Improved Heteroatom Nucleophilic Addition to Electron-Poor Alkenes Promoted by CeCl_3 centre dot 7H_2O/NaI System Supported on Alumina in Solvent-Free Conditions

摘要

Conjugate addition of heteroatom nucleophiles to carbon-carbon double bonds conjugated with a strong electron-withdrawing group is one of the most important new bond-forming strategies in synthetic organic chemistry.Among the methods for these Michael additions,Lewis acids have shown the best promoter activity,and in particular,the use of reagents impregnated over inorganic supports is rapidly increased.With the increase of environmental consciousness in chemical research,the solvent-free Michael addition has attracted our attention.In continuation of our ongoing program to develop synthetic protocols utilizing cerium trichloride,we report an extension of the CeCl_3 centre dot TEkO/Nal combination supported under solvent-free conditions to promote heteroatom Michael addition.Using neutral alumina(Al_2O_3)as solid support permits us to circumvent some of the problems associated with the procedure where the inorganic support is silica gel.The CeCl_3-7H_2O/NaI/Al_2O_3 system works well for hetero-Michael additions utilizing weakly nucleophiles such as imidazoles and carbamates,and also the reaction proceeds with good yields in the case of Michael acceptors different from a,beta-unsaturated carbonyl compounds.An important synthetic application of this our methodology is the intramolecular aza-Michael reaction in producing 4-piperidinone derivatives,which are of interest as synthetic intermediates toward important classes of heterocycles.