Arenhydride, 8. Konkurrenz zwischen SET und nucleophilem Angriff bei Reaktionen von α‐Bromisobutyrophenon mit Carbanionen. Fragmentierung des Anions von Tetrahydrobianthracen

Arene Hydrides, 8. ‐ SET vs. Nucleophilic Attack in Reactions of α‐Bromoisobutyrophenone with Carbanions. Fragmentation of the Anion of Tetrahydrobianthracene SET is the main reaction pathway between α‐bromoisobutyrophenone ( 1 ) and the carbanions 7a – j − of diarylmethanes or disubstituted acetonitriles: 7 − → 7 . + e and e + 1 →→ Br − PhCOCMe . 2 ( 3 ). Main secondary reactions are dimerization of the radical 7 . (to form 6 ) and further reduction of 3 : 7 − + 3 → 7 . + 4 [enolate of isobutyrophenone ( 5 )]. Occasionally substitution products ( 9 ) of 1 are obtained. They are probably formed by combination of 7 . with 3 (0% 9e at room temperature, 38% 9e at −65°C). This combination seems to be favored by cation coordination. In the reaction with 7f − (“anthracene hydride”) the dimer 6f (and probably 9f , too) undergoes fragmentation to form anthracene. The epoxide 16 , arising from 1 by carbonyl attack, has been found only once with 7a – j −; (1% 16b ). In contrast, 16 was the (elusive) main product in the reaction of 1 with the carbanions 7k – n − of monosubstituted acetonitriles. Here, 6 and 9 have been found only once ( 61, 9n ). The elusive 16k – n underwent eliminative ring fission.