Transannulare Hydridverschiebung versus Cyclokondensation bei 5‐(2‐Biphenylyl)‐10,11‐dihydro‐5 H ‐dibenzo[ a , d ]cyclohepten‐5‐ol‐Derivaten

Transannular Hydride Shift versus Cyclocondensation in 5‐(2‐Biphenylyl)‐10,11‐dihydro‐5 H ‐dibenzo[ a , d ]cyclohepten‐5‐ol Derivatives The title compounds 1a – c , stable under thermal and basic conditions, undergo a solvent‐assisted concerted hydride shift/deprotonation reaction to 5‐(2‐biphenylyl)‐5 H ‐dibenzo[ a , d ]cycloheptene ( 4 ) in weak acids such as acetic acid, acetic anhydride, phenol, and nitromethane. In strong acids like formic acid or trifluoroacetic acid cyclization to 10,11‐dihydrospiro[5 H ‐dibenzo[ a , d ]cycloheptene‐5,9′‐fluorene] ( 3 ) occurs via the carbenium ion intermediate 5 .