Studies on 1,2-Difunctionalization of Alkenes by Harnessing the Unquenched Reactivities of Lewis Pairs

Abstract

1,2-Difunctionalizations of alkenes represent a versatile and powerful class of reactions in organic synthesis. These transformations enable the introduction of two functional groups across a carbon-carbon double bond, thereby converting simple alkenes into more complex and functionalized molecules. Such transformations are of immense value in the construction of pharmaceuticals, natural products, and other complex organic molecules. Consequently, these fields have been expanded over the past several decades. Despite significant advancements, stereospecific vicinal difunctionalization remains challenging and elusive in several reactions. Among them, stereospecific ketene-alkene [2+2] cycloaddition and alkene dihalogenation have been underdeveloped. Here, we report a novel approach to the 1,2-difunctionalization of alkenes by exploiting the reactivities of unquenched Lewis pairs. We found that a tertiary amine can serve as both a hydride source and a proelectrophile in the presence of B(C6F5)3 during studies on ketene-alkene [2+2] cycloaddition. In this process, ,β-unsaturated ketones undergo olefination by hydride and iminium cation which derive from amine. Furthermore, we have developed alkene dihalogenation via BN-compound. Notably, it was found that the halogen source does not react directly with the alkene but is delivered into alkenes through a halogen-adduct. Although the reaction did not achieve high stereoselectivity, it demonstrated considerable promise for syn- dihalogenation.