Regioselective Robinson annulation realized by the combined use of lithium enolates and aluminum tris(2,6-diphenylphenoxide) (ATPH)

Article abstract of DOI:10.1246/bcsj.70.1671

Michael addition of lithium enolates derived from ketones to a variety of a, β-unsaturated ketones was realized in the presence of aluminum tris(2,6-diphenylphenoxide) (ATPH). In this reaction, ATPH can be used as a carbonyl protector of a, β-unsaturated carbonyl substrates upon complexation, which facilitates the regioselective 1,4-addition of lithium enolates to Michael acceptors. Similarly, dianions of β-dicarbonyl compounds undergo Michael addition smoothly using ATPH as an effective promoter of the reaction. Subsequent regioselective, intramolecular aldol condensation was also demonstrated, leading to bicyclic carbon ring systems. Such systems are difficult to obtain by the Robinson annulation usually performed in protic media.