No abstract

No abstract

Linkage of conjugated segments of polyenes (ribbond']) via a formally sp3-hybridized C atom should lead to a spirene exhibiting an interaction designated as spiroconju-gationf2]. HMO['] and CND0/2 calculations[31 on [ 1.2]spirene[**] predict stabilization of the H O M O by interaction between the x ribbons while the energy of the LUMO remains largely unaffected[', ' I. This should result in a hypsochromic shift of the longest wavelength UV band compared with that of the partially hydrogenated system (7). However, both electronic and steric substituent effects can perturb the system and mask the spiroconjugation. Thus the spirene (5c) provides no unequivocal evidence for spiroconjugation[21, whereas ( 5 d ) and ( 5 e ) exhibit a marked hypsochromic shift in the UV spectrum[4]. These differing results prompted us to synthesize the alkyl-substituted [1.2]spirenes ( 3 a ) and ( 3 b ) in order to substantially eliminate substituent effects. R R Compounds ( 3 a ) and ( 3 b ) were prepared by irradiating diazocyclopentadiene ( I ) in 2-butyne ( 2 a ) or 3-hexyne ( 2 b ) with long wave UV light (?i>360nm) until evolution of nitrogen had ceased (cf. ref. IS]). ( 3 a ) and ( 3 b ) are pale yellow oils (yield 47 and 35% respectively) which decompose on attempted gas chromatography but could be purified by chromatography and vacuum rnicrodistillation at room temperature. The structure follows from the spectra. IR: ( 3 a ) : 1938; ( 3 6 ) : 1925 cm-' (cyclopropene stretching mode); NMR: ( 3 a ) : .r=3.8-4.0 (m) and 3.3-3.5 (m) (cyclopentadiene ~~~ -[*] Prof.

No 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 :