Cyclopentane Construction by Rh-Catalyzed Intramolecular C-H Insertion

On exposure to a catalytic amount of rhodium acetate (5 mol % or less), an α-diazoketone will smoothly undergo 1,5 C-H insertion to give the corresponding cyclopentane. This reaction presumably proceeds via the corresponding metallocarbene. In substrates having more than one site where C-H insertion could occur, steric and electronic considerations govern selectivity. Strategies for making this process enantioselective are discussed.