Intramolecular dehydrogenative cyclization involving twofold Csp2–H bond cleavages directed by the amino- or carboxy group proceeds smoothly when using a rhodium–copper catalyst system under air as the terminal oxidant. A variety of fluorene derivatives can be prepared by the environmentally benign procedure.
An iodine-mediated 1,2-arylmigration reaction of primary benzhydryl amines under transition metal-free conditions has been achieved. The crude imines generated by this rearrangement reaction can be directly transformed into various aromatic secondary amine derivatives via reduction or addition reactions. This sequential synthetic process is operationally simple and can be successfully conducted on
Doubling up: Two CH bond activations took place efficiently upon treatment of 1 with a rhodium catalyst to form dehydrogenative cyclization products 2. Furthermore, 3 undergoes similar cyclization and subsequent decarboxylation through the cleavage of two CH bonds and one CC bond. Both reactions provide straightforward routes to the fluorene framework.