Linear free energy relationships in the Bergman cyclization of 4-substituted-1,2-diethynylbenzenes

Abstract A series of 4-substituted-1,2-diethylnylbenzenes were prepared ( 1a – f ) and subjected to Bergman cyclization. Bulk cyclization proceeded to produce the corresponding 2-substituted naphthalenes ( 2a – f ) in good yields (59–78%). Kinetic experiments show a linear free energy relationship between the cyclization rate and the Hammett σ m substituent coefficient and the Swain–Lupton field and resonance parameters.