 1 0] HEPTA-1,3,5-TRIENE... 

The two-step process, depicted by path b, involves initial addition of the carbene carbon to an adjacent it bond to form bicyclo[4.1,0]hepta-2,4,6-triene (2a). This process has precedent in the analogous rearrangement of vinylcar-bene to cyclopropene (Scheme 6),lc18 and is supported by Gaspar s work on 1-cyclohexenylcarbene.17 In the second step of the mechanism in Scheme 5, subsequent six-electron electrocyclic ring opening of 2a yields the cyclic allene 3a. 

All three levels of theory predict the ring expansion of singlet phenylcarbene ( A -la) to cycloheptatetraene (3a) to occur in two steps, via bicy-clo[4.1.0]hepta-2,4,6-triene (2a) as an intermediate. The first step is addition of the carbene carbon to an adjacent 7t bond of the ring. The second step involves a six-electron, disrotatory, electrocyclic ring opening, which is allowed by orbital symmetry67 and thus proceeds by a highly delocalized transition state. Fig. 4... 

Thus, heptafulvalene (522) was isolated in 33 and 65% yield after thermolysis of 517 in diglyme and its photolysis in THF, respectively [193]. An almost quantitative yield of 522 resulted when a mixture of 1-, 2- and 3-chloro-l,3,5-cycloheptatriene (518a) was treated with KOtBu in THF [206]. Even on variation ofthe concentration of the starting material and the temperature of the reaction, 522 turned out to be the exclusive product [207]. Also, the treatment of (trimethylsilyl)tropylium tetrafluoro-borate (519) with tetrabutylammonium fluoride [208] and the gas-phase pyrolysis of 7-acetoxynorbornadiene and 7-acetoxy-l,3,5-cycloheptatriene [209] afforded high yields of 522. Further, 522 was observed on FVT of N-nitroso-N-(7-norbornadienyl)-urea at 350 °C, which is believed to be converted into 7-diazonorbornadiene initially. Its decomposition should proceed via 7-norbornadienylidene to bicyclo[3.2.0]hepta-l(2),3,6,-triene (514) (Scheme 6.103) and then on to 5 [210]. The intermediacy of 514 is also suspected in the formation of 522 from 7-acetoxynorbornadiene. 

Scheme 6.114, a carbene-carbene rearrangement transforms diphenylcarbene to o-phenylphenylcarbene, which is the progenitor of 565. Two phenylbicydo[4.1.0]-hepta-2,4,6-trienes and l-phenyl-l,2,4,6-cycloheptatetraene (562) have to be assumed as further intermediates. The participation of 562 is supported by the structure of the products 563 and 564, which should result from the addition of 562 to diphenylcarbene and the dimerization of 562, respectively. By thermolysis of the sodium salt of 2-phenyltropone tosylhydrazone, 562 was generated directly. At 100 °C in diglyme as solvent, 564 was identified as the only product and at 340°C/4Torr in the gas... 

The nucleophilic attack on an acceptor-substituted allene can also take place at the acceptor itself, especially in the case of carbonyl groups of aldehydes, ketones or esters. Allenic esters are reduced to the corresponding primary alcohols by means of diisobutylaluminum hydride [18] and the synthesis of a vinylallene (allenene) by Peterson olefination of an allenyl ketone has also been reported [172]. The nucleophilic attack of allenylboranes 189 on butadienals 188 was investigated intensively by Wang and co-workers (Scheme 7.31) [184, 203, 248, 249]. The stereochemistry of the obtained secondary alcohol 190 depends on the substitution pattern. Fortunately, the synthesis of the desired Z-configured hepta-l,2,4-trien-6-ynes 191 is possible both by syn-elimination with the help of potassium hydride and by anti-elimination induced by sulfuric acid. Analogous allylboranes instead of the allenes 189 can be reacted also with the aldehydes 188 [250]. 

Another paper64, which also contains a literature survey about the problem discussed, describes the rearrangements of C7H6 systems which can be generated by thermolysis of phenyldiazomethane. By using spectral methods and chemical reactions, the formation of bicyclo[4.1.0]hepta-2,4,6-triene (139), cycloheptatrienylidene (137a) and bicyclo[3.2.0] hepta-l,3,6-triene (135) was excluded, and evidence for the formation of intermediate cycloheptatetraene (137b) (see equation 45) was furnished. 

The prototype of this reaction is the Myers-Saito reaction, the rearrangement of eneyneallene (Z)-hepta-l,2,4-triene-6-yne (70) to a,3-didehydrotoluene (71). This C2—C7 cyclization yields a benzylic 7i-conjugated a,7t-biradical and is therefore... 

Anhydrous silver-olefin complexes are readily dissociable, low-melting, and variable in composition 92a, 176, 183). Cyclic olefins and polyolefins form stable complexes with silver nitrate or perchlorate, but again the Stoichiometry of the complexes varies considerably, sometimes depending on the conditions of preparation. The following types have been isolated [Ag(un)2]X (un = e.g., cyclohexene, a- and /3-pinene) ISO), [Ag(diene)]X diene = e.g., dicyclopentadiene 220), cyclo-octa-1,5-diene 50, 130), bi-cyclop, 2,1 ]hepta-2,5-diene 207), and cyclo-octa-1,3,5-triene 52), and [Ag2(diene)]X2 (diene = e.g., cyclo-octa-1,3- and -1,4-diene 180), bi-cyclo[2,2,l]hepta-2,5-diene 1) and tricyclo[4,2,2,0]-decatriene 10)). Cyclo-octatetraene (cot) forms three adducts with silver nitrate 52), viz., [Ag(cot)]NOs, [Ag(cot)2]N03, and [Ag3(cot)2](N03)3. On heating, the first two lose cyclo-octatetraene and all three decompose at the same temperature. From the stoichiometry of the above complexes it appears that the... 

Oxabicyclo[3.2.0]hepta-l,4,6-triene (289), a planar Sn-electron analog of 4, has been prepared by flow pyrolysis of 288 (both cis and trans) in approximately 10% yield (>95% purity) 289 is an extremely sensitive compound, polymerizing instantaneously on exposure to oxygen. In solution, where it is stable for several days, it slowly dimerizes to give the known compound 291 the pentacyclic intermediate 290 is possibly involved. In Diels-Alder reactions, 289 behaves like an olefin with cyclopentadiene it reacts immediately to give 292. Hydrogenation occurs at the same site. ... 

Computational studies of the electrocyclic ring closures of cycloheptatetraene to bicyclo[3.2.0]hepta-l,3,6-triene and bicyclo[3.2.0]hepta-2,3,6-triene have been reported,292 and the reaction of P-chloroiminophosphine with 1 -(dialkylaminojalkynes has been shown to yield 1,2-azaphosphetines via the (E)-1 -aza-2-phosphabuta-1,3-dienes.293... 

ALUMINUM. PENTAKIS(N(sup 2)-ACETYL-L-GLUTAMINAT0)TETRAHYDR0XYTRI-ANDROST-4-EN-3-ONE, 17-beta-HYDROXY- 17-METHYL-7 ARSABICYCLO (2.2.1) HEPTA-2. 4, 6-TRIENE, 1-HYDROXY-, 1-OXIDE ARSENIC ACID (solution)... 

The mechanism of the pyrolysis of (Z)-hepta-l,2,4-trien-6-yne in methanol at 100 °C to give benzyl methyl ether as a major product and 2-phenylethanol as a minor product has been studied by computational and experimental methods and shown to occur by way of a zwitterion only if a component of the reaction follows a non-adiabatic course (Scheme 120).177... 

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