Synthesis of fully substituted dispirocyclohexanes by organocatalytic [2 + 2 + 2] annulation strategy between 2-arylideneindane-1,3-diones and aldehydes

An interesting organocatalytic reaction between 2-arylideneindane-1,3- diones and aldehydes has been developed that gives fully substituted cyclohexanes that bear two all-carbon quaternary centers. The dispirocyclohexanes were obtained in reasonable-to-good chemical yields and with high stereoselectivities (>95:5 d.r. and up to 99% ee) using a catalytic amount of commercially available α,α-l-diphenylprolinol trimethylsilyl ether (5 mol %) and DABCO (20 mol %) in DMF at -20 °C. The reaction proceeds through a unique Michael/Michael/aldol reaction that requires 2 equiv of the 2-arylideneindane-1,3-dione.