Tandem addition β-lithiation-alkylation sequence on α,β-unsaturated aldehydes

A tandem reaction between (E)-cinnamaldehyde, la, and phenyllithium affording beta -substituted dihydrochalcones was recently reported. NMR spectroscopic studies on the reaction mixture, as well as isotopic exchange reactions and trapping of two intermediates, provide clues on the several mechanistic steps of this new reaction. Extended studies revealed that beta -alkyl-substituted alpha,beta -unsaturated aldehydes and aliphatic lithium reagents did not afford good yields of the tandem reaction products, while aromatic lithium reagents gave good results. The aggregation features of the aryllithium reagents and the extended charged delocalization effects are considered to promote beta -selectivity. This approach provides a convenient route for the synthesis of a wide variety of beta -alkylsubstituted dihydrochalcones.