| Description |
During the past decade, palladium-catalyzed alkene functionalization reactions that intercept the Pd-alkyl intermediate for further functionalization has attracted significant interest because of its ability to generate diverse C-O, C-N and C-C bond connections. However, developments of these reactions are considered to be challenging due to the propensity of the Pd-alkyl intermediate for ?-hydride elimination. The Sigman group has been involved in developing methods to stabilize the Pd-alkyl intermediate that is formed at the benzylic or allylic positions to generate interesting product. Herein, we describe the discovery of new efficient methods to stabilize these intermediates to achieve difunctionalization and hydrofunctionalization products. First, a highly cationic PdII-catalyzed alkene difunctionalization of terminal olefins using organostannanes is developed in which a conjugated alkene can lead to a 1,2-addition product. However, electron withdrawing styrenes gave a mixture of 1,2- and 1,1-addition products. Based on an observed linear free energy relationship, it was found that electronic nature of the styrene determines the ratio of the 1,2- vs 1,1-diarylation product. This study ultimately lead us to develop a 1,1-diarylartion reaction using simple olefins. The mechanistic experiments suggested that the electrophilic nature of the palladium catalyst is necessary to stabilize the resultant ?-benzyl species, that yields the alkene difunctionalization product. |
