Homologative alkene difunctionalization.

Systematic evaluation of homologous series plays a pivotal role in synthetic and medicinal chemistry. Despite their structural resemblance, the preparation of homologues often requires individual synthetic planning tailored to distinct precursors and reactions. Here we introduce a strategy that integrates single-carbon insertion into established methods, specifically redirecting alkene vicinal difunctionalization towards direct routes for 1,3-difunctionalized products. This transformation is enabled by a designer methylene dication reagent, iodomethylthianthrenium salt, which facilitates the photocatalytic conversion of alkenes into linchpin 1,3-dielectrophilic intermediates, allowing seamless incorporation of nucleophiles at distal positions. Mechanistic studies suggest that the reaction proceeds via an α-thianthrenium methyl radical with unusual ambiphilic reactivity governed by multiple stereoelectronic effects. This approach shows high compatibility in pharmaceutical and late-stage settings, providing broad access to diverse 1,3-difunctionalized products, including azetidines, 1,3-diazides and 1,3-dihalides. This work establishes 'homologative alkene difunctionalization' as a powerful platform for repurposing ubiquitous alkenes as meritorious synthetic intermediates to unveil heretofore unknown 1,3-substitution patterns.