Abstract
The synthesis of a novel azulene containing phane, a/m'-[2.2](2,6)azulenophane (1), is described. It is prepared by the Hofmann pyrolysis of jV-(2-methyl-6-azulyl)-MMAr-trimethylammonium hydroxide (14b) in 4.3% yield along with poly-
mer, 29%, 2,6-dimethylazulene (16), 1.1%, and 2-hydroxymethyl-6-methylazulene (17), 12%. syn-[2.2](2,6)Azulenophane (2) is not generated in the reaction. The quaternary ammonium salt used for pyrolysis is synthesized from propiophenone (3) in 13 steps. The azulene skeleton is constructed in good yield by a modification of the Buchner reaction. This modification, which seems general for the construction of substituted azulene nuclei, involves the addition of a carbene to a 4,7-dihydroindan system instead of the less reactive indan ring system. The addition occurs predominantly at the external rather than the inter- nal double bond of the 4,7-dihydroindan ring. Charge-transfer interaction between the two azulene nuclei in 1 is indicated but is not a certainty from its electronic spectrum, where the longest wavelength band tails out to about 900 nm. Mono- and dipro- tonated forms are spectroscopically observed when 1 is treated with trifluoroacetic acid. The monoprotonated form exhibits a charge-transfer band in its electronic spectrum indicative of transannular charge-transfer interaction between the protonated and unprotonated azulene rings. In the diprotonated form there is no charge-transfer band consistent with the repulsive nature
of the two protonated azulene nuclei. When compared with 2,6-dimethylazulene, 1 is a stronger reaction with tetracyanoethylene corroborating the - interaction between two azulene rings.