Palladium(II)-Catalyzed SN2‘ Reactions of α-Allenic Acetates. Stereoconvergent Synthesis of (Z,E)-2-Bromo-1,3-dienes
摘要:
The reaction of acetylated a-allenic alcohols with LiBr in the presence of 1.5 mol % of Pd(OAc)(2) provides easy access to substituted (Z,E)-2-bromo-1,3-dienes in good yields with excellent diastereoselectivity. Both secondary and tertiary acetates as well as terminal and nonterminal allenes were studied to investigate the scope and the limitations of the reaction. A mechanism is proposed to clarify how a diastereomeric mixture of the starting compound is transformed into a single diastereomer of the product.
Palladium(II)-Catalyzed SN2‘ Reactions of α-Allenic Acetates. Stereoconvergent Synthesis of (Z,E)-2-Bromo-1,3-dienes
摘要:
The reaction of acetylated a-allenic alcohols with LiBr in the presence of 1.5 mol % of Pd(OAc)(2) provides easy access to substituted (Z,E)-2-bromo-1,3-dienes in good yields with excellent diastereoselectivity. Both secondary and tertiary acetates as well as terminal and nonterminal allenes were studied to investigate the scope and the limitations of the reaction. A mechanism is proposed to clarify how a diastereomeric mixture of the starting compound is transformed into a single diastereomer of the product.
Catalytic Asymmetric Allenylation of Malonates with the Generation of Central Chirality
作者:Qiankun Li、Chunling Fu、Shengming Ma
DOI:10.1002/anie.201204346
日期:2012.11.19
Water plays an important role in a palladium‐catalyzed allenylation of diethyl malonate with 2,3‐allenyl acetates to yield centrallychiral allenyl malonates bearing synthetically useful functional groups (see scheme). The products were formed with 92–96 % ee in the presence of a bulky, electron‐rich biphenyl ligand at room temperature.
An efficient Pd/Cu co-catalyzed dynamic kinetic allenylic alkylation of racemic allenylic acetates with aldimine esters has been developed. Various allenes bearing α,β-adjacent centralchiralities were obtained with excellent stereoselectivities. The easy interconversion between the uncommon η3-butadienyl palladium intermediates featuring a weak C=C/Pd coordination bond and a stable Csp2−Pd bond is