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.