Tackling the Reactivity of Propadiene: Palladium Metallaphotoredox Dual Catalyzed Multi‐Component Allylation and Dienylation of Styrenes

Catalytic transformations of feedstock chemicals into value-added products are a long-standing challenge. A side product of the steam-cracking process - propadiene - which is formed in 2.5 x 10⁵ t/y - regardless of its potentially rich chemistry - is usually wasted by burning it. To make more economical and sustainable use of valuable carbon atoms from feeds stocks, herein we report a palladium metallaphotoredox dual catalyzed multi-component allylation and dienylation of styrene derivatives with propadiene as either an allylation or a dienylation reagent. The chemoselectivity for both directions are higher than 20:1 and pronounced functional group tolerance has been elucidated in both cases. Gram scale synthesis and orthogonal reactivities towards thermo allylation demonstrate the practicability of our protocols. Moreover, DFT calculation suggested an outer-sphere reductive elimination at a Pd^I complex to be the most energetically favored route for both directions.