We have developed a copper/manganese-mediated oxidative rearrangement of benzylamines to 4H-3,1-benzoxazines of potent interest in medicinal applications. The reaction proceeds uniquely through the initial copper/manganese-promoted intramolecular C-H amination giving benzazetidine intermediates and subsequent 4n electrocyclic ring opening/6 pi electrocyclic ring closing cascade. The key to success is the introduction of picolinamide-based N,N-bidentate directing group. The obtained benzoxazines can also be readily hydrolyzed to the corresponding 2-aminobenzyl alcohols, thus indicating that the overall transformations is regarded as the ortho-aminative rearrangement of benzylarnines to benzylic alcohols.
The rhodium-catalyzed cyclization of a series of 2,2-diarylalkanoic acids in the presence of copper acetate as an oxidant smoothly proceeded through double C-H bond cleavages and subsequent decarboxylation to produce the corresponding fluorene derivatives. The direct cyclization of triarylmethanols also took place efficiently by using an iridium catalyst in place of the rhodium, while the hydroxy function was still intact.