A Facile Synthesis of 2-Methyl-3-oxoindoline-2-carboxylates Utilizing Aza-Brook Rearrangement as a Crucial Step

Synthesis of 2-methyl-3-oxoindoline-2-carboxylates is developed using a bis(trimethylsilyl)aluminum chloride-induced aza-Brook rearrangement as a crucial step. Regarding the organoaluminum species, use of readily available tris(trimethylsilyl)aluminum·ether complex was not suitable for the present cyclization. After a series of examination of the reaction conditions, the aza-Brook rearrangement and the subsequent cyclization with 2 equivalens of bis(trimethylsilyl)aluminum chloride were found to be the most effective. An application to the synthesis of a potential intermediate of duocarmycin A is also described, in which ozonolysis of the styrenyl moiety and the Barton–McCombie deoxygenation of the hydroxymethyl group were successfully carried out.