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Abstract

A conceptually novel reaction cascade is presented, which allows readily available enynes to be converted into functionalized 1,3‐dienes comprising a stereodefined tetrasubstituted alkene unit; such compounds are difficult to make by conventional means. The overall transformation is thought to commence with formation of a metallacyclic intermediate that evolves via cleavage of an unstrained C−X bond in its backbone. This non‐canonical cycloisomerization process is followed by a cross‐coupling step, such that reductive C−C bond formation regenerates the necessary low‐valent metal fragment and hence closes an intricate catalytic cycle. The cascade entails the formation of two new C−C bonds at the expense of the constitutional C−X entity of the substrate: importantly, the extruded group X must not be a heteroelement (X=O, NR), since activated β‐C−C bonds can also be broken. This concern was reduced to practice in two largely complementary formats: one procedure relies on the use of alkyl‐Grignard reagents in combination with catalytic amounts of Fe(acac)₃, whereas the second method amalgamates cycloisomerization with Suzuki coupling by recourse to arylboronic acids and phosphine‐ligated palladium catalysts.