Photoredox cobalt-catalyzed stereodivergent synthesis of 1,4-dienes
1,4-Dienes are important scaffolds widely used in natural products and medicinal compounds.Herein,we report a highly efficient method for the straightforward synthesis of 1,4-dienes via regio-and stereoselective reductive coupling of alkynes and allenes,catalyzed by visible-light photoredox cobalt.In contrast to the conventional E-alkene products,both(Z,E)-and(E,E)-1,4-dienes were synthesized with good regio-and stereoselectivities under mild conditions.In this photoredox reac-tion,Hünig's base and water were utilized as hydrogen sources instead of the commonly used Hantzsch esters.The mechanistic and density functional theory studies indicate that the reaction undergoes protolysis of a cobaltacyclopentene intermediate and photocatalytic E→Z isomerization of(E,E)-1,4-dienes to(Z,E)-1,4-dienes via an energy transfer process.
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