Synthesis of Fully Substituted Dispirocyclohexanes by Organocatalytic [2 + 2 + 2] Annulation Strategy between 2-Arylideneindane-1,3-diones and Aldehydes
摘要:
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 alpha,alpha-L-diphenylprolinol trimethylsilyl ether (5 mol %) and DABCO (20 mol %) in DMF at -20 degrees C. The reaction proceeds through a unique Michael/Michael/aldol reaction that requires 2 equiv of the 2-arylideneindane-1,3-dione.