Dibenz[a,j]anthracene via Photo-cyclodehydrogenation of 9,10-Dihydro-2-styrylphenanthrene
✍ Scribed by Diederich, Françlois ;Schneider, Karin ;Staab, Heinz A.
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 1984
- Tongue
- English
- Weight
- 189 KB
- Volume
- 117
- Category
- Article
- ISSN
- 0009-2940
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✦ Synopsis
Dibenzfaj lanthracen durch Photocyclodehydrierung von 9,lO-Dihydro-Zstyrylphenanthren Wiihrend aus 2-Styrylphenanthren (1) durch Photocyclodehydrierung Benzo[c]chrysen (2) entsteht, I2Rt sich unter Ausnutzung der ,,ZF*-Regel"5) aus 9,10-Dihydro-2-styrylphenanthren (4) durch Photocyclodehydrierung zu 6 und anschliefiende Dehydrierung Dibenz[a,j]anthracen (3) erhalten.
In connection with the synthesis of kekulene') we were looking for an alternative synthetic route to dibenz[a,j]anthracenes. Considering the wide application which photo-cyclodehydrogenation reactions of 1,2-diarylethenes found for the synthesis of polycyclic aromatic systems2), a photochemical formation of the dibenz[a,j]anthracene skeleton was of special interest. Photocyclodehydrogenation of 1 ,3-distyrylbenzene3) as well as of 2-styrylphenanthrene (1)4), however, led to benzo[c]chrysene (2) almost exclusively besides only trace amounts of dibenz[aj]anthracene (3). This result is in accordance with the rule that in the case of competing cyclisations the product formed predominantly is the one for which the sum of free valence indices in the excited state ZF* of the two atoms involved in the cyclisation is highest5).
1
Starting from 9,10-dihydro-2-styrylphenanthrene (4), however, photoconversion should result in the formation of 5,6-dihydrobenzo[c]chrysene (5) and 5,6-dihydrodibenz[a, jlanthracene (6) in about equal amounts since for both cyclisations in first approximation the same ZF* value (1.007) was calculated6).