title: Regioselective Alkylative Carboxylation of Allenamides with Carbon Dioxide and Dialkylzinc Reagents Catalyzed by an N-Heterocyclic Carbene-Copper Complex.
abstract: The alkylative carboxylation of allenamide catalyzed by an N-heterocyclic carbene (NHC)-copper(I) complex [(IPr)CuCl] with CO2 and dialkylzinc reagents was investigated. The reaction of allenamides with dialkylzinc reagents (1.5 equiv) and CO2 (1 atm.) proceeded smoothly in the presence of a catalytic quantity of [(IPr)CuCl] to afford (Z)-α,β-dehydro-β-amino acid esters in good yields. The reaction is regioselective, with the alkyl group introduced onto the less hindered γ-carbon, and the carboxyl group introduced onto the β-carbon atom of the allenamides. The first step of the reaction was alkylative zincation of the allenamides to give an alkenylzinc intermediate followed by nucleophilic addition to CO2 . A variety of cyclic and acyclic allenamides were found to be applicable to this transformation. Dialkylzinc reagents bearing β-hydrogen atoms, such as Et2 Zn or Bu2 Zn, also gave the corresponding alkylative carboxylation products without β-hydride elimination. The present methodology provides an easy route to alkyl-substituted α,β-dehydro-β-amino acid ester derivatives under mild reaction conditions with high regio- and stereoselectivtiy.
authors.affiliation: Organometallic Chemistry Laboratory and Center for Sustainable, Resource Science, RIKEN, 2-1 Hirosawa, Wako, Saitama, 351-0198, Japan.|Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama, 338-8570, Japan.
authors.forename: Sandeep Suryabhan
authors.initials: SS
authors.lastname: Gholap
authors.affiliation: Organometallic Chemistry Laboratory and Center for Sustainable, Resource Science, RIKEN, 2-1 Hirosawa, Wako, Saitama, 351-0198, Japan. houz@riken.jp.
authors.forename: Masanori
authors.initials: M
authors.lastname: Takimoto
authors.affiliation: Organometallic Chemistry Laboratory and Center for Sustainable, Resource Science, RIKEN, 2-1 Hirosawa, Wako, Saitama, 351-0198, Japan. mtakimoto@riken.jp.|Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama, 338-8570, Japan. mtakimoto@riken.jp.
authors.forename: Zhaomin
authors.identifier: 0000-0003-2841-5120
authors.initials: Z
authors.lastname: Hou
keywords: allenamides; carbon dioxide; carboxylation; copper; zinc