Nickel-catalyzed Ring-opening-cyclization Of O-bromophenylcyclobutanones

Transition metal-catalyzed carbon-carbon bond activation reactions can directly break individual carbon-carbon bonds to retrosynthesize new complex molecules.Activation of carbon-carbon bonds is also a necessary process for transition metal-catalyzed ring-opening-cyclization reactions of small ring compounds.Transition metal-catalyzed activation of carbon-carbon bond cleavage can be accomplished through direct oxidative addition andβ-carbon elimination.Cyclobutanones are widely used as substrates for carbon-carbon bond activated ring expansion reactions due to their high strain.Despite recent advances in catalytic ring-opening/cross-coupling process of o-halogen tethered phenylcyclobutanones with other partners,single-component ring expansion of such precursors towards 3-methylindanones has not been disclosed.3-methylindanones and their derivatives widely exist in various synthetic precursors and active compounds in the fields of medicine,agriculture and natural products.Based on our interests in nickel catalysts and selective C-C bond activation of small rings,we present herein the nickel-catalyzed single-component ring expansion of o-bromophenylcyclobutanones.Supplemented with appropriate additives,using water as the hydrogen source,and optimizing the reaction conditions through screening of ligands,catalysts,solvents,additives,temperature and reaction time,3-methylindanone was obtained.Using aryl aldehydes or ketones as raw materials,the o-bromophenylcyclobutanone substrate was prepared by witting reaction and cycloaddition reaction.Afterwards,the compatibility of substrate functional groups was investigated by electronic effect and steric hindrance effect,leading to a series of indanones,which can be further converted into other benzene-fused cyclic compounds.The preliminary reaction mechanism was proposed through deuterium experiments and literature research,mainly through oxidative addition,β-carbon elimination,β-hydrogen elimination and other elementary reaction steps.The reaction system has the characteristics of simple reaction conditions,cheap and easy-to-obtain catalysts,and good substrate universality.The structures of the compounds were determined by testing and characterizing the data of ¹H NMR,¹³C NMR and high-resolution mass spectrometry of all compounds.