Heptatrienals—

These acids (51) are organic molecules that contain a plurality of cyano groups and are readily ionized to hydrogen ions and resonance-stabilized anions. Typical cyanocarbon acids are cyanoform, methanetricarbonitrile (5) 1,1,3,3-tetracyanopropene [32019-26-4] l-propene-l,l,3,3-tetracarbonitrile (52) 1,1,2,3,3-pentacyanopropene [45078-17-9], l-propene-l,l,2,3,3-pentacarbonitrile (51) l,l,2,6,7,7-hexacyano-l,3,5-heptatriene [69239-39-0] (53) 2-dicyanomethylene-l,l,3,3-tetracyanopropane [32019-27-5] (51) and l,3-cyclopentadiene-l,2,3,4,5-pentacarbonitrile [69239-40-3] (54,55). Many of these acids rival mineral acids in strength (56) and are usually isolable only as salts with metal or ammonium ions. The remarkable strength of these acids results from resonance stabilization in the anions that is not possible in the protonated forms. 

Tropolone has been made from 1,2-cycloheptanedione by bromination and reduction, and by reaction with A -bromosuccinimide from cyolo-heptanone by bromination, hydrolysis, and reduction from diethyl pimelate by acyloin condensation and bromination from cyclo-heptatriene by permanganate oxidation from 3,5-dihydroxybenzoic acid by a multistep synthesis from 2,3-dimethoxybenzoic acid by a multistep synthesis from tropone by chlorination and hydrolysis, by amination with hydrazine and hydrolysis, or by photooxidation followed by reduction with thiourea from cyclopentadiene and tetra-fluoroethylene and from cyclopentadiene and dichloroketene. - ... 

Tropidine CgHj3N —Tropilidene C,Hg (S-cyclo Heptatriene) Anhydroecgonine C9H13O2N —> -eycloHeptatrienccaTboxylic acid CjHgOj... 

Obtain the energies, carbon-carbon bond distances and electrostatic potential maps for 3-ethyUdene-l,3-pentadiene and 1,3,5-heptatriene. Which data are consistent with the usual resonance argument and which are not ... 

The 18-electron rule is especially useful when considering complexes containing ligands such as cyclo-heptatriene, C7H8, abbreviated as cht. This ligand, which has the following structure, can bond to metals in more than one way because each double bond can function by donating two electrons ... 

The simplest cross-conjugated polyene is 122, 3-methylene-1,4-pentadiene or 1,1-divinylethylene itself. Accepting the analysis in Reference 2 that was made using Roth s data, we find this species to be some 23 kJ mol 1 less stable than the simplest conjugated polyene, 80, (li)-, 3,5-hexatriene or 1,2-divinylethylene. The next simplest cross-conjugated polyenes are 3-methylene-l,4,6-heptatriene, 123, and 3,4-dimethylene-1,5-hexadiene, 124, that would naturally be compared with ( , )- ,3,5,7-octatetraene,... 

Remembering that a typical endothermicity of very approximately 5 kJ mol 1 is found when there is no strain accompanying combination of two olefins to form a conjugated diene23,24, the cyclization reaction of (Z)-l,3,6-heptatriene, 137 (equation 43)... 

Pulse radiolysis is used also for preparation of excited states of dienes and polyenes. This is done by irradiation of the diene/polyene in toluene solution. The radiolysis of toluene yield high concentration of molecules in the triplet excited state of the solute. Wilbrandt and coworkers61 pulse-radiolysed 1 mM solution of al I -lrans-1,3,5-heptatriene in toluene solution and observed the absorption spectra of the triplet state of the heptatriene with a maximum at 315 nm. The same group62 produced and measured the absorption spectra of several isomeric retinals in their lowest excited triplet state by pulse irradiation of their dilute solution in Ar-saturated benzene containing 10 2 M naphthalene. Nakabayashi and coworkers63 prepared the lowest triplet states of 1,3-cyclohexadiene,... 

Similiar to the case of bicyclo[4.1.0]heptatriene (2a), the proposed31 bi-cyclic intermediate (2b) in the ring expansion of lb has never been directly observed. However, the analogous azirines, formed by photolysis of 1- and 2-naphthyl azides, have been characterized by IR (Scheme 13)47 and both trapping48 3,6,0 and IR spectroscopic characterization484 of substituted derivatives... 

Earlier, Dunkin and Thomson had observed that matrix-isolated triplet 10a did not undergo photochemical ring expansion.83 However, Morawietz and Sander have recently provided evidence for photochemical conversion of 310a and 310b to the corresponding fluorinated azirines (Scheme 19).48d This represents a rare instance where an azabicyclo[4.1.0]heptatriene, the putative intermediate in the ring expansion of a phenylnitrene, has actually been observed. 

Our calculations showed that the first step, cyclization of the nitrene to an azabicyclo[4.1.0]heptatriene, is rate-determining. Our calculated barriers for cyclization of four fluorinated derivatives of lb are given in Table 6.87 The CASPT2/cc-pVDZ barrier of 13.4 kcal/mol for cyclization of 2,6-difluoro-phenylnitrene (10b) is 4.1 kcal/mol higher than the barrier computed for lb -+ 2b. In contrast, the calculated barriers to rearrangement of 3,5-difluoro-phenylnitrene (lOe) and 4-fluorophenylnitrene (10c) are very similar to that computed for unsubstituted phenylnitrene (lb). These computational results are consistent with the observed reluctance of pentafluorophenylnitrene (10a) and 2,6-difluorophenylnitrene (10b) to rearrange,48 1 81 83 and with the relative ease... 

The formation of the same cyclopropylamine from 2-methyl-l,3-pentadiene as from 4-methyl-l,3-pentadiene (entries 2 and 3 in Table 11.11) can most probably be attributed to initial isomerization of the former to the latter under the conditions employed. The fact that the conjugated 6-methyl-l,3,5-heptatriene yields only the 2,3-dialkenylcyclopro-... 

The acetylene 27 became of interest since it undergoes a novel type of thermal cyclization reaction, later to be called the Myers or Myers-Saito cyclization (see Chapter 20 for a discussion of its relevance). The Z-diastereomer of 1,2,4-heptatrien-6-yne (27) was prepared by the sequence summarized in Scheme 5.33 [85]. 

Much experimental and theoretical work has been performed with the two allenes 1,2,6-heptatriene (32) and 1,2,6,7-octatetraene (34). Thermal isomerization of 32 leads to 3-methylene-l,5-hexadiene (346), a process that at first sight looks like a typical Cope rearrangement. However, trapping experiments with either oxygen or sulfur dioxide have shown that at least half of the rearrangement passes through the diradical 345 (Scheme 5.52) [144],... 

The ability of (Z)-l,2,4-heptatrien-6-ynes (enyne-allenes) and the benzannulated derivatives to undergo cyclization reactions under mild thermal conditions to produce biradicals has been the main focus of their chemical reactivities [1-5]. With the development of many synthetic methods for these highly conjugated allenes, a variety of biradicals are readily accessible for subsequent chemical transformations. Cyclization of the enyne-allene 1 could occur either via the C2-C7 pathway (Myers-Saito cyclization) leading to the a,3-didehydrotoluene/naphthalene biradical 2 [6-10] or via the C2-C6 pathway (Schmittel cyclization) producing the fulvene/benzofulvene biradical 3 [11] (Scheme 20.1). 

Scheme 20.3 The Myers-Saito cyclization reaction of (Z)-l, 2,4-heptatrien-6-yne.

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