Palladium-Catalyzed Alkylation and Dienylation of Propargylic Carbonates with Hydrazones through Carbonyl Umpolung

Abstract

Controlling the reaction selectivity to realize divergent syntheses is a permanent pursuit for chemists. Reported herein is a chemodivergent palladium-catalyzed method that enables the synthesis of structurally valuable internal alkynes and/or terminal 1,3-dienes from readily available propargylic carbonates through carbonyl umpolung. In the presence of Pd catalyst/P-ligand, the propargyl alkylation reaction complements the traditional coupling of nonstabilized nucleophiles with propargylic electrophiles by employing carbonyls as a source of umpolung alkyl carbanions and surrogates of alkyl organometallic reagents. In dienylation chemistry, the use of the Pd–NHC combination regulated the product distribution, thus providing a catalytic alternative to otherwise inaccessible branched 1,3-dienes through a sequence of allenylation and skeletal isomerization in a chemoselective and regioselective manner. Additionally, versatile products can be transformed from the resulting alkynes and 1,3-dienes, further highlighting the broad synthetic potential of these discoveries.