1.6-Methano annulene

The 11-membered ring carbene was generated by thermolysis recently. To ensure coplanarity a brigded precursor such as 4.9-methano (11) annulenone-tosylhydrazone was used to give thus 4.9-methano (11) annulenylidene 6 39). The isomeric annulenylidene was synthesized from the tosylhydrazone of 1.6-methano-annulene-2-carboxaldehyde 39). 

It had been suggested that substituent groups at C(ll) which are known to stabilise.three-membered rings should favour the methano-annulenes existing in norcaradiene forms rather than as bridged annulenes [117]. These substituents include bulky as well as electron--withdrawing groups. 

A triple scission of a six-membered ring on the surface of C60 leading to one of the most remarkable transformations in metal-fullerene chemistry has been observed in 219. This reaction occurred via addition of CpCo(CO)2 on the bis-methano annulene 218 (Equation (36)). 

Heteroannulenes electrophilic reactions, 7, 726 tr-excessive synthesis, 7, 727 nucleophilic reactions, 7, 727 Hetero[l IJannulenes structure, 7, 715 Hetero[ 12]annulenes pyridine-like methano-bridged, 7, 715 Hetero[ 13]annulenes unrestricted structure, 7, 716... 

A similar tandem Dotz-Mitsunobu reaction has been reported starting from a l,6-methano[10]annulene carbene complex, but no conclusion could be reached on the influence of the chiral information regarding the stereoselective course of the reaction since the chromium fragment could not be kept coordinated to the benzannulation product [47]. 

The preparation of l,6-oxido[10]annulene, described simultaneously by Sondheimer and Shani4 0 and by Vogel, Biskup, Pretzer, and Boll, is illustrative of the rather general synthesis of aromatic 1,6-bridged [10]annulenes starting from 1,4,5,8-tetrahydronaphthalene. Apart from the present compound, the following bridged [10]annulenes have thus far been obtained by this approach l,6-methano[10J-annulene,2-8-9 the ll,ll-dihalo-l,6-methano[10]annulenes,9 10 and 1,6-imino [ 1 OJannulene.11... 

Oxido[10]annulene closely resembles l,6-methano[lOJannulene in many of its spectral properties, particularly in its proton magnetic resonance, ultraviolet, infrared, and electron spin resonance spectra,1 but is chemically less versatile than the hydrocarbon analog due to its relatively high sensitivity toward proton and Lewis acids. 

Thus, l,6-methano[10]annulene (77) and its oxygen and nitrogen analogs 78 and 79 have been prepared and are stable compounds that undergo aromatic substitution and are diatropic. For example, the perimeter protons of 77 are found at 6.9-7.3 5, while the bridge protons are at —0.5 5. The crystal structure of 77 shows that the perimeter is nonplanar, but the bond distances are in the range 1.37-1.42A. It has therefore been amply demonstrated that a closed loop of 10 electrons is an aromatic system, although some molecules that could conceivably have such a system are too distorted from planarity to be aromatic. A small distortion from planarity (as in 77) does not prevent aromaticity, at least in part because the s orbitals so distort themselves as to maximize the favorable (parallel) overlap of p... 

When 2-methoxy-l,6-methano[10]annulene 32 was subjected to a cyclopropana-tion with diazomethane and cuprous chloride as catalyst reaction occurred preferentially at the 5,6-, 6,7- and/or 1,10-bonds and the adducts spontaneously underwent disrotatory opening yielding the corresponding methoxybicyclo[5.4.1]dodecapen-taenes. Hydride abstraction with triphenylmethyl fluoroborate was performed on the mixture and the ions 33 and 34 so produced were treated with dilute aqueous potassium hydroxide. The annulenones 13 and 14 were then separated by chromatography. 

The same method was also applied to 3-tert-butoxy-1,6-methano[ 10]annulene which gave 3,8-12 and 3,9-methano[ 1 ljannulenones 15. 

It is interesting that attachment of — ( 2)4— and —CH2CH=CHCH2— to benzene results in nearly the same enthalpy of formation change but it is not obvious how fortuitous this equality is we have reasons for considerable skepticism of its validity68. That formation of naphthalene from benzene is accompanied by a lessened enthalpy of formation increase than that of l,6-methano[10]annulene (yet another name for species 90) from tropilidene would appear to be more of a strain than a resonance derived effect. From Roth, we find the resonance energy increase on going from tropilidene to l,6-methano[10]annulene is 55 kJmol-1 and from benzene to naphthalene the increase is nearly the same, nearly 59 kJmol-1. By contrast, the l,5-methano[10]annulene (99) is less stable by 77 kJmol 1 than the species it appears most naturally to be compared with, namely the isomeric 90. 

SCHEME 7. Competition between cycloadditions and retro- Diels -Alder reactions in the reaction of dicyanoacetylene and ll-methylene-l,6-methano[10]annulene... 

Commercially available 2,3-dichloro-5,6-dicyano-l,4-benzo-quinone was employed. 1,6-Methano[10]annulene was obtained in equally good yields, when 2,3-dichloro-5,6-dicyano-l,4-benzoquinone, prepared by the method of Walker and Waugh,4 was utilized. 

By contrast to the filtrate and washings, which are rather dark, the eluate is yellow due to the color of l,6-methano[10]annulene. 

The purity of the l,6-methano[10]annulene was shown by g.l.c. (SE-30 on kieselguhr, 150°) to be higher than 99%. Recrystallization of the hydrocarbon from methanol raises its melting point to 28-29°. 

Methanethiol, 54, 19 1,6-METHANO [10]ANNULENE, 54, 11 Methanol, (2-dimethylamino-5-methylphenyl)diphenyl-, 53,... 

The synthesis of l,6-methano[10]annulene outlined above is an improved version of the method first suggested by Vogel and Roth.13... 

Methano[10]annulene represents a Hiickel-type aromatie(4w. + 2)jr-system and is reminiscent of benzene or napthhalene in both its physical and chemical properties.14 The aromatic nature of the hydrocarbon is... 

Dimers with a 1,2-bismethylenecyclobutane structure were obtained from 585 [240], 590 [238], 591 [241], 592 [242], 593 [243] and from the pinene derivative 597 [244]. The interception of 592 by 1,3-diphenylisobenzofuran (DPIBF) afforded two diastereomeric [4+ 2]-cycloadducts [245], Bicyclo[5.1.0]octa-3,4-diene (594) was generated by /3-elimination and trapped by sodium pyrrolidide because of the question of the extent to which the corresponding bicyclooctyne is formed in addition to 594 [184], Liberated by /3-elimination from ll,ll-dichloro-l,6-methano[10]annulene in... 

A case of a thermally induced phase change involving ring inversion was recently described by Kaftory (31). He found that a crystal of the exo isomer of the adduct, 7a, of ll-cyano-l,6-methano[10]annulene with 4-methyl-1,2,4-triazoline-3,5-dione is transformed to the endo isomer 7b on heating to 175°C. The process involves nucleation and growth of the product phase, but maintains... 

Alder-Rickert cleavage was also examined as a potential route for 100 and 102, but the required precursors could not be synthesized. Bis-methano[14]annulene 105 added dicyanoacetylene in the wrong sense, and did not yield 106, which could have served as precursor of 102. Similarly, the attempted Diels-Alder reaction of the bridged cyclopropafl OJannulene 107 with dlmethoxycarbonylacetylene, which should furnish 108, produced only decomposed material. This is consistent with the observation of Halton and Russel that 107 does not add to 4-phenyl-1,2,4-tria-zoline-3,5-dione. In order to circumvent the low reactivity of 107 in cycloaddi-... 

Other approaches to alkylidenecycloproparenes have been attempted without success. Aromatization of appropriate alkylidenecyclopropanes or their precursors could not be realized, and flash vacuum pyrolysis of methylene phthalide and 3-methylene-2-coumaranone afforded rearrangement products rather than alkylidenecycloproparenes via extrusion of 002. The photochemical or thermal decomposition of the sodium salt of benzocyclobutenone p-toluenesulfonyl hydrazone led to products derived from dimerization of the intermediate benzocy-clobutenylidene, or from its reaction with the solvent, but no ring-contracted products were observed. When the adduct of methylene-l,6-methano[10]annulene to dicyanoacetylene (249) was subjected to Alder-Rickert cleavage, phenylacety-lene (250) was formed, which derives reasonably from the parent 234. ... 

The cycloaddition of 1 with 1,2,4-triazines (324), bearing one or more electron-accepting substituents, directly affords the 3,8-methanoaza[10]annulene 325 after loss of N2 from the cycloadduct. Similarly, the tetrazine-dicarboxylate 326 reacts with 1 via cycloaddition/cycloelimination to 327, which has norcaradiene struc-ture. a-Pyrones (328) and 1 undergo cycloaddition/C02 extrusion to 1,6-methano[10]annulenes (329). The sequence cycloaddition/C02 extrusion has also been reported for the reaction of cyclopropa[/]phenanthrene (142) with a-pyrone (328, R = H). ° Substituted 1,6-methano[ 10]annulenes 331 are obtained by analogy via cycloaddition/S02 extmsion of 1 with thiophene-1,1-dioxides (330). ... 

Alkoxy-4-(3-pyrazolylazo- bzw. -3-indazolylazo)-l,6-methano[10]annulene allgemeine Arbeitsvorschrift2 ... 

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