Spiroheptatrienes by [1 + 2]‐Cycloaddtion

Abstract

7 ) , thefirst representative of this type of compound. In the presence ofether (3 b) gives a mixture of insertion products. The structure of ( 7 ) follows from the spectroscopic data. CN stretching vibrations appear at 2200 and 2230 cm-in the I R spectrum. Further unambiguous evidence for a norcaradiene structure is provided by the 'H-NMR spectrum: .r(CDCI,)=2.2-2.8 (m), 3.70 (m, vinyl H), and 6.95 (br. s, cyclopropane H) in the ratio 8 :4 : 2.( 7 ) definitely exists as the norcaradiene; even at 110°C it is not converted into the cycloheptatriene valence isomer (NMR) but instead rearranges to the phenylfulvene (8) (m. p. 183--184°C; correct elemental analysis; see ref.[5]). The synthesis of the first fulvenylnorcaradiene ( 7 ) proceeds via the diazofulvene (5) to the fulvenylcarbene (6) which gives ( 7 ) in an intermolecular cycloaddition. This course has also been established for the photolysis of 5-cyano-3 Hpyrazoles'61. 7-Cyano-7-(6-cyanodibenzofulvenyl) norcaradiene ( 7 )A solution of (3 b ) (1.00 g, 3.73 mmol) in anhydrous benzene (200 ml) is irradiated under N, with a Philips HPK 125-W lamp for 15 min. After removal of the benzene in vacuo, the yellow residue was treated with chloroform to give 1.00g (85 %) of yellow crystalline ( 7 ) . Spiro[2.4]heptatrienes of type ( I ) [ ' ]are of interest for two main reasons :

Oligounsaturated Five‐Membered Carbocycles – Aromatic and Antiaromatic Compounds in the Same Family

“…In these experiments, a special ion source was used to generate an ion beam that was stable for several hours even though only a few milligrams of the respective materials were at hand. The PE spectra of the mass-selected C 20 .À clusters obtained from these three sources showed significantly different features. While the PE spectrum of the monocycle 62 had previously been assigned in combination with ion mobility experiments [60d], the spectra of the other two isomers 4 and 61 had not been observed before.…”

“…It has frequently been used as a precursor to other theoretically interesting molecules containing annelated cyclopentadiene moieties, because its irradiation readily generates the cyclopentadienylidene 29. This carbene has, for example, been trapped with alkynes to form spiro-annelated cyclopentadiene derivatives 30 (Scheme 5) [20]. It has been proved by UV spectroscopy [21] and supported by calculations [22] interaction, so-called spiroconjugation, across their central sp 3 carbon atom in spite of the orthogonal orientation of the two p-systems.…”

“…Thus, the ideal starting material is the most highly symmetrical C 20 H 20 hydrocarbon, the so-called pentagondodecahedrane (65), which also represents the lowest energy structure of all (CH) 20 isomers. The first synthesis of 65 by Paquette et al has been a landmark in organic synthesis [64].…”