Dual rhodium/copper catalysis: synthesis of benzo[b]fluorenes and 2-naphthalenylmethanones via de-diazotized cycloadditions.

A novel synergistic rhodium/copper catalysis has been established, enabling de-diazotized cycloadditions of 1,5-enynes and α-diazocarbonyls toward the selective formation of densely functionalized benzo[b]fluorenes and 2-naphthalenylmethanones. α-Aryldiazoesters result in the formation of triple C-C bonds through bimetallic catalysis whereas a range of functionalized naphthalenes with a 1,5-dicarbonyl unit were accomplished using α-diazocarbonyls without any substituent at the α-position, indicating that substituents at the α-position of the α-diazocarbonyl unit could control the selectivity of the reaction.