π-Allylpalladium-Mediated Catalytic Synthesis of Functionalized Allenes

Highly Selective Nucleophilic 4‐Aryl‐2,3‐allenylation of Malonates†

“…We wonder whether such a protocol may be applied to the syntheses of the thermo‐sensitive aryl‐allenes (Scheme 1c). The challenges are as follows: (1) such reactions with 4‐aryl‐2,3‐allenol derivatives may be too reactive, resulting in the formation of a mixture of mono‐ and bis‐allenylation products with non‐substituted malonates (for such a report with 1,3‐dien‐2‐yl derivatives, see: Scheme 1d); [ 9 ] (2) the reported enantioselectivity with 4‐phenyl‐2,3‐allenyl derivatives is low even with the sterically bulky diethyl 2‐acetamidomalonate (Scheme 1e); [ 7a,8 ] (3) a more active catalytic system, which will work at very mild reaction conditions to avoid the racemization of in situ generated sensitive aryl‐substituted allenes, is required. Herein, we wish to report our recent realization of Pd‐catalyzed highly chemoselective mono‐allenylation of non‐substituted malonates (Scheme 1f).…”

Enantio‐ and Diastereoselective Synthesis of Chiral Allenes by Palladium‐Catalyzed Asymmetric [3+2] Cycloaddition Reactions

“…Furthermore, metal‐catalyzed asymmetric allene syntheses have been developed based on transformations of achiral dienes, terminal alkynes, or vinyl triflates . Noteworthy examples include Alexakis's synthesis of chloro allenes from propargyl dichlorides, Ma's Pd‐catalyzed synthesis of tri‐substituted chiral allenes from racemic propargyl carbonates, Maruoka's phase transfer catalysis, Hayashi's palladium‐catalyzed S N 2′ substitution of 2‐bromo‐1,3‐butadienes, and Bäckvall's chemoenzymatic approach (Figure ) . However, a significant drawback of these methods is the lack of ability to build up more molecular complexity at the substituents of the allene in a step economic way.…”

Enantio‐ and Diastereoselective Synthesis of Chiral Allenes by Palladium‐Catalyzed Asymmetric [3+2] Cycloaddition Reactions

“…Furthermore, metal‐catalyzed asymmetric allene syntheses have been developed based on transformations of achiral dienes, terminal alkynes, or vinyl triflates . Noteworthy examples include Alexakis's synthesis of chloro allenes from propargyl dichlorides, Ma's Pd‐catalyzed synthesis of tri‐substituted chiral allenes from racemic propargyl carbonates, Maruoka's phase transfer catalysis, Hayashi's palladium‐catalyzed S N 2′ substitution of 2‐bromo‐1,3‐butadienes, and Bäckvall's chemoenzymatic approach (Figure ) . However, a significant drawback of these methods is the lack of ability to build up more molecular complexity at the substituents of the allene in a step economic way.…”